Abstract Book

06/25/2007 06:28 PMAbstract Book

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1. Self assembly and immunity of microemulsion and polymer networksSamuel A. Safran, Weizmann Institute of Science, Rehovot, Israel

Self-assembling networks occur in diverse colloidal systems including cylindrical micelles and microemulsions,ferrofluids, and polymer-colloid assemblies. Although the microscopic nature of these systems can be quite different, thestatistical thermodynamics and phase behavior can be quite similar. In particular, we show theoretically that suchnetworks generally exhibit phase coexistence between dilute and dense network phases; these transitions are driven bythe competition of the translational entropy (that dominates in the dilute phases) and the configurational entropy (thatdominates in the dense network phases). The predictions are in agreement with both structural and thermodynamicstudies. Recently, we have focused on the immunity of networks comprising (several) telechelic polymers that connectoil in water microemulsion drops. The dense network phase of this system has higher immunity if it survives a randomdegradation of polymers, that is, if the network is more likely to maintain a macroscopic connected component. Wepredict that gel immunity decreases with an increase of the variance of the distribution of the number of polymers thatconnect a given pair of drops. Repulsive interactions between the polymers decrease the variance, while attractiveinteractions increase the variance.

*Work done in collaboration with: G. Hed, T. Tlusty, A. Zilman - theory; A. Bernheim, T. Foster, G. Porte, T. Sottmann,R. Strey, Y. Talmon - experiment.

2. Keynote: DFT Modeling of Novel MaterialsMatthew Neurock, University of Virginia, Charlottesville, VA

DFT Modeling of Novel Materials

3. Mechanisms of Metal Atom Clustering and Nanofilament Formation in Vapor Depositionof Metal Atoms on Alkanethiolate Self-Assembled Monolayers on Au{111}Masato Maitani, Thomas A. Daniel, Orlando M. Cabarcos and David L. Allara, The Pennsylvania State University,University Park, PA

A fundamental understanding of the metal deposition process on organic self-assembled monolayers (SAMs) isimportant in designing high quality interfaces between metal and organic materials for organic electronic deviceapplications. The behavior of thermally evaporated Al deposition on S(CH2)15CH3 SAMs on Au {1 1 1} is interesting,since a previous report showed a distinct transition in the deposition process from penetration through the SAM to theunderlying substrate to cluster generation at the vacuum interface, based on in-situ XPS, IRS, and ToF-SIMS probes[1]. We have now studied this behavior with in-situ AFM to observe the topographic features and electricalconductance properties with increasing Al coverage. The AFM results confirm Al penetration in the initial stage, then atransition to a uniform growth of metal nanofilaments and finally surface cluster generation. We have probed the I-Vcharacteristics of individual filaments which can be as small in diameter as single atoms in the limit.

[1] A. Hooper, G.L. Fisher, K. Konstadinidis, D. Jung, H. Nyugen, R. Opila, R.W. Collins, N. Winograd, and D.L. Allara,J.Am.Chem.Soc., 121, 8052-8064 (1999).

4. Selective deposition of metals on patterned self-assembled monolayer surfaces: Towardsmolecular electronic circuitryAmy Walker, Washington University, St. Louis, MO

We have developed a robust method by which to construct complex two- and three- dimensional structures based oncontrolling interfacial chemistry. This work has important applications in molecular/organic electronics, sensing, andother technologies. Our method is extensible to many different materials, easily parallelized, affords precise nanoscaleplacement and is fully compatible with photolithography. Our work to date has provided a simple method for theconstruction of complex 2D molecular electronic circuitry using UV-photopatterning and the reaction of deposited metals



with self-assembled monolayers (SAMs). To demonstrate the method we have selectively vapor-deposited Mg on apatterned -CH3/-COOH terminated alkanethiolate surface. The deposited metal penetrates through the -CH3 SAM tothe Au/S interface while reacting with and accumulating on top of the -COOH SAM. In a second demonstration we haveemployed room temperature chemical vapor deposition (CVD) to selectively deposit on patterned -CH3/-COOHterminated alkanethiolate SAMs. Applying these ideas to the rational design of metal/organic structures requires afundamental understanding of the underlying metal-molecule interactions; we therefore shall also discuss experimentsthat elucidate these.

5. Surface preparation of supported flat gold nanoparticles for use as Au{111} substratesDaminda H. Dahanayaka, Wesley D. Tennyson, Christopher E. Allen, Preston R. Larson, Daniel J. Wasielewski,Marshall D. McCutchen, David S. Hartnett, Matthew B. Johnson and Lloyd A. Bumm, University of Oklahoma, Norman,OK

Flat gold nanoparticles (FGNPs) grown in aqueous solution have large Au{111} facets that are excellent substrates forscanning probe microscopy. However adsorbed stabilizers (e.g. polyelectrolytes) must be removed or displaced beforethe FGNP surfaces can be used as single crystal surfaces. We have explored the effects of plasma cleaning, UVozone, CO2 snow cleaning, and thermal annealing on the Au{111} terrace structure using STM. We have also appliedan addressed grid system to track and to correlate images of selected particles through the cleaning and annealingprocedures using SEM, AFM, and optical.

This work has been supported by NSF CAREER grant No. CHE- 0239803, NSF MRSEC No. DMR-0080054, andAFOSR No. FA9550- 06-1-0365.

6. The Initial Stages of Self-Organization of Silica-Alumina Gels in Zeolite Synthesis

Joseph M. Fedeyko1, Dustin Fickel2, Raul F. Lobo2 and Dionisios G. Vlachos2, (1)Johnson Matthey Catalysts,Wayne, PA, (2)University of Delaware, Newark, DE

Zeolites have consistently been a topic of intense research because of their tunable catalytic properties, the result of theincorporation of different elements (aluminum, germanium, boron, etc.) in the silica crystalline framework. For manyyears, alumina incorporation has been shown to result in different crystalline structures and particle morphologies;however, the majority of studies focusing on the nucleation and growth of zeolite materials have focused solely on all-silica syntheses. Here, we expand on our recent research of the self-assembly of silica in basic solutions of smallorganic cations by studying the impact of alumina on these systems.

The effect aluminum on the initial condensation of silica in basic solutions of organic and inorganic cations is analyzedusing conductivity, pH, NMR spectroscopy and small angle scattering methods. The addition of alumina to thesesolutions decreases substantially the point at which nanoparticles form. At high alumina concentrations, the particlesare smaller than those found in all-silica solutions and spherical in shape. We argue, using equilibrium thermodynamictheory, that the composition should be rich in aluminum. In the case of sodium, larger rather than smaller particles areobserved and the data strongly suggests that sodium cations are being incorporated within the inorganic silica/aluminacore, as opposed to organic cations that appear to be excluded from such clusters. As was the case for the pure-silicasystem, important insights are gained by making analogies to the behavior of mixed surfactant systems.

7. The Effect of an Embedded Mid-Chain Dipole on the Properties and Characteristics ofEster-Functionalized Self-Assembled Monolayers on Au{111}

Orlando M. Cabarcos1, Andrey Shaporenko2, Sundar Uppili3, Michael Zharnikov2 and David L. Allara1, (1)ThePennsylvania State University, University Park, PA, (2)Universtät Heidelberg, Heidelberg, Germany, (3)University ofKansas, Lawrence, KS

Over the last 20 years, self-assembled monolayers (SAMs), particularly those with alkyl chains, have been extensivelystudied by modifying the terminal group present at the air/SAM interface. Less well known are the effects whichincorporation of a functional group within the middle of the chains might have on the overall monolayer structure andproperties. We have used IRS, XPS and NEXAFS to examine the structure and characteristics of mid-chain esterfunctionalized alkanethiols, SH(CH2)10CO2(CH2)4CH3, SH(CH2)10CO2(CH2)9CH3, SH(CH2)15CO2(CH2)4CH3 and



SH(CH2)5CO2(CH2)9CH3 on Au{111}. The embedded functional group leads to a model “stratified layer” type systemwith the chain below the functional group exhibiting different orientation and conformational order then the upper chain.XPS measurements show that the electrical dipole moment of the ester group affects the photoemission workfunction ofthe two chains differently, relevant to the phenomena arising in devices such as organic electroluminescent devices andorganic field-effect transistors.

8. Keynote: Electrical microchips in the biocolloidal domain: On-chip assembly anddetection of live cells and biological moleculesOrlin D. Velev, Shalini Gupta and Peter Kilpatrick, North Carolina State University, Raleigh, NC

Two examples of the use of biocolloidal interactions for on chip synthesis of materials and biosensing will be presentedand discussed. In the first part we will demonstrate how biocomposite materials can be fabricated by precise electricfield driven co-assembly of live cells and synthetic colloidal particles. The process is based on dielectrophoresis (DEP),mobility and interaction of particles in AC electric fields. Live cells such as baker's yeast and mouse fibroblasts wereco-assembled with colloidal particles into freely suspended 1D chains and 2D membranes. Experimental observations ofthe DEP co-assembly dynamics showed that particles smaller in size than the cells were drawn and captured into thecell junctions by the electric field. The process was modeled by a combination of electrostatic field computation andMD-type of particle motion simulation. Magnetic microparticles conjugated with lectins could be used to bind the cellsirreversibly via bio-specific lectin-saccharide interactions. The cell membranes and chains formed could be manipulatedby magnetic field and interfaced with on-chip electrodes. Such functional biomagnetic cell-particle assemblies may findapplications in sensors, microassays, microsurgery, or as responsive biomaterials. In the second part of the talk we willpresent a simple new technique for the on-chip detection of antigen induced binding of particles coated with antibodies.The detection of antigen-induced agglutination is performed by impedance measurement through arrays ofmicroelectrodes interfacing the microchamber with the particle suspension.

9. The zeta potential of freshly cleaved mica just after immersionPaul J. Sides, James D. Hoggard and Dennis C. Prieve, Carnegie Mellon University, Pittsburgh, PA

Muscovite mica was cleaved in air and quickly submerged in aqueous solutions of alkali metal salts. The zeta potentialwas measured as soon thereafter as possible with the aid of an apparatus based on detection of streaming potential inthe vicinity of a rotating disk. The time between cleaving the sample and immersion was less than one minute and theelapsed time before the first measurement after immersion was as low as 20 seconds with subsequent measurementsbeing taken at intervals of similar duration. When mica was immersed in 1 mM KCl at pH 5.8, the mica adopted a zetapotential that was essentially constant within this time frame at -80 mV. When the mica was submerged in 1 mM NaClat a similar pH, however, the first measured zeta potential was -120 mV and a decay to a steady value at -95 mV wasobserved with a decay time of order 1000 s. When freshly cleaved mica was immersed in solutions at lower pH, amaximum appeared in the zeta potential and the transition time was reduced. These results are discussed in thecontext of a dynamic single site binding model that tracks the surface coverage of potassium, sodium, and hydrogenions. Appropriate choices of dissociation and association rate constants allow fitting of the dynamic response of themica to the model.

10. A scalable route to gold nanoshell - liposome composites for photothermal therapiesBrian G. Prevo, Shelley Esakoff and Joseph A. Zasadzinski, University of California, Santa Barbara, Santa Barbara,CA

Near infrared (NIR) light is especially useful for in vivo applications as physiological media are relatively transparent tothese wavelengths. Nanoscopic hollow shells of gold possess a strong NIR plasmon absorption. Recently, manyresearchers have demonstrated an array of different imaging and therapeutic applications taking advantage of thesephenomena. Galvanic replacement chemistry (GRC) offers a facile and scalable ‘one pot' route to metal nanoshellsynthesis, providing a distinct advantage over conventional layer by layer nanoshell fabrication techniques. Using GRC,template metallic nanoparticles (e.g. silver) act as reductants, nucleating the desired metal nanoshell (e.g. gold) aroundthem provided that the template metal has a lower standard reduction potential. The resulting aqueous core/metal shellparticles are formed in minutes, and can be tunably varied from ~ 20 – 75 nm shells with varying thickness (dependingon reagent ratios). The use of pulsed NIR laser irradiation for inducing plasmonic heating effects minimizes the



temperature rise in the surrounding media due to the fast relaxation times (~ ps) of the metal particles. The kinetics ofthe laser attenuation by the particles correlates well with the corresponding UV/Vis/NIR spectroscopy, TEM,experimental calorimetry, and heat transfer calculations. We are currently exploring these particles as remotephotothermal actuators within submicron liposomes. While bilayer compartments are quite deformable, they pop likeballoons if stretched too far (in excess of approximately 5-10%). This could give both spatial and temporal control ofdrug delivery from liposomes without the need for specialized liposome compositions or large scale heating of the tissueitself.

11. Synthesis and Imaging of Plasmonic Magnetic NanoparticlesJitKang Lim, Robert D. Tilton, Alexander Eggeman, Frederick Lanni and Sara A. Majetich, Carnegie Mellon University,Pittsburgh, PA

We describe the development of iron oxide-core, gold-shell nanoparticle probes for eventual use in cell or singlemolecule sorting technologies and as intracellular probes. These nanoparticles combine the potential for magneticmanipulation and plasmonic sensing in a single entity. The surface plasmon resonance of gold makes it possible totrack the positions of individual nanoparticles with darkfield microscopy. In addition, the gold shell is more easilybiofunctionalized than the surface of a bare iron oxide nanoparticle. This presentation will emphasize the synthesis andphysical characterization of the hybrid nanoparticles. Eighteen nanometer magnetic cores are first synthesized inorganic solvents, then transferred into water and coated with gold nanoparticle seeds that are further grown to acomplete shell. Transmission electron microscope images obtained at various stages of the process reveal thedevelopment of the core-shell morphology. The completion of the gold shell produces an intensification and pronouncedshift of the surface plasmon resonance peak in the optical absorbance spectrum. These particles aresuperparamagnetic at room temperature. Darkfield optical imaging shows the feasibility of detecting single nanoparticlesundergoing Brownian motion. Magnetophoretic and drag force calculations will be described that indicate the potentialutility of these nanoparticles for microfluidic single molecule and cell sorting applications. The calculations are tested bymeasuring magnetophoretic velocities using darkfield microscopy and a micropatterned magnetic array.

12. Squishy particles: modulating the mechanical properties of polymer vesiclesJames A. Silas, Jeffery Gaspard and Karym Kinnibrugh, Texas A&M University, College Station, TX

Polymer vesicles show great promise as both a targetable delivery vehicle and a platform for cellular mimicry. In pursuitof both these goals, it is important to exercise control over the final properties of the colloid, including surfacechemistry, surface topology and mechanical properties. Since polymer vesicles are self-assembled fluids, they respondto all stresses imposed by the solution by changing shape and size. The self-assembly process is critical to forminguniform and reproducible surfaces on the particles, but limits the conditions in which the particles can be utilized. Tostabilize the vesicles and introduce a structural element to the particles that can be both solution responsive andtunable, we confined hydrophilic monomers inside the polymer vesicles and polymerize them in situ. The crosslinkedparticles are the same size as the starting vesicle population, which can be tailored from several hundred nanometers totens of microns. Since the resulting particles have the same surface as the original vesicle population, this approachallows the mechanical properties of the particles to be tuned independently of the surface chemistry and bilayerproperties. By varying the monomer composition and crosslink density, the deformability of the polymer vesicles may bevaried continuously from a fluid to nearly a solid particle.

13. Bio-polyelectrolyte deposition and stabilisation of mineral colloidal particlesPeter Peter Versluis, Alois Popp, Leonard Flendrig and Krassimir Velikov, Unilever Food & Health Research Institute,Vlaardingen, Netherlands

Polymer - colloidal particle mixtures are encountered in many industrial products like paints, agricultural, home andpersonal care, and pharmaceutical products. Understanding the interactions and stability of such soft mater systems,where biopolymers are added both to alter material and particle surface properties, in many cases remains achallenging task. Here we present results on stabilisation of colloidal particles of sparingly soluble minerals bydeposition of bio-polyeletrolytres. Because of the strong electrostatic interactions with ions, the bio-polyectrolytes canabsorb on the particles, can partially dissolve the colloidal particles, and also form insoluble complexes with free ions.These interactions result in change of stability and material properties of the system.



14. Keynote: Some theory of colloid transport in aquatic environmentsCharles R. O'Melia, The Johns Hopkins University, Baltimore, MD

The author's perspective on the current status of the aquasol transport theory in environmental systems is presented.Gaps in knowledge and future directions are proposed.

15. Effects of surfactant and ionic strength on transport and retention of colloid particles inpartially saturated porous mediaYuniati Zevi, Annette Dathe, Bin Gao, Brian K. Richards, J-Yves Parlange and Tammo S. Steenhuis, CornellUniversity, Ithaca, NY

The effect of surfactant and ionic strength concentration on colloid transport through saturated or partially saturatedmedia has typically been studied using breakthrough curves. In this study, we performed pore-scale observations in asmall flow chamber to quantify colloids retained on the grain, air and liquid interfaces using a confocal microscopesystem and ImageJ image analysis software. Stacks of images were analyzed for colloid retention in tests in which theionic strength and concentration of surfactant (nonionic Surfynol 485) were varied. Colloid retention primarily occurred atthe thin film along the edge of meniscus where the air-water and water-solid (AW, WS) interfaces closely approacheach other (also called the air-water meniscus-solid (AWmS) interface). The results show that colloid retention at theAWmS decreased with increasing concentrations of ionic strength. At the same time more colloids were attached to thesand grains, resulting in overall increased colloid retention with increasing ionic strength. We also observed thatincreasing the surfactant concentration reduced colloid retention at the AWmS interfaces due to decreased contactangle and surface tension. The results are consistent with the theory that capillary forces are mainly responsible forcolloid retention at the AWmS interface.

16. On role of air-water interface and surface tension in colloid transportVolha Lazouskaya and Yan Jin, University of Delaware, Newark, DE

Current environmental and health concerns associated with transport of colloids, bio-colloids, and nanoparticles in soilsand aquifers increase the demand of predictive ability in colloid transport. Although colloid transport and colloid-facilitated transport of contaminants have received close attention in past years, gaps in knowledge remain. To improvefundamental understanding of colloid retention and transport processes, complex natural soil media are often simplifiedto model porous media. At present, the major physical mechanisms involving colloids in unsaturated porous mediainclude retention on solid-water interface (SWI), air-water interface (AWI), and contact line (where all three phasesmeet). Additionally, physical straining of colloids in pore spaces has been discussed in the literature. However, someuncertainties in colloid transport exist, and many are related to colloid retention on air-water interface. While someresearchers considered AWI as an important retention site others did not observe significant retention of colloids onAWI. The capillary structure of porous media suggests the importance of surface tension, and its experimental variationwould provide valuable information about underlying retention mechanisms. In our experiments, we investigate the effectof surface tension on colloid behavior in model static and dynamic systems. The principle experimental design includesan open capillary channel observed with confocal microscope. Such design allows direct observation of colloid retentionon AWI with different surface tensions. In addition to primary retention mechanisms studied in static system, dynamicexperiments aid the estimation of the relative impact of colloid retention on AWI and surface tension values on theoverall colloid transport.

17. Grain Surface-Roughness Effects on Colloidal Retention in the Vadose ZoneVeronica Morales, Cornell University, Ithaca, NY

The retention and release of micron sized particles and organisms in the vadose zone greatly affect the degree ofcontamination to groundwater systems. Existing models need improvement to more accurately predict the physicalconditions under which such particle transportation occur. Recent theory on capillary and friction forces acting at theair/water meniscus/solid (AWmS) interface suggests that grain roughness is an important factor in colloid retention inunsaturated media. The objective of this work is to further investigate the effects of grain surface roughness and size asa primary contaminant transport variable. Unsaturated column experiments with sands of different grain roughness were



performed to determine colloidal retention at the AWmS interface. A rectangular 40 mL acrylic vertical flow chamberwas built to take advantage of collecting visual and numerical data under the effects of gravity. Colloid behavior wasvisualized in situ with digital bright field microscopy and breakthrough colloid concentrations were measured withspectrophotometry. Spherical, 5 ìm sized, synthetic colloids were chosen to emulate homogeneous bacteria in shapeand size. Two sizes of quartz sand were modified and thoroughly pre-cleaned for tests of unaltered and smoothed (bylapidary rotation) grain surfaces. Completed experimental results demonstrate that smoother grain surfaces retain alesser amount of colloids than rougher grain surfaces. This effect has shown to be consistent, although in differentmagnitudes, for both saturated and unsaturated conditions. Current results indicate that the effects of surfaceroughness diminish with increasing grain size.

18. Adsorption of nanomaterials to air-water interfaces in porous media during primarydrainageLixia Chen, David A. Sabatini and Tohren C. G. Kibbey, University of Oklahoma, NORMAN, OK

Nanomaterials are being produced and used in increasingly significant amounts. Although they can enter theenvironment in a number of ways, little is known about their fate or environmental implications as emergingcontaminants. To understand the transport of nanomaterials in the unsaturated zone, the dynamic adsorption ofnanomaterials to the air-water interface during primary drainage was studied in laboratory experiments using twodifferent sizes of glass beads. Three similarly-sized nanomaterials were selected for this work: polystyrene latexnanospheres, and tin oxide (SnO2) and titanium dioxide (TiO2) nanopowders. Measurements involved tracking theconcentration decrease of nanomaterials in the pore solution due to adsorption to air-water interfaces created duringdrainage, and simultaneous tracking of capillary pressure and saturation in the porous medium. A continuous massbalance was used to calculate the mass of nanomaterials adsorbed at air-water interfaces. Results indicate that totalmass adsorbed to air-water interfaces increases with decreasing saturation, as more interfacial area is formed.However, normalization to measured interfacial areas indicates that for most systems, the adsorbed nanomaterial massper unit area is approximately the same for both sizes of glass beads over a wide range of saturations. Experimentswith three different concentrations of SnO2 showed increased adsorption at the air-water interface with increasingconcentration. Differences between the adsorption behavior of the three nanomaterials will be discussed.

19. Colloid deposition in a radial stagnation point flow system: The role of hydrodynamicand DLVO forces

Gexin Chen1, Saeed Torkzaban1, Scott A. Bradford2 and Sharon Walker1, (1)University of California, Riverside,Riverside, CA, (2)USDA-ARS George E. Brown, Jr. Salinity Laboratory, Riverside, CA

The influence of hydrodynamic conditions on the deposition of 1.1 ìm carboxylate-modified polystyrene latexmicrospheres has been investigated using a radial stagnation point flow (RSPF) system. This experimental systemutilized an optical microscope and an image-capturing device to directly observe and determine the colloidal depositionkinetics near the stagnation point. Experiments were carried out under well-controlled solution and surface chemistry,allowing for the sensitivity of colloidal adhesion behavior to be examined under a wide range of hydrodynamicconditions (capillary flow velocity from 0.01 m/s to 0.1 m/s), simulating various natural and engineered environments.Deposition kinetics was quantified at two ionic strengths (0.01 and 0.1M KCl) under electrostatically unfavorable andfavorable attachment conditions (using pure quartz and quartz that was modified to have a positive charge,respectively). Hydrodynamic forces were implicated as an important factor on the initial colloidal deposition under bothunfavorable and favorable conditions. The colloidal attachment efficiency decreased with increasing flow rate and wasalso a function of the system chemistry. To better understand and interpret these observations, numerical simulations ofthe RSPF system were conducted that considered relevant hydrodynamic and DLVO forces. The results of theexperimental and theoretical studies will be presented and the implications for various water quality and industrialapplications will be discussed.

20. Keynote: Imaging the flow of colloidal glassesWilson C. K. Poon, University of Edinburgh, Edinburgh, United Kingdom

Using fast confocal microscopy, it is now possible to study the flow of concentrated colloidal suspension at the singleparticle level. In this talk, I will briefly review this methodology, and present results obtained in two simple flow



geometries: shearing between parallel plates, and pipe flow in a square capillary. Both flows display features thatcannot be understood under a traditional rheology paradigm. Instead, the flows exhibit features reminiscent of granularmaterials. Indeed, in the case of capillary flow, a stress fluctuation model borrowed from granular materials can be usedto understand our observations in considerable detail.

21. Glass-like dynamics of microgel suspensions

Giovanni Romeo1, Alberto Fernandez-Nieves1, Domenico Acierno2 and David A. Weitz1, (1)Harvard university,Cambridge, MA, (2)University of Naples Federico II, Napoli, Italy

Materials consisting of concentrated soft particles closely packed in an amorphous state are found in many day-to-daysystems like pastes, tissues or emulsions. The rheological properties of these systems are usually characterized byslow relaxations and by the existence of a yield stress, among other signatures, reflecting the existence of glassydynamics. A key point in soft condensed matter is to establish a link between the macroscopic properties and themicroscopic structure and dynamics of these glassy systems. We show that suspensions of microgel particles are aflexible model system sharing some of the fundamental characteristics of molecular glasses. Here, the particle sizedepends on external variables, such as temperature and pH, and on the degree of network cross-linking. Size can alsobe tuned with concentration above random close packing, since microgels are then forced to shrink to fit in the givenvolume. By changing any of these parameters the system shows a rich behavior. In particular, it undergoes glass-like toliquid-like to gel-like dynamics as function of temperature; this is shown with bulk rheological measurements and withthe use of dynamic light scattering and confocal imaging to access the system local dynamics.

22. Ideal glass transitions, barrier hopping and viscoelasticity in fluids of nonsphericalcolloidsGalina Yatsenko and Kenneth S. Schweizer, University of Illinois, Urbana, IL

The slow translational dynamics of glassy isotropic fluids of hard polyatomic rods and spherocylinders of aspect ratiosup to forty have been theoretically investigated. The approach is based on a preaveraging of orientational degrees offreedom to a center-of-mass description, and a nonlinear stochastic Langevin equation of motion that includes activatedbarrier hopping on a nonequilibrium free energy profile. Variable site bond length effects have also been studied forsymmetric diatomics and linear triatomics. The excluded volume driven ideal glass transition (GT) boundary is predictedto be a nonmonotonic function of particle length-to-width ratio, and rather remarkably resembles the random closepacking volume fraction of nonspherical granular objects. The location of the rod and spherocylinder ideal GT boundaryrelative to the percolation threshold, isotropic-nematic liquid crystal phase transition, and mechanical jamming volumefraction has been determined. The ideal GT signals a crossover to noise-driven activated barrier hopping dynamics.The consequences of shape anisotropy on the entropic barrier height, localization length, elastic modulus, yield stressand nongaussian dynamic heterogeneity aspects have been studied. The theory has also been applied to suspensionsof rigid disks, in both the isotropic and discotic liquid crystalline state, and the results contrasted with the rod-likesystems.

23. Aging and non-Gaussian dynamics in a colloidal glassGianguido C. Cianci and Eric R. Weeks, Emory Universty, Atlanta, GA

As a hallmark of the glassy state of matter, aging has attracted substantial attention, yet it remains a poorly understoodphenomenon. It manifests itself by a dependence of the dynamical properties of the sample on the time elapsed sincevitrification. The glassy state is also marked by dynamics that are heterogeneous in both time and space, and thatexhibit non-Gaussian statistics over moderate to long timescales. We use a density and refractive index matchedsuspension of micron sized PMMA colloids as a model glassy material. At these length scales, laser scanning confocalmicroscopy allows us to follow the motion of a few thousand particles in real time and real space. We study theinterplay between the timescales at which the dynamics are non-Gaussian and the age of the sample. We also analyzethe spatial extent over which the dynamics are heterogeneous and examine the age dependence of this length scale.

24. Microscopic structure and collapse of depletion-induced gels in vesicle-polymermixtures



Ji Yeon Huh1, Eric M. Furst1 and Matthew L. Lynch2, (1)University of Delaware, Newark, DE, (2)Procter & GambleCompany, Cincinnati, OH

Non-adsorbing polymers are added to colloidal dispersions to tailor their rheological properties. However, this leads to anumber of undesirable phenomena including phase separation and gel collapse. Because they affect the stability ofmany food and personal care products, understanding and controlling these issues remains a crucial aim. In this study,we present the time-dependent collapse and microstructure of depletion-induced vesicle gels. The vesicle dispersion isprepared from a commercial-grade dichain cationic surfactant through a standard milling process (dmean=256nm and Φ=0.46). As a depletant, we add the cationic poly(diallyldimethylammoniumchloride) (MW=14.5kDa and Rg=11.2nm).To investigate the phase behavior, vesicles (Φ=0.05~0.3) are systematically mixed with polymer (Cp=0.01~2.0wt%). Asdensity gradients build up, an interface is developed between a vesicle-rich phase and a polymer-rich phase uptoCp=0.2wt%. Increasing the polymer concentration further forms a gel, which subsequently collapses. Height profiles arecharacterized by a slow initial rising for a finite delay time, a rapid collapse, and a slow final compaction to anequilibrium height. The time-scale associated with the collapse rate is predicted by the poroelastic model [1]. However,we observe a remarkably different polymer concentration dependence on the collapse rate. Unlike other colloidal gels[2], we find the delay time decreases with increasing polymer concentration. We show this surprising behavior can beexplained by considering the permeability for solvent backflow [3], which is directly related to the characteristic porearea of the gel obtained using confocal microscopy.

[1] Manley et al. (2005), [2] Kilfoil et al. (2003), [3] Buscall and White (1987)

25. Origin of the slow dynamics and the aging of a soft glassSylvain Mazoyer, Luca Cipelletti and Laurence Ramos, University of Montpellier and CNRS, Montpellier, France

We study by light microscopy a soft colloidal glass consisting of a compact arrangement of polydisperse elastic spheres.We show that its slow and non-stationary dynamics results from the unavoidable small fluctuations of temperature,which induce intermittent local shear deformations in the sample, because of thermal expansion and contraction.Temperature-induced shear provokes both reversible and irreversible rearrangements whose amplitude decreases withtime, leading to an exponential slowing down of the dynamics with sample age. Moreover, we find that the motion ofthe irreversible rearrangements is close to ballistic, in agreement with our previous light scattering results. Ourobservations provide the first direct experimental evidence of ballistic motion associated with the slow dynamics of avariety of soft glassy materials, as inferred from scattering techniques, and suggest a possibly general mechanism forthese dynamics.

26. Keynote: Langmuir-Blodgett films of oriented collagen films as cell culture substratesGerald G. Fuller, Stanford University, Stanford, CA

It is known that embryonic skin can heal without scarring prior to the first trimester. Although the reasons for thisremarkable ability to recover from a wound are not completely understood, it is known that the nature of the collagenmaking up the embryonic skin becomes progressively disorganized and disoriented with age. This lecture describes amethod of distributing thin layers of soluble collagen at the air/water interface. These films can sustain high surfacepressures and can be subjected to surface flow that lead to uniform orientation of the collagen protein. This orientationis verified directly at the air/water interface by measuring dichroism arising from sirius red dye molecules that areintercalated within the collagen chains. Appropriate Langmuir-Blodgett deposition of the layers onto smooth substratesresults in coatings of uniaxially oriented protein. The influence of collagen orientation on the growth and proliferation ofboth human fibroblast cells and adipose-derived stem cells has been studied. It is demonstrated that these substatescause the cells to become polarized and oriented parallel to the collagen orientation. In addition, the cells proliferate toa much greater extent on the oriented collagen in comparison with standard cell culture media.

27. Barcoded microparticles for multiplexed biomolecule analysis

Patrick S. Doyle1, Daniel Pregibon1 and Mehmet Toner2, (1)Massachusetts Institute of Technology, Cambridge, MA,(2)Massachusetts General Hospital and Harvard Medical School, Boston, MA

High-throughput screening for genetic analysis, combinatorial chemistry, and clinical diagnostics benefits from



multiplexing, which allows for the simultaneous assay of several analytes but necessitates an encoding scheme formolecular identification. Current approaches for multiplexed analysis involve complicated or expensive processes forencoding, functionalizing, or decoding active substrates (particles or surfaces) and often yield a very limited number ofanalyte-specific codes. We present a method based on continuous-flow lithography (Dendukuri et al. Nat. Mat. 2006)that combines particle synthesis, encoding, and probe incorporation into a single process to generate multifunctionalparticles bearing over a million unique codes. By using such particles, we demonstrate a multiplexed, single-fluorescence detection of DNA oligomers with encoded particle libraries that can be scanned rapidly in a flow-throughmicrofluidic channel. Furthermore, we demonstrate with high specificity the same multiplexed detection using single,multiprobe particles.

28. A new biosensor chip: local mapping of mechanical properties using suspended lipidbilayers as “nano drums“

Siegfried Steltenkamp1, Ingo Mey2 and Andreas Janshoff2, (1)University of California, Santa Barbara, CA,(2)Johannes Gutenberg Universitaet, Mainz, Germany

Suspended bilayers, which bridge the gap between solid-supported and black lipid membranes, have been developedto cover a of porous alumina substrates. The so called “nano drums”, help solve the problem of close membranesurface contact and concomitant limited lateral mobility. Scanning force microscopy was employed in order to visualizeand probe the free standing membranes with regard to mechanical stability. The starting point is a planar gold-coatedalumina substrate with a chemisorbed 3-mercaptopropionic acid monolayer displaying circular pores of very well definedand tunable size, over which N,N,-dimethyl-N,N,-dioctadecylammonium bromide or N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl-sulfate bilayers are spread. Indenting these “nano drums” centrally with an AFM tip yieldsforce-indentation curves which were quantitatively analyzed by solving the corresponding shape equations of continuumcurvature elasticity. Since the measured response depends in a predictable way on the system geometry (pore size, tipradius) and on material parameters (bending modulus, lateral tension), this opens the possibility to monitor local elasticproperties of lipid membranes in a well-controlled setting by addressing each pore separately. Thus we have developeda technique for forming a biosensor, utilizing suspended bilayers allows for the first time to locally determine themechanical properties of the bilayer such as bending modulus or surface tension.

29. Hyaluronan-based hydrogel particles and particle crosslinked networks with tunablemechanical propertiesXinqiao Jia, University of Delaware, Newark, DE

Recent studies suggest that cells preferentially differentiate on artificial extracellular matrices that have mechanicalstiffness similar to that of their natural tissues. Therefore, hydrogels to be used for soft tissue regeneration need exhibitviscoelasticity that approximates that of the targeted tissue. To this end, we have developed hyaluronan (HA)-basedsoft hydrogel particles (microgels and nanogels) with controlled size, chemistry and structure. HA microgels wereprepared by in situ crosslinking of chemically modified HAs within an inverse microemulsion stabilized by Span 80.Similarly, HA nanogels were synthesized by in-situ crosslinking of HA with divinyl sulfone (DVS) using the AOT reversemicelle system. In vitro cytotoxicity studies using vocal fold fibroblasts indicate that these hydrogel particles areessentially non-toxic. HA microgels exhibit residual functional groups that can be used to form doubly crosslinkednetworks (DXN) with tunable viscoelasticity. Alternatively, free radical polymerization/crosslinking of acrylamide (AAm) inthe presence of HA nanogels resulted in semi-interpenetrating networks (IPN) that are highly elastic. Mechanicalmeasurements using torsional wave apparatus indicate that the HA DXN have mechanical properties similar to that ofthe vocal fold mucosa; whereas the HA/PAAm IPN exhibit viscoelastic responses close to that of the vocal ligament.Controlled release of model drugs was achieved through their anchorage at predetermined locales of the particulatehydrogel system. These materials are promising candidates for vocal fold tissue regeneration.

30. Multilayer drug delivery films studied by sum frequency generation spectroscopy andattenuated total reflection fourier transform infrared spectroscopyMichael E. Pedley, Michael T. L. Casford and Paul B. Davies, University of Cambridge, Cambridge, United Kingdom

Hydroxypropylmethylcellulose (HPMC) matrices are commonly used as drug delivery media providing controlled release



of pharmaceuticals. HPMC films also find application as tablet coatings, rapid release carrying media and buccaldelivery systems. Combining thick films of water soluble, swellable and edible polymers with a substrate material, forexample polyethylene terephthalate (PET) film, to reinforce the polymer media presents the potential to create adisposable topical or buccal drug delivery system.

While films of HPMC and PEG on their own have been extensively studied, the use of multilayer films as drug carryingsubstrates has not been widely considered. In particular the structure of cast films of HPMC has not received muchattention using vibrational spectroscopy. For example, the techniques of attenuated total reflection fourier transforminfrared spectroscopy (ATR-FTIR) and sum frequency generation spectroscopy (SFG) have not been extensively usedfor this purpose.

This work reports studies on mixed films of HPMC or PEG cast upon a PET film, using both ATR-FTIR and SFGtechniques. Whilst the former provides information about many different functional groups and about how water isincorporated in or near the film, the SFG technique provides information in the C-H stretching region only but whichnevertheless is interface specific. Results will be presented on the stability of the films in aqueous environments underboth static and flowing conditions. These results will precede experiments designed for controlled release ofpharmaceutical or taste additives enclosed in composite films of two or more layers.

31. Polycation-Clay Composites as a Basis for Controlled Release Herbicide FormulationsYael G. Mishael and Adi Radian, Hebrew University of Jerusalem, Rehovot, Israel

Herbicide controlled release formulations (CRFs) are designed to reduce undesired herbicide leaching and increase theherbicide concentration at the top of the soil for reduced soil and water contamination and improved herbicidal activity.In the current study we developed novel CRFs for the anionic herbicide imazapyr (IMP) based on its binding to polydimethyldiallylammonium chloride (PDADMAC)-montmorillonite composites. Polycation adsorption on the clay was rapidand reached a high loading of 0.9 g/g which results in charge reversal of the surface. Fourier transform infrared and X-ray diffraction of the composites indicated electrostatic interaction between the polycation and the surface, intercalationof the polycation in the clay and formation of loops and tails on the surface at high polycation loadings. Such aconfiguration, in comparison to a train configuration, creates available positive binding sites resulting in high IMPbinding. However, IMP binding to the composites was found to be affected not only by polycation configuration but alsoby composite flocculation. Upon adding high concentrations of IMP to a PDADMAC-montmorillonite composite (0.16 gpolymer/g clay) a high herbicide loadings was reached (66% active ingredient). Testing IMP release from formulationsapplied on a thin layer of soil demonstrated that its release from PDADMAC-montmorillonite formulations wassubstantially slower than its release from the commercial formulation. The ability of the newly designed formulations todecrease leaching while maintaining good herbicidal activity was demonstrated by applying a soil column bioassay.

32. Keynote: Self-assembly of colloids: The shapes of things to comeSharon Glotzer, University of Michagan, Ann Arbor, MI

Recent breakthroughs in particle synthesis leading to nanocolloidal particles of unusual shape and patterning havepaved the way for a revolution in materials formed from the self-assembly of these building blocks. The unprecedentedanisotropy of today's new nanoparticle and colloidal building blocks starkly contrasts with the isotropic, spherical colloidsthat have been the focus of particle assembly for more than a generation. No general theory exists to predict the rangeof structures possible for these new building blocks as a function of thermodynamic conditions, and the complementaryproblem of inverse design of a particular building block that can self-assemble into a desired target structure is difficultwith as yet no standard design algorithm. In this talk, we present a conceptual framework with which to consider thekey factors controlling the assembly of these new building blocks. We present results of computer simulations of patchyparticle nanoparticle design and assembly, and show how various measures of anisotropy, including particle shape,patterning, functionalization and interaction selectivity, can be combined and exploited to achieve complex mesoscaleone-, two- and three-dimensional structures such as wires, sheets, virus-like shells and colloidal “molecules”, diamond,icosahedral, gyroid, and other complex structures through self-assembly.

. DNA directed assembly of non-close-packed colloidal crystalsPaul V. Braun, Margaret Shyr, Daryl Wernette, Yi Lu and Pierre Wiltzius, University of Illinois at Urbana-Champaign,



Urbana, IL

DNA directed assembly of non-close-packed colloidal crystals

34. An investigation of the assembly conditions of dielectric particles in polymers using theelectrorheological effect

Jacques Persello1, Aladin Kossi1, Bernard Cabane2 and Georges Bossis3, (1)University of Franche-Comte,Besancon, France, (2)Ecole superieur de physique et de chimie industrielles, Paris, France, (3)University of Nice SofiaAntipolis, Nice, France

Some fluids can respond to an applied electric fluid, switching from a disordered structure with a fluid-like response toan ordered structure with a solid-like response. These fluids are called electrorheological fluids. These fluids are madeof polymeric materials into which colloidal particles are dispersed. When an electrical field is applied, the particles arepolarized and become small electrical dipoles. If the field exceeds a certain threshold, these dipoles attract each otherand assemble into chains that are aligned along the field direction.

We show that electric field induced ordering of dielectric nanoparticles in a polymeric liquid is a potential fabricationmeans to assemble nanoparticles-polymer composites. The resulting composite material consists of a quasi 1–3connectivity pattern due to the formation of chains by the nanoparticles. The degree to which these rows form isstrongly dependent on both the magnitude and frequency of the applied field.

A critical feature in the performance of such fluids is the control of interparticle interactions. We report a real-time,Small Angles Neutrons Scattering and dynamic rheological measurements study of the evolution of structure in aelectrorheological fluid during the particles ordering. When an electrical field was applied, a two-dimensional set ofdiffraction spots was obtained, located in the direction of chain alignment. The spacing of these diffraction spots yieldsthe average interparticle distance, which is found to vary with the electrical field, the field frequency and the surfacechemistry of the nanoparticles.

35. Disappearance of the gas-liquid phase transition for highly charged colloidsAntti-Pekka Hynninen and Athanassios Z. Panagiotopoulos, Princeton University, Princeton, NJ

We calculate the full phase diagram of spherical charged colloids using Monte Carlo free energy calculations. Thesystem is described using the primitive model, consisting of explicit colloids and counterions in a uniform dielectriccontinuum. We show that the gas-liquid critical point becomes metastable with respect to a gas-solid phase separationat colloid charges Q>=20e. Figure shows the phase diagram for colloid charge Q=20e in the colloid packing fraction,reduced temperature representation. The phase diagram consists of a broad gas-solid phase coexistence at lowtemperatures, a narrow fluid-solid coexistence at high temperatures, and a metastable gas-liquid coexistence (whosecritical point marked by the star). Employing approximate free energy calculations, we are able to determine the criticaltemperature Tc below which a broad gas-solid phase separation occurs for highly charged colloids up to Q=2000e andpropose a scaling law Tc = Q^0.5. We therefore extend the knowledge of like-charge attraction from modestly chargedmicellar systems with charge Q < 100e to highly charged colloidal suspensions with Q=2000e.



36. Patchy Particles and their Assembly PropertiesIlona Kretzschmar, The City College of City University of New York, New York, NY

Our work is concerned with fabricating particles with reactive patches and testing the assembly and interactions ofthese particles. Specific spatial modification of spherical particles with patchy anchor points presents an exciting newarea of directed particle assembly. The position of the patches, the patch material and possibly linker moleculesassembled onto these patches as well as the patch roughness result in a variety of new parameters important for theassembly, which may allow predicting of structures and directing of particles into desired structures.

We have developed methods for the synthesis of silver- and gold-capped 2.4 µm polystyrene particles using bothtemplate-assisted electroless deposition1 and physical vapor deposition. We find that electroless deposition results inpatches with rough surfaces, while vapor deposition gives much smoother patch surfaces. We have begun to study theassembly of these patchy particles into two-dimensional monolayer films. In addition, we have employed a latticedensity functional method to model parameters important for patchy particle assembly such as temperature,concentration and binding strength.2

We will report our results from the two- and three-dimensional assembly of the patchy particles. For example,preliminary data show a striking difference in the assembly of particles with rough and smooth patches.

1) Cui, J.; Kretzschmar, I. Langmuir 2006, 22, 8281-8284.

2) A. B. Pawar, I. Kretzschmar, G. Aranovich, M. D. Donohue J. Phys. Chem., 2006, in press.

37. Dielectrophoretic assembly and electrohydrodynamic mobility of "Janus" particles in ACelectric fields

Sumit Gangwal1, Olivier J. Cayre1, Martin Z. Bazant2 and Orlin D. Velev1, (1)North Carolina State University, Raleigh,NC, (2)Massachusetts Institute of Technology, Cambridge, MA

The synthesis of “Janus” particles (whose hemispheres are physically or chemically different) is of growing importancefor the development of novel materials, but the behavior of such particles in external fields has not been studied indepth. We investigated the effect of external AC electric fields on Janus particles consisting of a dielectric hemisphereand a conductive hemisphere. The operational diagram of particle response and structure assembled as a function offrequency and field intensity will be presented. At low frequencies (< 10 kHz) of the applied AC fields, the tangentialcomponent of the electric field on the polarized double layer at the metal-dielectric interface leads to directional ionicflow along the surface. This AC electrohydrodynamic (EHD) flow forces the particles to move normal to the electric fieldwith their dielectric hemispheres facing forward. We present the first experimental verification of this EHD effect, whichhas been recently predicted theoretically. The EHD effect is suppressed in AC electric field of higher frequency (> 15kHz). In this case the particles self-assemble by dielectrophoresis into new types of metallodielectric colloidal crystals,where the metallized halves of neighboring particles align into conductive lanes through the crystals (see Figure). Thepropelling metallodielectric particles could be used as microscopic mixers, "shuttles" and self-propelling on-chipsensors. Their self-assembly at high frequency could be used in the fabrication of photonic crystals of new symmetries,massively parallel waveguides, and materials with directional electrical and heat transfer.



38. Keynote: Controlling the packing of block copolymer micelles: interfacial tension,depletion, and superlatticesTimothy P. Lodge and Sayeed Abbas, University of Minnesota, Minneapolis, MN

Solutions of block copolymers in selective solvents exhibit a rich variety of structures, both intramicellar (spheres, disks,worms, vesicles…) and intermicellar (fcc, hcp, bcc, A15, AB13,…). The choice of structure may be dictated by a host ofvariables, including block molecular weights, concentration, choice of solvent, temperature, blending, and addition ofhomopolymers. In this talk we will describe three illustrative examples, involving (i) the control of micelle morphology bytemperature, (ii) the disruption of ordered phases by addition of homopolymer, and (iii) the formation of superlattices bymixing two different micelle populations. Scattering techniques (X-ray, neutron, and light) play the crucial role inquantifying these phenomena.

39. Morphological Transitions in dilute region of CTAB/SDS/Water system: a SAXS studyA.S. Abdul Rasheed and Jayesh R. Bellare, Indian Institue of Technology,Bombay, Mumbai, India

Mixtures of oppositely charged surfactant in aqueous system self assemble to form to a variety of microstructures suchas micelles, vesicles, lamellar sheets and nano discs. In this study, various microstructures arising in the water richcorner of CTAB/SDS/Water system with excess anionic surfactant is evaluated with Small Angle X-ray Scattering(SAXS) and the partial phase diagram is obtained. Unique microstructural transformation in the presence of excessanionic surfactant at the dilute region led to prolate micelles first transforming to spherical micelles and then to rod-likemicelles. The strong electrostatic interaction between ions in these mixed surfactant aqueous solutions leads to phaseseparation with multitude of microstructures. The size and shape of a self–assembled aggregate is the product of abalance between different free energy contributions. In order to minimize the electrostatic repulsions between the polarhead groups pure SDS self-assemble to form prolate micelles. Upon addition of the cationic surfactant CTAB to SDS,electrostatic attraction circumvents repulsion between like charges of the surfactant, and elongated microstructuresevolve by counteracting the initially formed anisotropic structure. The growth and transition of micelles from prolate torod-like is evident from SAXS scattering curves. Also, spontaneous formation of vesicles is observed at a locus ofconcentrations depending on mole fractions of the surfactant mixture and the overall concentration. Light scatteringconfirms that vesicles are poly disperse with average size of 200 nm. Transition from micelle to vesicle seems to be firstorder from the study.

40. Fast Dynamics of Wormlike MicellesFlorian Nettesheim and Norman J. Wagner, University of Delaware, Newark, DE

We present first measurements of the segmental diffusion of cationic wormlike micelles using neutron spin echo (NSE).The measured scaling of the relaxation rate with wavevector is observed to follow the predictions of Zilman andGraneck ( Phys. Rev. Lett., 1996) for semi-flexible chains. The rate of segmental diffusion does not depend strongly oneither surfactant or salt concentration, in agreement with expectations. NSE has been proposed as a method todetermine the bending constant kappa and thus persistence length (lp=kappa/kT) of wormlike micelles; howeverprevious measurements on nonionic WLMs by (Seto et al. J. Phys. Chem. Solids, 1999) showed large discrepancies



with light scattering measurements. Here, we resolve these discrepancies by identifying the lower cut-off length for thebending modes a, which is a parameter in the theory. Therefore, NSE is demonstrated to be a quantitative tool todetermine the bending modulus and persistence length of wormlike micelles.

41. Scattering form-factors for self assembled Y-junctions

Tobias Foster1, Samuel A. Safran2, Thomas Sottmann1 and Reinhard Strey1, (1)University of Cologne, Cologne,Germany, (2)Weizmann Institute of Science, Rehovot, Israel

Networks of branched cylinders are found as microstructures in many different self-assembled systems such asmicroemulsions, dipolar fluids or tubulin- and actin-filaments. In order to structurally characterise these cylindernetworks, we have calculated the scattering functions that can be used to analyse small angle neutron scattering dataobtained from such microstructures. We first focused on microstructures with high densities of network junctionsconnecting the cylindrical elements. In this limit, the network microstructure can be regarded as an assembly ofrandomly oriented, closed packed network junctions (i.e. we neglect the cylinder scattering contributions). In this case,the scattering spectrum of the network microstructure can be calculated as the product of the junction number density,the junction form-factor, that describes the scattering from a single junction, and a structure factor, that describes thelocal correlations of different junctions due to junction interactions (including excluded volume type interactions). In asecond approach, we included the cylinder scattering contribution in the junction form-factor. The theoretical predictionsare compared with results of scattering measurements of several microemulsion systems.

42. Analysis of Microemulsions Containing a pH-Degradable Alkyl Ethoxylate Surfactant bySmall-Angle Neutron Scattering

Douglas G. Hayes1, Javier A. Gomez del Rio1, Mayson H. Alkhatib2, Volker S. Urban3, J. S. Lin3 and GuangmingLuo3, (1)University of Tennessee, Knoxville, TN, (2)University of Alabama in Huntsville, Huntsville, AL, (3)Oak RidgeNational Laboratory, Oak Ridge, TN

A 1,3-dioxolane alkyl ethoxylate surfactant (CK) that undergoes hydrolysis in acidic pH has been successfully combinedto form binary surfactant systems with Aerosol-OT (AOT), employed to form 3-phase microemulsion systems with waterand heptane which effectively isolate proteins (within the middle, bicontinuous microemulsion phase), and temperature-insensitive phases that may be useful for drug delivery. Small-Angle Neutron Scattering (SANS) experiments have beenuseful in further understanding the systems' nanostructures. SANS analysis of water-in-oil microemulsionsdemonstrates that the substitution of AOT with CK (20%) has no effect on geometrical parameters, but greatlyincreases the level of attractive interactions. At 20-25% surfactant (equimolar amounts of AOT and CK) and sub-ambient temperature, highly anisotropic phases form, with a reversible transition to a less-ordered, slightly anisotropicsystem occurring upon the increase of temperature and salinity. Analysis by polarized light microscopy suggests theiridentity as reverse hexagonal phases. SANS analysis using three different contrasts is consistent with a cylinder formfactor, in agreement with the H2 assignment, but inconsistent with H2's structure factor. SANS analysis of protein-containing middle (bicontinuous) phases of 3-phase systems suggest that proteins with amphiphilic structure, such ascytochrome c, alter the nanostructure, and that oil-in-water microemulsions form in the bottom, aqueous, phase.

43. Interplay between surface and solution behaviour in di-alkyl chain cationic / nonionicsurfactant mixturesJeffrey Penfold, ISIS , CLRC, Didcot, United Kingdom, I. Tucker, Unilever Research and Development Laboratory, PortSunlight, United Kingdom and R. K. Thomas, Oxford University, Oxford, United Kingdom

Understanding the complex surface and solution behaviour of di-alkyl chain cationic and nonionic surfactant mixtures isimportant for a wide range of applications including detergents, shampoos, and conditioners. Furthermore, by analogy,it has wider implications for membrane solubilisation, a key technique in biochemistry, and for the manipulation ofmembrane properties.

Neutron reflectivity, small angle neutron scattering, light scattering, and surface tension have been used to characterizesurface and solution behaviours of the cationic surfactant, di-hexedecyl dimethyl ammonium bromide, DHDAB, with arange of different nonionic surfactants, from C12E3 to C12E12.



Solution phase behaviour for the different cationic / nonionic mixtures has been determined in some detail. For thenonionic surfactants C12E6 and C12E12 the nonionic rich region of the phase diagram is comprised of mixed globularmicelles. For the cationic rich composition the predominant microstructures are bi-lamellar to multi-lamellar vesicles andLβ lamellar phase. At intermediate compositions there is a coexistence region comprised of micellar and planarstructures in coexistence. For C12E3 the phase behaviour is different and shows an evolution of different planarstructures with composition.

The surface behaviour is characterized by a much more marked departure form ideal mixing than is normallyencountered in surfactant mixtures. For solutions rich in cationic the surface adsorption is dominated by the cationicsurfactant, and the nonionic only competes for the surface for solutions rich in the nonionic surfactant. It is shown howthis surface behaviour is correlated with the solution phase behaviour which is determining the relative monomercomposition and concentrations.

44. Keynote: Self-Assembly: Connecting academia with industrial perspectivesAlex Lips, Unilever, Trumbull, CT

TBA

45. Self-assembly in anhydrous sugar glassesHiteshkumar Dave, Chia-Chi Ho and Carlos Co, University of Cincinnati, Cincinnati, OH

In aqueous systems, the hydrophobic effect drives the self-assembly of amphiphiles into a broad range of micellar, rod-like, bicontinuous, and liquid-crystalline complex fluids, which have myriad biological, materials, and productapplications. Amphiphilic self-assembly is not limited to aqueous systems, however. Replacement of water withsupercritical carbon dioxide, for example, results in complex fluids that combine the best properties of gases andliquids. Along this vein, we explored the self-assembly of surfactants in anhydrous sugars, where the low-cost, water-solubility, low toxicity, and stabilizing properties of glassy sugars make them ideal water-replacements for manypharmaceutical, food, and materials synthesis applications.

A recent letter to Nature Materials reported how anhydrous powders of sugars and surfactants suspended in oil canspontaneously form molten glasses with nanometer size domains of sugar and liquid oil without mixing. In thispresentation, we will discuss the latest findings on the liquid-crystalline phase behavior and microstructure ofglucamide- and lactobionamide-based surfactants in sucrose/trehalose glasses.

46. Surfactants for carbon dioxideJulian Eastoe, University of Bristol, Bristol, United Kingdom

For some 15 years the attainment of efficient, non-fluorinated CO2-active surfactants has been a “Holy Grail” forresearchers spanning pure and applied chemical sciences. This talk outlines the history of small molecule CO2-activesurfactants, from the first tentative observations with fluorinated compounds in 1991, up to recently discovered fluorine-free oxygenated amphiphiles.

Reference Surfactants for CO2 Julian Eastoe, Sarah Gold, David C Steytler, Langmuir 2006, 22, 9823-9842.

47. Characterization of nanostructures of mixed surfactant aggregation using AnalyticalUltracentrifugationShaohua Lu and Ponisseril Somasundaran, Columbia University, New York, NY

Nanostructures of aggregation determine the behavior and performance of surfactant systems, especially surfactantmixtures. However, the characterization of nanostructures remains a challenge due to the lack of techniques. Analyticalultracentrifuge (AUC) was first successfully used to study surfactant micellar systems to obtain quantitative data onmicelles including size, shape, aggregation number and diffusion coefficients. Various mixed surfactant systems andindividual surfactants involved have been studied using AUC in this work, including both nonionic/nonionic and



nonionic/ionic combinations. The aggregation numbers obtained for sugar based n-dodecyl-â-D-maltoside (DM) andnoneyl phenol ethoxylated ester (NPn) are in accordance with literature values. In contrast, those for anionic sodiumdodecyl sulfate (SDS), cationic dodecyltrimethylammonium chloride(DTAC) and the cationic gemini surfactant aresmaller than the literature values, because the electrostatic repulsion reduce the sedimentation velocity. Sphericalmicelles were identified in mixed DM/SDS and DM/DTAC systems, while cylindrical micelles were observed in mixednonionic DM/NPn and NPn/NPm system,. It was found that the decrease of the average number of ethoxylated groupsin NPn surfactants increases the size and aggregation number of the system and also causes a shape transition fromspherical to cylindrical. Interesting to note that the coexistence of two different types of micelles was identified in themixed nonionic systems, depending on the mixing ratio. The information obtained will help quantitatively understand thepacking of surfactant molecules in micelles, which leads to a relationship between the nanostructure of aggregates andthe chemistry of the molecules.

48. Characterization of alkyl polyglucoside microstructure and phase behaviorChristina M. Russo and Eric W. Kaler, University of Delaware, Newark, DE

Due to rising environmental concerns, nonionic alkyl polyglucosides, such as decyl-b-glucoside (C10bG1) anddodecyl-b-glucoside (C12bG1), have been seen as an alternative to conventional surfactants. Unfortunately, thesenonionic surfactants phase separate at the concentrations and temperatures of interest. A common solution to thisproblem is the use of hydrophilic co-surfactants, in this case the maltosides, to close the miscibility gap. Our interest isto link the thermodynamics of the phase behavior with changes in micellar microstructure. The model of Zilman et al.(Langmuir, 2004) provides a way to do this by connecting the formation of a saturated network to phase separation.

This model has been fitted to cloud point data of aqueous solutions of C10bG1/C10bG2 and C12bG1/C12bG2. Thetransition in micellar shape from spheres to cylinders was characterized using quasi-elastic light scattering (QLS), andthe micellar network region was probed using small angle neutron scattering (SANS), pulsed-gradient spin-echoneutron magnetic resonance (PGSE NMR), and direct imaging cryogenic transmission electron microscopy (cryo-TEM).

49. In-situ polymerization and self-assembly of cationic surfactantsKathryn A. White, Edinburgh University, Edinburgh, United Kingdom and Gregory G. Warr, The University of Sydney,Sydney, Australia

Polymerization of self-assembled amphiphiles with preservation of nanostructure is a goal that is not commonlyachieved. Often the properties of the monomer and the oligomers produced as reaction proceeds differ so dramaticallythat the polymerized structure is unrecognizable from its starting point. Successful control over self-assembly as thestructure evolves from dynamic equilibrium into a permanently-rendered polymerized state offers a novel route to thepreparation of hierarchically structured, functional and novel composite materials.

In this work we will describe a base-catalysed ionic polymerization of derivatives of cationic, N-alkylpyridiniumsurfactants that may be carried out in polar or aqueous solutions. The reaction may be started and stopped at will byaddition of base or acid, allowing oligomer distributions to be isolated and characterized. Characterization of the micellesand lyotropic phases formed by the monomer and oligomer mixtures by optical microscopy and small-angle x-rayscattering will be described.

We will also report on the in-situ polymerization and controlled reorganization of an aqueous micellar solution ofmonomer into a dispersion of polymerized hexosomes. Using real-time kinetic small-angle neutron scattering togetherwith SAXS and electron microscopy characterization of the nanostructured dispersion, we will demonstrate how the sizeof the hexosomes can be controlled by acid quenching.

50. Keynote: Surfactant Effects at Alkane-Water Interfaces: Freezing and DeformationColin D. Bain, Durham University, Durham, United Kingdom

Surfactants have dramatic effects on the properties of oil-water interfaces. This talk will describe two avenues ofresearch conducted in our group in recent years. The first concerns surface freezing. Pure alkanes are almost unique inshowing surface freezing at the air-liquid interface. Interfacial freezing is not observed at the alkane-water interface, but



can be induced by the presence of surfactants. One consequence of interfacial freezing is that the interfacial tensioncan vanish. The second area of research concerns the deformation of emulsion droplets with optical fields. Opticaltweezers do not normally deform oil droplets since the force constant of optical traps is much weaker than theinterfacial tension. Near microemulsion phase boundaries, the interfacial tension drops to ultralow values and opticalfields can then be used to sculpt the shape of droplets. One unexpected observation is the formation of stablenanothreads of oil.

51. Lateral Adhesion Balance (LAB) -- a Novel Surface Characterization TechniqueRafael Tadmor, Lamar University, Beaumont, TX

Drop lateral adhesion to a surface and the condition for drop sliding along a surface are key issues in many disciplinesincluding biophysics, environmental science, fluid dynamics and agriculture. Yet, to date, except for the tilt stagemethod, which is extremely limited in range of forces, there is no systematic experimental instrumentation to measurethe forces required for drop sliding. We present a new instrument that uses centrifugal forces to slide any drop along asurface. Beyond extending the range of measurable drop-surface interaction, the instrument enables decoupling ofsome parameters that are bound to be coupled with the simple tilt stage method. Specifically the tilt stage method hastwo variables varying at the same time: the lateral and normal forces. This violates a fundamental principle ofexperimental science which leads to obscured understanding of surface characteristics. The LAB avoids this problem.

52. Classification of Nano-Friction Characteristics of Silica Surfaces in Electrolyte SolutionsInvestigated by AFME. Taran, D.C. Donose, I.U. Vakarelski, H. Shinto, Y. Kanda and Ko Higashitani, Kyoto University, Kyoto, Japan

We conducted very carefully a series of friction measurements between completely-hydrophilic silica surfaces in variouselectrolyte solutions of normal and high pH's, and found that the friction behaviours are classified into 4 Cases.

In the case of normal pH, the lubrication was observed for solutions of mono-valent cations, which was classified asCase A, although the degree of lubrication depends on the kind and concentration of cations. As for the divalentcations, the transition from Case A to Case B was found with increasing hydration enthalpy of cations. In the case oftrivalent cations, the behaviour was classified as Case, where the anions play an important role.

In the case of high pH, the surfaces were hairy-like and elastic. It was found that (1) the relation of the friction FL vs.the loading force L is non-linear, (2) whether the friction behaviour was classified as Case C or D depends on theadhesive property of adsorbed layers of cations on the hairy-like surfaces. The interesting relation of FL vs. v shown inCase B and D was explained theoretically. The details will be given in the talk.

53. Surfactant Adsorption at the Air-Liquid and Hydrophobic Solid-Liquid Interfaces:Unraveling the Mechanism for Superspreading

Makonnen M. Payne1, Alexander Couzis2 and Charles Maldarelli2, (1)Graduate School of CUNY (City College of NewYork), New York, NY, (2)The City College of New York, New York, NY

In this paper we report our findings with regard to the synergistic interactions between polyethylene oxide surfactants ofthe general structure CiEj and compare the behavior to a known super wetting surfactant. Pendant drop tensiometryexperiments and sessile drop contact angle measurements on hydrophobic surfaces were conducted on combinations ofCiEj surfactants with 1-dodecanol. We found that a number of combinations were capable of reducing significantly theair-liquid tension, however only systems that exhibited the propensity to form extended liquid crystalline phases, asshown by the combination of cross-polarized microscopy, cryo-TEM, and light scattering experiments, were able toimprove on the wetting performance of the these systems. We have also conducted the parallel experiment focused onthe surfactant adsorption at the hydrophobic solid-liquid interface. Using in-situ infrared internal reflection spectroscopyand complimentary sum-frequency generation spectroscopy, we are able to dynamically interrogate the surfactantadsorption kinetics and interfacial water structure evolution at the hydrophobic solid-liquid interface. We will relate thesefindings to gain insight into the molecular requirements for superspreading.

54. Adsorption of highly extended polymers using Optical Reflectometry



Shaun C. Howard1, Vincent SJ Craig1, Erica Wanless2 and Paul Fitzgerald2, (1)the Australian National University,Canberra, ACT, Australia, (2)The University of Newcastle, Callaghan, NSW, Australia

Optical Reflectometry (OR) is a form of ellipsometry that is used to measure adsorption of surfactants, polymers andparticles at the solid-liquid interface and is ideal for following the kinetics of adsorption. Certain polymer systems havebeen shown to produce unphysical results when observed using the standard OR setup including some adsorbedpolymeric layers measuring up to several hundred nanometres in thickness. These systems yield an apparent negativeadsorption at the interface when measured by OR. Investigation of this phenomenon has revealed that this occurs inpart due to the minimal difference in the refractive indices of highly solvated adsorbed polymer and solvent. Furtheranalysis has resulted in a more robust model for the OR technique which greatly broadens its applicability to themeasurement of polymers and particles which were previously impractical.

Recent developments in the technique of Optical Reflectometry will also be presented. These include improvedversatility in substrate selection and the effect of external forces on adsorption.

55. Ion-specific bubble coalescence inhibition in single and mixed electrolytesChristine L. Henry and Vincent S.J. Craig, Australian National University, Canberra, Australia

Ion specificity is at the heart of many biological processes and is important in all soft matter systems at high electrolyteconcentrations, under which conditions the double layer interaction is screened and short-range forces determinecolloidal behavior. Consequently interactions become considerably more complex and the precise character (charge,size, polarisability etc.) and pairing of ions are important. It remains a great challenge for colloid scientists to develop adetailed understanding of ion-specificity.

A simple system that reveals such complex behavior is that of gas bubbles in salty water. For one hundred years it hasbeen recognized that some electrolytes at sufficiently high concentrations can inhibit bubble coalescence relative to thepure liquid. Electrolytes inhibit coalescence or have no effect as predicted by ion combining rules based on empiricalcation and anion assignments. The mechanism behind electrolyte inhibition, as well as the salt differentiation, is notunderstood.

I here report a considerable volume of work on measurements of surface tension and bubble coalescence in aqueoussolutions of both single electrolytes and electrolyte mixtures. This has enabled us to rule out surface tension effects asthe mechanism of bubble coalescence inhibition. Mixed electrolyte results are consistent with the hypothesis recentlyput forward by Marcelja, that electrolyte effects depend upon ion separation within the interfacial region. I exploremechanisms by which the organization of molecules at the interface can control film rupture at separations of tens ofnanometers. We have further extended our investigation to electrolyte effects on bubble coalescence in non-aqueoussolvents.

56. Keynote: Alcohol Reforming over Pd/ZnO CatalystsJohn Vohs, University of Pennsylvania, Philadelphia, PA

Alcohol Reforming over Pd/ZnO Catalysts



57. Reforming of Oxygenates for H2 Production on Bimetallic Surfaces

Orest Skoplyak, Mark A. Barteau and Jingguang G. Chen, University of Delaware, Newark, DE

Production of hydrogen for use in fuel cells can be achieved by selective reforming of oxygenates. The oxygenates maybe derived from renewable biomass and offer advantages such as low toxicity, low reactivity and compatibility with thecurrent infrastructure for transportation and storage. In this study, the reactions of oxygenates, such as methanol,ethanol and ethylene glycol, were investigated on 3d-Pt(111) bimetallic surfaces using temperature-programmeddesorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and Density Functional Theorycalculations (DFT). The bimetallic surfaces were prepared by physical vapor deposition (PVD) of the desired secondmetal onto Pt(111), using Auger electron spectroscopy (AES) to monitor surface compositions. Oxygenates reacted on3d-Pt(111) to primarily form H2 and CO. Surfaces prepared by deposition of a monolayer of Ni on Pt(111) at 300 K,designated as Ni-Pt-Pt(111), displayed increased reforming activity compared to Pt(111), subsurface monolayer Pt-Ni-Pt(111), and thick Ni/Pt(111). The experimentally measured reforming yield displayed a linear trend with the surface d-band center for both ethylene glycol and ethanol. The reforming activity increased as the surface d-band center movedcloser to the Fermi level, opposite to the trend previously observed for hydrogenation reactions. DFT results indicatedthat the binding energy of methanol and ethanol increased as the d-band center of the bimetallic surface shifted closerto the Fermi level, which could be achieved by choosing 3d metals from the left side of the periodic table as thesurface monolayer. Further studies are underway to investigate oxygenate reforming on other 3d-Pt-Pt(111) bimetallicsurfaces.

58. Photocatalytic properties of ETS-10 & ETVS-10s toward the reduction of VOCsMichael J. Nash, Anne Marie Shough, Doug Doren and Raul Lobo, Univesity of Delaware, Newak, DE

We have investigated ETS-10 and vanadium-incorporated ETS-10 as photocatalysts for the reduction of volatileorganic components (VOCs) since their unique structure may help elucidate the material and surface properties neededto overcome some of the disadvantages of traditional semiconductors like anatase. ETS-10 is a microporoustitanosilicate composed of octahedral chains of TiO6 embedded in a tetrahedral SiO4 framework. These chains stackperpendicular to each other to form a 7.5 Å, three-dimensional channel structure with an ideal stoichiometry of (Na,K)2TiSi5O13. Vanadium has been shown to substitute for the titanium along the chain forming (V/(V+Ti))ETVS-10s andcan completely replace titanium forming an analogous structure to ETS-10, called AM-6. This incorporation of vanadiumhas also shown visible photocatalytic activity that has been explained experimentally and theoretically. These chains ofTiO2 behave as 1D semi-conducting wires which are insulated by the SiO2 framework. Therefore chain terminationsites on the surface of the crystal or at defects along the chain play a crucial role in the electron-hole transfer from thechain to adsorbed organic molecules. Previous work has shown that ion exchange leads to an increase in chaintermination for ETS-10 samples along with different photocatalytic properties. In this research we will determine theeffects of acid site formation through NH4 ion exchange in an attempt to maximize the photocatalytic reactivity of theETVS-10 samples for VOCs decomposition.

59. Wet oxidation of phenol over transition metal oxide catalysts supported onCe0.65Zr0.35O2 prepared by continuous hydrothermal synthesis in supercritical water

Kyoung-Hun Kim, Jeong-Rang Kim and Son-Ki Ihm, KAIST, Daejeon, South Korea

Continuous hydrothermal synthesis in supercritical water (supercritical synthesis) is a method to prepare highlycrystalline nanoparticles of homogeneous complex metal oxides as well as single metal oxides rapidly and continuouslyusing supercritical water as antisolvent. Ceria-zirconia mixed oxide has widely been used as catalytic promoter due toits oxygen storage capacity (OSC). Ceria-zirconia mixed oxide with high surface area could be prepared by thesupercritical synthesis, so that it also has the potential application as catalyst support due to its high surface area. Inthis study, ceria-zirconia mixed oxide with high surface area prepared by the supercritical synthesis was used as asupport of transition metal (Mn, Fe, Co, Ni, Cu) oxide catalysts for wet oxidation of phenol. Intermediate selectivity andmineralization selectivity were investigated together with catalytic activity. Copper oxide catalyst showed the highestcatalytic activity which could be explained with the surface reducibility of the catalysts. Also, copper oxide catalystshowed the highest mineralization selectivity indicating that it remarkably enhanced the deep oxidation of phenol. Ceria-zirconia mixed oxide prepared by superciritical synthesis is a promising catalyst support for wastewater treatment. Its



oxygen storage capacity can assist the active element in removing organic pollutant such as phenol.

60. Characterization of K-promoted Ru catalysts for ammonia decomposition discoveredusing high-throughput experimentationWilliam D. Pyrz, Rohit Vijay, Raul F. Lobo, Dionisios G. Vlachos, Jochen Lauterbach and Douglas J. Buttrey, Universityof Delaware, Newark, DE

The necessity for alternative energy solutions is motivated from increasing fuel prices, stringent emission regulations,and depleting fuel resources. The most attractive option is H2, as it has high-energy efficiency and H2O is the onlybyproduct of its combustion. Ammonia has emerged as an attractive source for H2 because of its high hydrogenstorage capacity (17.7 %), energy density (3000 Wh/kg), and the catalytic decomposition of NH3 is free of COxemissions. Ru catalysts have been successful for this reaction and we have chosen to examine this system further. Using incipient wetness impregnation, we have investigated the effect of several promoters (K, Cs, Ba, Na, Rb, Li, Sr)and solvents (H2O, DMSO, ACN, THF, MEK, 2-propanol) on the low-temperature ammonia decomposition over Rucatalysts supported on Al2O3. Using the high-throughput screening, we have determined that K promotion providesdramatic enhancement (up to 30%) in the conversion of NH3 at a reduced temperature of 350°C (Figure 1). Using TEMand SEM, it was discovered that the addition of K to Ru induces the formation of potassium ruthenium oxide“nanowhiskers” as opposed to Ru agglomerates (Figure 1) that appear to be responsible for the enhancedperformance. Furthermore, it was discovered that changing the preparation solvent from H2O to an alcohol for anidentical Ru/K ratio provides an additional boost in the NH3 conversion (up to 30%) at even lower temperatures (T=300°C).

61. Preparation of MgO (111) Nanosheets and their Catalytic BehaviorRyan M. Richards, Juncheng Hu and Kake Zhu, International University Bremen, Bremen, Germany

Information about the elementary processes involved in heterogeneous catalysis is often obtained from studies withwell-defined crystal surfaces. However, current techniques are not efficient in preparing the desired well-defined crystalsurfaces. In particular, preparation of MgO (111) has remained illusive to date although theoretical studies havepredicted its' stability in the form of a hydroxide. Recently, we reported a simple, efficient and cheap wet chemical routefor preparation of MgO (111) nanosheets. We have discovered that MgO nanosheets possessing the exposed (111)plane as a main surface can grow preferentially from magnesium methoxide-benzyl alcohol via self-assembly throughslow hydrolysis. The MgO (111) nanosheets have a thickness of less than 10 nm, typically between 3 and 5 nm. The(111) surface is particularly interesting; because it possesses alternating polar monolayers of negatively charged oxygenanions and positively charged magnesium cations. Thus, a strong electrostatic field perpendicular to the (111) surface iscreated. Such a surface has provided a prototype for the study of surface structure and surface reactions of oxides,which drew great attention for both experimental and theoretical studies. The MgO (111) nanosheets have been studiedby in-situ DRIFT spectroscopy and TPD revealing insights into the surface chemistry. Additionally, the catalyticproperties of the nanosheets for the Claisen-Schmidt reaction and low temperature decomposition of methanol havebeen studied and mechanistic insights have been elucidated spectroscopically.

62. Keynote: Self-assembly of static and dynamic nanostructured materialsBartosz A. Grzybowski, Northwestern University, Evanston, IL



Self-assembly of nanoscopic components into higher-order architectures defines the forefront of fundamentalnanoscience research and is important for the development of new materials with potential applications inoptoelectronics, high-density data storage, catalysis, and biological sensing. In my talk, I will discuss how the peculiarnature of electrostatic and photoinduced dipole-dipole forces acting between nanoscale components can mediate theirself-assembly into various superstructures and materials. I will show how the interactions underlying self-assembly canbe studied and understood in quantitative detail, and how they can be tailored to synthesize unusual higher-orderarchitectures: ionic-like crystals of nanoparticles, crystalline aggregates that can be assembled and disassembled bylight, as well as extremely durable and yet very flexible metallic structures. Since these materials display a range ofnovel optical, electrical and mechanical properties, the discussion of experimental results will be accompanied bytheoretical analyses combining elements of thermodynamics, statistical mechanics, electrodynamics and elasticity.

63. Light induced property changesAna Vesperinas and Julian Eastoe, University of Bristol, Bristol, United Kingdom

Recent advances address the capability to exert externally-triggered photo-control over interfacial and aggregationproperties. If a surfactant molecule contains a suitable chromophore, illumination can be used to achieve differentphysical photo-induced responses. The advantage of this approach is it eliminates the need for composition ortemperature changes. Photodestructible surfactant sodium 4-hexylphenylazosulfonate (C6PAS) has been used to driveinteresting and dramatic changes in properties of different systems by UV light. Light-induced macroscopic phaseseparation of micelles and emulsions systems occurs when C6PAS is mixed with an inert noninoic surfactant in thepresence of salting-out electrolyte. The initial mixed micelle systems can disperse an insoluble additive marker dye thatmay be recovered and spatially segregated from the starting heterogeneous aqueous environment by UV light. Othersamples, employing photodestructible surfactants in gelatin-based aqueous gels present a novel approach to controlrheological and aggregation gel properties with possible applications in systems requiring rheological switches. Light-triggered breakdown of the gelatin-bound photosurfactant aggregates causes dramatic changes in viscosity andaggregation.

64. Partition of a Cleavable, 1,3-Dioxolane, Nonionic Surfactants, sodium bis (2-ethylhexyl)sulfosuccinate and n-octyl-beta-D-glucopyranoside in 2- and 3-Phase Water-IsooctaneMicroemulsion SystemsJavier A. Gomez del Rio and Douglas G. Hayes, University of Tennessee, Knoxville, TN

The equilibrium partitioning of a 1,3-dioxolane (pH-degradable) alkyl ethoxylate surfactant in 2- and 3-phasemicroemulsion systems formed from equal volumes of water and isooctane was determined as a function oftemperature (20-50oC) and surfactant concentration (5-10 wt. %), in single and binary surfactant systems, the latterwith Aerosol-OT and octyl-beta-D-glucoside. The head group of the surfactant molecules consist of poly(ethyleneglycol) monomethyl ether (or MPEG) with degree of polymerization distributed around the average value of 7.2 as aPoisson function. Semilog plots of partition coefficient (surfactant concentration ratio of isooctane to water-rich phases)versus MPEG degree of polymerization correlate well to straight-line models, consistent with theory and previouslypublished results for alkyl ethoxylate surfactants. The slope and the y-intercepts of the linear models are strongfunctions of temperature. The addition of a second surfactant had only a minor effect on the equilibrium partitioning ofthe 1,3-dioxolane surfactant.

65. A journey towards novel template materials for nanoparticle synthesisRegina Schwering, Thomas Sottmann and Reinhard Strey, University of Cologne, Colgone, Germany

Dynamic self-assembled structures found in complex fluids containing surfactant, water, and oil, range from sphericaland cylindrical swollen micelles to bicontinuous microemulsions and ordered liquid crystalline phases [1]. Thesestructures are extensively used as templates for the synthesis of nanomaterials [2,3]. However, up to date, it is notpossible to copy the microemulsion-structure to the microstructure of polymer particles on a one-to-one scale. RecentlyCo et al. [4,5] used a new class of highly viscous microemulsions that comprise surfactant, polymerizable oil, andconcentrated water/(sucrose/trehalose) solutions to maintain the microstructure. The addition of sugar enables thekinetic of the phase behaviour to be slowed down compared to the changing monomer/polymer ratio duringpolymerization. In this study we systematically investigated the phase behaviour of highly viscous sucrose-



microemulsions. Starting from the sugar-free nonionic system H2O – n-octane – C10E6 the amount of sucrose withinthe water phase was increased up to 75%. It is found that the addition of sucrose shifts the phase behaviour to lowtemperatures. By replacing the surfactant C10E6 by a more hydrophilic surfactant the temperature drop can becompensated. The system H2O/(sucrose/trehalose) – C6MA – Agnique PG 264-G which is a highly viscous,polymerizable microemulsion was further polymerized with varying amounts of cross-linker in the oil phase and thestructures were investigated by SEM and TEM. Additionally, the kinetics of the phase behaviour of systems containingvarious amounts of sugar in the water phase was investigated by temperature jump experiments.

66. Controlling Demixed Micelle Architectures in Silica Particles Templated with CombinedFluorinated and Hydrogented Cationic Surfactants

Stephen E. Rankin1, Rong Xing1, Barbara L. Knutson1 and Hans-Joachim Lehmler2, (1)University of Kentucky,Lexington, KY, (2)University of Iowa, Iowa City, IA

When incompatible surfactants are combined to serve as micellar templates for porous metal oxides, a large variety oforganizations of the surfactants can be imagined. These include (1) a single type of particle with a mesophasedetermined by the majority surfactant and a morphology determined by the minority surfactant, (2) completely demixedparticles, each containing different surfactants and different mesophases, (3) a single type of particle composed of amixture of separate phases formed by the two surfactants, (4) a single type of particle in which separate micellescomposed of the two types of surfactants mix into a single disordered phase, and (5) a single type of particle in whichthe two demixed surfactants organize into a novel mesophase. We will show that silica particles with any of the firstfour structures can be prepared by the hydrolysis of tetraethoxysilane in aqueous ammonia in the presence of mixturesof 2-perfluorooctylethylpyridinium chloride and cetyltrimethylammonium chloride. The first type of particles is formedunder mildly alkaline conditions, without added salts or alcohol. The second is favored by a moderate amount ofethanol, although excess ethanol leads to surfactant mixing. The third type of particle is formed by increasing theammonia concentration. The fourth structure is formed by adding salts. These results are discussed in terms of theeffects of additives on micelle mixing, precipitation rate, and partitioning between the bulk solution and the precipitatedphase. The third and fourth structures are of particular interest for their controlled bimodal mesopore size distributions.

67. Carbon Dioxide Processing of Surfactant Templated Nano-Structured Silica Probed byIn-Situ Spectroscopy

Barbara L. Knutson1, Kaustav Ghosh1, Stephen E. Rankin1 and Hans-Joachim Lehmler2, (1)University of Kentucky,Lexington, KY, (2)University of Iowa, Iowa City, IA

Synthesis of nanoporous ceramic materials by surfactant templating provides opportunities to control pore size, shape,and functionalization for advanced materials applications. Ordered silica material is synthesized through a co-assemblyprocess, in which the hydrophobicity of the surfactant tail group drives the formation of the mesophase, while thehydrolyzed silica precursor associates with the surfactant head group. Polymerization of the precursor and subsequentsurfactant removal results in pore structures that mimic the surfactant mesophase. We have demonstrated the ability totune pore size of fluorocarbon surfactant templated nanoporous silica thin films and precipitated particles usingcompressed and supercritical CO2. Compressed CO2 results in a significant increase in pore diameter for cationicfluorinated surfactant templated materials due its favorable interactions with the ‘CO2-philic' fluorinated tail. In-situfluorescence spectroscopy is used to monitor the dynamic changes in the film structure in the presence of CO2 and tointerpret the difference in pore size increase observed for hydrocarbon and fluorocarbon templates. The structures ofthe fluorescent probes are tuned to preferentially localize them in either the hydrophobic interior of the micelles or at theionic silicate-tail interface and their responsiveness to CO2 pressure is demonstrated. A significant increase in the timeperiod of modulable steady state (MSS), indicating delayed condensation of silica structure, is observed in the presenceof CO2. The results suggest time scales and approaches to further refine the nano-structured materials (i.e., infusepores with reactive agents, functionalize pores, and reorient functional groups within the pores) using CO2 processing.

68. Kinetics of Coupled Primary- and Secondary-Minimum Deposition of Colloids UnderUnfavorable Chemical Conditions



Yan Jin1, Chongyang Shen1 and Yuanfang Huang2, (1)University of Delaware, Newark, DE, (2)China AgriculturalUniversity, Beijing, China

This study examines the deposition/release mechanisms involved in colloid retention under unfavorable conditionsthrough theoretical analysis and laboratory column experiments. A Maxwell approach was utilized to estimate thecoupled effects of both primary- and secondary-minimum deposition. Theoretical analysis indicates that the secondaryenergy minimum plays a dominant role in colloid deposition even for nano-sized particles (e.g., 20 nm) and primary-minimum deposition rarely happens for large colloids (e.g. 1000 nm) under unfavorable conditions. Polystyrene latexparticles (30 nm and 1156 nm) and clean sand were used to conduct three-step column experiments at different ionicstrengths and a constant pH of 10. The results confirm that small colloids can also be deposited in the secondaryminimum. Additional column experiments involving flow interruption further indicates that the deposited colloids can bespontaneously released to bulk solution when the secondary energy minimum is comparable to the average Browniankinetic energy. Experimental collision efficiencies are in good agreement with Maxwell model predictions but largelydifferent from the theoretical calculations by the interfacial force boundary layer approximation. Our study proposes apriori approach to estimate collision efficiencies accounting for both primary- and secondary-minimum deposition andsuggests that the reversibility of colloid (e.g. viruses and bacteria) deposition must be considered in transport modelsfor accurate predictions of their travel time in the subsurface environments.

69. Transport Behavior of Adhesion-Deficient Bacterial Strain in a Radial Stagnation-PointFlow System

Vishal Gupta1, William P. Johnson2 and Jan D. Miller1, (1)Department of Metallurgical Engineering, University of Utah,Salt Lake City, UT, (2)Department of Geology & Geophysics, University of Utah, Salt Lake City, UT

The fate, transport and adhesion characteristics of microbes are of significant interest in restoration and maintenance ofdrinking water supplies, and as infectious agents from which drinking water supplies must be protected. Thisinvestigation examines the origins of observed differences in transport behavior of two different adhesion-deficient,gram-negative bacterial strains – DA001 & OY107 in a radial stagnation-point flow system. Measured surfacecharacteristics (e.g. surface potential, electrostatic interaction chromatography, and hydrophobic interactionchromatography) indicate equivalent surface properties for these two strains. However, field scale and benchtoptransport experiments demonstrate strongly contrasting transport behaviors for these two strains in porous media.Observation of these strains in the radial stagnation-point flow system provides directly-observed differences in theirattachment detachment behaviors that may lead to better understanding of their contrasting transport behaviors despitetheir equivalent surface characteristics.

70. Activity, growth, and transport of Dehalcoccoides sp. in saturated soilCharles E. Schaefer, Charles W. Condee and Robert Steffan, Shaw Environmental, Inc., Lawrenceville, NJ

Chlorinated ethene contamination in groundwater is a major environmental concern at several sites. Bioaugmentation,which involves in situ delivery of electron donor, nutrients, and microorganisms to degrade the chlorinated ethenes, hasbeen shown to be a cost-effective approach for addressing such sites. Dehalococcoides sp. (DHC) is the only microbialspecies known to completely dechlorinate PCE and TCE, and have been used extensively for bioaugmentationtreatment of chlorinated ethenes. Despite their widespread application, a fundamental understanding of DHC activity,growth, and transport in situ is lacking.

A series of laboratory batch and column experiments were performed to evaluate the activity (with respect to chlorinatedethene biodegradation), growth, and transport of a commercially available DHC consortia. The specific objective of thestudy was to determine the mechanisms controlling DHC migration through the column while the bacteria were activelygrowing and degrading the contaminants.

Results of the column experiments showed that only a small fraction (<1%) of the injected DHC eluted through thecolumn. No spatial gradient in aqueous phase DHC concentrations were observed, but measured aqueous phase DHCconcentrations increased with time at a rate that was well-predicted by the Monod model coupled with a microbialtransport model. VOC concentrations were also well-predicted by the coupled model. Overall results of the columnexperiments suggest that observed DHC distribution and VOC degradation during bioaugmentation is dependent upon arelatively small fraction of mobile and active DHC that grow and detach from retained biomass.



71. Escherichia coli deposition and transport in porous media: the coupled role oftemperature and solution chemistryHyun J. Kim and Sharon L. Walker, University of California, Riverside, Riverside, CA

The influence of temperature and solution chemistry on cell deposition in porous media has been investigated in a well-controlled packed-bed system using Escherichia coli D21g. Three different temperatures (4, 10, and 25oC) and twodifferent electrolytes (KCl and CaCl2) were employed for the experiments. To compliment the transport experiments,the bacterial viability, cell size, hydrophobicity, elecrophoretic mobility, and extracellular polymeric substances (EPS)composition were characterized. These analyses indicated the cell surface chemistry's sensitivity to solution chemistryand temperature. Additionally, transport experiments using 1 μm carboxyl modified latex (CML) particles wereconducted to compare with E. coli D21g deposition trends. The experimental results showed that the deposition rate ofCML particles increased with temperature in the presence of both electrolyte, suggesting that enhanced Brownianmotion and decreasing viscosity results in greater transfer of particles to the collector surface. On the other hand, theE. coli D21g experimental results indicated the deposition rate and attachment efficiency (α) of the cell were greatest at10oC in the presence of KCl; however, the impact of temperature was negligible in the presence of CaCl2. Based uponthese results, it has been observed that an additional biological phenomenon, which has not been involved in classicalfiltration theory (CFT), contributes to the deposition kinetics of E. coli D21g in addition to physicochemical mechanisms.

72. Impact of bacterial surface exopolysaccharide (EPS) composition on cell deposition inporous mediaYang Liu and Jin Li, University of Wisconsin, Milwaukee, Milwaukee, WI

The attachment of three genetically well-defined isogenic Pseudomonas aeruginosa strains (PAO1, PAO1 psl pel andPDO300) with different EPS secretion capability and EPS composition were studied over a range of solution chemistryin glass beads packed columns, to examine the removal of P. aeruginosa from the bulk fluid due to their attachment tothe solid surfaces. The deviation of experimental data from classic colloid filtration theory (CFT) was investigated bycomparing the distribution of bacterial as a function of column depth with CFT model. The results show that thepresence of EPS on nonmucoid strain PAO1 and mucoid strain PDO300 significantly increased bacterial adhesion overthe EPS deficient PAO1 psl pel, despite their similar surface charges as indicated by the zeta potential measurement.EPS deficient strain exhibited the log-linear deposition pattern under high ionic strength conditions, consistent withtrends predicted from the filtration theory. In contrast, non-monotonic deviations in the form of down-gradient movementof the maximum retained cell concentration from the column inlet were observed when the EPS secretion strains wereexamined. The retained polysaccharides (carbohydrates and uronic acids) and protein profiles inversed bacterialdeposition profiles, indicating that bacterial re-entrainment and re-entrapment may have contributed to the non-monotonic retained profiles. The detachment of bacteria leaves behind various constituents of EPS as their “footprints,”which can interfere with cell deposition.

73. Bacterial interactions with natural organic matter, proteins, and peptidesTerri A. Camesano, Laila I. Abu-Lail, Arzu Atabek and Joshua Strauss, Worcester Polytechnic Institute, Worcester, MA

The interactions of bacteria with organic matter affects applications ranging from natural processes such as bacterialtransport in the subsurface and in situ bioremediation, to engineered processes such as bioaugmentation and bacterialinactivation with antimicrobial peptides. In the environment, natural organic matter (NOM) is a complex mixture thatincludes identifiable compounds such as proteins and polysaccharides, but is generally defined operationally into groupssuch as humic and fulvic acids. This work describes how atomic force microscopy (AFM) can be used to characterizeand quantify the interfacial forces between microbes and organic matter-coated surfaces. A model polymer,poly(methacrylic) acid, was chosen as a simple model for NOM, due to its highly charged nature and presence ofcarboxylic groups. The way that the model NOM interacted with bacteria was compared with the behavior of SuwaneeRiver Humic Acid and a Soil Humic Acid. Based on AFM measurements of adhesion forces between bacteria and anNOM-coated probe, PMA was not a good model for the way bacteria interacted with the humic acids. To try anddevelop a more fundamental understanding of bacterial interactions with organic molecules, we also quantified theadhesion forces between bacteria and model proteins (BSA, con A), and determined that these interactions are



dependent on bacterial LPS structure. Finally, new results are presented on the binding between bacterial LPS andpeptides having antimicrobial properties.

74. Nanofiltration of complex fluids containing colloid materials and dissolvedmacromolecules: the combined fouling effectAlison E. Harris, Jack S. Hale, Brent C. Houchens and Qilin Li, Rice University, Houston, TX

Natural waters and wastewater contain both colloidal materials and dissolved organic matter. Although extensiveresearch has been done on colloidal fouling and organic fouling processes separately and their mechanisms arerelatively well understood, little is known about the combined fouling process during filtration of a complex suspensioncontaining both types of foulants. Using a combination of experimental measurement and computational modeling, thisresearch explores the physicochemical mechanisms involved in the combined fouling process. In particular, the twomajor mechanisms investigated were hindered back diffusion due to the high concentration of each foulant near themembrane surface and changes in colloid deposition behavior due to adsorption of macromolecules onto the colloidsurface. The impact on the characteristics of the membrane due to macromolecule adsorption is also considered. Themodel incorporates the hindered back diffusion mechanism by calculating the local fluid viscosity in the concentrationpolarization layer and modifying the diffusion and flow accordingly. Fouling experiments in a cross-flow filtration systemusing nanofiltration membranes were conducted with colloidal silica and two model organic foulants: a non-interactingmacromolecule, Dextran, and an interacting macromolecule, bovine serum albumin (BSA). The model organic foulantswere chosen for their respective adsorptive properties in order to isolate the effects of hindered back diffusion from theeffects of macromolecule-mediated colloid deposition. Model predictions are compared to experimental results as wellas existing concentration polarization/fouling models.

75. Polyelectrolyte-surfactant Complexes as Nanoscale Zerovalent Iron (NZVI) SurfaceModifiers for In Situ NAPL TargetingTanapon Phenrat, Hye-Jin Kim, Navid B. Saleh, Kevin Sirk, Robert D. Tilton and Gregory V. Lowry, Carnegie MellonUniversity, Pittsburgh, PA

For in situ Non-Aqueous Phase Liquid (NAPL) source zone remediation, NZVI must be mobile in porous media and itshould have an affinity for the NAPL source zone. There are two methods to promote NAPL targeting, includinginterfacial targeting where the particles adhere and become immobilized at the NAPL/water interface, anddestabilization targeting where a surface coating is desorbed in the presence of NAPL saturation or near-saturation,leaving behind a bare, immobile particle. In this study, we assess the potential of mixtures of an anionic polyelectrolyte,poly(styrene sulfonate) (PSS), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB), as NZVI surfacemodifiers to enhance NAPL targetability via interfacial targeting or destabilization targeting. Two methods of NZVIsurface modification were evaluated; 1) sequential adsorption of CTAB followed by PSS to provide a layered CTAB-seq-PSS structure, and 2) adsorption of a premixed PSS-co-CTAB complex .CTAB-seq-PSS and PSS-co-CTABmodified NZVI dispersions were mixed with excess NAPL (dodecane, TCE, or PCE) in water, or with NAPL-saturatedwater to evaluate their affinity for the NAPL-water interface (interfacial targeting) and the desorption of PSS and CTABfrom NZVI due to the change of solvent quality for the complex (destabilization targeting). Complex desorption andNZVI destabilization in the presence of NAPL was more extensive for the layered CTAB-seq-PSS than for the PSS-co-CTAB complex . Transport of both types of modified NZVI dispersions are through a column of sand partially saturatedwith NAPL will be discussed to evaluate the potential for in situ NAPL targeting.

76. Phase diagram and dynamics of patchy colloidal systemsEmanuela Zaccarelli, CNR-INFM-SOFT and Universita' La Sapienza, Rome, Italy

We study patchy models for colloidal systems to investigate the suppression of phase separation at low packing fractionΦ. We find that, on reducing the number of patches, the critical point moves towards zero packing fraction, providingthe possibility to generate "empty liquids"[1]. Moreover, we find a new topology for the interplay of dynamical arrest withthe phase separation region, that appears universal for various models of patchy systems[2]. Differently from sphericallysymmetric attraction where the glass line merges into the spinodal at large Φ allowing only for dynamic arrest as anarrested spinodal decomposition, for patchy interactions a whole region of optimal network formation opens up, wherearrested states (gels) can be approached in equilibrium. We also discuss the deep analogy between patchy colloids and



network-forming liquids (e.g. water, silica)[3].

[1] E. Bianchi et al., Phys. Rev. Lett. 97, 168301 (2006)

[2] E. Zaccarelli et al, J. Chem. Phys. 124, 124908 (2006)

[3] C. De Michele et al, J. Phys. Chem. B 110, 8064 (2006); J. Chem. Phys. 125, 204710 (2006).

77. Gels, glasses and attractive glasses in the Laponite systemDaniel Bonn, University of Amsterdam and Ecole Normale Superieure, Amsterdam, Netherlands

The study of colloids allowed for a significant contribution to elucidating the basic physics of glass transition. In colloidalsystems, as the particle volume fraction is increased, the particles become increasingly slower and for even highervolume fractions the glass transition is encountered. On the other hand, colloidal gels are known to form at extremelylow volume fractions in the presence of strong attractions. Gelation and the glass transition have important similarities.Both are ergodic to non-ergodic transitions that are kinetic, rather than thermodynamic in origin, and distinguishingbetween these two types of non-ergodic states experimentally is a longstanding controversy We report experiments thatallow for distinguishing gels from glasses in the Laponite system. This allows us to show that for a range ofconcentrations, two distinctly different non-ergodic states can result at late times: either the glass or the gel forms atlate times with roughly equal probability. There is no way to tell beforehand which of the two options will be taken bythe sample, suggesting that there are at least two metastable minima in the system. We also report that a third state:an attractive glass may be found in the same system.

78. Gel Transition in Silica Nanoparticle/Kaolinite SuspensionsJohn Y. Walz, Virginia Tech, Blacksburg, VA and Jason C. Baird, Yale University, New Haven, CT

Addition of silica nanoparticles and salt to an aqueous suspension of kaolinite particles can cause a rapid transition to agel. SEM micrographs indicate that the structure of the gel consists of the disk-like kaolinite particles arranged in edge-to-face contacts, forming a porous honeycomb structure. The gel also shows a remarkable ability to rejuvenate afterbreakage by shear. Although the exact mechanism responsible for this gellation is not known, it is hypothesised thatthe nanoparticles first completely cover surfaces of the clay particles. Upon addition of sufficient amounts of electrolyte,the electrostatic repulsion between silica particles on opposing kaolinite surfaces is screened enough that a van derWaals bond can form. Random Brownian motion of the clay particles would create the edge-to-face arrangement. Inaddition, because of the relatively large size of the clay platelets (several microns), this structure could be easily brokenby shear. This ability to rejuvenate is completely different from the behavior of gels formed from silica nanoparticlesonly.

79. Direct Imaging of Biphasic Colloidal MixturesSummer K. Rhodes, Robert H. Lambeth, Jeffrey S. Moore and Jennifer A. Lewis, University of Illinois, Urbana-Champaign, Urbana, IL

Concentrated colloidal gels have been utilized as inks for the direct-write assembly of complex 3D architectures.However, such inks undergo a “jamming transition” when deposited through cylindrical nozzles with diameters on theorder of 100 mm or less. To overcome such difficulties, we are exploring a new ink design based on mixtures ofattractive and repulsive colloidal particles. Specifically, these biphasic inks are composed of silica microspheres coatedwith either a cationic polyelectrolyte or a comb polymer consisting of a cationic backbone and charge neutralpolyethylene oxide teeth. Upon adding salt to this system, the cationic polyelectrolyte-coated silica microspheresspontaneously flocculate while the comb polymer-coated colloids remain fully stabilized. Using confocal microcsopy, wehave directly imaged the 3D structural evolution of such mixtures as a function of total microsphere volume fraction,ratio of attractive-to-repulsive microspheres, and salt concentration. Experiments are now underway to characterize thestructural evolution of ink filaments patterned by direct ink writing.

80. Gelation of Carbon Nanotube Networks

Daniel T.N. Chen1, Larry A. Hough2, Mohammad F. Islam3 and Arjun G. Yodh1, (1)University of Pennsylvania,



Philadelphia, PA, (2)Rhodia Inc., Bristol, PA, (3)Carnegie Mellon University, Pittsburgh, PA

We investigate the gelation of a rigid rod network comprised of an aqueous suspension of surfactant stabilized Single-Wall Carbon Nanotubes (SWNT). Using particle tracking microrheology, we follow the gelation of the SWNT suspensionfrom an initial sol of contacting, but unbonded, tubes to a fully cured gel of contacting tubes bonded by van der Waalsinteractions. The SWNT network exhibits many features found in critical sol-gel transitions, including divergence of theviscosity as the gel point is approached from below, emergence of a finite elastic modulus above the gel point, andpower law scaling of the viscosity and shear modulus below and above the gel point, respectively. The viscoelasticmoduli obtained at different times above the gel point can be collapsed onto a master curve using time-curesuperposition. Additionally, we present a scheme based on two-point statistics to characterize rheologicalinhomogeneities in the network during gelation.

81. Slow dynamics and ageing in soft colloidsDimitris Vlassopoulos, Christina Christopoulou, Emmanuel Stiakakis and George Petekidis, FORTH and Univ. ofCrete, Heraklion, Crete, Greece

Using light scattering (multispeckle DLS) and rheological (dynamic frequency sweep, creep and start-up in shear)techniques, we investigate the slow dynamics of concentrated suspensions of star polymers, a model soft colloidalsystem with tunable interactions. We focus on the transition to the glassy regime which, depending on the suspendingmedium used, can be reached by increasing the number concentration or the temperature. We observe a rich dynamicsassociated with this reversible liquid to solid transition. The rheology changes from viscoelastic to viscoplastic rathergradually, and very long stress transients are detected. At the same time, the appearance of slow relaxation process inthe intermediate scattering function is evidenced, which appears to be responsible for the macroscopic immobilization ofthe system. This relaxation process exhibits a logarithmic decay over 3 decades in time with extremely slow kinetics(ageing); the latter is also manifested in a second ultraslow process in start-up experiments. The above relaxationprocess decays gradually from stretched to logarithmic manner at high temperatures. We attempt at comparing thissystematic information with the analogue experimental evidence from hard sphere suspensions, attributing thesimilarities to universality in behavior, the differences to the nature of the interactions, and leaving several openquestions for further research.

82. Flow of attractive colloidal suspensions in microchannelsJacinta C. Conrad and Jennifer A. Lewis, University of Illinois, Urbana-Champaign, Urbana, IL

We use confocal microscopy to investigate the behavior of suspensions of attractive colloids at a constriction. We flowsuspensions of attractive silica colloids through microchannels and directly image both their structure and dynamicsduring flow. Specifically, we investigate the flow properties as a function of applied pressure, microchannel geometry,and the colloid volume fraction. When the applied pressure or displacement is relatively small, the particle velocity isnearly constant across the channel, yet small rearrangements can still occur in the gel structure. When the appliedpressure or displacement is large, the gel structure is disrupted and the flow velocity changes across the channel width.In addition, we also explore the non-equilibrium clogging that occurs when the system experiences jamming withinthese microchannels.

83. Anomalous behavior in aqueous thin liquid films between hydrocarbons and fluorinatedhydrocarbonsRaymond R. Dagastine, Ivan U. Vakarelski, Lucy Y. Clasohm, Geoffery W. Stevens, Derek Y.C. Chan and FranzGrieser, The University of Melbourne, Melbourne, Australia

Recent advances in the atomic force microscopy (AFM) force measurement techniques have allowed the directmeasurement and theoretical interpretation of the interaction between a liquid droplet and a solid surface or two liquiddroplets.1 Here we investigate the interaction across an aqueous thin film between fluorocarbon oil droplets,hydrocarbon droplets or a droplet and a flat solid in the absence of stabilizers. The initial interest of the study was tomeasure the short ranged van der Waals interaction forces operating in these systems. The van der Waals interactionis usually attractive, but it can become repulsive when two dissimilar phases interact through a third phase ofintermediate optical properties.2 Preliminary results between fluorocarbon droplets and solid surfaces did show



repulsion, but forces between symmetric oil droplets also show repulsion, even at high electrolyte concentrations.These repulsive interactions also exhibited a pH dependence. Theoretical analysis of the magnitude and the range ofthese forces suggest that DLVO forces can not explain the observed behaviour. The force behaviour will be discussedin the context of ion adsorption and charging effects at bare oil water interfaces.

1. Dagastine, R.R, Manica, R., Carnie, S.L., Chan, D.Y.C., Stevens, G.W., Grieser, F. Science, 2006, 313, 210.

2. Milling, A., Mulvaney, P., and Larson, I., J. Colloid and Interface Sci., 1996, 180, 460.

84. Stability of foams and single foam films in the presence of n-alkyl polyoxyethylenehomologuesRuijia Wang and Roe-Hoan Yoon, Virginia Tech, Blacksburg, VA

It was shown previously that at low concentrations of sodium dodecylsulfate (SDS) and methylisobutylcarbinol (MIBC),hydrophobic force plays an important role in the stability of foam films (Wang and Yoon, 2005, 2006). In the presentwork, effects of nonionic surfactants (n-alkyl polyoxyethy1ene homologues) on the stability of foam films have beenstudied, with particular emphasis on the role of hydrophobic force. The magnitudes of the hydrophobic forces in foamfilms were determined from the equilibrium film thicknesses and the film thinning kinetics measured using the thin filmpressure balance (TFPB) technique. The results show that single foam films thin much faster than predicted by theDLVO theory due to the presence of hydrophobic force. In general, hydrophobic force decreases with increasingconcentration of a non-ionic surfactant. It was found also that hydrophobic force decreases with increasing chain lengthof the n-alkyl group and with decreasing chain length of the EO groups.

85. Unexpected non-ideal mixing in homologous surfactants

Laura K. Hudson1, Julian Eastoe1 and Peter J. Dowding2, (1)University of Bristol, Bristol, United Kingdom, (2)InfineumUK Ltd, Abingdon, United Kingdom

Air-water interfacial studies with mixtures of linear and branched analogue give rise to surprising and unexpectedbehavior: apparently a strong interfacial partitioning of branched chain surfactant at the expense of the linear chainrelative (non-idealities). This behavior is not predicted by the established theories, where it is believed that surfactantsbearing the same headgroup type and similar chains (hydrocarbons) mix ideally: i.e. it is straightforward to predictphysico-chemcial properties based on those of the individual compounds, and the known mixture composition. Thesetrends are also seen in water-in-oil (w/o) microemulsion phase stabilities and aqueous solubility measurements.

Neutron reflectivity (NR), small angle neutron scattering (SANS), surface tension (ST), phase behavior and aqueoussolubilities have been used to interrogate these mixed surfactant systems (comprising a homologous series of di-alkylanionic surfactants based on Aerosol-OT (AOT, sodium bis(2-ethyl-1-hexyl)sulfosuccinate - linear and branched alkylchains).

The understanding of complex surface chemistry and bulk behavior of mixtures of surfactants from a homologous seriesis important for a wide range of applications such as detergents, drug delivery systems and tertiary oil recovery. This isbecause mixtures provide synergistic enhancement of properties, or because commercial surfactants are naturally adistribution of molecular masses.

86. Micellization of charged, water-soluble triblock copolymers with polyethylene oxide endgroupsRichey Davis, Beth Caba and Judy Riffle, Virginia Tech University, Blacksburg, VA

Novel triblock copolymers consisting of end blocks of polyethylene oxide (PEO) and a center block consisting ofurethane and carboxylic acid groups constitute an interesting class of polymers that can self-associate to form micellesin water. Micelles of hydrophilic block copolymers are of interest due to their use in the controlled delivery of drugs andother bioactive molecules. Micellization of these block copolymers results from a balance between hydrogen bondingand hydrophobic attraction in the core and repulsion between PEO chains in the corona. The size and mass of thesemicelles can be tuned by controlling pH and temperature, with ionic strength playing a lesser role. At pH 7 and 25 C,



the copolymers are fully soluble unimers with hydrodynamic radius RH ~2 nm whereas at pH 2-3, protonation of thecarboxylic acid groups in the core drives assembly of micelles with RH ~10-15 nm over a range of temperatures (25-65C). These micelles were characterized by static and dynamic light scattering and small angle neutron scattering. Themicelle size can be predicted with reasonable accuracy from aggregation number measurements using the DensityDistribution model by Vagberg, et.al., that was based on the blob model for star polymers. The second virial coefficientscan be predicted semi-quantitatively using a model by Likos, et al., also based on star polymers.

87. Thermoreversible micellization and gelation for a blend of PEO-PPO-PEO and PPO-PEO-PPO copolymersLin Li, Qiqiang Wang and Lee Hoon Lim, Nanyang Technological University, Singapore, Singapore

Aqueous solutions of a blend consisting of a PEO-PPO-PEO triblock copolymer and a PPO-PEO-PPO triblockcopolymer were prepared. Thermoreversible micellization and gelation properties of the blend were studied as afunction of temperature and molar ratio of two copolymers by means of micro-DSC and rheology. The completelythermoreversible behaviors of micellization and gelation were observed for all solutions with various molar ratios. At agiven concentration of the PEO-PPO-PEO copolymer, three effects of the PPO-PEO-PPO copolymer were found: (a)micellization shifted to a lower temperature with increasing the concentration of the PPO-PEO-PPO copolymer,implying a “salt-out” like effect; (b) there appeared a secondary peak due to the interaction between two copolymers,which increased in height with increasing the PPO-PEO-PPO copolymer; and (c) also the significant changes inenthalpy and entropy were shown. The rheological studies allowed the determination of the sol-gel transition, the gelstrength, and the polymer-polymer interaction-induced unique features of rheology. The possible mechanism for thePPO-PEO-PPO copolymer induced micellization and gelation will be proposed and discussed.

88. Dependency of calcium carbonate inhibition on structural characteristics of carboxylic-acid containing polymeric antiscalants

Matthew R. Dubay1, Steven J. Severtson1 and Brian N., Brogdon2, (1)University of Minnesota, Saint Paul, MN,(2)Kemira Chemicals, Inc., Marietta, GA

Formation of inorganic deposits or scale is a serious issue for industries that process large quantities of water. Thesedeposits increase energy consumption by heat transfer units, hinder separation and transport processes, and mandateregular shutdowns for cleaning. One approach for mitigating this problem is the use of chemical additives that slowcrystal growth processes leading to deposit formation. These additives work primarily by adsorbing to developing nucleiand growing crystal faces to slow the further incorporation of mass. These interactions are poorly understood andinformation to guide the selection of an effective treatment chemical is not readily available. In this presentation,research aimed at identifying the optimal structure for polymeric additives used to inhibit scale formation will bereviewed. Discussed will be the use of polymeric additives to inhibit calcium carbonate scale formation in kraft pulpingliquors, which are processed at high temperatures and supersaturations. The focus will be on carboxylic acid containingpolymers, whose performance appears to be strongly dependent on its structural characteristics. Naturally occurringpolymers such as lignin along with synthetic co- and terpolymers produced from maleic and acrylic acid monomers willbe of particular interest. The most effective molecular weight distributions will be identified and possible explanations forthis dependency will be discussed. Also reviewed will be the role of other structural characteristics such as theconcentration of carboxylic acid functional groups and their distribution throughout the polymer backbone and the role ofchain flexibility.

89. Morphology evolution through viscous oil emulsification by catastrophic phaseinversion in semi-batch process

Johanna M. Galindo1, Veronique Sadtler1, Lionel Choplin1 and Jean-Louis Salager2, (1)Laboratoire GEMICO, ENSIC- INPL, Nancy, France, (2)Laboratorio FIRP, Universidad de los Andes, Merida, Venezuela

Viscous oil emulsification by catastrophic phase inversion allows to obtain fine and homogeneous drop size without anexcessive energy addition. During the inversion process, a competition between composition (water/oil ratio) andformulation induces the formation of unstable multiple emulsions.



We studied aqueous phase addition rate and stirring speed effects on emulsion characteristics, particularly on watermass fraction value (Fw) at the inversion point. The studied system is composed of silicone oils (viscosities between 1and 12 Pa.s), aqueous phase (1 % NaCl) and a mixture of nonylphenol polyethoxylate as surfactant. The emulsificationprocess is followed-up, in situ, by simultaneous viscosity and conductivity measurements. The aqueous phase is addedto the oily one, under continuous agitation until the inversion point, detected by an abrupt change in viscosity andconductivity measurements, is reached.

Water mass fraction (at the inversion point) depends on multiple emulsion formation, and is also affected by the oilphase viscosity. There is a total or partial inversion depending on the viscosity phase ratio. According to microscopicobservations of local morphologies obtained during the inversion process, for systems with low viscosity phase ratio,the inversion is triggered through the following morphology evolution: W/O → w/o/W/O → w/O/W → O/W. For moreviscous oils, no morphology formation of type w/o/W/O has been observed before inversion point. Final emulsions arehighly concentrated emulsions either because Fw is about 5 to 9% in high oil viscosity systems, or because of thepersistence of multiple emulsions (w/O/W) in low oil viscosity systems.

90. Shear deformation in polymer networksQi Wen, Anindita Basu, Arjun G. Yodh and Paul A. Janmey, University of Pennsylvania, Philadelphia, PA

We explore the effects of macroscopic shear stress applied to a filamentous polymer network. In particular, we aim tounderstand whether the network transforms affinely on microscopic length scales. Network deformations in response toexternal stress were measured by tracking fluorescent beads embedded in the networks, using the 3D imagingtechniques. Networks of both flexible and semi-flexible polymers, for example, polyacrylamide and fibrin gels, arestudied at strain values ranging from linear to nonlinear regime. (This work is supported by the MRSEC grant DMR-0520020, NSF grant DMR-0505048, and NSF MRSEC grant DMR00-79909.)

91. Critical stresses and cracking in thin films of colloidal dispersionsWeining Man Man, William B. Russel and Ning Wu, Princeton University, Princeton, NJ

Colloidal dispersions are often coated on a substrate to allow the solvent to evaporate and leave a uniform thin film.However, cracks can form in the latter stages of drying. A negative capillary pressure develops as the air-waterinterface is pulled down into the interstices between particles, putting the drying film in tension. The film responds bycollapsing normal to the surface but is constrained from shrinking laterally unless cracks open. Only throughunderstanding of the mechanism can colloidal dispersions be formulated to produce crack-free films.

In this study, we use a high-pressure ultra-filtration device to measure directly the pressure responsible for cracking inuniform films of latex or silica dispersions containing particles of varying radii. The results confirm that cracking iscontrolled by the recovery of elastic energy with the critical pressure increasing with the modulus of the particle,decreasing with increasing film thickness, and independent of particle size. The Griffith¹s criterion for equilibrium crackpropagation along with the nonlinear stress-strain relation for drying films provides a necessary, but not sufficient,condition for crack formation. As the pressure is increased beyond the critical value, additional cracks open inqualitative agreement with our elastic energy recovery model. Films that lack of defects crack at a higher pressure thanpredicted, while introducing flaws at the edges promotes cracking at the critical pressure. These observations suggestan important role for defects in nucleating cracks.

92. Cracking in Drying Colloidal FilmsKarnail B. Singh and Mahesh S. Tirumkudulu, Indian Institute of Technology-Bombay, Mumbai, India

When a thin film of wet paint or coating is dried on a substrate, evaporation of the solvent concentrates the particlesinto a closed packed array. Further evaporation generates a compressive capillary force on the particle network. Thefilm generally binds to the substrate and resists deformation in the transverse direction giving rise to transverse tensilestresses. If the particles are soft, they deform to close the pores but in case of hard particles the film cracks to releasethe stresses. Though cracking has been investigated on various systems such as wet clays, ceramic films, latex andmodel colloidal dispersions, it is only recently that a fundamental understanding of the cracking mechanism is beginningto emerge. In the present investigation, we identify two distinct regimes for obtaining crack free films. The firstcorresponds to soft particles that completely deform to give impermeable crack free films. The second regime is



applicable for films containing hard particles where the existence of a maximum attainable capillary pressure limits thedeformation and leads to porous crack free films. The measured critical heights for the latter regime over four orders inshear modulus and an order in particle size are in remarkable agreement with the theoretical predictions. We anticipateour results to not only form the basis for design of coating formulations for the paints, coatings and ceramics industrybut also assist in the production of crack free photonic band gap crystals.

93. Novel Dispersion and Self-Assembly of Single Wall Carbon NanotubesMohammad F. Islam, Carnegie Mellon University, Pittsburgh, PA

I will describe our explorations of carbon nanotube science and technology from a soft materials perspective. We firstcreated stable dispersions of purified single wall carbon nanotubes (SWNTs) using an anionic surfactant, sodiumdodecyl benzene sulfonate (NaDDBS), and then studied their structure and rheology in suspension, demonstratinginterconnected networks of stiff filaments. Our attempts to induce nematic liquid crystalline alignment of SWNTs insuspension did not succeed, but eventually led us to create a new class of nanocomposite: nematic nanotube gels.These gels exhibit rich physical properties due to a coupling between the nematic alignment and the polymer networkelasticity.

94. Structure and phase behavior of melts and dense solutions of polymer tetherednanoparticles and colloidsArthi Jayaraman and Kenneth S. Schweizer, University of Illinois Urbana-Champaign, Urbana, IL

The microscopic Polymer Reference Interaction Site Model (PRISM) theory has been generalized and applied to studydense solutions and melts of polymer tethered spherical particles. Intermolecular pair correlation functions, collectivestructure factors, and bulk moduli are calculated to understand the equilibrium organization and tendency to microphaseseparate. The complex interplay of entropy (translational, conformational and packing) and enthalpy (monomer-particleattraction) leads to different spatial arrangements with distinctive scattering signatures, and a rich phase behavior. Formelts of these tethered particles, at low monomer-particle cohesive strengths the particles experience depletionattraction. As the monomer-particle attraction is increased strong polymer mediated bridging of particle cores isobserved. The location of the peaks in the structure factors suggest that these tethered particles prefer to organizethemselves in a specific geometry that is dictated by the subtle competition of depletion attraction, osmotic repulsion,monomer adsorption and grafting constraints. The effect of the length of tethered chains, number of tethered polymersper particle, core radius, total fluid packing fraction, and monomer-particle interfacial attraction strength on the statisticalstructure, properties and phase behavior will be discussed.

95. Modelling colloidal suspensions: Gelation, network formation and phase separationEmanuela Del Gado, ETH Zurich, Zurich, Switzerland

In attractive colloidal suspensions at low volume fractions the underlying thermodynamics may significantly interplayand/or compete with gel formation via phase separation processes. In particular I will consider the case of a colloidalsuspension with competing attraction and repulsion, where gelation results to be directly coupled to microphaseseparation[1]. Then I will discuss a model in which directional interactions are able to produce a persistent gel networkat relatively high temperatures, where phase separation does not occur, without imposing a local functionality of themeso-particle[2]. The numerical study shows in this case that the formation of the gel network does induce a non-triviallength scale dependence of the dynamics in a simple model for colloidal gels: In the incipient gel, the relaxation at highwave vectors is due to the fast cooperative motion of pieces of the gel structure, whereas at low wave vectors theoverall rearrangements of the heterogeneous gel make the system relax via a stretched exponential decay of the timecorrelators. The coexistence of such diverse relaxation mechanisms is determined by the formation of the gel network(i.e. the onset of the elastic response of the system) and it is characterized by a typical crossover length which is of theorder of the network mesh size. [1] A. de Candia, E. Del Gado, A. Fierro, N. Sator, M. Tarzia and A. Coniglio, Phys.Rev. E 74, 010403(R) (2006). [2] E. Del Gado and W. Kob, Europhys. Lett. 72,(2005) 1032; Phys. Rev. Lett. 98,028303 (2007).

96. Depletion-driven Colloidal Packing in Emulsions



Liang-jie Lai1, Chih-Chung Chang1, Yun-ting Chen1, Hui Chen1 and Keng-hui Lin2, (1)National Central University,Jhongli City, Taiwan, (2)Academia Sinica, Taipei, Taiwan

Here we observe new types of colloidal clusters produced from oil-in-water emulsions with microspheres and polymerdispersed in oil droplets. We follow the cluster formation process as Manoharan's work [1]. The polymer inducesdepletion interaction between microspheres. When the number of particles N inside the droplet is larger than 4 and notequal to 6, we observe new configurations of final packing besides besides what Manoharan observed. Extraconfigurations of packing are due to depletion interaction which gives rise to different initial packing of microspheres onthe surface of oil droplets. [1] V.N. Manoharan, M.T. Elsesser, D.J. Pine. Science 301, 483 (2003)

97. SANS studies of magnetically chained ferrofluid emulsionsGregory G. Warr, Nirmesh J. Jain and Brian S. Hawkett, The University of Sydney, Sydney, Australia

Forces between aqueous ferrofluid droplets dispersed in tetradecane have been determined by small angle neutronscattering (SANS) and optical interferometry using the magnetic chaining technique in an external magentic field. Forceversus separation curves obtained from both techniques are in excellent agreement for droplets stabilised by sorbitanmonooleate and polymeric emulsifiers. The anisotropic SANS pattern from magnetically-chained droplets can beaccurately described analytically as a one-dimensional string of regularly spaced spheres. In contrast with theinterferometric approach, SANS enables the droplet dimensions, separation and any deformation to be monitored in situas a function of applied field. SANS also thus provides a direct measure of the absolute droplet separation.

98. Small Angle Neutron Scattering Studies of the Counterion Effects on the MolecularConformation and Structure of Charged G4 PAMAM Dendrimers in Aqueous Solutions

Wei-Ren Chen1, Lionel Porcar2, Yun Liu1, Paul. D. Butler1 and Linda J. Magid3, (1)Oak Ridge National Laboratory,Oak Ridge, TN, (2)National Institute of Standards and Technology, Gaithersburg, MD, (3)the University of Tennessee,Knoxville, TN

The structural properties of generation 4 (G4) poly(amidoamine) starburst dendrimers (PAMAM) with anethylenediamine (EDA) central core in D2O solutions have been studied by small angle neutron scattering (SANS).Upon the addition of DCl, SANS patterns show pronounced inter-particle correlation peaks due to the strong repulsionintroduced by the protonation of the amino groups of the dendrimers. By solving the Ornstein-Zernike integral equation(OZ) with hypernetted chain closure (HNC), the dendrimer-dendrimer structure factor S(Q) is determined and used to fitthe experimental data, where Q is the magnitude of the scattering wave vector. Quantitative information such as theeffective charge per dendrimer and its conformational change at different pD values is obtained. The results show clearevidence that significant counterion association occurs, strongly mediating the inter-dendrimer interaction. The influenceof interplay between counterions and molecular protonation of dendrimers imposes a strong effect on the dendrimerconformation and effective interaction. Careful analyses of the high Q data indicate a possible development of asecondary structure in a dendrimer evidenced by the appearance of a small high Q feature after the tertiary aminogroups begin to be charged.

99. Characterization of magnetic nanoparticles used for cancer thermotherapy

Robert Ivkov1, Julie Borchers2, Allan R Foreman1, Cindi Dennis2, P. J. Hoopes3 and Cordula Gruettner4, (1)TritonBiosystems Inc., Chelmsford, MA, (2)NIST, Gaithersburg, MD, (3)Dartmouth College, Hanover, NH, (4)MicromodPartikeltechnologie, GmbH, Rostock-Warnemuende, Germany

Magnetic nanoparticles heat when exposed to an alternating magnetic field through hysteresis losses. These materialsoffer the potential to selectively treat cancer by heating cancer tissue from within at the cellular level. This can besuccessful provided a sufficient concentration of particles is achieved in the tumor possessing a sufficiently highspecific absorption rate (SAR) to deposit heat quickly while minimizing thermal damage to surrounding tissue. High SARmagnetic nanoparticles have been developed comprised of iron oxide magnetic cores that have been used in mousemodels of cancer. Colloidal stability of these particles, mean diameter of 80 nm, is maintained by the incorporating apolymer layer to form a "core-shell" construct. Structural, heating, and magnetic properties of these suspensions havebeen characterized using a variety of techniques including light and neutroon scattering. These data will be presented,as will the results of in vitro cell culture and in vivo mouse trials.



100. Slippery diffusion-limited aggregation of attractive nanodroplets measured by time-resolved small angle neutron scatteringThomas G. Mason, UCLA, Los Angeles, CA

The nature of the bonding between highly attractive colloids can lead to a profound difference in the structures ofaggregates, as revealed through scattering. In particular, colloidal bonds can either be 'shear-rigid', as is the case inclassic diffusion limited aggregation (DLA) experiments on solid gold particles, or they can be 'slippery', as we show forattractive dispersions of uniform nanoscale droplets, or 'nanoemulsions', comprised of silicone oil in water. Despite thestrong attraction between the oil droplets, which has been induced by adding salt, a thin layer of the continuous phaseremains between droplets, precluding coalescence. Slippery attractions occur when the well depth of the secondaryminimum is much greater than thermal energy and the range is much smaller than the droplet radius. We use time-resolved small angle neutron scattering (TR-SANS) to study the kinetics of the appearance of peaks related tocorrelations between nearest neighbor droplets at high wavenumber, q, after abruptly creating an attractive interaction.We show that small dense clusters of droplets are first formed, and these, in turn, aggregate into tenuous fractalnetworks and gels. Simulations of slippery diffusion-limited aggregation (S-DLA) confirm an earlier hypothesis thatattractively jammed tetrahedra of spheres can be considered as the basic building block of space-filling clusters andnetworks of slippery attractive spheres. The similarity between the computed structure factor, S(q), of S-DLAaggregates and the measured S(q) indicates that slippery DLA is a useful concept for understanding scatteringsignatures of attractively jammed networks of spheres.

101. Static and Dynamic X-ray Scattering from Nanoparticle Stabilized LiposomeSuspensions

Laurence B. Lurio1, Mrinmay Mukhopadhyay2, Yan Yu3, Liangfang Zhang3 and Steve Granick3, (1)Northern IllinoisUniversity, DeKalb, IL, (2)University of California at San Diego, La Jolla, CA, (3)University of Illinois at UrbanaChampaign, Urbana, IL

Small angle x-ray scattering and dynamic x-ray scattering (XPCS) has been measured from nanoparticle stabilizedaqueous suspensions of approximately 200 nm diameter liposomes. Small angle x-ray scattering was used to extractthe overall liposome size, the surface distribution of the nanoparticles on the liposomes and the liposome-liposomestructure factor. Dynamic x-ray scattering was used to measure the translational motion of the liposomes in both diluteand concentrated suspensions.

102. Small angle neutron scattering under shear flow: a new 1-2 plane flow-SANSexperiment with results for shearing colloids and surfactants

Norman J. Wagner1, Florian Nettesheim1, Dennis P Kalman1, Matthew E. Helgeson1, Matthew W. Liberatore2 andLionel Porcar3, (1)University of Delaware, Newark, DE, (2)Colorado School of Mines, Golden, CO, (3)National Instituteof Standards and Technology, Gaithersburg, MD

“Rheology without morphology...,” as the saying goes, becomes more unsatisfactory as complex fluids with increasinglycomplex rheological behavior are investigated. However, developing structure-property relationships for flowing colloidaldispersions, self-assembled surfactant solutions, polymer solutions and other complex fluids requires measurements ofthe microstructure under flow. Small angle scattering, and in particular, neutron scattering with the advantages ofcontrast matching techniques, provides one of the most complete methods for interrogating microstructure on thesubmicron length scale. The most relevant microstructure for a system in simple shear is in the flow-flow gradient plane(1-2 plane), which is the hardest to access in a scattering experiment. To address this need for direct measurementsunder flow, we have developed instruments for flow-SANS in the 1-2 plane based on a short-gap Couette cell. Further,as some systems can exhibit flow instabilities, such as shear banding, we have collimated the beam into slits as thin as100 microns to enable exploring structure in different regions of the flow field. The instrument, its calibration, andexamples of results are presented. Case studies include a shear thinning and shear thickening near hard-spherecolloidal dispersion, a prototypical wormlike micelle system, and a shear banding wormlike micellar system that alsoexhibits shear-induced phase separation. In each case, 1-2 plane flow-SANS data provides critical information aboutthe mechanisms underlying the highly nonlinear rheological behavior.



103. Light scattering studies of the aging of Laponite glasses and gelsDaniel Bonn, University of Amsterdam and Ecole Normale Superieure, Amsterdam, Netherlands

In the free energy landscape picture of glassy systems, the slow dynamics characteristic of these systems is believed tobe due to the existence of a complicated free-energy landscape with many local minima. We show here using lightscattering that for a colloidal glassy material multiple paths can be taken through the free energy landscape, that caneven lead to different 'final' non-ergodic states at the late stages of aging. We provide clear experimental evidence forthe distinction of gel and glassy states in the system and show that for a range of colloid concentrations, the transitionto non-ergodicity can occur in either direction (gel or glass), and may be accompanied by 'hesitations' between the twodirections. This shows that colloidal gels and glasses are merely global free-energy minima in the same free energylandscape, and that the paths leading to these minima can indeed be complicated.

104. Characterization of micellar interfaces by Fluorescence Quenching and Electron SpinResonance: Mixed micelles of lipids and detergentsJasmeet Singh, Justin Miller and Radha Ranganathan, California State University Northridge, Northridge, CA

The purpose of this contribution is two-fold: (1) to show the complementary application of the techniques of timeresolved fluorescence quenching (TRFQ) and electron spin resonance (ESR) in the investigation of the physicochemicalproperties of micellar interfaces and (2) present results of such a study on mixed micelles of phospholipids anddetergents. We have characterized mixed micelles of the phospholipid, dimyristoyl phosphatidyl choline (DMPC) and (i)the bile salt sodium deoxycholate (NaDC); and (ii) the zwitterionic dodecyl dimethyl ammonio propanesulfonate (DPS).These mixed micelles are model substrates for studying phospholipase activity. Results of characterization of enzymeactivity are also presented.

Aggregation numbers of DPS/DMPC and NaDC/DMPC micelles and micellar quenching reaction rate constants aredetermined by TRFQ. The hydration and microviscosity of the micelle/water interface are measured by ESR of spin-probes inserted into the micelles. These properties vary with composition and total concentration. The ESR and TRFQdata are interpreted together within the framework of a polar shell model of the micelle to derive its features. In thecase of NaDC/DMPC, small globular micelles are formed at low NaDC to DMPC ratios (<5), whereas DPS/DMPC formsstable globular micelles for a wide range of compositions. These properties are found to contribute to the observed rateenhancement of micellar lipid hydrolysis by lipolytic enzymes.

105. Micellar networks and dilute lamellar phase: transitions observed by cryogenictransmission electron microscopy

Travis K. Hodgdon1, Hidehiro Nagasawa2 and Eric W. Kaler1, (1)University of Delaware, Newark, DE, (2)KaoCorporation, Tokyo, Japan

Sugar based surfactants like n-dodecyl-β-D-glucoside (C12G1) are made from renewable resources and are non-toxicand environmentally benign; unfortunately, their use is often restricted by limited solubility in water due to Krafftboundaries and miscibility gaps. Introducing a small amount of the ionic surfactant sodium dodecyl sulfate (SDS)reduces the miscibility gap for C12G1, and SDS concentration is an excellent control parameter for tuning a widevariety of available microstructure and macroscopic physical properties.

The phase behavior and resulting microstructure in the dilute region of C12G1/ SDS mixtures has been established.The microstructure was studied with light and neutron scattering techniques and by direct observation using cryogenictransmission electron microscopy (cryo-TEM). The presence of a lamellar phase between the miscibility gap and themicelle phase results in a wide range of microstructure. Of special interest is the evolution of microstructure betweenthe lamellar and micelle phases.

The elongated micelles and networks that are present near the miscibility gap are often associated with strongincreases in the viscosity of solutions. Peaks in viscosity of several orders of magnitude have been found when thecontrol parameter is either surfactant ratio or the addition of a simple salt (NaCl). An initial increase in viscosity as acontrol parameter is increased is directly related to the axial growth of micelles. The decrease in viscosity that follows a



further increase of the control parameter is the result of branch point formation, and eventually the creation of asaturated micelle network.

106. Myelin Formation during the Dissolution of Lamellar Phase

Louisa Reissig1, David Fairhurst2, Andrew Mount1, Michael E. Cates1 and Stefan U. Egelhaaf3, (1)University ofEdinburgh, Edinburgh, United Kingdom, (2)Nottingham Trent University, Nottingham, United Kingdom, (3)Heinrich-HeineUniversity, Duesseldorf, Germany

After contact with water, lamellar phases can show spectacular instabilities: multi-bilayer tubules, so-called myelins,grow from the Lalpha/water interface into the water. We study Myelin formation in aqueous solution of the non-ionicsurfactant C12E3. We quantitatively investigate the growth of these myelins as well as changes in the lamellar phaseusing confocal and optical microscopy as well as direct obsevation. This provides detailed quantitative information onthe dynamics of the myelin growth, the myelin size as well as the swelling and textural changes of the lamellar phase.The dependence of these parameters on surfactant concentration and sample size is investigated. Based on theseobservations a semi-quantitative model for myelin growth is proposed.

107. Helical tubule self-assembly using a single-tailed surfactant

Heeyoung Lee1, Jae-Ho Lee2 and Srinivasa R. Raghavan1, (1)University of Maryland, College Park, MD, (2)NationalInstitutes of Health, Bethesda, MD

Hollow micro or nanotubules are a remarkable type of self-assembled structure formed in aqueous solution. Self-assembled tubules may find applications in controlled release, drug delivery, and in electroactive composites. However,these structures are typically formed only by certain specific lipids (i.e., two-tailed amphiphiles), gluconamides or certainpeptides. While the utility of tubules has been clearly shown, at the moment, their high cost limits their accessibility andapplicability. Here we present an easy and inexpensive method for forming stable tubules in water by using a single-tailed diacetylenic acid surfactant in conjunction with an alcohol. We will describe the formation of tubules as a functionof solution composition and temperature by using the techniques of optical and electron microscopy. Interestingly, thetubules show helical markings, which is unusual considering that the precursor molecules are achiral. This suggests thatmolecular chirality is not essential to form tubules, and this is in agreement with recent theoretical studies. Theformation of tubules from achiral molecules is believed to proceed via a chiral symmetry-breaking process.

108. Structure and rheology of self-assembled wormlike micellar networks withincorporated nanoparticlesMatthew E. Helgeson, Florian Nettesheim, Norman J. Wagner and Eric W. Kaler, University of Delaware, Newark, DE

We study the rheology and microstructure of self-assembled wormlike micellar solutions (WLMs) in the presence ofnanoparticles smaller than the mesh size of the micelle network. The addition of cationically modified silicananoparticles (d = 30 nm) to WLMs of cetyltrimethylammonium bromide (CTAB) significantly modifies the linear and



non-linear rheology of the micellar network. Combining rheology, flow-birefringence, light and neutron scattering andcryo-electron microscopy measurements provides a microstructural basis for the effects of the nanoparticles on theWLM network. The results indicate densification of the micellar mesh near the particles, suggesting that the particlesactively participate in the micellar network due to specific micelle-particle interactions. Measurements of the energeticsof these interactions have been carried out using isothermal titration calorimetry, suggesting that the micelles associatewith an adsorbed surfactant layer on the surface of the particle. This leads to increases in elasticity of the network aswell as hindered micellar alignment under flow, resulting in macroscopic increases in viscosity and suppression of theshear banding instability for concentrated CTAB solutions. The distribution of particles in the WLM network is consistentwith an effective interparticle attraction mediated by the adsorbed surfactants, which leads to phase separation athigher nanoparticle loading.

109. Composition effects on lipid domain size in model membranesAngela C. Brown and Steven P. Wrenn, Drexel University, Philadelphia, PA

The lipid raft hypothesis describes ordered domains of cell membranes, enriched in cholesterol, sphingolipids, andsaturated phospholipids, that are responsible for a number of cellular processes such as lipid sorting, protein signaling,and signal transduction. These lipid rafts are highly mobile, and it is believed that their coalescence and separation iswhat drives these cellular processes. For this reason, cellular function depends not only on the presence of lipid raftsbut also on raft size. This work uses steady-state fluorescent techniques, specifically Förster Resonance EnergyTransfer (FRET) along with a mathematical model to detect and estimate the size of lipid domains in membranesystems modeling natural cell membranes. The fluorescence study was initially performed on a simple two-componentphospholipid and cholesterol system in order to characterize the behavior of the fluorescent probes using anestablished phase diagram and was then extended to more complex, three-component systems. In these ternarysystems, the effect of phospholipid type, sterol type, and sterol composition on domain size was determined. It wasfound that very slight changes in the composition of the membrane (i.e., both type and amount of “line-actant”) havesignificant effects on domain formation and size by changing the amount of line tension present in the membrane.

110. Interaction of Surfactin with Phospholipids Bilayer:Neutron Reflection and Small AngleNeutron Scattering StudiesHsin-Hui Shen and R. K. Thomas, University of Oxford, Oxford, United Kingdom

Surfactin is a lipopetide produced by Bacillus substilis strains which contains a cyclic heptapetide and a beta-fatty acidchain. It has biological properties such as antiviral, antibacterial and hemolytic. Although the biological properties aresuggested to be the consequence of its interaction the membrane of the target cell, the detailed molecular mechanismof action is not clearly understood. There is a substantial interest in understanding the molecular organization andnanomechanical properties of mixed surfactin/lipid bilayers system. Neutron reflection and small angle neutron scattering(SANS) are able to give a direct view of how surfactin interact with phospholipid bilayers.

The results obtained on different contrasts of DPPC bilayers built on the silicon-D2O interface verify the idea ofsurfactin penetrating into bilayers below the critical micelle concentration (CMC). Two mechanisms may be predicted,(a). at low concentrations, surfactin penetrates into the phospholipid membrane by interacting via its fatty acid chain,(b). near the CMC, surfactin self-associates to form micelles involving membrane phospholipids and leading tomembrane rupture.

Although experimental results have proved strong haemolytic activity of surfactin with blood cells, the mechanism is notknown. By using SANS technique for a series of DPPC/surfactin ratios, strong evidence of its haemolytic activity hasbeen found. There is insertion of surfactin into the lipid bilayer and self-aggregation of surfactin within the membranewhich results in pore formation. The results show a large surfactin aggregation number about 150 (diameter: 25 Å) andwith a d-spacing of about 200 Å between the aggregates in the membrane.

111. Binary Mixtures of β-Dodecylmaltoside (β-C12G2) with Cationic and Non-IonicSurfactants: Surface and Micellar Compositions

Sandeep Patil1, Natalie Buchavzov2, Enda Carey1, Marion Lescanne1 and Cosima Stubenrauch1, (1)UniversityCollege Dublin, Dublin, Ireland, (2)Universität zu Köln, Köln, Germany



Surfactants used for practical applications are usually surfactant mixtures because they often exhibit superiorperformance than the individual surfactants. In the present study binary mixtures of the sugar based n-dodecyl-β-D-maltoside (β-C12G2) with cationic dodecyltrimethyl-ammonium bromide (C12TAB) and nonionic hexaethyleneglycoldodecyl ether (C12E6), respectively, have been investigated at different mole fractions. Surface tension measurementswere used to determine the critical micelle concentration and the surfactant composition at the surface. Interactionparameters and the mole fractions of the individual surfactants in the mixed air/water monolayer as well as in the mixedmicelles were calculated using regular solution theory. It was found that n-dodecyl-β-D-maltoside interacts weakly withthe cationic surfactant (C12TAB) and it dominates in both the mixed monolayer and the mixed micelles. On the otherhand, β-C12G2 and C12E6 mix ideally in solution. For both surfactant mixtures the surfactant composition at thesurface determined by surface tension measurements and by the regular solution theory, respectively, has beencompared and discussed in detail.

112. Adsorption of Polymer/Surfactant Mixtures at the Air-Water Interface

X. L. Zhang1, J. Penfold2, D. J. Taylor1, J. Zhang1, R. K. Thomas1 and I. Tucker3, (1)Oxford University, Oxford,United Kingdom, (2)ISIS, Rutherford Appleton Laboratory, CCLRC, Chilton, Didcot, Oxon, United Kingdom, (3)UnileverResearch and Development Laboratory, Port Sunlight, United Kingdom

The interactions between oppositely charged polymer/surfactant mixtures at the air-water interface have been studiedusing neutron reflectivity techniques with supplementary surface tension measurements. The cationic polyelectrolytepoly(ethyleneimine)(PEI)/anionic surfactant sodium dodecyl sulfate(SDS) system is compared with a series of systemscontaining cationic ethoxylated poly(ethyleneimine)(PEI-EOn) with different degrees of ethoxylation of the PEI/anionicsodium dodecyl sulfate(SDS). The surface tension behavior and adsorption patterns for these systems show a strongdependence upon the solution pH. However, the SDS adsorption for PEI/SDS and PEI-EO1/SDS at the interface isunexpectedly most pronounced when pH is high (when polymer is essentially a neutral polymer). An obvious surfactantmultilayer adsorption can be observed especially at intermediate concentrations at higher pHs 7 and 10 (area per SDSmolecular ~20Å2). Based on fits to the neutron reflectivity data from different isotopic compositions the multilayerstructure is consistent with a sandwich structure with an outer surfactant layer and a submerged micellar layer ordefective bilayer. In contrast, for PEI-EO3/SDS and PEI-EO7/SDS, only monolayer adsorption is seen (area per SDSmolecular ~50Å2). Furthermore, the pattern of SDS, PEI-EO3 and PEI-EO7 adsorption is indicative of a strongpolymer/surfactant interaction at low pH, which decreases with increasing pH. Hence, the ethoxylation of the PEI indeedimposes a degree of surface activity on the polymer and modifies the nature of the surface adsorption.

113. Adsorption of Lennard-Jones Surfactant Mixtures at the Liquid/Vapor Interface Studiedby Monte Carlo SimulationC. J. Radke, University of California, Berkeley, Berkeley, CA

Based on our previous work on single surfactants, we study mixed adsorption of nonionic surfactants consisting of anamphiphilic block-copolymer chain of Lennard-Jones solvophobic and solvophilic interaction centers, designated asH4Tm in a monotonic LJ solvent. Single-surfactant adsorption follows the Langmuir isotherm. Larger tail lengths lead tolarger maximum coverages because the surfactant penetrates further into the vapor allowing closer packing.Increasingly attractive tail-tail interactions produce the same effect, again because the surfactant penetrates further intothe vapor. Even small attractive tail interactions lead to drastically lower critical aggregation concentrations.

Binary mixtures of H4Tm surfactants display adsorption and tension isotherms intermediate between those of the twosingle surfactants. Langmuir-based mixture theories do not obey thermodynamic consistency for unequal size species.We successfully apply ideal adsorbed solution theory for all mixtures studied with and without lateral tail interaction. LJsurfactants prove very useful for understanding real surfactant behavior without excessive computation time.

114. Time-Chain Length Equivalence in the Tribology of the Organic Ultrathin FilmsKenji Hisada, Akiko Hino, Daisuke Sanaka, Toshiyuki Baba and Teruo Hori, University of Fukui, Fukui, Japan

In this study, Langmuir-Blodgett (LB) films were prepared with the compounds having long alkyl tails, and their



tribological behaviors were investigated. The frictional forces were measured with lateral-force microscope (LFM), andthey were discussed as a function of chain length, scanning rate and loading force. . The LB films gave maximumfriction at a specific scan rate. For example, the LB film of poly(tetradecyl acrylate) showed maximum friction forcewhen it deformed with probe tip at 8–12 µm/s. The LB film having longer alkyl tails, e.g. poly(octadecyl acrylate),showed maximum friction at slower scan rate. Deceleration of the scan rate showed an equivalent effect with shorteningthe chain length. In the phase transition of the Langmuir monolayer, equivalence was reported between temperatureand the number of carbon in the alkyl tail. The phase transition temperature increased with the elongation of alkylchain. These results show that there is some equivalence between shear deformation rate and chain length on thefriction of the organic ultrathin films, which was similar to the time-temperature equivalence in the viscoelasticdeformation of polymers. The scanning rate at frictional maximum, νSR,max, was expressed as follows,log(nSR,max(n))=log(nSR,max(n+m)×aCLm) where n and m are number of carbon atoms in alkyl chain, aCL is a shiftfactor. The equation supports that the energy dissipation at the phase transition causes the frictional shift with chainlength for the ultrathin films.

115. Understanding chitosan enhancement of interfacial lung surfactant adsorptionPatrick C. Stenger, Omer M. Palazoglu and Joseph A. Zasadzinski, University of California, Santa Barbara, CA

The adsorption of lung surfactant to an air-water interface is strongly inhibited by the competitive adsorption of albuminand other surface active serum proteins, and is likely the explanation of surfactant inactivation in Acute RespiratoryDistress Syndrome (ARDS). In vitro, lung surfactant adsorption to the interface is restored by the addition of hydrophilicnon-adsorbing polymers and increased mono and divalent salts, suggesting a promising therapy for ARDS. Thedifferent approaches can be explained and quantified using classic colloidal science such as the Smolukowski analysisof colloid stability. This paper will primarily address the mechanism by which chitosan, a highly cationic biopolymer,enhances lung surfactant adsorption to the air-water interface. Chitsoan reverses albumin induced surfactant inhibitionat significantly lower concentrations (0.01 mg/mL) than non-ionic polymers (10 mg/mL) though its effect is surprisinglymuted by increasing the concentration greater than tenfold. Fluorescence and confocal microscopy images of theinterface show distinct changes in morphology between albumin and surfactant-covered regions offering a visualconfirmation of surfactant adsorption to the interface. We will compare these results to the depletion attractiongenerated by non-ionic polymers and the electrostatic effects generated by mono and divalent salts which have bothbeen shown previously to enhance surfactant adsorption.

116. Limiting Extremes of Adhesion Dynamics between Polymeric VesiclesJin Nam and Maria Santore, University of Massachusetts, Amherst, MA

This work examines the adhesion dynamics between copolymer vesicles of poly(dimethylsiloxane)-poly(ethyleneoxide)[PDMS-PEO], where one membrane spreads over the second to partially engulf it. The project considers limitingextremes with respect to the translational diffusion of ligands and receptors in the membrane: In one extreme, densemembrane functionalization facilitates adhesion without requiring translational diffusion of receptors while in the otherextreme, translation diffusion of ligands and receptors within the plane of the membrane surely dominates kinetics. ThePDMS-PEO was functionalized with biotin to enable ligand-receptor binding to avidin-functionalized membranes. Usingmicropipettes, an avidin-coated vesicle was brought into contact with biotinylated one and the contact area and anglemonitored in time. Densely functionalized vesicles, where diffusion was unimportant, showed strong and irreversibleadhesion dynamics which could be described in three steps: pre-adhesive latency period, rapid adhesion which wasinitiated suddenly, and finally gradual relaxation. With 50 or more mol% functionalization, all three phases proceededrelatively quickly and independent of membrane functionality. At lower functionalities, the process was slower, as aresult of diffusion, and roughly in proportion to the density of ligands and receptors. At the lowest functional densities,adhesion proceeded without membrane deformation, giving the appearance of a latency period, but still with irreversibleadhesion. The maximum adhesion contact angles were almost same regardless of the initial membrane tensions, theirfunctional density, or the tension ratio between substrate and adherent one. This suggests the ultimate state isdominated by the irreversibly binding ligands and receptors, though membrane mechanics affects adhesion dynamics.

117. Drop Retention Force as a Function of Waited TimePreeti S. Yadav, Prashant Bahadur, Kumud Chaurasia, Aisha Leh and Rafael Tadmor, Lamar University, Beaumont,TX



The force required to slide a drop past a surface is shown to be a growing function of the time the drop waited on thesurface prior to the commencement of sliding along it. In this first report on the “waited time” effect we explore anumber of systems and show that this phenomenon is general and takes several minutes before reaching a plateau.Then we use one system to study the phenomenon in greater detail. We provide some semi-quantitative explanation tothe experiments.

118. The Balanced Nucleation and Growth Model for Controlled Crystal Nucleation and SizeDistribution – II. Experimental SupportIngo Leubner, Crystallization Consulting, Penfield, NY

Based on the Balanced Nucleation and Growth (BNB) model, experiments are presented that quantitatively relate thenumber and size of crystals formed in controlled batch processes to reaction variables. The experimental results aresummarized for variations of the reaction addition rate, crystal solubility, and reaction temperature, and the effect ofOstwald ripening agents and crystal growth restrainers.

The models were initially developed and applied to the precision precipitation of silver halides in research, productdevelopment, and manufacturing. They have since been successfully applied to the precision precipitation of boro-fluoride salts, calcium carbonate, silicates, superheavy metal compounds, and polyacetylenes. Knowledge of the modelis essential for the control of crystallization of organic and inorganic materials from the lab to manufacturing.

119. Hydrogen reduction of perchlorate in dilute aqueous solutionsDemin Wang, H. Y. Lin, S. Ismat Shah, J. G. Chen and C. P. Huang, University of Delaware, Newark, DE

Perchlorate ion is the current candidate contaminant in drinking water under regulatory consideration by U. S. EPA. It isof current urgency to remove perchlorate ion at low concentrations (ppb to ppm) from contaminated groundwater orsurface water to safeguard the public safety. Reduction of perchlorate by hydrogen (molecular or atomic) in thepresence of catalyst has undisputed advantages in cost, operation, and public-acceptance. In the present study, theremoval of perchlorate ions from dilute solutions was attempted in the presence of catalytic surface by either molecularhydrogen or electrically-generated atomic hydrogen. All experiments were performed at ambient conditions, i.e., roomtemperature and neutral pH. For molecular hydrogen, results indicated that perchlorate ions could be reduced tochloride at slow but significant reaction rate. The maximum removal efficiency was less than 20% at an initialperchlorate concentration of 10 ppm. In order to enhance the adsorption of perchlorate at catalytic membrane, positive(anodic) potential was applied onto Ti-TiO2 surface. Significant removal efficiency of higher than 90% was achieved atan initial perchlorate concentration of ppm level. For atomic hydrogen, reduction of perchlorate at catalytic membranewas also found by applying constant current. Higher reaction rate was achieved with a 40% removal in 8 hours at aninitial concentration of 10 ppm. Perchlorate was reduced to chloride at catalytic membranes coated with Pt, Sn, or Cr.However, the end product was chlorite rather than expected chloride at catalytic membrane coated with Co catalyst.

Keywords: perchlorate removal, hydrogen reduction, catalyst, catalytic membrane

120. Novel capsule formation based on stimulus responsive block copolymer filmsTimothy W. Addison and Simon Biggs, University of Leeds, Leeds, United Kingdom

In recent years the layer-by-layer (LbL) technique has been demonstrated as a versatile method to provide routes toencapsulation, surface coatings and functional capsule formation. Driven by the affinity of a charged species in solutionto that of an oppositely charged surface it provides a pathway to create multilayer films with unique properties. Manysubstrates have been successfully coated using the LbL method ranging from flat surfaces to colloidal particles andbiological cells/enzymes, likewise composite films have been created with many different species includingnanoparticles, polyelectrolytes and micelle structures. Working with two diblock copolymers that undergo micellizationabove a critical concentration and pH when in aqueous solution, multilayer films have been deposited on to idealcolloidal particles. After the charged micelles are adsorbed from solution it can be demonstrated that they retain much oftheir ordered nature once present within the film. It is found that these adsorbed micelles, much like when in solutionundergo a reversible change in structure when the pH of their environment is cycled between pH 4 and pH 9. Prior toadsorption, the cores of such micelles can be pre-loaded with hydrophobic molecules. Once adsorbed, the resulting film



has the ability to be used as a nano-sized delivery system with material being released from within the micelles with aspecific trigger, in this case pH. Such delivery systems are of great interest in the development of agrochemicalformulations, personal care products and drug release systems.

121. Low Temperature Mixed Lipid Phase: Understanding Bicelle Formation

Lionel Porcar1, Divya Singh2, Gina Polimeni3, Paul D. Butler1, William Hamilton4, Ursula Perez-Salas5 and GaryLynn6, (1)National Institute of Standards and Technology, Gaithersburg, MD, (2)John's Hopkins University,Gaithersburg, MD, (3)Georgia Tech, (4)ANSTO, Sydney, Australia, (5)Argonne National Laboratory, Argonne, IL, (6)OakRidge National Laboratory, Oak Ridge, TN

Systems consisting of mixtures of a long and a short-tail lipid have recently shown promise in membrane proteincrystallization and have been used for some time as an alignable media for use in NMR protein structure determination.However, the phase diagram of these lipid mixtures remains poorly understood. In particular, much of the literatureposits the existence of bicelles, or discotic micelles, as the agents of the useful properties. Recent work howeversuggests that such structure only exist below the melting transition temperature of the long tail lipid (Tm), with atransition to a lamellar phase at higher temperature. A detailed understanding of the phase behavior is essential toadapting these systems for more general applications. We report on a systematic study at the lowest temperatureisotropic fluid like phase. Small angle neutron scattering (SANS) experiments with hydrogenated and deuterated lipidsgive direct evidence of the segregated discoidal morphology, while use of standard mixed surfactant theories account tofirst order for the size of the discs. SANS at higher temperatures along with phase studies and SANS measurementson systems with different Tm and chain lengths are discussed in terms of the influence of Tm on the general phasebehavior and observed structures.

122. Time-resolved Dynamincs of Stereocomplexation of Polylactide Enantiomers on theWater Subphase using a Planar Array Infrared (PA-IR) Spectrograph

Young Shin Kim1, Christopher M. Snively1, D. Bruce Chase2 and John F. Rabolt1, (1)University of Delaware, Newark,DE, (2)DuPont Experimental Station, Wilmington, DE

Although the previously developed technique of planar array infrared (PA-IR) spectroscopy offers a number ofadvantages over Fourier transform infrared (FT-IR) methods such as ultrafast speed (<100 µsec) and excellentsensitivity, obtaining a spectrum of films in the range of 1800-1000 cm-1 on a water subphase of a Langmuir troughremains difficult. This is due to the poor IR reflectivity of water, the extremely low concentration of the thin film on thesurface, and the interference of water bands. In this study, we report a new planar array infrared reflection spectrograph(PA-IRRS), which has several advantages over conventional approaches. By splitting the incident infrared beam intotwo sections on a plane mirror or a water trough, instead of at the front of the globar source, the performance of thisinstrument is shown to be comparable to that of the dual-beam instrument although this instrumental setup is the samewith that of the single-beam instrument. Due to this design, the instrument accommodated large infrared accessories,such as the water trough, without a loss of infrared beam intensity. Using this instrument water vapor could besubtracted out and was obtained a high quality spectrum for a poly(L-lactic acid) Langmuir film on the water subphase,with a resolution of about 8 cm-1, in 10.8 sec. Hence, this PA-IRRS system has great potential for investigating thetime-resolved dynamics of a broad range of Langmuir films, such as cellular membranes or biopolymers, on the watersubphase.

123. Next generation neutron scattering analysis Tools

Jing Zhou1, Divya Singh2, Matthieu Doucet1 and Paul D. Butler3, (1)The University of Tennessee, Gaithersburg, MD,(2)John's Hopkins University, Gaithersburg, MD, (3)National Institute of Standards and Technology, Gaithersburg, MD

Small Angle Neutron Scattering (SANS) is a unique scattering tool used by a broad and diverse set of users and ofparticular interest for colloidal and complex fluid systems. Complex fluids scientists have traditionally written their own



analysis code, used simple analytical model fitting provided by various sources, or remained at a very qualitative levelof data interpretation. A strongly integrated, easy to use, and well documented and extensible suite of tools would notonly lower the barrier for the casual user to employ SANS without having to rely on an expert (or become onethemselves), but significantly increase the amount of information extracted from the data. Over the next five years weplan on developing SANS data analysis libraries within the DANSE framework being constructed at Caltech, that willallow integration of various analysis and modeling methods with GUI front ends for general users, while also providingan extensible platform for scientific programmers who want to extend the functionality beyond the existing tools withoutwriting everything from scratch. A first prototype/demo version of a package which will allow comparison of scatteringdata to the scattering from arbitrarily complex shapes will be demonstrated along with a vision for where thedevelopment is headed.

124. The Synthesis of meso/macroporous SBA-15 through dual-templating method(combination of liquid crystal and colloidal crystal templating method)Ji Sun Yun and Son-Ki Ihm, KAIST, Daejeon, South Korea

Since the existence of hierarchical pores can provide multiple advantages derived from each pore-size regime,hierarchical porous materials have been synthesized by many researchers. SBA-15 has obvious advantages such asgood hydrothermal stability induced from thicker wall than that of MCM-41, and high surface area generated frommesoporous structures. Furthermore, when macropores are introduced in to the mesostructure of SBA-15, the materialhas additive advantages like ease access to active sites derived from macroporous structures. In this regard,meso/macroporous SBA-15 should be very attractive for their application in the area of adsorption, catalysis andseparation. The meso/macroporous SBA-15 were prepared by a new and simple dual-templating method, which is thecombination of replicating the closed packed array of colloidal crystal and liquid crystal mesophase of surfactant. Themeso/macroporous silicate can be successfully synthesized without losing unique properties of each pore size regime.With the PS:Si ratio, not only was the volume of macroporous space increasing, but also the macrostructures wasbetter ordered. The adsorption dynamics were also improved with the increase in the volume of macroporous space.This result seems to confirm that the macropores in mesoporous silicates really provide an easy access to active sites.

125. Correlating Electronic and Catalytic Properties of Bimetallic SurfacesAmit Goda, Mark Barteau and Jingguang Chen, University of Delaware, Newark, DE

The formation of bimetallic surfaces leads to a change in the electronic properties of the parent metal surface, whichresults in changes in chemical reactivity. In this work we illustrate the correlation of electronic properties of bimetallicsurfaces with the reaction pathways of C2 hydrocarbons and of the selective reduction of acetic acid to acetaldehyde.

For the study on C2 hydrocarbons, Density Functional Theory (DFT) was used to study the binding of hydrogen,ethylene, acetylene, ethyl and vinyl on monometallic and bimetallic transition metal surfaces. The binding energies(B.E.) of these species were found to correlate with the d-band centers of the surfaces. DFT-calculated B.E. and BOC-calculated activation barrier values were used to calculate the selectivity for acetylene hydrogenation vs. ethylenehydrogenation. The results showed that for monometallic fcc(111) surfaces, the selectivity for acetylene hydrogenationfollowed the trend Ni > Pt > Pd.

In the case of selective reduction of acetic acid, DFT calculations were used to study the modes and energies ofadsorption of the involved intermediates along with the overall reaction energies for the elementary steps. It wasobserved that ethanol binds more strongly than acetaldehyde on Pt(111) as well as the subsurface Ni on Pt surface,but the trend reverses for monolayer Ni on Pt. This change in B.E. affects the overall heat of reaction for ethoxy goingto ethanol. These changes in the thermodynamics of reactions should affect the overall selectivity toward acetaldehyde,which would be determined be calculating the activation barriers for the elementary steps.

126. General trends in hydrogen binding energy and hydrogenation activity on Pt-3dbimetallic surfacesMichael P. Humbert, Luis E. Murillo and Jingguang G. Chen, University of Delaware, Newark, DE

Bimetallic surfaces often show novel properties that are not present on either of the parent metal surfaces. Our group



has recently investigated the electronic and chemical properties of model bimetallic surface structures, using acombination of experimental and theoretical modeling to gain insights into these factors. Density functional theory (DFT)can provide insight into the interaction between molecules and model surfaces. In this study we attempt to correlateDFT findings to experimental results. Specifically, temperature programmed desorption (TPD) is performed on modelsurfaces with various probe molecules to determine if reactivity can be determined from first-principles. Extensivecharacterization has been performed on Ni-Pt bimetallic surfaces. The findings of this study are that Ni deposited at 300K on Pt(111) results in a surface configuration of Ni, while Ni deposited at 600 K diffuses into the bulk resulting in asubsurface Ni configuration. This has also been found to be the case for Co-Pt surfaces, and this idea is extended toother 3d metals based on DFT results.

127. Gas Phase Perchlorate Reduction by Mono- and Bimetallic Catalysts Supported onActivated Carbon

C. P. Huang1, Jingguang Chen1, Yuying Shu2, Sergey Rykov1 and Rovshan H. Mahmudov1, (1)University ofDelaware, Newark, DE, (2)Virginia Polytechnic Institute & State University, Blacksburg, VA

Catalytic reduction of perchlorate has challenged chemical and environmental communities for decades. In this work wereport the results of gas phase reduction of perchlorate by hydrogen gas in the presence of Pd- and Pt- based monoand bimetallic catalysts supported on activated carbon. Five types of Pd and Pt based bimetallic catalysts supported onactivated carbon (AC) were tested: Pd (5% W:W), Pt (5% W:W), Pt/Ni (Pt 5% W:W, Pt:Ni = 1:1), Pt/Co (Pt 5% W:W,Pt:Co = 1:1), and Pt/W (Pt 5% W:W, Pt:W = 1:1). First perchlorate was preadsorbed on the activated carbonimpregnated with the appropriate catalysts. The activated carbon was then separated and placed in the oven under10% H2 + 90% N2. Results showed that bimetallic catalysts supported on activated carbon had better hydrogenadsorption capacity and perchlorate reduction efficiency than monometallic catalysts with Pt/Co being the best.Reaction temperature was crucial for perchlorate reduction. More than 95 % of adsorbed perchlorate was reduced in 5hrs at temperatures > 50 oC when the Pt/Co catalyst was used. Such fast reduction of perchlorate at moderatetemperatures has not been reported in the aqueous phase. Major drawback, as showed in the XPS and EDX analysis,was the dissolution of the second metal in the aqueous phase. Upon submerging in water relative surfaceconcentrations of Co and Ni dropped by factor of 2 whereas Pt was stable. Further research is needed to develop thecatalysts combination that will have better stability and efficiency.

128. Surface science studies of tungsten carbides as alternative electrocatalysts for directmethanol fuel cellsAlan Lee Stottlemyer and Jingguang G. Chen, University of Delaware, Newark, DE

The motivation of this research is to assess the feasibility of tungsten carbides as alternative electrocatalysts in directmethanol fuel cells (DMFC). DMFC are one possible source of energy which can be used to directly convert chemicalenergy into electrical energy by the electro-oxidation of methanol. Current fuel cells require the use of Pt/Ru bimetallicanode catalysts which suffer from CO poisoning and high cost. The commercialization of such technologies requiresless expensive and more CO tolerant materials. Transition metal carbides often show catalytic properties similar to thePt-group metals and recent research suggests that tungsten carbides may be an appropriate substitute.

Temperature programmed desorption (TPD) was used to draw both qualitative and quantitative conclusions about thereactions of CO, H2, CH4 and CH3OH on polycrystalline platinum, tungsten carbide and platinum modified tungstencarbide foils. Results from TPD studies show that all tested surfaces are capable of methanol decomposition and thepropensities for each decomposition pathway were calculated. A qualitative assessment of TPD data coupled withGaussian deconvolution of peaks suggests that methanol decomposition chemistry occurs predominately on the Pt(100)face. This conclusion is supported by past Pt(111) single crystal work that suggests that the Pt(111) face is inert tomethanol decomposition. Ultimately, such studies suggest that platinum modified transition metal carbides may bereasonable alternative electrocatalysts for direct methanol fuel cells.

129. Study of Ag and Re promoted Ag catalysts for ethylene epoxidation using traditionaland high-throughput experimentationJoseph C. Dellamorte, Jochen Lauterbach and Mark A Barteau, University of Delaware, Newark, DE



Current global production of ethylene oxide (EO) exceeds 14 million tons per year. The current industrial process, directgas phase production of EO, is expensive with 20-25% of the main reactant, ethylene, being combusted in anunselective reaction on the base catalyst, Ag. Several patents claim that promoters on Ag catalysts, such as Re, Cs,and co-fed organic chlorides, yield EO selectivities over 80%. However, only the effects of Cs and organic chlorideshave been studied in detail. In order to establish a more fundamental understanding of the Ag and Re-Ag catalysts,traditional and high-throughput reactor studies were executed. As Fig. 1 shows, the Ag catalyst activity wasdramatically affected by the calcination conditions, without change to the selectivity. Based on this result, it is thoughtthat catalyst sintering decreases the activity with larger calcination times. Results from studies with Re-Ag indicate thatRe increases the EO selectivity at the expense of catalyst activity. The optimum performance of 45% EO selectivity forthe Re-Ag, compared to 30% for Ag, was found for catalysts with 25 ppm Re. Characterization, using SEM, shows thatthe addition of Re also causes an increase in the Ag particle size from 15-35 mm. An analysis of the oxygen reactionorders showed that the Re-Ag catalyst presents a more uniform distribution of sites for oxygen adsorption thanunpromoted catalysts. Thus, it is hypothesized that Re is blocking/destroying Ag step sites, increasing the EOselectivity.

Fig. 1. Performance of Ag catalysts calcined at 400oC for 1-21 hours

130. Photocatalytic Performance of Pulsed Laser Deposited TiO2 Thin Film – Effects ofOxygen Vacancy, Phase Composition, and Energy Band Configuration

Hong-Ying Lin1, Abdul Rumaiz2, Demin Wang1, Meghan Sculz1, S. Ismat Shah1 and C. P. Huang1, (1)University ofDelaware, Newark, DE, (2)University of Delaware, Newark

Nanoscale TiO2 thin films were prepared by pulsed laser deposition (PLD) technique on Indium Tin Oxide (ITO)surfaces. TiO2 thin films were deposited as a function of oxygen pressure and substrate temperature. Results from X-ray photoelectron spectroscopy (XPS) show a 0.6 eV shift in binding energy of Ti 2p3/2 with variation on oxygen partialpressure. Based on linear scan voltammetry (LSV), we found that the onset potential of TiOx thin films increased inabsolute energy scale by a magnitude of 0.2 to 0.8 eV when deposition temperature decreased from 873 to 298 K. Thisimplies that the flatband potential as well as the Fermi energy of the TiO2 thin film vary with the concentration ofoxygen vacancies. Rutile weight fraction ranged from unity to near zero was observed, depending on experimentalcondition. In photoelectrochemical study, the best incident photon conversion efficiency (IPCE) was observed atdeposition temperature of 873K which yielded 2.5 to 5 % of IPCE(l=320nm). The differences were attributed to thevariation in degree of crystallization and phase composition of TiO2. Our results suggest that the photocatalytic



reactivity of TiO2 thin film can be optimized depending on the desired redox reaction and this can be achieved bymoderately manipulating oxygen pressure and substrate temperature since these two parameters greatly impact theoxygen vacancy concentration in the TiOx thin film deposited in PLD. This, in turn, affects the position of the flatbandpotential and its photocatalytic reactivity.

131. Line energy and Line ForceRafael Tadmor, Lamar University, Beaumont, TX

What is the physical meaning of line tension? Is it the same as line energy? How does it relate to the forces retaining adrop to a surface? These are fundamental questions in surface science and we address them. We show that lineenergy derived from energy minimization and retention force derived from fluid dynamics consideration not only havethe same dimensions (“Energy/Length” and “Force”) but also relate by their physical interpretation and one can bederived from the other. We provide some experimental evidence for the physical picture that we present.

132. DYNAMIC arrest and activated transport in molecular colloidal glasses and gelsMukta Tripathy, University of Illinois, Urbana-Champaign, Urbana, IL and Kenneth S. Schweizer, University of Illinois,Urbana, IL

Molecular integral equation, simplified mode coupling, and activated barrier hopping theories have been combined tosystematically investigate the structure, slow translational dynamics, vitrification and gelation of suspensions composedof nonspherical colloids. One (rod), two (planar) and three (e.g. cube, octahedron) dimensional shapes have beenstudied. For purely excluded volume interactions, the effective dimensionality of the rigid object is the primary variablecontrolling the ideal glass volume fraction and entropic barrier height. Subtle effects occur within a fixed dimensionalclass (e.g., triangles versus hexagons). In the presence of strong, short range inter-site attractions, glass formationcompetes with gelation, and re-entrant glass-fluid-gel behavior is predicted at high volume fractions, the quantitativeaspects of which depend on colloidal shape. Correlations of the slow dynamics with the packing, and number of stickycontacts between the nonspherical objects, has been investigated. All the results for molecular colloids are contrastedwith their spherical particle analogs to establish the consequences of shape anisotropy. Finally, a new unifiedunderstanding of how barriers in colloidal gels composed of sticky spheres depend on local structure, attractionstrength, and volume fraction has been achieved. The emergent physical picture suggests analogies with glasses andmechanically jammed systems.

133. CO oxidation over Ag/TiO2 and Au/TiO2 supported nanoparticles prepared byphotodepositionSze Chi Chan and Mark A. Barteau, University of Delaware, Newark, DE

It has been shown that gold nanoparticles supported on metal oxides with sizes below 5 nm exhibit unique catalyticproperties for CO oxidation, water-gas shift, and epoxidation of propylene. In particular, Au/TiO2 exhibits CO oxidationactivity at temperature as low as 90K. By far, deposition-precipitation is the most extensively used method for thepreparation of Au/TiO2 catalysts. The main disadvantage of this method is that the weight loading of Au is very low.Our previous study demonstrated that metal photodeposition on TiO2 nanoparticles gives rise to high highly uniformmetal nanoparticles in the 1-2 nm size range and provides new route to generate supported nanoparticles with highlyuniform sites on nanoscale. In our present work, we have scaled-up the Ag and Au photodeposition on TiO2nanoparticles. Ag/TiO2 and Au/TiO2 nanoparticles obtained from the scaled-up process were characterized by atomicabsorption spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible absorption, and high-angleannual dark-field scanning transmission electron microscopy. In addition, Ag/TiO2 and Au/TiO2 nanoparticles were alsoprepared using traditional deposition precipitation method. The catalytic activity for CO oxidation of Ag/TiO2 andAu/TiO2 nanoparticles prepared by both methods were investigated using a high-throughput reactor.

134. Spin-Leakage in Nanoparticles of Paramagnetic EndometallofullerenesVitaly K. Koltover, Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, MoscowRegion, Russia



Endohedral fullerenes (M@C2n) are carbon clusters that contain atoms trapped within the fullerene cage. This “atomicpark” of the 21st century counts approximately 30 elements, mainly of 2nd group (Ca, Ba, Sr) and 3rd group (Sc, Y,Ln). Some of them, like La@C2n, have unpaired electrons. For La@C2n embedded in the polycarbonate film, wediscovered an intense 1H-ENDOR (electron-nuclear double resonance) signal. Since there are no protons in La@C2n,this was a matrix 1H-ENDOR that testifies permeability of the fullerene shell for the electron spin density. For liquidsolutions of La@C2n in hexamethylphosphoramide (HMPA), molecules of which contain NMR active phosphorus-31,the paramagnetic shift of 31P NMR of bulk HMPA molecules in the presence of La@C2n was revealed. Thus, ENDORand NMR testify that the area of localization of unpaired electrons is not restricted by the fullerene shell but a partialrunoff of the electron spin density outside the fullerene cage (“spin-leakage”) takes place. Furthermore, M@C2n formnanoparticles, the mean size of which ranges up to 100 nm in polar solvents. The “spin-leakage” leads to the partialloss of molecular paramagnetism of M@C2n at forming the nanoparticles. The magic angle spinning (MAS) NMR ofsolid complexes of La@C82 and Y@C82 with HMPA revealed the enormous shifts for 139La lines along with the vastrange of the shifts for 31P of the bound HMPA. Being unchanged with temperature, such shifts suggest their Knightnature caused by the density of conduction electrons at the positions of the NMR observed nuclei.

135. Effect of contact time and pushing force on adhesion force between glass particle andmica plate in electrolyte solutionYasushige Mori and Keisuke Shimamura, Doshisha University, Kyotanabe, Japan

It is well known that the adhesion force between surfaces in an aqueous solution depends on ionic species andconcentration, and increases with contact time, when two surfaces are pressed each other. This phenomenon could beexplained that the adsorbed layer of water or cation was destroyed, and then the adhesion force mainly due to the vander Waals attraction force increased because two surfaces could be approached each other. However, the dependenceof pushing force is not clear. In this study, an atomic force microscope was used to determine the adhesion forcebetween a glass particle and a mica plate in lithium chloride, cesium chloride, or calcium chloride solution forunderstanding of the effects of the contact time and the pushing force. The adhesion force in these aqueous solutionsincreased with the impulse, that is the product of pushing force and contact time. As the adhesion force in electrolytesolution mainly depends on the van der Waals force, the distance between a glass particle and a mica plate could beestimated by the calculation of van der Waals force. At the high impulse, the distance between a glass particle and amica plate decreased up to the diameter of a water molecule in lithium chloride and calcium chloride solution. In cesiumchloride solution, however, the distance only decreased to twice length of the diameter of cesium ion, because cesiumions would strongly absorb on the surface.

136. Non-Surface Active Amphiphilic Diblock Copolymers. --- The Effect of Chain Lengthand Hydrophobicity ---Hideki Matsuoka, Ploysai Kaewsaiha, Shuji Kage and Hao Chen, Kyoto University, Kyoto, Japan

The "Non-Surface Active Amphiphilic Diblock Copolymer" is a novel class of molecules which is contradict with the"common sense" of the surface and interface science. They are certainly amphiphilic so they form micelles in aqueousmedia when dissolved. However, they do not adsorb onto the air/water interface. Hence, the surface tension of thesolution does not decrease with polymer concentration and the solutions show very less foam formation activity. Thiscurious molecule is in principle ionic amphiphilic diblock copolymers, which consist of polyelectrolyte and hydrophobicchains. The origin of this "curious phenomenon" is thought be the balance of image charge repulsion at the air/waterinterface and hydrophobic adsorption force. In addition, the "polymerity" was found to be an important factor: the blockcopolymer m:n=64:53 (poly(stynrene)-b-poly(styrene sulfonate)) showed non-surface activity but that with m:n=18:18showed very high surface activity, although the block ratio is almost 1:1 for both of these polymers. The(poly(fluorinated styrene)-b-poly(styrene sulfonate)) with m:n=30:64 showed non-surface activity but that with m:n=11:64showed surface activity. Hence, it can be concluded that the minimum length exists for appearance of non-surfaceactivity, which might be around m=30 for hydrophobic chain and n=50 for ionic chain. The effect of hydrophobicity of thehydrophobic chains on the non-surface active nature was also investigated. Unexpectedly, the non-surface activity wasin the order of poly(n-butylacrylate) < poly(styrene) < poly(fluorinated styrene) as the hydrophobic chain with same ionic



block, although the hydrophobicity is higher in this order. Ref. P.Kaewsaiha, et al., Langmuir, 21(22), 9938 (2005).

137. Shear Ordering of Concentrated Particle SuspensionsJason M. McMullan and Norman J. Wagner, University of Delaware, Newark, DE

Highly ordered particle crystals trapped in an exterior matrix can be used in applications that require regular structureswith uniform material properties. Creating ordered structures with particles in the ~10-100 μm range is a challenge.This study examines oscillatory shear as a method to provide particle mobility and drive ordering. Structures are formedwith monodisperse particles in this size range above a particle loading of 54 volume percent then arrested within apolymer matrix. This study explores the degree of order by varying particle loading and other rheometric parameterssuch as shear amplitude and frequency. The bulk properties are examined as a function of the order of the particles,particle materials and matrix materials. The extent of ordering is compared with colloidal systems under similarconditions. Shear ordering occurs under multiple sets of conditions but is reproducible and scalable for industrialproduction.

138. Quantitative parameters for surfactant-dye interactionSyed Waqar Hussain Shah, OPF Boys College, Islamabad, Pakistan

Quantitative parameters for behavior of homologous hemicyanine dyes in micellar media were determined usingultraviolet and visible differential spectroscopic technique. The impact of varying dye hydrophobicity on aggregation ofsurfactant was related to the extent of depression in critical micelle concentration of sodium docecyl sulfate caused bythe addition of each dye. Spectral shifts were translated in terms of binding constants to highlight the involvement ofdye molecules in the formation of surfactant-dye aggregates. Both spectroscopic and conductometric data were used toshow the thermodynamic feasibility of the phenomenon.

139. Large Scale Synthesis of Magnetite PowdersBrett M. Silverman, Headwaters Technology Innovations, Lawrenceville, NJ

This research focuses on a low-cost, large-scale synthesis of magnetite nanoparticles using two different techniques.This material will be uniform in shape, and have the characteristic magnetic properties relative to its particles size.Thefirst experimental detail is the formation of a colloid made from the dissolution of Fe metal in an aqueous acid solution.Once the base colloid is prepared, there are two distinct routes to synthesizing magnetite powders. One methodinvolves the evaporation of the colloid followed by reduction in hydrogen. The second method involves direct reductionof the colloid followed by centrifugation. The resulting material can be made in batches up to 0.5 kg, and have beenidentified as 95-99% magnetite.

140. Deactivation of Bacteria by Blockcopolymer Micelles Loaded with BiocideRenata Vyhnalkova, Adi Eisenberg and Theo G.M. van de Ven, McGill University, Montreal, QC, Canada

We studied micelles of PS197-b-PAA47 loaded with thiocyanomethylthiobenzothiazole (TCMTB) biocide. Crew-cutmicelles of PS197-b-PAA47 are prepared in dioxane by slow water addition. The micelles size is 26 nm by TEM and50 nm by DLS. The micelles are loaded afterwards with the hydrophobic antibacterial agent – TCMTB. The efficiency ofmicelles loading is measured by the UV-vis technique. Maximum loading of biocide in micelles is around 30 wt%.Loaded micelles are exposed to bacteria (E.coli) and their deactivation is evaluated. SEM shows that the micellesadsorb on the surface of the bacteria; also, distinct differences are seen between bacteria treated with empty micellesand those treated with biocide-loaded micelles. Deactivation of the bacteria by TCMTB biocide is studied by exposingE-coli BL-21 bacteria to the loaded micelles. The deactivation is measured using a UV-vis technique. The absorbanceof bacteria deactivated by loaded micelles is compared to the absorbance of bacteria in water and to those exposed tosolutions containing empty micelles. It was found that E-coli bacteria do not grow with time in the presence of TCMTBloaded micelles; they are deactivated. Empty micelles of PS197-b-PAA47 do not affect the growth of the E-colibacteria; the bacteria behave similarly to those exposed to a food-water solution.

141. Validity of various relationships available for determining surface tension of solids



Samad Ahadian, Siamak Moradian and Mohammad Amani Tehran, Amirkabir University of Technology, Tehran, Iran

The contact angles of various solids and four probe liquids (i.e. diiodomethane, formamide, glycerine and water) werevaried in the range 0-180 degrees by the aid of different approaches such as the equation of state (i.e. the Neumann'sequation), the Owens/Wendt, the harmonic mean, the van Oss et al. and the combined mean relationships. All the 11possible 2, 3 and 4 combinations of the liquid mixtures were used. These contact angles were then employed tocalculate the corresponding surface tensions by the aid of the mentioned relationships. For each solid/liquidcombination, the acceptable range of contact angles for calculating the real as compared to the imaginary surfacetension of solid or its components was determined. Generally, the Neumann's equation of state showed the widestrange of acceptable contact angles as compared to the others. In contrast, the van Oss et al. relationship had thenarrowest range. Additionally, the most valid range of the Neumann's equation of state was when all the probe liquidswere polar. On the other hand, for other relationships, the valid range occurred when at least one of the probe liquidswas apolar.

142. Polyelectrolyte Gel-Surfactant Complexes with Shape Memory EffectsGuoqin Liu, Henan University of Technology, Zhengzhou, China and Chunlong Guan, Henan University ofTechnology,, Zhengzhou, China

The complex of Poly(acrylic acid-co-acrylamide) gel with cetyltrimethylammonium bromide (P(AA-co-Am)-C16TAB) wassynthesized. It has shape memory behavior due to the formation of thermodynamically homogeneous structure. Aspecific feature of this type of shape memory complex is that the transition temperature at which the complex abruptlybecomes soft and deforms can be controlled by changing the degree of cross-linkage, which enables one to adjust theshape memory effect at desired temperature. Mechanism and process of the shape memory behaviors were discussed.

143. Statistical and mathematical investigations for determining the binding constants ofmicelle with reactants molecules from kinetic dataRabah A. Khalil, College of Science, University of Mosul, Mosul, Iraq, Mosul, Iraq

The research concerns with the determination of binding constants of bimolecular reactants with micelle from kineticdata. Recently, we have developed a statistical method based on multiple linear regression for determining those

parameters and according to the following source equation:

where . In the present work, we have derived further two statistical equationsfrom the above source equation using multiple linear regression method. A substantial difference has been foundbetween the results of those equations and also with that of the recent one. This strongly indicates that the statisticalprocedures are not valid for such purpose. In other word, the available statistical and graphical methods in the literatureare also not suitable for such treatment.

A mathematical procedure using iterative method for evaluating the binding constants has been employed. Anequation for such treatment has also been derived from the above source equation. The method was based upon that

hypothetical values of and could estimate at various C. The correct values of and must give

constant values of at these C. A computer program for this purpose using Visual Basic 6 software has been written.Application of the method to the kinetic data has been found to be quite successful through giving a minimum value ofthe variance. A characteristic feature of the last method is its inability to give a minimum variance if there is an error inthe introduced experimental data. It has been concluded that the presented mathematical method is simple, reliable andaccurate.



144. Synthesis of new amine oxide type surfactants having dual function of cleaning andsoftening effects and their physical properties

JongChoo Lim1, JunSeok Park1, In-Sik Cho2, KiMoo Lee2, GyeongYup Chi2, DongSung Han2 and KyungMin Yoo2,(1)Dongguk University, Seoul, South Korea, (2)Aekyung, Daejeon, South Korea

It is very important to ensure mildness of detergents to the skin in the fields of all household products, as detergentsare to be in direct or indirect contact with the human body. As surfactants are the major components in detergentformulations, many studies have been performed to develop surfactants of improved biodegradability and mildness. Inthis study, amine oxide type surfactants having a dialkyl amide chain were synthesized mainly for detergent formulationpurposes and their physical properties such as critical micelle concentration (CMC), surface tension, contact angle, andviscosity were measured. Since these newly synthesized amine oxide surfactants are the bulky amphoteric surfactants,they can serve as dual function surfactants by a single molecule through the interconversion of cleaning and softeningeffects depend on pH variations of the aqueous solution. In a general laundry process, cleaning is accomplished in analkaline condition, pH gradually decreases after rinsing steps, and then softening is accomplished in a neutral pHcondition. The newly synthesized surfactants shows not only detergency but also softening effect since they showcharacteristics of a nonionic surfactant in an alkaline condition, while showing characteristics of a cationic surfactant ina neutral condition. Their dual function characteristics depending on pH of the aqueous solution were investigated andtheir related cleaning and softening effects were measured. In addition to cleaning and softening effects, phase behaviorof the newly synthesized surfactants were studied.

145. Preparation of two dimensional silver nanoparticles in aqueous solutionZusing Yang, Tai-Chia Chiu and Huan-Tsung Chang, National Taiwan University, Taipei, Taiwan

We have developed a new and simple one-pot synthetic approach for the preparation of single-crystalline rose-, spike-,and snowflake-shaped silver nanoparticles (NPs) in aqueous solution. We obtained these variously shaped Ag NPs bycarefully controlling the nature and concentration of the stabilizers, which included sodium acetate, sodium citrate, andpoly(ethylene glycol). To the best of our knowledge, this paper is the first to describe the preparation of rose-shaped AgNPs, also called Ag nanoflowers (NFs), through such a simple synthetic route. The thus-prepared Ag NFs exhibited aspecific surface area of 15.6 m2 g-1, a contact angle of 97.6 °" 2.2¢X, high conductivity (1.97 „e 106 S/cm), andefficient optothermal conversion efficiency (the temperature rose 23.03 °" 0.21 ¢XC after laser irradiation at 808 nm for3 min). The snowflake-shaped Ag NPs allowed the enhancement of Raman scattering (SERS) signals of rhodamine 6Gby a factor of 2.4 „e 106, with a detection limit of 10 nM

146. Gel diodes: Unidirectional current response of an ionic junction betweenpolyelectrolyte aqueous gelsSuk Tai Chang, Oliver J. Cayre and Orlin D. Velev, North Carolina State University, Raleigh, NC

Electronic components based on organic materials are of interest because they possess a number of potentialadvantages over traditional silicone-based junctions. Here, we demonstrate unidirectional ionic current flow across afixed junction between two aqueous agarose gel phases containing oppositely charged polyelectrolytes. The promisingfeature of this new type of rectifying junction is that it is operates on the basis of water-borne ions. We show that thenon-linear current response of the interface between the cationic and anionic gels originates directly from anisotropy inthe mobile charges within the system. The current densities in the forward bias and current rectifying ratios in these geldiodes are higher or comparable to those using ionic carries and junctions built from conductive polymers. The devicesare extremely simple, inexpensive and possess good long-term stability in both DC and AC conduction modes. Suchdevices based on aqueous gel phases can easily be fabricated and could be used in numerous applications requiringflexible and biocompatible electronic components.



147. Effect of surfactant on mechanical properties of a nanoparticulate gelJiong Liu, Saran Poovarodon and John Berg, University of Washington, Seattle, WA

An aluminum oxide hydroxide AlO(OH) nanoparticulate sol was synthesized using a Yoldas process. The AlO(OH)nanoparticle was found to catalyze the ring-opening and condensation reactions of a glycidoxypropyltrimethyloxysilane(GPS) gel derived from an aqueous solution. FT-IR and SEM results showed that the nanoparticles participate informing the network structure of the gel. The effect of a Pluronic surfactant on the mechanical properties of thenanoparticulate AlO(OH)/GPS gel was investigated. It is found that the connectivity of the network structure decreasesslightly with the addition of a small amount of surfactant, which leads to a significant increase in fracture toughness ofthe gel materials.

148. A Systematic Study of Triglyceride Molecular Structure Effects on Surfactant-oilInteractionsTri T. Phan, Jeffrey H. Harwell and David A. Sabatini, University of Oklahoma, Norman, OK

Triglyceride molecules, with their unique structure of three ester groups and three long chains, are among the mostchallenging oils with which to form a microemulsion. While triglyceride microemulsion formation has been reported, theimpact of molecular triglyceride structure on interactions with surfactants is poorly understood. In the present study,surfactant-oil interactions were evaluated by comparing optimum salinities, interfacial tensions (IFTs) and EquivalentAlkane Carbon Number (EACN) values of individual triglycerides with various chain lengths and degrees of saturation.The results revealed that the chain length showed less effect on EACN and IFT as compared to the degree ofsaturation. An increase in the chain length from C14:1 (trimyristolein) to C18:1 (triolein) resulted in an increase in EACNfrom 18 to 19 while IFTs remained similar (10-3 mN/m). In contrast, an increase in the number of double bonds (e.g.from one in triolein, C18:1, to three in trilinolenin, C18:3) led to an increase in EACN to 22 (versus 18) and IFTincrease to 10-1 mN/m. This can be explained by the more complicated spatial arrangement resulting from the doublebonds caused a steric hindrance to the oil-surfactant parallel arrangement.

149. Adsorption of nano-sized TiO2 particles onto surface of algae exemplified byPseudokirchneriella subcapitata

Ming-Yu Lin, David M. Metzler and C. P. Huang, University of Delaware, Newark, DE

Nano-sized titanium dioxide (TiO2) has wide industrial applications with considerable chance of exposure to humansand ecosystem. As a photocatalyst, nano-sized TiO2 has been used in various environmental remediation applicationsimplying its potential environmental impact. In order to better understand the interaction between nano-sized TiO2 andphytoplankton in the aquatic environment, we first studied the adsorption of nano-sized TiO2 (Degussa P25) onto thealgae exemplified by Pseudokirchneriella subcapitata. P. subcapitata were exposed to TiO2 in a series ofconcentrations and at various pH and ionic strength. The sedimentation experiments were conducted to determine theTiO2 adsorption density using turbidity and dynamic light scattering measurements. Results show that the kinetics andthe extent of TiO2 adsorption are highly dependent on pH, which indicates the electrostatic nature of the interaction.The maximum adsorption density occurred (9x105 particles per cell) at pH 5.5. As the ionic strength increased, the rateof adsorption increased but the saturation adsorption density remained relatively unchanged. The adsorption was multi-layered and the presence of isotherm plateau suggested that the adsorption energy between layers decreased toward



the outer layer. The flocculation of algae was observed. At pH 4.6, the aggregate size reduced from hundred microns toa few microns as the number ratio of TiO2 to algae increased from 3 x 105 to 106. The decrease in aggregate size canbe explained by the increase in stability due to charge reversal on the algal surface brought by TiO2 adsorption.

150. Effects of noble metal particles and salts on the light stability of Safranin OMoonsuk Han, Young-ho Lee, Dae-wook Kim and Seong-geun Oh, Hanyang university, Seoul, South Korea

Organic dyes are used in many industrial and chemical analytic fields. They are easily degraded under severe light andheat owing to be organic materials even though they could have good chromogenic ability. If the colors of organic dyeswere faded or discolored, the dyes would be no use as coloring agents by degradation. While inorganic materials havestrong light and heat stability in their own properties, organic materials usually have poor fastness of light and heat.Each material used in this research has remarkably different physical and chemical properties. Hence It wasinvestigated how organic dye as organic materials would be affected by noble metals as inorganic materials. In thisstudy H2O2 were added to the Safranin O aqueous solution. H2O2 might serve a part as pseudo catalyst of dyedegrading reaction. We applied noble metal nanoparticles such as Ag, Au, Pt in colloidal condition and AgNO3, HAuCl4,H2PtCl6 as the noble metal salts. The Safranin O solutions containing noble metal and H2O2 were irradiated by UVlamp (wavelength=254nm). The effects of noble metal nanoparticles and salts on the light stability of Safranin O wereinvestigated. Effect of pH was also considered. HCl and NaOH were used to control the pH of the solution. Opticalproperties of the noble metal and organic dye were investigated by UV-vis spectroscopy and naked eyes as time went.The complexes between noble metals and the organic dye were confirmed by TEM and Raman spectroscopy.

151. Affect of Boric Acid on the Temporal Evolution of Siliceous Nanoparticles formed inAqueous Solutions of Tetraethylammonium HydroxideNathan D. Hould and Raul F. Lobo, University of Delaware, Newark, DE

A thorough understanding of the formation of crystalline materials from solution is crucial to predicting the final structureand properties of the resulting solids such as zeolites. One system that is particularly interesting is an aqueous solutioncontaining of tetraethyl orthosilicate (TEOS), tetraethylammonium hydroxide (TEAOH), and boric acid, which is known tolead under hydrothermal conditions to zeolite-Beta (BEA), a material with many industrial applications due to its uniquemicroporous structure. The current study is aimed at understanding the mechanism of formation of the nanoparticulateprecursors that are formed in clear gel solutions of similar composition to those which yield beta. Data shows that thesemodel systems have a critical aggregation concentration above which the silicate species in solution aggregate intonanoparticles. This critical aggregation concentration is sensitive to the concentration of boric acid in the solution geldue to its dissociation to form B(OH)4–. We have investigated the structural evolution of the nanoparticles, at elevatedtemperatures with Small Angle X-ray Scattering.

152. Effects of Particle Additions on the Rheological Properties of Polyacrylate /Polyacrylamide Hydrogels

Bryan A. Baker1, Rebecca L. Murff2 and Valeria T. Milam2, (1)Georgia Institue of Technology, Atlanta, GA, (2)GeorgiaInstitute of Technology, Atlanta, GA

Polyacrylamide-based hydrogels are popular materials that have been extensively studied for their applications in thefield of biomaterials due to their permeability and biological compatibility. A major limitation of this polymeric material,however, in biological applications stems from their limited mechanical stiffness. In order to increase the mechanicalstiffness of these hydrogels, colloidal particles are added to act as interactive filler and reinforce the soft hydrogel matrix.Various surface chemistries are being explored to alter the nature of particle-matrix adhesion. The current studyexamines the effects of the surface chemistry and volume fraction of particles on the mechanical properties ofpolyacrylamide-polyacrylate-based hydrogels using oscillatory rheology.

153. Synthesis and characterization of PEG-grafted silica particles by one-step novelmethodHyojung Jun, Yong-Geun Lee, Chul Oh and Seong-Geun Oh, Hanyang University, Seoul, South Korea



The development of new organic-inorganic hybrid materials is a great interest with respect to obtaining their specialproperties and the sol-gel process has provided new possibility for preparing the composite materials. Poly(ethyleneglycol) (PEG) is a non-toxic flexible polyether with chemical structure HO-(CH2-CH2-O)n-H. It has hydrophilic headscomprised of hydroxyl groups providing a good water-solubility at low temperature. PEG has been widely used invarious pharmaceutical and biological applications as well as in many commercial products. For instances, drug deliveryresearch has obtained from singular pharmacokinetics and biodistribution. In our previous work, PEG-grafted silicaparticles were prepared through sol-gel processing using a W/O emulsion as the reaction media. By utilizing a sol-gelmethod in a W/O emulsion, spherical PEG-grafted silica particles were obtained. However, the emulsion method hasthe complicated steps to prepare silica particles and PEG-grafted particles. In this study, we prepared PEG-graftedsilica particles in water phase without catalyst by using a new and simple method. To graft PEG onto the surface ofsilica particles, poly(ethylene glycol) methyl ether (PEGME) polymers of various molecular weights were reacted with 3-(triethoxysilyl)propyl isocyanate (IPTES). PEGME-IPTES conjugates with urethane groups were synthesized by reactingthe isocyanate group of IPTES with the hydroxyl group of PEGME. The synthesis of PEGME-IPTES and the PEG-grafted silica particles were confirmed using FT-IR spectroscopy. The surface morphology of particles was investigatedby FE-SEM, TGA and OM. Through BET adsorption isotherm, surface characteristics were measured after calcinationsof samples over 600°C.

154. Dynamic interactions between nanoparticles during confinment

Younjin Min1, Mustafa Akbulut1, Yuval Golan2, Joseph Zasadzinski1 and Jacob Israelachvili1, (1)University ofCalifornia, Santa Barbara, Santa Barbara, CA, (2)Ben Gurion University, Beer Sheva, Israel

Using a surface forces apparatus (SFA) we have measured the normal forces between mica surfaces across varioustypes of nanoparticles consisting of ZnS cores coated with a monolayer of physisorbed surfactant, dissolved in organicsolvents. We focused on the effects of nanoparticle size, shape and concentration on the force-distance profiles. Forceswere exponentially repulsive when the surfactant layers were strongly bound to the nanoparticles; and were roughlylinear when there was adhesion between the nanoparticle cores, i.e., when the surfactant layers detached from thenanoparticles. In both cases, the range and magnitude of the forces were dependent upon the particle size and solutionconcentration. Fine details in the otherwise smooth force-distance profiles indicate specific effects due to particlechemistry and geometry, and the existence of first-order disorder-order phase transitions upon confinement.Understanding and controlling the effects of particle shape, size and concentration on particle-particle and particle-surface interactions should be important for the processing of nanoparticles into ordered nanostructured materials.

155. Dual-Functional Cancer-Targeted Delivery Carriers based on Poly(amino acid)derivativesHyun Jin Lee, Kwang-Suk Jang, Hee-Man Yang and Jong-Duk Kim*, Korea Advanced Institute of Science andTechnology, Daejeon, South Korea



We report self-assmebled nanocarriers of poly(amino acid) derivatives loaded with superparamagnetic iron oxide(SPIO) nanoparticles for magnetic resonance imaging (MRI) and anticancer drug for chemotherapy. Hydrophobicallymodified synthetic poly(amino acid), poly(2-hydroxyethyl L-aspartamide) grafted with octadecyl chains (PHEA-g-C18)which self-assemble into spherical micellar aggregates in aqueous phase, was synthesized. For cancer-targetedsystem, cyclic RGD peptide was conjugated to the polymer system. Synthesis and molecular composition wereconfirmed with 1H-NMR and elemental analysis. SPIO nanoparticles well known as strong signal enhancer of T2-weighted MRI were synthesized with four different diameters, 4, 6, 8, and 10 nm, as previously reported by Sun et al.and characterized with XRD, TEM, SQUID magnetometer and FT-IR. The surface of nanoparticles is highlyhydrophobidized with oleyl chains and the nanoparticles can be solubilized in nonpolar solvents. Solution of SPIOnanoparticles in mixture of chloroform/dimethylchloride was added into polymer solution in water and the mixture wasvigorously vortexed to form microelusion. By remove of organic solvents and unloaded nanoparticles, stable micellarcarriers loaded with SPIO nanoparticles were prepared. Physicochemical characteristics with variables of nanoparticlesize and SPIO/Polymer ratio were studied by with DLS, TEM, ICP-AES and T2 mapping. Anticancer drug, doxorubicin(DOX), was successfully co-loaded by addition of DOX solution in THF into the carrier solution. Loading and in vitrorelease behavior of DOX was studied with UV/Vis spectroscopy. Since they show the great stability in aqueous phaseand the high efficiency in enhancing MR contrast etc., their potential use as advanced delivery carriers is highlyexpected.

156. Reversibly-swelling polyelectrolyte-surfactant microgel spheres by electrosprayingMatthew E. Helgeson, Yakov Lapitsky, Kristie N. Grammatikos and Eric W. Kaler, University of Delaware, Newark, DE

Polyelectrolyte-surfactant microgel particles can be made by electrospraying of cationic N,N,N-trimethylammonium-derivatized hydroxyethyl cellulose (JR-400) into an oppositely charged surfactant solution. The electrospraying processexhibits several modes of behavior, which produce drops (and ultimately gel particles) of diameters ranging from lessthan 1 um to over 1 mm. Sub-micron particles are produced by Cuolombic rupture of electrosprayed droplets asobserved by high speed videography. The particles are rendered stable over a broad range of conditions by covalentlycross-linking the polyelectrolyte, and are colloidally stable due to the excess of charge on the gel network. Optical andscanning electron micrographs suggest that the sub-micron gel particles have a hollow core-shell morphology, which isconfirmed by estimates of the shell thickness from viscometry and densitometry measurements. Quasi-elastic lightscattering is used to obtain the final size distribution of the microspheres, which undergo reversible swelling in thepresence of excess surfactant in solution. Such attractive physical properties make the particles ideal for encapsulationand release on the colloidal scale.

157. Investigations of large scale structure in shear thickening silica suspensions by flow-USANSDennis P. Kalman and Norman J. Wagner, University of Delaware, Newark, DE

Shear thickening in particle suspensions is a problem in processing and coating industries; shear thickening fluids havealso been utilized with ballistic fabrics in protective armor applications. Shear thickening is known to occur via theformation of load bearing hydroclusters from theory, simulations, flow-SANS experiments, and indirect rheologicalmeasurements. Here, a flow-USANS experiment is performed in the radial direction (1-3 or flow-vorticity plane) in thelow q regime of 3.3x10-5 to 3.3x10-3 Å-1 on a model monodisperse, ~0.5µm diameter, near hard-sphere silicasuspension in polyethylene glycol. A dilute measurement is used to determine the particle form factor, which is used toquantitatively model the structure of 3 concentrated samples (Φ=0.213, 0.419, and 0.520) under static conditions. Inaddition, the structural changes under flow in the shear thinning, Newtonian plateau, and shear thickening regimeswere investigated for all 3 suspensions. Evidence of shear-induced clusters of finite size are apparent in the scatteringfrom samples in the shear thickened regime. A substantial degree of shear-induced order is observed for this highestvolume fraction sample, which is observed to dissolve into an amorphous, hydroclustered structure upon shearthickening. The results provide new information about the structure of the hydroclustered microstructure in shearthickened colloidal dispersions and aid in the development of STF-based technologies.

158. Noro and Frenkel generalized law of correspondent states in attractive colloidalsystems: thermodynamics and dynamicsGiuseppe Foffi, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland and Francesco Sciortino,



Universita' di Roma La Sapienza, Roma, Italy

It is well established that the range of the attraction is a key parameter for both the thermodynamical and dynamicalproperties in short ranged attractive colloidal systems. I will show the effect of going to an extremely short range, a limitthat is the basis of the celebrated Baxter (or adhesive) model, where the range is taken to the zero limit. I will discussthe reason of the success of the Baxter model, showing that the equivalence of all the short range potential systems(the Noro and Frenkel "generalized law of correspondent states"), can be explained in the rigorous PEL thermodynamicformalism as arising from the multiplicative contribution that each bond add to the vibrational entropy and from thepossibility of separating vibrational and floppy contributions (a condition which requires a small bond width). Incidentally,I will show how our approach allows to count the fraction of floppy modes in a system of bonded particles. The case ofnon isotropic interaction potentials will be discussed as well as the connection to the dynamical properties of the shortranged attractive colloidal systems and the gel transition.

159. Thermodynamic Equilibrium of ZSM-5 FormationDustin Fickel, University of Delaware, Newark, DE

Understanding zeolite growth mechanisms is important for futher advancement in zeolite science. This work focuses onthe formation of ZSM-5 through non-organic synthesis. To understand the formation of this zeolite, thermodynamics isused to quantify the relationship between the resulting zeolite and the supernatant remaining after synthesis. Acomplete range of Si/Al ratios for ZSM-5 formation, between approximately 10 and 50, is studied so that a completephase equilibrium diagram can be formulated. In accomplishing this thermodynamic equilibrium equations along withregular solution theory are used. The techniques of x-ray diffraction, NMR, ICP, and small angle x-ray scattering areused in this research. Our research has shown a direct correlation between the amount of aluminum in the synthesisgel and that in the resulting ZSM-5. We have also shown that the supernatant contains exceedingly small amounts ofaluminum, which implies that it is expended rapidly during the synthesis. Overall the results of this research will help inthe understanding of ZSM-5 formation.

160. Thermodynamic stability in binary mixtures of eye lens proteins

Nicolas Dorsaz1, Giuseppe Foffi1, Anna Stradner2, George M. Thurston3 and Peter Schurtenberger2, (1)EcolePolytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, (2)University of Fribourg, Fribourg, Switzerland,(3)Rochester Institute of Technology, Rochester, NY

The eye lens consists of a solution of mainly three classes of water soluble proteins called alpha-,beta- and gamma-crystallins. A uniform packing of crystallins guarantees the correct index of refraction necessary for the eyetransparency. Local aggregation or phase separation of these proteins, however, can increase dramatically thescattering of light with a consequent loss of transparency of the lens leading to cataract disease. We studiednumerically the binary alpha-gamma mixture by molecular dynamics simulations of a coarse-grained model of theseproteins. Combining our numerical results with experimental neutron scattering data, the interactions between theproteins has been devised. We have then started a systematic study of the thermodynamic stability of binary mixturesvia Barker-Henderson perturbation theory. Within this approach, the instability surface of the alpha-gamma asymmetricmixture was determined for the whole concentration-density parameter range. The stability of these high concentrationcrystallin mixtures was found to depend on the alpha-gamma attraction in a manner that is both extremely sensitiveand non-monotonic in agreement with the experimental and numerical results. Such high sensitivity enforces thepossible implication of thermodynamic instabilities in some forms of cataract. The present results also suggestmechanisms to tune the stability of more general colloidal solutions and binary mixtures.

161. Selective Hydrogenation on Zeolite-Supported Bimetallic CatalystsWei Huang, Raul F. Lobo and Jingguang G. Chen, University of Delaware, Newark, DE

Novel catalysts have been synthesized and evaluated by supporting Pd-based bimetallic nanocatalysts on zeolites toachieve higher selectivity for the selective hydrogenation of acetylene in a stream containing excess ethylene atrelatively low temperatures (300-339K). Low-temperature hydrogenation offers the opportunity of using competitiveadsorption to achieve preferential hydrogenation of acetylene. Previous work from our group has found that bimetalliccatalysts favor low temperature hydrogenation. Results from many other groups have also shown that Pd is a good



catalyst for the selective hydrogenation of alkynes in excess ethylene. Therefore the strategy of the present work wasto modify Pd catalysts and to embed bimetallic nanoparticles in an environment that is highly selective for acetylenehydrogenation. Cation-g interaction offers the potential for selective adsorption of acetylene on the zeolite supports. Inthe current work we used the ion-exchanged â-type zeolite as the support of the bimetallic catalysts. The zeolitestructure should have multiple dimensions and contain large pores, in order to house the bimetallic nanoparticles insidethe pores. Flow reactor studies using GC, batch reactor studies using FTIR, EXAFS and CO-Chemisorption evaluationhave been performed. Our results indicate that the Pd-Ag bimetallic catalyst has a much higher selectivity for acetylenehydrogenation in excess ethylene than either Pd or Ag. Modeling of reactions in FTIR shows significant differences inthe hydrogenation rate constant, adsorption equilibrium constant, as well as the selectivity of the ã-Al2O3 supportedcatalysts and â-zeolites supported catalysts, with â-zeolite supported catalysts showing much higher selectivity than theã-Al2O3 supported catalysts.

162. Ozone/Ultrasound Oxidation of Single-walled Carbon Nanotubes (SCNTs) in WaterMinghua Li, Thomas P. Beebe and Chin-Pao Huang, University of Delaware, Newark, DE

Functionalization of carbon nanotubes (CNTs) is critical for enhancing its application, processability and performance invarious fields. Changes of surface characteristics can also affect the fate, transport and effects of these particulates inthe environment. A clean and simple wet chemical oxidation method involving only ozone and ultrasound (US)processing in water was used to functionalize single-walled CNTs (SCNTs). SCNTs were disintegrated, oxidized andeven shortened by O3 or O3/US treatment for 24 hr. After treatments, the solubility and aqueous phase stability ofSCNTs were improved. Oxygen functional groups were formed on the SCNTs surface. Surface oxygen to carbon ratioincreased by more than 600% after 72 hr of O3 treatment based on the X-ray photoelectron spectroscopy (XPS)results. XPS showed evidence for surface C-OH, C=O and COOH groups as oxidation products. The effective particlelength was reduced from initial 5000 to 300 and to 150 nm, respectively after 24 hr of O3 and O3/US treatments,indicating SCNTs shortening during the oxidation process. The surface potential of SCNTs decreased from 5 to -29 mV(at pH 2) after 2 hr O3 US treatment. Results of sedimentation and turbidity measurements were consistent with that ofXPS analysis. An oxidation pathway was proposed and results were fitted with various kinetic models to identify thepertinent oxidation kinetic parameters. The oxidation state of the SCNTs can be controlled by the O3/US exposure timewithout any additional treatments; this aqueous phase oxidation offers the potential for use as a low-cost CNTs surfaceprocess.

163. Molecular Dynamics Simulations of Surfactant and Nanoparticle Self-assembly atLiquid-Liquid InterfacesMingxiang Luo and Lenore L. Dai, Texas Tech University, Lubbock, TX

We have performed molecular dynamics (MD) simulations to investigate self-assembly at water-trichloroethylene (TCE)interfaces with the emphases on systems containing modified hydrocarbon nanoparticles (1.2 nm in diameter) andsodium dodecyl sulfate (SDS) surfactants. The nanoparticles and surfactants were first distributed randomly in the waterphase. The MD simulations have clearly shown the progress of migration and final equilibrium of the SDS molecules atthe water-TCE interfaces with the nanoparticles either at or in the vicinity of the interfaces. One unique feature is the “attachment” of surfactant molecules to the nanoparticle clusters in the water phase followed by the “detachment” at thewater-TCE interfaces. At low concentrations of surfactants, the surfactants and nanoparticles co-equilibrate at theinterfaces. However, the surfactants, at high concentrations, competitively dominate the interfaces and depletenanoparticles away from the interfaces. The interfacial properties, such as interfacial thickness and interfacial tension,are significantly influenced by the presence of the surfactants, but not the nanoparticles. The order of the surfactants atthe interfaces increases with increasing surfactant concentration, but is independent of nanoparticle concentration.Finally, the simulation has shown that surfactants can aggregate along the water-TCE interfaces, with and without thepresence of nanoparticles.

164. Redox Transformation of Organic Contaminants Mediated by Black CarbonNanoparticlesPei Chiu and Seok-Young Oh, University of Delaware, Newark, DE



Black carbon is a collection of carbon-rich nanoparticles that are ubiquitous in the environment. Black carbon plays apivotal role in controlling the fate and transport of hydrophobic organic contaminants. The current dogma states thatgeosorbents such as black carbon can act as contaminant adsorption sites, and the adsorbed molecules are immobileand nonreactive. However, our data suggest that black carbon can serve as both an adsorbent and a mediator of redoxreactions. We showed that molecules adsorbed to black carbon have dramatically higher reductive reaction rates. Wehypothesize that this is because black carbon contains microscopic graphitic domains in its structure and thus canconduct electron and atomic hydrogen from a reductant to adsorbed contaminant molecules. This study willdemonstrate the adsorptive and catalytic roles of black carbon and will attempt to elucidate the mechanism for blackcarbon-mediated degradation of organic contaminants. Experiments were conducted using graphite and soot as modelblack carbons to assess the reduction of black carbon-bound nitroaromatic and heterocyclic nitramine explosives in thepresence of an environmentally relevant reducing agent, such as thiol and sulfide. Our presentation will demonstratethis previously unrecognized role of black carbon and will discuss the potential impact of natural and synthetic blackcarbon on the fate of organic contaminant in aquatic and terrestrial systems.

165. Controlled crossflow of liquids within particle-stabilized bicontinuous emulsionsKathryn A. White, Eva M. Herzig, Andrew B. Schofield and Paul S. Clegg, Edinburgh University, Edinburgh, UnitedKingdom

Recent theoretical work[1] has led to new soft-solid materials consisting of bicontinuous emulsions stabilized by colloidalparticles[2]. The ‘jamming' of these particles at the liquid-liquid interface prevents an otherwise unstable emulsion fromcoarsening, and effectively freezes the interpenetrating fluid networks in a metastable sponge-like configuration. Theresult is a microporous material with a characteristic channel size; this is referred to as a bicontinuous interfaciallyjammed emulsion gel, or ‘bijel'.

Given that such a material contains a considerable interfacial area between two immiscible liquids, a number ofpossible applications exist, one of which is as a crossflow microreaction medium. An attractive property of bijels is thatthe structure is preserved when exposed to an excess of either of the two component liquids. Using custom-built flowcells, we study the properties under flow conditions of particle-coated flat liquid-liquid interfaces as models for the morecomplicated bijel, and the bijel itself. Here we present results on the transfer of fluorescent species across theinterface, and demonstrate the influence of variables such as flowrate, channel size and interfacial tension on thestability and rheology of the bijel.

[1] K. Stratford, R. Adhikari, I. Pagonabarraga, J.-C. Desplat and M. E. Cates. Science 309, 2198 (2005)

[2] European Patent Application EP05761568.4 (M. E. Cates, W. C. K. Poon, S. Egalhaaf, P. S. Clegg)

166. Coupled effects of attachment and straining on retention of colloids under unfavorableconditions

Chongyang Shen1, Yan Jin1 and Yuanfang Huang2, (1)University of Delaware, Newark, DE, (2)China AgriculturalUniversity, Beijing, China

This study examines effects of solution chemistry on the straining of colloids in porous media under unfavorableconditions. Saturated column experiments were conducted with various sizes of latex particles and glass beads atdifferent ionic strengths. A two- or three-step procedure was used for colloid attachment and release, followingdissection of the columns to determine distribution profiles of retained colloids. The effluent breakthrough curves andspatial distributions of the retained colloids in the columns were modeled with a convective diffusion equation includingterms of attachment and straining. Results show that (i) straining increases with the decrease of glass beads diameter(dc) and with the increase of colloid diameter (dp); (ii) fitted straining coefficient increases with the increase ofattachment rate (or ionic strength); (iii) the threshold of dp/dc (above which straining occurs) determined using glassbeads as porous media is much larger than those determined by sand grains. Our study indicates that a deepersecondary minimum depth facilitates colloids wedged and retained in straining sites, and the irregular shapes of naturalporous media (e.g. sand grains or soil) play critical roles in the straining (i.e., grain-to-grain contact) of colloids whendp/dc is small.

167. Initial stages of titanium nitride deposition on Si(100): Importance of the Ti-N bond



scission during the adsorption of tetrakis-(dimethylamino)-titaniumJuan Carlos F. Rodríguez-Reyes and Andrew V. Teplyakov, University of Delaware, Newark, DE

Tetrakis-(dimethylamino)-titanium (TDMAT) is a deposition precursor for titanium nitride and titanium carbonitridediffusion barriers. We investigated the reaction of TDMAT with the Si(100) surface because of its crucial impact on thegrowth of diffusion barrier films and on the interface formation. A combination of density functional calculations andinfrared (IR) spectroscopy suggests that TDMAT dissociatively adsorbs on Si(100). Such process involves the formationof a Ti-Si bond upon cleavage of a Ti-N bond. The reactivity of the Ti-N bond was also observed during TDMATadsorption on ammonia-covered surfaces, where our spectroscopic results indicate that transamination reactions occur.In addition to the possibility of Ti-N scission during the first stages of adsorption, the cleavages of both a C-H bond anda C-N bond are considered as alternative pathways of adsorption. Spectroscopic evidence of Si-H bond formation uponTDMAT adsorption indicates that scission of the C-H bond is possible, although as a minor channel. In contrast, we didnot find any experimental evidence of Si-CH3 bond formation, in agreement with the theoretical prediction that scissionof the C-N bond is thermodynamically stable but kinetically hindered. Due to the current importance of zirconium-,hafnium-, and tantalum-containing compounds for technological applications, the dissociative adsorption of theiralkylamino compounds is investigated by theoretical methods and compared to TDMAT. Elucidation of the first stages ofadsorption will allow a better control of thin film growth processes.

168. Desorption of Polyelectrolyte Coatings from Nanoscale Fe0 Used for EnvironmentalRemediationHye-Jin Kim, Tanapon Phenrat, Navid Saleh, Kevin Sirk, Robert D. Tilton and Gregory V. Lowry, Carnegie MellonUniversity, Pittsburgh, PA

Zerovalent iron nanoparticles (NZVI) are an emerging technology for ground water remediation of dense nonaqueousphase liquids (DNAPL). Polymeric surface coatings are required for mobility in the subsurface and can afford theparticles an affinity for DNAPL. The ultimate fate of the particles depends in part on the stability of the surface coatings.One often observes effectively irreversible adsorption of high molecular weight polymers on solid surfaces. This studyreports desorption rates of commercially available polyelectrolytes, including polyaspartate (MW=2.5k and 10k),carboxymethyl cellulose (MW=90k and 700k), and polystyrene sulfonate (MW=70k and 1M) from NZVI used for in situdegradation of DNAPL in groundwater. The initial adsorbed masses of polyelectrolyte ranged from 1.5 to 4.0 mg/m2.For a given polyelectrolyte, the adsorbed mass was independent of molecular weight. Desorption was very slow, withless than 30% of each polymer desorbed after 4 months. Quartz crystal microbalance (QCM) data confirmed thepresence of polymer on the particle surfaces by comparing the attachment of bare and modified particles to a silicasurface. Transport experiments also indicate that the polymer coating is still on the surface of NZVI. Based on theseresults, polymer modified nanoparticles will potentially remain mobile for long times after they are injected into thesubsurface. Other factors that might affect coated NZVI fate, especially the potential for microorganisms to degrade thepolymer coatings, must still be evaluated.

169. Preparation of multiple-functionalized surfaces with precise spatial resolution

Moniraj Ghosh1, Christina Alves1, Kathleen J. Stebe2 and Konstantinos Konstantopoulos1, (1)johns HopkinsUniversity, Baltimore, MD, (2)Johns Hopkins University, Baltimore, MD

Patterned surfaces presenting one or two functionalities are widely used in studies ranging from patternedelectrodeposition of materials to the studies of cell adhesion. These surfaces are often made using microcontact printingfollowed by backfilling, allowing the creation of functionalized regions of submicron dimensions. Here, we generalize thistechnique to allow the creation of multifunctional surfaces using a novel combination of microcontact printing, backfillingand microfluidics to present multiple functionalities (proteins, antibodies, surfactants) and lengthscales (sub-micron andabove) over areas of large extent. First, microcontact printing is used to place an active species in desired locations ofthe surface. The open regions are passivated by backfilling with a blocking agent, e.g. PEG via suitable surface linkers.This substrate is then used as a lid to a microfluidics device to form several channels. Species of interest are pumpedthrough the channels to adsorb on to the active regions. Alternatively, a PEGylated surfactant can be microcontactprinted to form a lattice pattern with open adherent regions. Thereafter, microfluidics can deliver desired functionalitiesto these open areas. The feature size on the printing stamp determines the size (i.e. resolution) of the printed species.



The width and the geometry of the microfluidics channels determine the number of patches presenting a particularfunctionality. The nature of the functionalization is guided by suitable surface chemistry. These patterned multifunctionalsurfaces are of particular interest in material manufacture and bioassays. Examples of multifunctional surfaces for celladhesion studies are shown.

170. INTERFACIAL INTERACTIONof SPENT SHALE with WATER in OIL PRODUCINGINDUSTRYToomas Tenno and Karin Hellat, University of Tartu, Tartu, Estonia

In retorting process of Estonian oil shale more than half of the sulfur occurring in the feed shale remains in the solidresidue, where the sulfur is mainly in the form of calcium and iron sulfides. CaS formation is connected with limestonebasement of the North East of Estonia and FeS originates from pyrites in the feed oil shale. The process of interfacialinteraction of CaS and FeS with water is taking place in the spent shale dumping sites. The dissociation of calcium andiron sulphides in water produces sulfide ions and as a result of S2- interaction with water, HS- and H2S will be formedand the pH of the water phase will be raised. As the solubility product of FeS is very low (6.3*10-18), in the firstapproximation the role of FeS is not taken into account when calculating the concentrations of Ca2+ and S2- ions in thesystem containing solid CaS and FeS. The system under investigation of solid CaS in equilibrium with water phase willcontain six species in significant levels: Ca2+, S2-, HS-, H2S, OH- and H3O+. As there are no data available forsolubility product of CaS, the equilibrium concentrations of Ca2+ ions and of sulfur containing species are taken for thebases of modeling the balanced system. The mass-balance expression for the system is [Ca2+] = [S2-/sup>] + [HS-] +[H2S]. For calculation the concentrations of the components of balanced system five equations were derived and simultaneously solved.

171. Interfacial Phenomena in Proton-Exchange Membrane Fuel Cells

Douglas Aaron1, Sotira Yiacoumi1, Costas Tsouris2, David J. Keffer3, Shengting Cui3, Junwu Liu3, Myvizhi E.Selvan3, Brian J. Edwards3 and William V. Steele3, (1)Georgia Institute of Technology, Atlanta, GA, (2)Oak RidgeNational Laboratory, Oak Ridge, TN, (3)University of Tennessee, Knoxville, TN

The operation of proton exchange membrane fuel cells (PEMFC) is highly dependent on interfacial phenomenaoccurring at the anode, cathode, and polymeric membrane. This work is focused on better understanding the effects ofhumidity, feed pressure/ratio, and temperature on the fuel cell performance. Experimental work is being performed toinvestigate the effects of these operating parameters on the power output of the cell. Current work is focused onemploying electrochemical impedance spectroscopy (EIS) to understand specific resistances at interfaces of the cellcomponents. The results from EIS experiments can be compared with those from molecular modeling to betterunderstand transport limitations at the interfaces. Molecular modeling focused on the structure and properties of aNafion membrane at various levels of hydration is also being performed. The hydration level in the PEM affects iontransport at the interface between the electrodes and PEM, as well as ion transport through the PEM from oneelectrode to the other. Our findings show that there is virtually no wetting of a graphitic electrode by water hydrating thePEM. There is significant wetting of Pt nanoparticles in close proximity to the PEM. This provides a molecular-levelpicture for the role of humidity at the electrode/electrolyte interface. If the system is too dry, only Pt nanoparticlesimmediately adjacent to the PEM can contribute to conductivity. If the system is too wet, the Pt nanoparticles can wetentirely and become inaccessible to gaseous hydrogen.

172. MEASUREMENTS of the Permeability of Oxygen through the Air-Water Interface at LowConcentration of Surfactants in Water PhaseToomas Tenno, Erik Mölder and Taavo Tenno, University of Tartu, Tartu, Estonia

Oxygen diffusion through the air-water surface layer at various surfactant concentrations in the solution wasinvestigated. Experimentally was established that at very low concentrations of surfactant (about 0,0001 mol/l)permeability of oxygen through air-water interface reduces about 40%, when at the same time surface tensiondecreases only about 0,1% from it's maximum value. The original technique for measurement of oxygen mass transferthrough the air-water interface was applied. The measuring device, which is based on an electrochemical oxygensensor measures decrease of oxygen concentration in the small volume of the measuring chamber, which is in contact



with deoxygenated solution of surfactant. Experimental data obtained were incorporated into mathematical model, whichallows calculate the oxygen mass transfer coefficient in the air-water surface layer. In addition to permeabilitymeasurements the surface tension of the same solutions containing surfactant was measured. On the bases of Gibbsadsorption isotherm equation the amount of adsorbed surfactants was calculated using surface tension data. Forpreparing solutions of surfactants isomers of butanol [1- butanol, 2-butanol, 2-mehylpropanol (isobutanol), 2-methyl-2-propanol (tert-butanol)] were used.

173. DNA-separation using Self-assembled Peptide monolayersVikas P. Jain and Prof. Raymond S. Tu, City College of New york, New York, NY

The phenomenon of counterion-mediated DNA-condensation is fundamental to most DNA related activity in the cell,from chromosome packaging to control over translational mechanisms. Developing synthetic systems to manipulateDNA-condensation is essential for the development of biotechnologies for gene encapsulation and DNA-separation.The main purpose of this study is to elucidate the cooperative process of DNA-condensation with a set of self-assembling peptide building blocks, particularly studying the effect of charge distribution. The peptide that has beendesigned is a b-hairpin (two b-strand “legs” connected by a b-turn). The design incorporates the alternating periodicity,where hydrophobic and hydrophilic residues are presented on either face of the b-strand. This periodicity gives a planaramphiphilic character to each hairpin. Also, the b-turn of the hairpin is constructed from the inclusion of residues D-Proand Gly, and the peptide is positively charged because of an abundance of lysine amino-acids. The secondary structureis characterized by using circular dichroism spectropolarimetry and its behavior at the air-water interface is investigatedby using pendant drop/bubble method. We characterize the peptide behavior as a function of salt (electrolyte), whichshould provide the information about the effect of charge on the self-assembled structure of the peptide. We expectobserve similar behavior for the peptide as it complexes with negatively charged DNA.

174. Energy Storage through Electrical Double Layer Formation in Nanostructured Carbon-based Materials

Chia-Hung Hou1, Patricia L. Taboada-Serrano2, Sotira Yiacoumi1 and Costas Tsouris3, (1)Georgia Institute ofTechnology, Atlanta, GA, (2)Georgia Institute of Technology, Oak Ridge, TN, (3)Oak Ridge National Laboratory, OakRidge, TN

Electrical double layer (EDL) formation or electrosorption in nanostructured carbon-based materials is critical to manyelectrochemical processes, such as energy storage and water purification. Cyclic voltammetry experiments show thatmesopores and micropores exhibit significantly different behaviors in an electrosorption process. This phenomenon is aresult of the occurrence of EDL overlapping, which has a major influence on the mass transfer rate of ions and thenumber of ions inside the pores at equilibrium. Cyclic voltammetry revealed that the relationship between the pore sizeof nanoporous electrodes and the dimension of ionic species can determine the capacitance of nanoporous carbon inelectrolyte solutions. In addition to experimental information, an extended EDL model based on the classical Gouy-Chapman theory indicates that the pore size distribution plays an important role in the determination of the EDLcapacitance. Monte Carlo simulation techniques have also revealed the EDL behavior in the presence of multivalentand monovalent ions confined to a charged nanopore. Simulation results demonstrate the mechanisms ofelectrosorption in terms of pore size and ionic species. This work presents the fundamental aspects of EDL formation innanostructured carbon-based materials via a combination of electrochemical experiments and molecular andmacroscopic modeling. Novel carbon materials of controlled porosity are also presented and discussed in light of energystorage applications.

175. Removal of Waterborne Viruses Using Nano-scale Zerovalent Iron and the Effect ofOrganic Matter on the RemovalLiping Zhang, Pei P. Chiu and Yan Jin, University of Delaware, Newark, DE

Microbial pathogens (bacteria, protozoa, and viruses) in waters present serious threats to public health. Viruses areparticularly problematic because they are smaller, more mobile in the environment, and more resistant to chlorinationand filtration. Our previous studies showed that viruses were efficiently removed from water by zerovalent iron particles,which was mainly achieved through reactions with iron oxidation products formed through corrosion of iron. It is



therefore expected that nano-scale iron will have a greater viral removal capacity given its larger specific surface areathan granular iron particles. This hypothesis was tested through batch experiments using two bacteriophages, φX174and MS2, as model viruses. The effect of natural organic matter (NOM) on the removal of viruses was also evaluated.Results show that removal of both φX174 and MS2 followed a first-order reaction and that the removal rate coefficientsare similar to that when 10X (mass basis) of PeerlessTM iron granules were used. The mechanisms of virus removal bynano-scale iron and the potential of using nano-scale iron in applications related to water treatment under relevantenvironmental conditions (e.g., presence of varying levels of NOM) will be discussed.

176. Multithiolated dendrimers as linkers for DNA immobilization on gold surfacesB. Scott Day, Huan Cao and Michael L. Norton, Marshall University, Huntington, WV

Modification of surfaces with DNA is an area of increasing importance to many scientists and engineers. Interest isdriven by the fact that fabrication of DNA ‘chips' with both a high density of probe sites and a large number of probemolecules per site will allow numerous high quality experiments to be conducted on a single substrate. DNA chips havebeen fabricated using a variety of substrates and attachment strategies. One of the more common strategies employedto construct DNA chips relies on gold-thiol bonding, where thiolated DNA is attached to the surface of gold coatedsubstrates via self assembly. Fabrication of DNA arrays on gold surfaces is fitting because the materials necessary toconstruct them are relatively inexpensive and readily available. One of the major disadvantages of using the thiol-goldbond is the limited long term stability of the probe molecule attachment. To overcome this limitation we have developeda relatively simple synthetic approach to place multiple thiol groups on a single DNA strand to increase the long termstability of the DNA probe attachment. We react N-succinimidyl 3-(2-pyridyldithiol)-propionate) (SPDP) with the primaryamine groups of a generation 3 dendrimer, polyamidoamine. The disulfide groups are next reduced. In the last step ofprobe synthesis, acrylamide-modified DNA is reacted with the dendrimers. This synthesis places a multithiolated headgroup on the DNA for robust attachment to gold surfaces. We have observed this immobilization strategy to displaysuperior stability when compared to analogous single thiolated DNA strands.

177. Protonation of adsorbed phosphate on oxides and its effect on adsorption behaviorsXiao Huang and Gregory D. Foster, George Mason University, Fairfax, VA

This study attempts to identify the adsorption behaviors which are characteristic of protonation of adsorbed phosphateon oxides. We have experimentally observed the following three characteristic behaviors for P adsorption on alumina:1) an adsorption maximum at pH 4.0-4.5 at final P concentration of > 200 µmole l-1; 2) a plateau from pH 3.5 to 6.5 atfinal P < 100 µmole l-1 and an adsorption maximum at pH 5.5 at the extremely low concentration of 10 µmole l-1; and3) intersection of adsorption isotherms at the pH ranges of 2.5-4.5 and 5.5-6.5. Using surface complexation theory, wehave linked Behavior 1 to the phosphate being adsorbed as di-protonated monodentate complex; Behavior 2 to theadsorption as mono- and de-protonated monodentate complex; and Behavior 3 to the transition of phosphate frombeing adsorbed as di-protonated to mono-protonated monodentate complexes. Our analyses indicate that phosphate isadsorbed as a monodentate rather than a bridging bidentate complex; the three surface P complexes that have beenspectroscopically identified are di-, mono-, and de-protonated monodentate complexes, respectively.

178. Multi-sectioned Cylindrical Porous Polymeric MaterialsJung Hun Song, Graduate Center and City College of City University of New York, New York, NY and IlonaKretzschmar, City College of City University of New York, New York, NY

Control of the three-dimensional periodicity of porous polymeric materials (PPMs) has enormous potential for photonics,separations and tissue engineering. Controlled pore sizes and porosity of PPMs have shown to be essentialcharacteristics in all of these fields.1 Our work is concerned with the fabrication of three-dimensionally periodic PPMsthat have well-defined sections with different pore sizes using colloidal templating.

Colloids of different sizes are convectively assembled inside capillaries. A liquid polymer is used to fill the interstitialspaces formed by the colloidal assembly. Subsequently, the polymer is cured to form a solid colloid-polymer matrix. Aninverse opal structure forms upon dissolution of the colloids from the matrix, leaving behind a multi-sectioned PPM. Wehave assembled 0.5, 2.4, and 9.6 µm sized sulfate-polystyrene (PS) colloids in 50 µm inner-diameterpolymethylmethacrylate (PMMA) capillaries with various sequences. The hexagonally close-packed crystals formed



have been infiltrated by a UV curable prepolymer, which has been cured subsequently under a long-wave UV light (365nm). Treatment of the cured colloid-polymer matrix with organic solvents leads to porous polymeric materials with acontrolled pore size distribution.

We have investigated the structure of colloidal assemblies and the resulting PPMs using scanning electron microscopeand will present our findings. Further, knowledge of properties and characteristics of these PPMs are critical in practicalapplications, therefore, a preliminary tensile strength and UV-Vis analysis will be also presented.

(1) Xia, Y.N.; Gates, B.; Yin, Y.D.; Lu, Y.; Monodispersed colloidal spheres; Old materials with new applications.Advanced Materials 2000, 12, (10), 693-713.

179. Cooperative networks: Viscoelastic control in solutions of wormlike micelles andpolymersMatthew W. Liberatore and Nathan Work, Colorado School of Mines, Golden, CO

Mixtures of polymers and surfactants in solution are important in a wide range of applications including detergents,personal care products and oil recovery fluids impacting the chemical, pharmaceutical and petroleum industries. Theobjective of this project is creating synergy between the polymers and wormlike micelles allowing the properties of thesolution, especially the rheology, to be tuned. Maintaining the wormlike micelle state of surfactant aggregation in thepresence of an entangled polymer network is a viable challenge. Experimental protocols for studying the polymer-micelle mixtures include flow and oscillatory rheology, rheo-optics, scattering and phase mapping. Using theoreticalmodels from surfactant and polymer science, this experimental characterization allows tremendous insight into importantlength scales and time scales of the co-entangled network. Exploitation of solution conditions to increase the overalllength of the wormlike micelles creates either entangled or branched networks, which changes the viscosity of thesolution. Preliminary studies have identified solution conditions that change the rheology from weakly shear thinning tostrongly shear thinning to shear thickening. Overall, experimental control of pressure, temperature, macromoleculeconcentration and other variables allows structure-property relations of wormlike micelle-polymer cooperative networksto be measured, thus enhancing the theoretical understanding of surfactant-polymer interactions.

180. Surface Anisotropic (Patchy) Particles by Glancing Angle DepositionAmar B. Pawar and Ilona Kretzschmar, The City College of City University of New York, New York, NY

Inducing directionality in the self–assembly process has great potential in present day ‘bottom-up' approaches for thegeneration of supramolecular entities. Surface anisotropic (patchy) particles introduce directionality in self–assembly byspecific interactions between patches. Not only just relying on the physical forces between the patchy particles, theseparticles can be directed into a desired assembly through linker molecules, which covalently bind to the patches. Herewe present our results from the application of “Glancing Angle Deposition” for the production of patchy particles.

Vertical vapor deposition onto close-packed monolayers of colloids is a commonly used technique for the production ofJanus particles. The tilting and rotating of the colloidal monolayer allows the angled deposition of patches onto theparticles. The angle of the source with respect to the monolayer and the orientation of the particles in the monolayerdetermines the shape of the “patch” on the particles. Characterization of the patch size and geometry is crucial forfurther applications of these patchy particlesin the self–assembling of target structures.

This is the first time we report data on the geometry of the patches generated on the particles as a function of theangle of deposition. The experimental results are compared with the results obtained from a mathematical model usedto predict the patch geometry. Towards application of these patchy particles for self–assembly using linker molecules,we will present preliminary results on attaching organic linker molecules to the patches on the particles.

181. Like-charge interactions in membrane-coated colloidal monolayersEsther W. Gomez, Nathan G. Clack and Jay T. Groves, University of California, Berkeley, CA

Colloidal particles, near a like charged wall, have been observed to exhibit a long-range attraction under certaincircumstances. The observed attraction in these systems contradicts the Poisson-Boltzmann mean field theory, whichpredicts that similarly charged particles will repel each other. Here, we study an electrostatically levitated two



dimensional colloid in which the underlying planar surface and the particles are coated with lipid membranes. Thiscoating allows for the surface potential of the underlying substrate and particles to be varied continuously. By exploringa wide range of surface compositions and solution ionic strengths we find that anomalous long-range like chargeattraction only occurs between negatively charged particles.

182. Self-assembly of surface anisotropic (patchy) microspheresJing-Qin Cui and Ilona Kretzschmar, the City College, the City University of New York, New York, NY

Self-assembly has been shown to play an important role as a bottom-up approach in nanofabrication. However, mostcurrently used approaches are unable to produce structures with precise spatial positioning of particles when usingisotropic particles.[1] On the contrary, anisotropic particles may self-assemble into ordered structures taking advantageof their asymmetric functionalization. Recent work by Hong et al.[2] has shown that charge-asymmetric particles formclusters due to strong electrostatic interactions between particles in good agreement with MD simulations.

Here we present data on the self-orientation of surface-anisotropic microspheres with differing patch roughness viacontinuous convective assembly.[3] Surface-anisotropic spheres are harvested and re-suspended in DI-water. A specificvolume of re-suspended anisotropic spheres is added to a cell consisting of a Teflon ring with a 1-cm inner diametermounted on a piece of cleaned silicon (110) wafer. The solvent is allowed to evaporate and the orientation of thepatchy particles in the resulting monolayer is studied.

The sulfate-terminated polystyrene (sPS) spheres (2.4 µm) used in the experiments are asymmetrically modified withsilver using either template-aided electroless deposition[4] (rough surface) or physical vapor deposition (smoothsurface): and. The two processes give different morphology thus it is suggested that they show different orientationpreference during self-assembly.

1. B. D. Gates, Q. Xu et al, Chem. Rev. 2005, 105, 1171-1196

2. L. Hong, A. Cacciuto et al, Nano Letters, 2006, 6, 2510-2514

3. A. S. Dimitrov, K. Nagayama. Langmuir 1996, 12, 1303-1311

4. J.-Q. Cui, I. Kretzschmar, Langmuir, 2006, 22, 8281-8284

183. Zeta Potential Measurments via a Rotating DiskJames Hoggard, Paul Sides and Dennis C. Prieve, Carnegie Mellon University, Pittsburgh, PA

Measurement of the zeta potential of large planar surfaces is important in studies of membranes, proteins, polymersand surfactants. A novel method, called ZetaSpin, for measuring the zeta potential of disk shaped samples with radii onthe order of centimeters is presented. When a disk with a surface charge is rotated in solution, a streaming potential isgenerated in the bulk solution on the order of micro- to millivolts depending on the solution conductivity and the zetapotential of the surface. This streaming potential can be measured between a pair of electrodes located in the bulksolution. The theory relating the streaming potential to the zeta potential is presented. An advantage of the rotating diskis that the entire disk surface is uniformly accessible to mass transfer. This combined with the fact that measurement ofthe zeta potential can be made on the order of 10 second enables studies of adsorption or desorption of ions,surfactants, proteins, etc. on solid surfaces not possible with a capillary measurement.

184. Biological interactions with nano-patterened surface by gold nanoparticlesJun Zhang, Sudhanshu Srivastava, Vincent Rotello and Maria Santore, University of Massachusetts, Amherst, MA

Mixed monolayer protected gold clusters (MMPCs) functionalized with quaternary ammonium chains were employed topattern the surface on a 10-nanometer length scale. The gold nanoparticles were randomly deposited on silica surfacesunder diffusion-limited conditions and the deposition quantity was precisely controlled by varying the solutionconcentration and the flow time. The resulting surfaces imposed a complex field of attractions and repulsions onapproaching objects. In our study, silica particles were used to reveal the underlying adhesion physics with these



surfaces and to act as simple models of biological systems such as cells and bacteria. Using near-Brewsterreflectometry, we measured the the adhesive interactions between the nano-pattereded surface and the silica particles.The surface patteren possess a substantial random component and is expected to give rise to adhesive selectivity atthe micron scale. These surfaces, therefore, can form the basis for cell discriminating and sorting systems.

185. Structure and Dynamics of PEG-containing Surfactants/Copolymers on Hydrophobicand Hydrophilic SurfacesPazit Ofir Bar-Yosef, University of Massachusetts Amherst, Amherst, MA and Maria M. Santore, University ofMassachusetts, Amherst, MA

The adsorption behavior of different surfactants and polymers on surfaces of varying hydrophobicity, employing Near-Brewster angle reflectometry and Total Internal Reflectance Fluorescence (TIRF) was investigated. Using thesetechniques we were able to study the adsorption kinetics and adsorption reversibility of commercially availablesurfactants and tailor maid copolymers, which were adsorbed on three different substrates: acid etched microscopeslides, C16 self assembled monolayers and Polypropylene films (PP). This data alone provide insight into the adsorbedlayer structure: the integrity of the PEG brush and the continuity of adsorbed hydrophobic domains. We have furtherinvestigated the extent to which these pre-adsorbed surfactant/copolymer layers affect subsequent fibrinogenadsorption. Data are interpreted in terms of the extent to which the copolymers are displaced by the adsorbing proteinor merely tolerate modest protein adsorption. This work provides design rules for copolymer coatings in biomaterialapplications.

186. Optimization of pMHC/antibody microarrays for T cell binding and cytokine detection

Chaofang Yue1, Megan Balog2, Michael Paulaitis1, Jonathan Schneck3 and David Vanderah4, (1)Ohio StateUniversity, Columbus, OH, (2)Ohio State University, columbus, OH, (3)Johns Hopkins School of Medicine, Baltimore,MD, (4)National Institute of Standards and Technology, Gaithersburg, MD

For peptide-major histocompatibility complex (pMHC)/antibody microarrays to be a quantitative and reliable assays forthe simultaneous capture of T cells and detection of secreted cytokines, multiple variables related to the surfacearchitecture and the printing process need to be optimized. We compared two different types of slide substrates: onefabricated using novel surface patterning techniques to form gold/SAM (self-assembly monolayer) layers, and the othera commercially available hydrogel layer. Using neutron scattering, we characterized the multi-component, multi-layerstructure of gold slide. For both surfaces, we investigated the effects of various additives on spot morphology andintensity.

T cell crossreactivity is a fact that we must take into consideration when we use microarray to characterize a T cellpopulation. We propose a mathematical model to describe T cell crossreactivity as it occurs on microarray, which isdifferent from that in vivo.

187. POLY(DEAEMA-co-PEGMA): A NEW pH-RESPONSIVE COMB COPOLYMERSURFACTANT FOR DISPERSIONS AND EMULSIONSBrian R. Saunders and Sheikh Shahalom, The University of Manchester, Manchester, United Kingdom

Stimulus responsive copolymers are an important class of surfactants that are attracting growing attention in theliterature. When used to stabilise colloids they confer responsiveness to an otherwise non-responsive system. Thisprovides added versatility to the dispersions and enables new possibilities for application. Triggered release of activeswithin paint films is an area in which this behaviour is particularly sort. We sought to design a copolymer surfactant thatwould show a major conformational change within the pH range which is applicable to surface coatings. The pH of apaint dispersion is usually about 8, whereas that of the corresponding film is about 5. In this work a pH-responsivecomb copolymer surfactant is introduced that has a pKa of about 6.5. The copolymer is poly(DEAEMa-co-PEGMa),where DEAEMa and PEGMa are diethylaminoethyl methacrylate and poly(ethylene glycol) methacrylate. The copolymerenables preparation of fine particulate dispersions and emulsions. The dispersions used are based on carbendazim,which is a common fungacide used in paints. The oil-in-water emulsions discussed contain tetradecane. Thedispersions and emulsions remain as fluids above the pKa with evidence of flocculation. Interestingly, the emulsionscompletely phase separate when the pH is decreased to low values, releasing the oil phase. The mechanism for the



pH-triggered behaviour and the implications for polymer colloid applications are discussed.

188. Morphology controls of self-assembled nanoparticles by the secondary structures ofpoly(amino acid)sGo Un Han, Jae Hyun Jeong, Hyun Jin Lee and Jong-Duk Kim*, Korea Advanced Institute of Sciences andTechnology, Daejeon, South Korea

Poly(2-hydroxyethyl aspartamide) (PHEA) containing amine group in the side chain (PHEA-NH2) was prepared byaminolysis of poly(succinimide) (PSI) with 2-aminoethanol and 1,6-hexanediamine. PHEA-g-oligo(L-lysine) wassuccessfully synthesized by living polymerization of á-amino acid-N-carboxyanhydrides (NCA) of L-lysine using PHEA-NH2 as a macroinitiator. Self-assembled nanoparticles of PHEA-g-oligo(L-lysine) in an aqueous solution wasfabricated. The morphology changes of self-assembled nanoparticles were induced by the pH- or temperature-responsive conformational transition of specific poly(amino acid) group, which is grafted oligo(L-lysine) segment. Theconformational transition of secondary structure, the change between á-helix and â-sheet, of oligo(L-lysine) wasconfirmed by CD (circular dichroism). The morphology of self-assembled nanoparticles is studied by TEM and DLS. Thesurface plasmon resonance (SPR) biosensor has been widely used to investigate binding event occurring on biologicalsurfaces by the detection of a refractive index change on a gold surface without the need to label molecules. We alsoverify physicochemical properties of conformational transition of poly(amino acid) through the SPR study.

189. Surface Enhanced Raman Scattering of Energetic chemicals on colloidal nanoparticlesof Ag/TiO2Edwin De La Cruz Montoya, universidad de puerto rico mayaguez, mayaguez, PR

Silver nanoparticles coated with titanium dioxide was synthesized via simple route, where, the reduction of Ag+ to Ag0and the controlled polymerization of TiO2 on the surface of silver crystallites take place simultaneously. The preparednanoparticles were characterized by UV-visible absorption and by Energy dispersive X-ray spectroscopy-EDAX. Thespectrum of the suspension of Ag nanoparticles had a surface plasmon of 420 nm arising from the particles, in which ischaracteristic of Ag colloidal dispersion. Similar surface plasmon absorption due to Ag nanoparticles was observed forthe suspension of titania-coated Ag nanoparticles at longer wavelength than for the suspension of Ag nanoparticles.This absorption shift is caused by refractive index of titania and suggests coverage of Ag nanoparticles with titania.Ag/TiO2 colloids were used to measure FT-Raman spectra by capillary tube method in different excitation sources toobserve the enhancement of the Raman signatures of solution of TNT to different pH. The pH 10.30 showed anincrease of the NO2 stretching mode at the 1365cm-1 in comparison with the other pH and the solution withoutcolloids. Additionally the band 1213 cm-1 and NO2 band are shifted to higher wavenumbers.

Keywords: TNT, colloids, Titania.

190. Sticky mixture models of phase separation of eye lens gamma and alpha crystallinproteinsMaurino Bautista, Hossein Shahmohamad, David S. Ross and George M. Thurston, Rochester Institute of Technology,Rochester, NY

We apply an extension of the Baxter sticky-sphere model to mixtures of highly concentrated aqueous solutions of thebovine eye lens proteins gamma-B crystallin and alpha crystallin, which show enhanced phase separation[1] likely duein part to their effective radius ratio of close to 4.5. Gamma-B crystallin is smaller and is modeled with a temperature-dependent stickiness parameter that reproduces static light scattering near its upper consolute point[2], and small-angleneutron scattering at scattering vector magnitudes below 2 inverse nanometers[3]. Alpha crystallin is modeled as alarger, hard sphere, consistent with its scattering properties. With these choices together with hard-sphere gamma-B-alpha crystallin interactions, the Barboy-Tenne mixture extension of the Baxter model[4] predicts considerably higherphase separation temperatures than are observed. This is consistent with recent findings from molecular dynamicssimulations applied to model small-angle neutron scattering data, that hard-sphere gamma-B-alpha interactions wouldlead to mixture instability[5]. We examine the consequences of alternative gammaB-alpha interactions for phaseseparation and scattering.



[1] Thurston GM, J. Chem. Phys., 124, 134909 (2006) [2] Fine B.M., Lomakin A, Ogun OO, et al. J. Chem. Phys.,104(1):326-335 (1996) [3] Stradner A, Thurston GM, and Schurtenberger P, J. Phys. Cond. Matt. 17:1-12 (2005) [4]Barboy B and Tenne R, Chem. Phys. 38(3):369-387 (1979) [5] Stradner A, Foffi G, Dorsaz N, et al, to be submitted.

191. Characterization of metal-based nanofluids generated via laser ablation

Daniel M. Kuntz1, Lynn M. Walker1, Lee R. White1, Rakesh K. Gupta2, Yee Soong3 and Phuoc X. Tran3, (1)CarnegieMellon University, Pittsburgh, PA, (2)West Virginia University, Morgantown, WV, (3)U.S. Department of Energy NationalEnergy Technology Laboratory, Pittsburgh, PA

Metal nanoparticulate materials generated via laser ablation in solution have been characterized using a variety oftechniques (DLS, UV, TEM, electrophoretic mobility measurements) to determine particle size, stability and surfaceproperties. Information is being used to optimize and improve the laser ablation technique. The laser ablation techniqueproduces silver-based nanofluids of reasonable stability and controllable particle dimensions. The use of other metals(aluminum or brass) results in nanofluids that are not as stable the silver-based nanofluids. However, the ability toadjust nanofluid stability in all three systems by varying pH has been demonstrated. Characterization is being used tooptimize the solution conditions for the laser ablation that will give rise to stable nanoparticle suspensions.

192. Synergy among Surfactants in Solution and on Particles in SuspensionsShaohua Lu and Ponisseril Somasundaran, Columbia University, New York, NY

Surfactant mixtures are widely used in detergent, personal care, enhanced oil recovery and flotation applications.Adsorption of nonionic/cationic/anionic (ex: n-dodecyl-â-D-maltoside(DM), and sodium dodecyl sulfonate) on solidssuch as alumina was studied in this work at different solution conditions of pH, mixing ratio and salt contents along withthe wettability and zeta potential. Solution interactions were studied by analytical ultra centrifuge, surface tension, smallangle neutron scattering and cryoTEM. It was found that surfactant adsorption is dramatically affected under certain pHconditions. The effects of pH, however, are reduced by synergistic interactions in the case of nonionic/anionic mixtures.Surface tension results reveal a negative interaction parameter suggesting that there are synergistic interactionsbetween them. Importantly, only one peak indicative of one type of micelle was identified using analyticalultracentrifugation in the case of the above anionic/nonionic mixtures, while two types of aggregates were observed inthe case nonionic/nonionic mixtures. The above information on surfactant aggregation helps to reveal the mechanismsof interactions between surfactants as well as their efficient application in various industrial processes.

. Structure & dynamics of nanoparticle glassesXinhui Lu, Simon Mochrie, Suresh Narayanan, Alec Sandy and Michael Sprung, Yale University, New Haven, CT

Even after decades of study, understanding the glass transition remains a grand challenge for condensed matterscience. Especially interesting then are so-called mode coupling theory (MCT) predictions that there can exist twodistinct glass phases in systems with short-ranged attractive interactions. The present experiments were carried out toexplore this and related predictions. we report an x-ray photon correlation spectroscopy study of the re-entrant glasstransition of colloidal suspension. The system is a suspension of silica spheres of 3900 Angstrom diameter in the binaryfluid of water and 2,6- lutidine. By changing the temperature, the system is observed switching between two differenttypes of glass state.The transition exhibits a logarithmic dynamics as predicted.

. Solvent-reversible poration in ionic liquid copolymersFeng Yan and John Texter, Eastern Michigan University, Ypsilanti, MI

Microemulsions comprising methyl methacrylate (MMA) and a polymerizable ionic liquid (IL)-based surfactant, 1-(2-acryloyloxyundecyl)-3-methylimidazolium tetrafluoroborate (IL-BF4) water and cosurfactant,1-propanol, have beenpolymerized via thermal initiation in microemulsions. The resulting polymer hydrogels can be transformed to porouspolymers by anion exchange of BF4¯ by PF6¯ in the IL moiety. The pore size of the polymer varies with crosslinkercontent in the precursor microemulsions. The converted porous polymers can be transformed to solvogels by imbibingsolvents such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) and alcohols. These polymer solvogels can bereversibly transformed to porous polymers again by treatment with water. The basis for this reversible poration process



appears due to spinodal decomposition of the solvogel composition into the open cell nanoporous material, induced byaddition of a poor solvent (e.g., water) for the ionic liquid surfactant blocks of the copolymer.

193. Gelation versus liquid crystal phase transitions in suspensions of charged colloidalplateletsH. N. W. Lekkerkerker, Utrecht University, Utrecht, Netherlands

The liquid crystal phase behaviour of suspensions of charged gibbsite (Al(OH)3) platelets is investigated. We study thecompetition between sedimentation, gelation and liquid crystal formation at different initial concentrations and saltstrengths. By variation of the ionic strength we are able to tune the effective thickness-to-diameter ratio of the plateletsin suspension. This enabled us to experimentally test the liquid crystal phase transition scenario that was first predicteda decade ago by computer simulations for hard platelets, that is the isotropic (I) nematic (N) and isotropic to columnar(C) phase transitions in one colloidal suspension. In addition to the shape-dependent thermodynamic driving force, theeffect of gravity is important. For example a biphasic (I-N) suspension becomestriphasic (I-N-C) on prolonged standing.This effect is described by a simple osmotic compression model. Finally we discuss the possibility to produce photoniccrystals from the iridescent columnar phases of Gibbsite nanoparticles.

194. pMHC microarrays for characterizing protein-protein interactions in diverse T cellpopulations

Chaofang Yue1, Megan Balog2, Michael Paulaitis1 and Jonathan Schneck3, (1)Ohio State University, Columbus, OH,(2)Ohio State University, columbus, OH, (3)Johns Hopkins School of Medicine, Baltimore, MD

High-throughput protein microarrays for screening protein-protein interactions have promising applications inbiotechnology, medical diagnostics, vaccine development, and the treatment of cancer, autoimmunity and infectiousdiseases. We are using this technology to rapidly screen diverse populations of T cells to characterize human influenza-specific immune responses. An important early molecular recognition event that triggers an immune response is theinteraction of a T cell receptor (TCR) on the surface of the T cell with its complementary major histocompatibilitycomplex (MHC) on the surface of antigen-presenting cells. This protein-protein interaction is mediated by a smallpeptide (the antigen) 8-10 amino acids in length that is bound to the MHC, such that the amino acid sequence of thepeptide antigen determines the specificity of the TCR/peptide-MHC (pMHC) interaction. Individual T cells are alsocharacterized by a unique TCR; therefore, microarrays printed with the MHC containing peptides with different aminoacid sequences serves to distinguish T cells by their characteristic TCR/pMHC interactions. In addition, co-printingantibodies against cytokines secreted by the captured T cells enables an antigen-specific functional analysis of T cellactivation across this population. We show that pMHC microarrays can selectively capture and enumerate antigen-specific T cells in diverse populations at high sensitivity, and that this information provides insights into the generalprinciples governing early molecular recognition events in human immune responses. Results on the functional diversityof the human immune response will also be presented.

195. Role of solubility enhancers in the study of crystallization conditions for improvingcrystal hitsRajendrakumar A. Gosavi, Sasidhar Varanasi, Constance A. Schall and Timothy C. Mueser, University of Toledo,Toledo, OH

Abstract: Biomolecular crystallography strives to explore the appropriate growth conditions leading to diffraction qualitycrystals for structure determination. Various commercially available crystal screens are often used to search foroptimum crystallization conditions. These screens consist of combinations of buffers, salts, precipitant and additivesresulting in a large number of possible combinations of crystallization conditions. Increasing the solubility of the proteinin its buffer to an optimum level favors crystallization over precipitation. A recent study determined that using solutionconditions which enhanced protein solubility lead to better quality crystals in most cases examined. An enhancement inthe solubility lowers the attractive forces between the protein molecules and crystal-liquid interfacial tension. This lowersthe energetic barrier to nucleation of protein crystals as determined through nucleation kinetic data. Excessiveenhancement in the solubility may lead to the near elimination of the barrier thus leading to precipitation. This workfocuses on analyzing the effect of various solubility enhancers on the crystallization of selected proteins. The use of



organic solvents such as ethanol, ethylene glycol, glycerol and 2-methyl-2,4-pentane diol as solubility enhancers forselected proteins in their optimized buffer conditions is evaluated.

196. Charge and ionic strength dependence of phase separation and liquid structure ofsolutions of the eye lens protein, gamma-B crystallin

George M. Thurston1, Kenneth Desmond2, Dawn Carter1, Anna Stradner3 and Peter Schurtenberger3, (1)RochesterInstitute of Technology, Rochester, NY, (2)Emory University, Atlanta, GA, (3)University of Fribourg, Fribourg,Switzerland

We are studying liquid structure, phase separation and cluster formation in aqueous solutions of the bovine eye lensprotein, gamma-B crystallin, as functions of charge and ionic strength. The role of charge in lens protein phaseseparation is important for understanding cataract, since changes in lens protein charge, known to occur during aging,are expected to affect solution stability. At 0.24M ionic strength, decreasing pH from 7.1 to 5.5 and thereby increasingnet protein charge from +2 to +6 lowers the gamma-B upper consolute temperature by 8 degrees C. Further increasinggamma-B charge to +9 at pH 4.5 changes effective gamma-B interactions from attractive to repulsive at accessibletemperatures, as observed by small-angle neutron scattering, and no phase separation is observed. Lowering ionicstrength at pH 4.5 further increases repulsive interactions. Low-angle neutron scattering from gamma-B crystallin nearphase separation is well-fit by the Baxter sticky-sphere model, but larger-angle scattering may reflect anisotropy ofprotein features and interactions. We compare small-angle scattering results for gamma-B crystallin at low ionicstrength to evidence for lysozyme cluster formation under analogous solution conditions.

197. Hydration of proteins and weak protein-protein interactions

Dilip Asthagiri1, Amit Paliwal2, Abraham Lenhoff3, M. Hamsa Priya4 and Michael Paulaitis4, (1)Johns HopkinsUniversity, Baltimore, MD, (2)Johns Hopkins University, (3)University of Delaware, Newark, DE, (4)The Ohio StateUniversity, Columbus, OH

The structure and solution thermodynamic property of a protein is intimately tied to the structure of water around it, andan extant goal of experiments, theory, and simulation is to understand this inter-relation between the solvent water andthe solute protein. We pursue this question by modeling the hydration contribution to the osmotic second virialcoefficient, B2, of protein solutions. We adopt a quasi-chemical description in which a protein with the water moleculesassociated with it is treated as a distinct solution component. These associated water molecules are identified throughmolecular dynamics simulations. We examine this quasi-chemical view of hydration by predicting B2 and compare ourresults with those derived from light-scattering measurements of B2 for staphylococcal nuclease, lysozyme, andchymotrypsinogen at 25°C as a function of solution pH and ionic strength. We find that short-range protein interactionsare influenced by water molecules strongly associated with a relatively small fraction of the protein surface. We find thatthese water molecules reduce the surface complementarity of highly favorable short-range interactions, and thereforeplay an important role in mediating protein-protein interactions. Thus specific hydration effects need to be taken intoaccount for an accurate description of B2. We also observe remarkably similar hydration behavior for these smallglobular proteins despite substantial differences in their three-dimensional structures and spatial charge distributions,suggesting a general characterization of hydration for such globular proteins.

198. Biomolecules in water: From hydrophobic to hydrophilic hydration and interactionsShekhar Garde, Rensselaer Polytechnic Institute, Troy, NY

Water structure and dynamics play an important in protein structure, dynamics, and function. Water packing,orientations, and dynamics in the vicinity of proteins are affected by protein surface roughness as well as the chemicallyheterogeneous nature of protein surface, which ranges from hydrophilic to hydrophobic in character. We use moleculardynamics simulations of model solutes with varying sizes and charge densities to understand how they affect the vicinalwater structure and dynamics. Water-mediated interactions between solutes of varying charge densities yields (for thefirst time) "molecular volcano" relationships observed in experimental data on salt pairs in solution. We makeconnections of fundamental understanding of charge-density-dependent hydration obtained for model solutes withhydration of proteins through complementary simulations of several proteins in explicit water. Together, these studiesare beginning to provide molecular level insights into protein-X interactions (where X = ligands, chromatographic



displacers, and interfaces).

199. Proteins as model colloids: enhanced stability of eye lens protein mixtures throughmutual attraction

Giuseppe Foffi1, Anna Stradner2, Nicolas Dorsaz1, George M. Thurston3 and Peter Schurtenberger2, (1)EcolePolytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, (2)University of Fribourg, Fribourg, Switzerland,(3)Rochester Institute of Technology, Rochester, NY

Understanding interparticle interactions in protein solutions is of central importance to gain insight into the origin ofprotein condensation diseases. While the study of such condensation diseases has traditionally focussed on amolecular view point based on specific, detailed properties of the molecules involved, considerable progress has alsobeen made using statistical and colloid physics, in which the formation of condensed protein phases can bequantitatively analyzed in terms of a subtle interplay between interprotein attractions, repulsions, and entropy. Theanalogy between colloids and proteins has not only been driven by biological and biomedical research. Globularproteins have also drawn great attention in the colloid physics community due to their suitability as model colloids. Herewe demonstrate the importance of this approach for the lens crystallin proteins, which are vital for eye lenstransparency and for understanding cataract, a clouding of the eye lens due to increased light scattering. By combiningsmall-angle neutron scattering (SANS) experiments and molecular dynamics (MD) computer simulations, wedemonstrate that transparency of lens crystallin protein mixtures at high concentrations, comparable to those in theliving eye lens, is greatly enhanced by weak, short-range attractions between two of the prevalent mammaliancrystallins, alpha- and gamma-crystallin. Provided they are not too strong, such mutual attractions considerablydecrease the critical temperature and corresponding opacity due to light scattering, and are thus essential for lenstransparency.

200. Brownian and colloidal interactions in protein crystal growthJack Lum, Johns Hopkins University, Laurel, MD

Brownian dynamic simulations are used to elucidate some of the underlying transport processes of protein molecules inprotein crystallization. The dominant forces are modeled from colloidal interactions between a lysozyme molecule(sphere) and tetragonal lysozyme crystal (wall), both heterogeneously charged. The electrostatic portion is obtained bysolving the linearized Poisson-Boltzmann equation with a boundary elements method; the van der Waals force istreated as a function of only the Hamaker constant and sphere-wall separation. Simulation results show that proteinmolecules have greater translational diffusivity and are more concentrated near a highly charged crystal surface thannear a weakly charged one. This suggests that ordered protein assembly as a precursor to crystal growth is more likelyto occur at the crystal surface than in bulk solution.

201. Keynote: Surface chemistry of carbon on Ni and Ni-alloys: carbon-toleranthydrocarbon reforming catalysts from molecular insightsSuljo Linic and Eranda Nikolla, University of Michigan, Ann Arbor, MI

Reforming of hydrocarbon fuels is one of the most important heterogeneous catalytic processes. Particularly appealingis potential development of catalysts that could be used as direct, reforming anodes in solid oxide fuel cells (SOFCs).Current reforming catalysts such as Ni, however, suffer from two major problems: (i) carbon-induced deactivation and(ii) sulfur poisoning of the catalyst. We have utilized Density Functional Theory (DFT) calculations to study the surfacechemistry of carbon atoms and carbon fragments on Ni. These studies demonstrated that there is a strongthermodynamic driving force to form sp2-bonded carbon networks. These extended carbon networks diminish thereforming activity of Ni. We have further utilized DFT to search for Ni-containing alloys that are more carbon-tolerantthan monometallic Ni, i.e., that have a lower propensity to form the carbon networks. These studies have yielded a fewpromising alloy formulations. Subsequent steady-state reactor studies validated the predictions of the DFT calculations.Aside from the steady-state reactor tests, the catalysts were characterized with multiple spectroscopic and microscopictools.

1. E.Nikolla, A. Holewinski, J. Schwank, S. Linic; “Controlling Carbon Surface Chemistry by Alloying: Carbon TolerantReforming Catalyst”, Journal of the American Chemical Society, 2006; 128(35); 11354-11355.



202. Stability of Subsurface 3d Metals in Bimetallic Cathode ElectrocatalystsCarl Andrew Menning and Jingguang G Chen, University of Delaware, Newark, DE

For the cathode of a proton exchange membrane fuel cell (PEMFC), the current leading industrial electrocatalyst ispure platinum for the oxygen reduction reaction (ORR). The ORR reduces a stream of gaseous oxygen over anelectrocatalyst to form water and complete the electrical circuit. Even though platinum has been found to have thehighest activity for the ORR for pure catalysts, this activity is orders of magnitude lower than that found for othergeneral electrode reactions such as the hydrogen oxidation reaction (HOR). It has been shown previously in literaturethat the activity can be increased if the 2nd layer of a platinum surface is replaced with a 3d transition metal giving asubsurface bimetallic catalyst. In the current study, we attempt to quantify the stability of the Pt-3d-Pt(111) subsurfaceelectrocatalysts under an oxygen environment. Experiments were performed for the Pt-Ni and Pt-Co bimetallic systemsusing ultra-high vacuum (UHV) techniques. The segregation of Ni and Co was verified using high-resolution electronenergy loss (HREELS). The activation barrier for the segregation of the 3d transition metal to the surface wasdetermined using Auger electron spectroscopy (AES). The remaining Pt-3d bimetallic systems were compared usingpredicted thermodynamic stability calculated using density functional theory (DFT). Kinetically, the Pt-Ni subsurfaceconfiguration was determined to be more stable than the Pt-Co subsurface configuration when exposed to oxygen.Thermodynamically, the Pt-Ni subsurface configuration has been predicted to be the most stable of the Pt-3dsubsurface configurations when exposed to oxygen.

203. Unsupported Ir catalysts to probe for structural and size effects in surface chemistry

Wenhua Chen1, Timo Jacob2 and Theodore E. Madey1, (1)Rutgers, The State University of New Jersey, Piscataway,NJ, (2)Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin-Dahlem, Germany

Clean planar Ir(210) and clean nano-faceted Ir(210) with tunable sizes have been prepared from the same crystal insitu, which allows us to investigate structure sensitivity and size effects in surface chemistry on unsupported iridiumwithout switching from sample to sample. A series of chemical reactions have been carried out on clean planar andclean faceted Ir(210) using temperature programmed desorption (TPD) measurements. We have found clear evidencefor structure sensitivity in decomposition of acetylene, nitric oxide, ammonia and hydrogen, and for oxidation of CO onplanar Ir(210) versus faceted Ir(210). Our measurements of CO oxidation over planar and faceted Ir(210) are supportedby our DFT calculations of the energetics of adsorption and diffusion of oxygen; the results suggest that surfacediffusion may play a role in controlling CO oxidation over Ir. In addition, ammonia decomposition on faceted Ir(210)exhibits size effects on the nanometer scale, which is the first observation of size effects in surface chemistry onunsupported monometallic catalyst with well defined structure and controlled size.

204. A unified modeling framework for design of multi-site catalysts: application to NH3decomposition for H2 productionVinay Prasad, Altaf Karim, Niket Kaisare, Danielle Hansgen and Dionisios G. Vlachos, University of Delaware, Newark,DE

Challenges in using ammonia decomposition for hydrogen production include increasing catalyst activity and developingcheaper catalysts. While Ru is the best single metal catalyst, multi-site catalysts, including bimetallics, offer possibleimprovements. We aim to develop a unified modeling framework for understanding and designing multi-site catalysts tomeet these challenges.

Microkinetic models typically assume a homogeneous catalyst surface. A catalyst consists of various crystallographicplanes, steps and defects, and multiple chemical components (different metal islands), which form multiple, interactingsites. The kinetics on different sites and their interactions must be captured in predictive models for these spatiallydistributed situations. These interactions ‘couple' microkinetic models; we show that coupling is subject tothermodynamic constraints, and we develop appropriate multi-site models to compute reaction rates. The applicability ofsuch mean-field models is assessed via kinetic Monte Carlo simulations.

We show an example for ammonia decomposition on a bimetallic catalyst containing Pt and Ru, which have the samerate-determining step and fall on the same side of the “volcano curve”. Fig.1 shows ammonia conversion as a function



of Ru fraction. Both non-interacting and weakly interacting (adsorbed species can diffuse to and react on the othercatalyst surface) cases are shown. Pure Ru is the best catalyst, as expected for this situation. This approach is beingextended to a library of catalysts and best bimetallic catalysts will be discussed. The effect of steps will also beillustrated to underscore their relative importance.

205. Reactions of Complex Epoxides on Silver SurfacesAdrienne C. Lukaski and Mark A. Barteau, University of Delaware, Newark, DE

Direct oxidation processes, such as ethylene epoxidation to ethylene oxide, have been researched extensively due totheir commercial significance. Despite the importance of epoxide production, the mechanistic details of olefinepoxidation remained obscure until recently and the majority of significant advances in Ag-catalyst developmentoccurred primarily through empirical methods. Recent surface science studies of ethylene oxide and 1-epoxy-3-butenehave identified an oxametallacycle species as the active intermediate in Ag-catalyzed epoxidation of both ethylene and1,3-butadiene; expansion of the epoxide ring to incorporate surface silver atoms forms the oxametallacycle species.Oxametallacycles have been isolated by ring-opening ethylene oxide, 1-epoxy-3-butene, and styrene oxide on Ag(111)and 1-epoxy-3-butene on Ag(110). Surface science techniques and density functional theory were used in this study toinvestigate the interactions of styrene oxide and isoprene oxide with Ag-surfaces. In agreement with previous studies ofolefins on Ag(110) and Ag(111), these complex epoxides undergo activated ring-opening to form stable surface specieson silver; these intermediates reform their parent epoxides during subsequent temperature-programmed desorption.Because the molecular forms of both styrene oxide and isoprene oxide desorb molecularly from silver below 250 K, theintermediate species derived from the these epoxides are most likely surface oxametallacycles. Preliminary densityfunctional theory calculations predict that cleavage of the epoxide ring occurs at the carbon bearing the substituentgroup to form surface oxametallacycle intermediates.

206. Spatio-temporal Forcing of a non-linear Surface Reaction - Oxidation of CO on Pt(100)Danny Bilbao and Jochen Lauterbach, University of Delaware, Newark, DE

The oxidation of CO on Pt(100) exhibits complex non-linear behavior, such as reaction rate oscillations and spatio-temporal adsorbate patterning. The current focus of our work is to investigate the dynamics of this system when it issubjected to external forcing. Using gas microdosing to locally introduce reactants onto the catalytic surface and EMSI(Ellipsomicroscopy for Surface Imaging) to image changes in adsorbate activity, unique behavior has been observed forsystems at pressures of 1x10-4 Torr.

The local dosing of several gasses (e.g., CO, O2, NH3, etc.) onto the catalytic surface modifies the surface in such away as to lead to the formation of a ring shaped pattern generated by preferential adsorption of CO. An investigation ofthis ring formation concluded that the appearance of the ring depends on the surface temperature at the time ofmicrodosing as well as the time elapsed between dosing and the introduction of CO into the reactor.

External forcing was used to drive small areas of the surface residing in a monostable, CO covered state into anoscillatory state. Initial Reaction conditions were adjusted to produce a CO covered surface, lying close to the point atwhich the surface would become O saturated. Oxygen was then microdosed onto the surface creating an adsorbed Oisland that was eventually reacted away to leave the surface covered again with only CO. Decrease of the global COpressure lead to the onset of oscillations, which were spatially restricted to the previously dosed regions.

207. Mechanism of Assembly of Short, Highly Ordered, Single-Walled Mixed-OxideNanotubes



Sankar Nair, Sanjoy Mukherjee, Keesuk Kim and Suchitra Konduri, Georgia Institute of Technology, Atlanta, GA

Nanotubes are important ‘building block' materials for nanotechnology, but a synthesis process for short (sub-100-nm)nanotubes with structural order and monodisperse diameter has remained elusive. To achieve this goal, it is critical topossess a definitive mechanistic framework for control over nanotube dimensions and structure at very small lengthscales.

While no general strategy has thus far been proposed, we are interested in a unique model system that offersmechanistic insights into the assembly of nanotubular objects that could lead to a more general synthesis process. Wehave employed solution-phase and solid-state characterization tools to elucidate the mechanism governing theformation of short (20 nm), ordered, monodisperse (3.3 nm diameter), aluminum-germanium-hydroxide(‘aluminogermanate') nanotubes in aqueous solution. We show - via mechanistic synthesis experiments,dynamic light scattering, UV-Vis/Raman/IR spectroscopy, microscopy, and diffraction techniques - that the centralphenomena underlying this mechanism are: (1) the generation (via pH control) of a precursor solution containingaluminate and germanate precursors chemically bonded to each other, (2) the formation of amorphous nanoscale (~ 6nm) condensates via temperature control, and (3) the self-assembly of short nanotubes from the amorphous nanoscalecondensates.

Simultaneously, atomistic simulations reveal that the formation of ordered monodisperse nanotubes is strongly related tothe existence of unique energy minima in the nanotube structure as a function of diameter. This provides an additionalhandle for directing the assembly of metal oxide nanomaterials towards energetically favorable structures. Ourmechanism provides a model for controlled low-temperature assembly of small, monodisperse, ordered nanotubeobjects.

208. NOM Induced Dispersion and Disaggregation of n-C60 Aggregates in WaterBin Xie, Zhihua Xu, Wenhua Guo and Qilin Li, Rice University, Houston, TX

C60 fullerene and its derivatives have been used in a number of consumer products and their potential applications inbiomedical and environmental engineering are being actively pursued. Existing toxicity data indicate that industrial-scaleproduction of C60 fullerene poses a potential threat to the environment. Understanding the fate and transport of C60 inthe environment is necessary to evaluate its environmental impact. Although natural organic matter (NOM) is known tostabilize colloids, its influence on C60 behavior in aqueous phase has not been studied. Our study aims to determinethe effect of aquatic NOM on the formation and physicochemical properties of aqueous C60 suspension, also referred toas n-C60 due to the aggregate nature of the particles formed. The effects of two major NOM components, humic acid(HA) and fulvic acid (FA), were investigated using n-C60 samples prepared by two methods: emulsification of C60solution in toluene with water followed by sonicating volatilization of toluene, and directly mixing C60 dry powder withwater. Dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM)were employed to analyze particle size and morphology. Particle surface zeta potential was determined byelectrophoretic mobility measurement using phase analysis light scattering. NOM was found to induce disaggregation ofpreformed n-C60 particles. Moreover, directly mixing C60 dry powder with water containing NOM formed stable n-C60suspensions with particle sizes of 2-4 nm. These results indicate that NOM may play a critical role in transport andtoxicity of C60.

209. Molecular modeling of the interactions of sarcosine and AMPA with montmorilloniteLorena Tribe, Amanda J. Rennig and Annette K. Slutter, Penn State Berks, Reading, PA

The interactions of glyphosate molecules with montmorillonite clay have been studied with theoretical methods, rangingfrom molecular mechanics to ab initio quantum mechanical calculations to explore the ways in which this herbicide maybind to the interlayer surfaces of the mineral in natural soils. Free glyphosate is moderately biodegradable, due mostlyto soil microorganisms. Two pathways have been reported for its degradation in soils, one using the intermediateaminomethylphosphonic acid (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, AMPA) and the other usingthe intermediate sarcosine. In this work we extend the previous theoretical study of glyphosate adsorption onmontmorillonite surfaces to sarcosine and AMPA. The environment of the glyphosate, sarcosine and AMPA moleculesin the present calculations is the interlayer of the clay and the surrounding water molecules and cations, with a roughenergy landscape. The search for the global minima is not stressed in these conditions but rather a reasonable



structure for the molecules in solution determine is determined. A molecular modeling calculation was performed wherethe molecules were placed in the montmorillonite interlayer and were allowed to move freely, without constraints. Thegoal of these calculations was to establish if one of the three functional groups (COOH, NH2+ or PO3OH) isconsistently closer to the montmorillonite in the final state. The final distances between atoms of these moieties andatoms of the surface are reported here for several trials with random initial configurations.

210. Nanostructural analysis of poly(N-isopropylacrylamide) grafted on solid surface inaqueous solutionsNaoyuki Ishida, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan and SimonBiggs, University of Leeds, Leeds, United Kingdom

It is well known that poly(N-isopropylacrylamide) (PNIPAM), PNIPAM chains show a phase transition from a coil toglobule state at a lower critical solution temperature (LCST). A similar response is expected for surface grafted PNIPAMand such layers may have a number of interesting applications including drug delivery, permeation-controlled filters andcontrolled/sustained release. In order to control the structure of such layers effectively, it is important to investigate indetail the structural behaviour of immobilized PNIPAM chains responding to stimuli from external environment. In thisstudy, structural changes of PNIPAM chains immobilized on solid surfaces were investigated in aqueous solutions withan atomic force microscope (AFM) and a quartz crystal microbalance with dissipation (QCM-D). By AFM imaging, thetransition of the grafted PNIPAM chains from brush to mushroom state was clearly visualized; the surface images of theplate were featureless at temperatures below the LCST, whereas a large number of hemi-spherical structures whosesize was order of 100nm were found on the surface above the LCST. Both frequency and dissipation signals obtainedusing QCM-D showed significant change at around LCST, indicating that PNIPAM underwent a collapse by thedehydration of the chains. A complementary investigation indicated that a similar transition could be observed insolutions of high concentration electrolytes. It was also found that the grafting density of the PNIPAM chainssignificantly affected significantly the sharpness of the phase transition behaviour of them responding to change inenvironmental conditions.

211. Uniform Mechanically oscillating PNIPAM Particles with Covalently Bound RutheniumBZ Catalyst

Zhengdong Cheng1, Srinivasa Pullela1, Jingyi Shen1 and Manuel Marquez2, (1)Texas A&M University, CollegeStation, TX, (2)Phillip Morris USA, Richmond, VA

Uniform PNIPAM gel particles with covalently bound tris(bipyridyl)ruthenium(II) were synthesized via coordinationchemistry between a ruthenium complex and a monodispersed poly(N-isopropylacrylamide) (PNIPAM) gel bearingbipyridine ligand. UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and confocal microscopy wereemployed for the characterization of the gel particles. Loading of the tris(bipyridyl)ruthenium(II) complexes and theuniformity of the particle size were confirmed. The Mechanical oscillation of these particles was measured in a range ofthe BZ reactants' concentrations. Temperature change of the oscillation frequency and oscillation induction timerevealed activation energy of the nonlinear chemical reactions and the role of the polymeric network. These particleshave potential application in the study of the Belousov-Zhabotinsky (BZ) reaction facilitated annealing of colloidalcrystals.

212. Protein-stabilized colloidal particlesMaurice Mehagnoul, Peter Versluis, Johan Hazekamp, Eli Roijers, Ruud den Adel, Gert-Jan Goudappel and KrassimirVelikov, Unilever Food & Health Research Institute, Vlaardingen, Netherlands

Colloidal particles find many applications in the formulation of paints, agricultural and home & personal care products, indrug delivery, foods, and as a precursor for advanced nanostructured materials. Preparation and stabilisation of colloidalparticles in complex systems is a challenging task. To increase the stability of colloidal particles very often surfaceactive molecules are used to absorb on the particle surface. As being surface active, proteins are another large class ofmolecules that can provide stabilisation effect in colloidal dispersions. Here we present results on the wet chemistrysynthesis and characterisation of colloidal particles from sparingly soluble minerals in the presence of proteins.

213. Preparation of Melamine-Formaldehyde-Polyvinylpyrrolidone (MFP) novel resins, their



structural with IR-NMR and Friccohesive characterizations with Survismeter, and theirHydrodynamicsMan Singh and Vinod Kumar, Chemistry research lab., Deshabndhu college, university of delhi, new delhi, india, newdelhi, India

Cutting edge nanotechnological based material sciences have revolutionized the focus of research in all forefronts ofphysicochemical and medicochemical and electronic industries. Frontier of science and technology are tens for evolvingecofriendly, green chemistry and micro scale the devices for applications of them and a competition is being generatedfor cutting edge research in materials. In continuation of such efforts novel polymer resins of melamine-formaldehyde-polyvinylpyrrolidone (MFP) in 0.5:16:1 (R1), 1:16:1 (R2) and 0.5:10:1(R3) ratios have been prepared with condensationpolymerization. Their average viscosity molecular weights (`Mv) determined with Mark-Houwink and Friccohesity, astate of frictional-cohesive-adhesive forces with Man Singh equations, respectively. The viscous flow time (t) and dropcount (n) data for Man Singh equation were obtained with Survismeter respectively. Structural determinations weremade with IR and H1 NMR where specific proton singlet at ä 4.5 ppm, duplet at ä 3.13-3.17 and a quartet at ä 1.5-2.2ppm infer the positions of protons of methylen (-CH2 -) bridging groups, pyrrolidone and polyvinyl constituents of theresins. The 3389.25, 1290.38 and 1655.28 cm-1 stretching frequencies of –O----H-CH-, -C-O and –C=N- groupsrespectively infer its preparation. The`Mv of R1, R2 and R3 resins are 11,995, 12,250 and 11,709 g mol-1, structuraland physicochemical behavior is studied with survismeter to for adhesive properties. The viscosities and surface tensionwill be elaborated at deliverance of the lecture.

214. Keynote: Colloid Retention in Porous Media at Different Scales: Processes and Models

Scott A. Bradford1, Saeed Torkzaban2, Sharon L. Walker2 and Jirka Simunek2, (1)USDA-ARS, Salinity Laboratory,Riverside, CA, (2)University of California, Riverside, CA

An understanding and ability to predict the transport and deposition of colloids in porous media requires knowledge ofprocesses and interactions that occur at different spatial and temporal scales. The flow field can be solved and masstransfer processes can be quantified at the collector-scale. Here the potential for colloid attachment in the presence ofhydrodynamic forces is determined from a balance of applied (hydrodynamics) and resisting (DLVO) torques. Processesof colloid mass transfer and retention can also be calculated at the pore-scale (ensemble of collectors). Differences incollector- and pore-scale studies occur as a result of the presence of small pore spaces that are associated withmultiple interfaces and zones of relative flow stagnation. Illustrative examples of colloid retention processes in thesmallest regions of the pore space (straining locations) will be presented from micromodel studies and pore-scalecolloid transport simulations. Colloid deposition behaviour at the column-scale has frequently been reported to be non-exponential with distance under unfavourable attachment conditions. Profile shape has been demonstrated to bestrongly dependent on the colloid size, pore structure, colloid concentration, hydrodynamics, and solution chemistry. Toadequately simulate non-exponential deposition profiles, processes related to variability of the pore structure and flowfield, surface charge heterogeneity of colloids and porous media, and/or colloid-colloid interactions need to beconsidered. Various deterministic and stochastic modeling approaches to quantify non-exponential deposition profilesand to test hypothesis with regard to colloid retention will be summarized.

215. Colloid-colloid Interactions Influence Deposition in Porous MediaHuilian Ma and William P. Johnson, University of Utah, Salt Lake City, UT

Colloid-colloid interactions are often neglected in the past studies of particle deposition in porous media. Apart from thecomplexity involved in accounting for such interactions, this neglect may largely result from limitations of traditionalcolloid transport theories, which predict no attachment under unfavorable situations (i.e., in the presence of an energybarrier to deposition due to same-charged surfaces). Recent advances in understanding the mechanisms of colloidalretention in the presence of energy barrier provide a basis for inclusion of colloid-colloid interactions in predictions ofparticle deposition. Here, simulations incorporating colloidal interactions into a Langragian particle trajectory model arepresented. Results show that despite their mutual electrostatic repulsion, colloid-colloid interactions can mitigate orenhance retention in porous media depending on the fluid velocity and chemical conditions. The simulations reproduceblocking and ripening phenomena observed in experiments performed in the presence of an energy barrier todeposition.



216. Resolving the Coupled Effects of Hydrodynamic and DLVO Forces on Colloid Retentionin Porous Media

Saeed Torkzaban1, Scott A. Bradford2 and Sharon Walker1, (1)University of California, Riverside, Riverside, CA,(2)USDA-ARS George E. Brown, Jr. Salinity Laboratory, Riverside, CA

Transport of colloidal particles is governed by the rate at which the colloids strike and stick to collector surfaces.Filtration theory has classically neglected the influence of hydrodynamic forces and pore structure in the calculation ofcollision efficiency, as well as non-idealities associated with natural porous media such as non-spherical collectors andrough surfaces. Computational simulations will be presented that consider the influence of hydrodynamic and DLVOforces on colloid attachment to variously shaped collectors, and colloid retention processes that occur in small porespaces formed by multiple collectors and rough surfaces. Our analysis indicates that hydrodynamic forces, collectorshape, and pore structure significantly influences the colloid collision efficiency. Colloid attachment is only possible inregions of the pore space where the torque from hydrodynamic shear that acts on colloids adjacent to collector surfacesis less than the adhesive (DLVO) torque that resists detachment. The fraction of the collector surface area on whichattachment may occur increased with solution ionic strength and decreasing flow velocity. Our results also show that thecollision efficiency is sensitive to collector features such as roughness and shape, and to the pore space geometry.Simulation findings demonstrate that quantitative evaluation of colloid transport through porous media will requirenontraditional approaches accounting for physical (hydrodynamics, surface roughness, collector shape, and porestructure) and chemical (DLVO forces) conditions.

217. Numerical Investigation of Colloid Retention and Transport in Saturated Porous MediaJie Han, Hui Gao, Lian-Ping Wang and Yan Jin, University of Delaware, Newark, DE

Migration of colloids in porous media has been mainly studied through laboratory column experiments and simulation ofthe resulting breakthrough curves. In recent years, visualization experiments using micromodels are used as a newapproach for investigating mechanisms of colloidal retention in porous media at the pore-scale. However, paralleldevelopments in conceptual models and related numerical methods are lacking. In this study, a particle-trackingframework was developed and solved numerically, which allows simulation of a 2-D flow field and colloidal retentionand transport in a dense cubic packed medium. To conduct a simulation, the program is first run to establish steady-state flow that is driven by a pressure gradient before colloids are introduced. The model considers the Stokes dragforce, Brownian force, colloid-grain and colloid-colloid interaction forces (including electrostatic double layer, van derWaals, and acid-base forces) on every colloid and predicts the moving trajectory and deposition in a defined domain.The differential equation of Newton's Second Law of Motion is solved numerically with the Adams-Bashforth-Moultonmethod. Effects of hydrodynamics, solution chemistry and surface properties of colloids are examined by changing flowvelocity, solution pH and ionic strength, and surface hydrophobicity of colloids. Model analysis and simulation exercisesindicate that this 2-D model is a very useful tool that can provide mechanistic insight for improved understanding ofcolloidal retention and transport processes and how these processes are affected by the relevant parameters. Thismodel can also be used for guiding the design of and providing simulation to micromodel visualization experiments.

218. Straining of colloidal particles in intergranular gapsElena Rodriguez and Steven L. Bryant, The University of Texas at Austin, Austin, TX

A better understanding of the risk of water contamination from viruses, bacteria or contaminants adsorbed on colloidscan be achieved by modeling the retention of colloidal particles in soils. Colloids transported by fluid remain in the soilwhen they arrive at constrictions in pore space too small to admit them. Pore throats have been typically consideredthe place where colloids are trapped. However, numerous column experiments offer unequivocal evidence of strainingof colloids that are smaller than the smallest pore throat in the column.

We propose to explain this observation in terms of a geometric mechanism, independent of physicochemical factors.Our hypothesis is that colloids can be trapped not just in throats between three grains, but also in gaps between pairsof grains. The occurrence of appropriately sized gaps in model soils, represented by computer generated denserandom packs of mono-dispersed spheres, is large enough to trap a considerable number of colloids. A geometricanalysis of throats and gaps in the model soils was combined with a new methodology to compute flow rates in gaps.The results were input to an existent straining theory to study the dependence of straining rate on colloid size. The



analysis suggests that straining in a gap cannot be treated correctly without reference to the throat associated with thegap. A purely geometric argument gives a reasonably accurate prediction of the scaling of straining rate with particlesize. Refining this argument to account for flow distribution within a throat and associated gaps improves the prediction.

219. Colloid Retention in Porous Media: CFD Flow Field Modelling in Colloid TrajectorySimulations in Porous Media with Particular Consideration of Grain to Grain Contact

Marcin M. Niewiadomski1, Cynthia L. Rakowski2, Marshall C. Richmond2 and William P. Johnson1, (1)University ofUtah, Salt Lake City, UT, (2)Pacific Northwest National Laboratory (PNNL), Richland, WA

Colloid retention in porous media in the presence of an energy barrier to deposition is strongly influenced by wedgingwithin the grain to grain contacts and retention in flow stagnation zones. Development of accurate near-surface flowfields for colloid transport simulation is challenging, especially in grain to grain contact zones due to the finediscretization required. This paper presents generation of a volumetric 3-D mesh for computational fluid dynamics(CFD) and simulation of the fluid flow field. Simulated colloid trajectories will be compared between the CFD-generatedflow field and semi-analytical solutions for the flow field. These simulations will also be compared to experimentalresults for colloid retention in the presence of an energy barrier.

220. Dynamical arrest in clay suspensions - From Wigner glasses to viscoelastic phaseseparationAndrey Shalkevich, Anna Stradner, Suresh K. Bhat, Francois Muller and Peter Schurtenberger, University of Fribourg,Fribourg, Switzerland

We have systematically investigated the phase diagram of clay particles in water in order to understand the relationbetween the local and macroscopic properties and the structure of clay suspensions. We focused in particular onsodium Cloisite (CNa) particles at concentrations from 1 wt% to 4 wt%, and at an extended range of ionic strengths (10-5 to 10-2 M NaCl). The suspensions have been characterized using rheology and a combination of scatteringtechniques (neutrons, x-rays, light). We were able to demonstrate the existence of a liquid cluster phase at low clayand intermediate salt concentration, and obtained new insight into the nature of the solid-like dispersions at low andhigh ionic strength. In particular we were able to unambiguously demonstrate the existence of an arrested phase at lowconcentrations and ionic strength that corresponds to the Wigner glass predicted on theoretical grounds for suchsystems.

221. Minimal Models for Understanding Protein CrystallizationSanat K. Kumar and Hongjun Liu, Columbia University, New York, NY

The crystallization of proteins is a topic of great interest since the availability of macroscopically large crystalsrepresents almost the only means available to characterize native protein structures by scattering techniques. Twodecades of experiments have shown an extremely simple phenomenology describes this crystallization process:proteins crystallize if their second virial coefficients fall in a very small band [“crystallization slot”]. Since such universalbehavior has been observed it appears reasonable that simple models, such as spheres interacting through isotopicinteractions, are sufficient to understand these situations. We have employed a series of computer simulations to studythe validity of this simple model in describing protein crystallization: the results of this investigation will be discussed inthis talk

222. Proteins as model colloids exhibiting short-range attractions - The interplay betweenspinodal decomposition and glass formation

Frédéric Cardinaux1, Thomas Gibaud2, Anna Stradner2 and Peter Schurtenberger2, (1)Heinrich-Heine-UniversitätDüsseldorf, Düsseldorf, Germany, (2)University of Fribourg, Fribourg, Switzerland

Proteins interacting via a short-range attractive potential have been shown to serve as ideal model systems to study theinfluence of such an attraction on the equilibrium and non-equilibrium phase behavior of colloidal suspensions. Theirsize of only a few nm, their monodispersity, and the possibility to tune the attractive well depth simply by temperature,



make these proteins ideal for such studies. Here we report on a critical re-examination of the different scenariosproposed for the interplay between phase separation and dynamical arrest in colloidal suspensions. We have usedaqueous solutions of the globular protein lysozyme as a model system for colloids with a tunable short-rangedattraction. We were able to demonstrate that temperature quenches into the spinodal region and below an arresttemperature lead to the formation of a bicontinuous network, where the dense phase undergoes dynamical arrest onceit reaches the glass line at this temperature. Microscopically, this corresponds to a coexistence of a dilute fluid with adense percolated glass phase. Finally, deep quenches below the glass line result in the formation of a homogeneousglass phase. These measurements have allowed us for the first time to quantitatively locate the glass line in theunstable region below the spinodal, and thus provide a new test ground for computer simulations and theoreticalcalculations in the current attempt to understand and generalize dynamical arrest in soft matter.

223. Direct in-situ characterization of beta-hairpin peptide self-assembly into a hydrogelnetworkTuna Yucel, Joel P. Schneider and Darrin Pochan, University of Delaware, Newark, DE

In aqueous solution, MAX 1 peptide [(VK)4VDPPT(KV)4] is unfolded, freely soluble and does not self-assemble.However, the peptide intramolecularly folds into a beta-hairpin conformation when the electrostatic interactions betweencharged lysine residues are screened, through increasing the ionic strength at neutral pH. Beta-hairpin moleculesintermolecularly assemble via hydrophobic collapse and hydrogen bonding into a 3-D hydrogel network, consisting ofwell-defined fibrils on the nanoscale. Self-assembly triggered in cell-culture medium leads to rigid and shear thinninghydrogels, while the stiffness of the network recovers quickly when the stress is removed. Moreover, the hydrogels arecytocompatible, showing future prospects for biological applications such as injectable 3-D cell encapsulants. Bycombining the results of circular dichroism spectroscopy, cryogenic transmission electron microscopy, dynamic lightscattering, and oscillatory rheology, we observe that the self-assembly proceeds by nucleation of monodisperse beta-sheet fibrils, that elongate and branch to form clusters of fibrils. Assembly kinetics at this early stage indicates powerlaw growth with assembly time, similar to diffusion-limited clustering of clusters. Eventually, clusters of fibrils fill up thesample volume, and interpenetrate to form a percolated network, as evidenced by the increasing network rigidity. Theearly stage assembly process will be discussed and compared to published gelation models. Ultimately, our goal is tocorrelate the structural growth mechanism with in vitro cell function and response.

224. Rate of structural arrest in nanocolloidal suspensions undergoing gelation and aging

Hongyu Guo1, Subramanian Ramakrishnan2, Brian Chung1, Charles F. Zukoski3, James L. Harden4 and Robert L.Leheny1, (1)Johns Hopkins University, Baltimore, MD, (2)Florida State University, Tallahassee, FL, (3)University ofIllinois, (4)University of Ottawa, Ottawa, ON, Canada

We report a combined x-ray photon correlation spectroscopy (XPCS) and rheometry study of the evolution ofconcentrated suspensions of nanometer-scale colloids undergoing gelation and aging. The suspensions are comprisedof silica colloids, 45 nm in diameter, coated with octadecyl-hydrocarbon chains in decalin. At high temperatures thechains form a solvated brush that stabilizes the colloids. At low temperature, the brush collapses leading to a weak,temperature-dependent, short-range attraction between the colloids that drives a reversible ergodic to nonergodictransition in the suspensions. Following a quench through this transition, the shear modulus grows exponentially with atime constant that depends strongly on temperature. XPCS measurements following such a quench characterize theevolution of the intermediate scattering function at wave vectors corresponding to interparticle length scales. Theintermediate scattering function displays two features, a plateau value that provides information about constrained localdynamics in the suspensions and a terminal relaxation time that provides information about relaxation of residual stress.Both the plateau value and the terminal relaxation time increase exponentially following the quench with a timeconstant that closely matches the value for the growing shear modulus. Thus, a comparison between XPCS andrheometry indicates how the arrest of the particle-scale dynamics correlates with the growth in elasticity. Further, acomparison of intermediate scattering functions for suspensions with colloidal volume fractions ranging from 0.20 and0.43 shows a qualitative variation in the temporal evolution that indicates a crossover from gel-like to glass-likedynamical arrest with increasing volume fraction.

225. Using Triggered Gelation of Responsive Microgel Dispersions to Restore theMechanical Properties of Degenerated Soft Tissue



Brian R. Saunders and Tony Freemont, The University of Manchester, Manchester, United Kingdom

An interesting challenge for colloid chemists is to design injectable materials that enable the minimally-invasive repair ofdamaged, load-bearing tissue. A key criterion for these materials is that they must be able to support biomechanicalloads. Degeneration of the intervertebral disc (IVD) is a major cause of chronic low back pain. Microgel particles arecross-linked polymer colloid particles that swell in a good solvent. We hypothesised that a concentrated dispersion ofpH-responsive microgel particles that contained high carboxylic acid concentrations would give an injectable fluid at lowpH that would change to a gel at body pH capable of supporting loads similar to those experienced by IVD tissue in thebody. In this work model pH-responsive poly(EA/MAA/BDDA) (ethylacrylate, methacrylic acid and butanediol diacrylate)microgel dispersions were used to investigated this hypothesis. The pH-triggered swelling of the particles wasinvestigated using photon correlation spectroscopy and rheology. Strong pH-triggered particle swelling and fluid-to-geltransitions of the microgel dispersions occurred at pH values greater than 6.0 (Fig. 1a). The fluid-to-gel transition wasalso triggered within IVDs after injection of the microgel into model degenerated spinal units (Fig. 1b). Uniaxialcompression data for degenerated IVDs containing injected microgel dispersions showed that pH-induced particleswelling restores the mechanical properties of the IVDs to normal (non-degenerated) values. This work demonstrates anew general approach that has long-term potential to restore the mechanical properties of damaged load-bearingtissue.

226. Event-driven simulations of primitive models of Silica and Water: analogies betweengel-formation in patchy colloidal particles and glass-formation in network forming liquidsCristiano De Michele, Università di Roma "La Sapienza", Roma, Italy

Recently we developed a novel algorithm for simulating hard objects of arbitrary shape, decorated on their surface withspherical sites, that interact through an attractive step potential. Using this new algorithm, we simulated two recentlystudied primitive models of network forming liquids — a primitive model for water and for silica. We evaluated theisodiffusivity lines in the temperature-density plane to provide an indication of the shape of the glass transition line.Except for large densities, arrest is driven by the onset of the tetrahedral bonding pattern (i.e. the bonding energycontrols arrest) and the resulting dynamics is strong in Angell's classification scheme. Notably patchy colloidal particlesof new generation may designated to closely resemble the primitive models of Silica and Water, thus it is intriguing tothink that this arrest mechanism driven by bonding energy, at low volume fractions, is the same that controls the gelformation, entitling us to call glasses all arrested states, including the gel states.

227. Investigating complex fluids using a Quartz Crystal MicrobalanceSimon Biggs and Christopher Hodges, University of Leeds, Leeds, United Kingdom

Complex fluids are widely used in personal care products, where the bulk fluid is usually made of many components(non-ionic and ionic surfactants, long chain polymers, perfumes and sometimes nanoparticulates). These componentsform a fluid that is usually highly viscous. There are very few techniques that are capable of discerning both theinterfacial adsorption and the bulk properties at the same time. One possible way to access these properties is to use aQuartz Crystal Microbalance (QCM). A modern QCM can measure both the frequency response and the energy lost(the dissipation) from a laterally vibrating quartz crystal [1]. The QCM is highly sensitive to both the bulk fluid properties[2] and to any adsorption that may take place at the QCM crystal surface [3] and is thus ideally suited to complex fluidsadsorption. It is possible to monitor the changes in fluid response in real time such that the kinetics may be obtained.We will present data showing how the QCM responds to (a) non-adsorbing viscous fluids, (b) specifically adsorbingviscous fluids and (c) viscous micellar fluids that are not unlike the basis for many commercial products. These resultsare dependent on (a) the adsorption taking place and (b) whether slip is occurring at the crystal-fluid interface or not.

[1] Rodahl M. and Kasemo B., Rev. Sci. Instrum. 67 (9) 3238 (1996) [2] Kanazawa K.K. and Gordon J.D. II, Anal. Chim.Acta 175 99 (1985) [3] Webber G.B., et al., Farad. Discuss. 128 193 (2005)



228. Deposition and characterization of soluble surfactant along the solid-vapor interfaceusing an evaporative dip coating techniqueBenjamin K. Beppler and Stephen Garoff, Carnegie Mellon University, Pittsburgh, PA

The structure of a cationic surfactant deposited from an evaporating thin film onto a hydrophilic, anionic substrate wasinvestigated using atomic force microscopy (AFM) and imaging ellipsometry. A vertical substrate is receded fromsolution above a critical pulling speed, entraining a thin film on the substrate. The convective flow field near a contactline typical of sub-critical withdrawal is replaced by benign plug flow in the wedge-like film. Confinement of surfactantmolecules in this constantly thinning film environment results in a non-trivial arrangement of molecules along the solid-liquid and liquid-vapor interfaces into island self-assemblies (typically ~ few µm in lateral extent) along the solid-vaporinterface. AFM measurements show the heights of these assemblies are quantized in units consistent with the length ofthe surfactant molecule, beginning with a bilayer. Increasing the film residence time alters the distribution of theseheights and eventually causes dewetting patterns devoid of islands to appear along the interface. Island coverageincreases with pulling speed and soak time prior to recede, independent of film residence time. Switching the solute-substrate electrostatic interaction from attractive to repulsive by using an anionic surfactant does not inhibit islandformation, proving this technique could potentially be used to deposit a wide range of molecules.

229. Alternative Surfactant Characterization Method Using the Hydrophilic-LipophilicDifference (HLD)

Anuradee Witthayapanyanon1, Edgar Acosta2, Jeffrey H. Harwell1 and David A. Sabatini1, (1)University of Oklahoma,Norman, OK, (2)University of Toronto, Toronto, ON, Canada

Microemulsions have received widespread attention for industrial applications due to desirable low interfacial tensionand high solubilization properties. These unique characteristics can only be achieved at the optimum condition wherean equal balance between the surfactant-oil and surfactant-water interactions is obtained. The easiest way to attain theoptimum condition is by a proper surfactant selection. Thus, several empirical approaches (i.e. hydrophilic-lipophilicbalance (HLB), phase inversion temperature (PIT) or Winsor R-ratio etc.) have been proposed as convenient tools forcharacterize surfactants. Although, these existing methods provide an approximate estimation of the hydrophilic-lipophilic nature for most surfactants, they have some serious limitations. Recently, they have been proven inadequatefor characterizing a newly developed class of surfactants known as extended surfactants. Therefore, the goal of thisproject is to develop an alternative indicator for characterizing extended surfactant. This new indicator is named as asurfactant characteristic parameter or a sigma parameter (R) of the hydrophilic-lipophilic difference (HLD). Preliminaryresults show a nice correlation between the sigma value and the hydrophilicity and lipophilicity of conventionalsurfactants. Furthermore, the sigma parameter method has also proven applicable for characterizing the hydrophilic-lipophilic nature of extended surfactants.

230. Quantification of bioparticle adhesion to polyamides with atomic force microscopyB. Reginald Thio and Carson Meredith, Georgia Institute of Technology, Atlanta, GA

We present an update of a modified atomic force microscopy (AFM) technique for the measurement of adhesion forcesbetween synthetic polymers and bioparticulates implicated in asthma and indoor air pollution. We believe this wouldallow us to better understand the mechanisms by which bioparticles are entrained in man-made carpeting andupholstery. Polymers employed in our study were Nylon 6, Nylon 6,6, polyamide 12 and polystyrene (as a control). Wefirst describe the use of three previous models for interpreting AFM force-distance data and calculating work ofadhesion. We also discuss a square-pyramid-flat-surface (SPFS) model framework developed for calculating Hamakerconstants. We find that the SPFS model yields the most reliable estimates of contact radius. This model is applied tocalculate Hamaker constants for bioparticle-polymer interactions: E. coli with those of ragweed (A. artemisiifolia) andthe black mold (A. niger). Results of relative Hamaker constants between these three bioparticles and the four polymerswill be discussed in terms of their chemical surface features.

231. Polarization of Electrodes by Doped Nonpolar MediaJames Hoggard, Dennis C. Prieve and Paul J. Sides, Carnegie Mellon University, Pittsburgh, PA



While double-layer repulsion of charged particles in water is well known, even nonpolar solvents with a dielectricconstant as low as two can contain charged ions; and particles immersed in nonpolar liquids can be electrostaticallystabilized. Electric current versus time was measured between two flat plate electrodes 2.5cm x 7.5cm separated by 1.2mm of heptane doped with 0-15% w/w poly(isobutylene succinimide) (PIBS) having a molecular weight of about 1700.The initial current yields the specific conductance of the solution whereas the initial rate of decrease in current yieldsthe Debye length of the solution. Thus we deduced Debye lengths of 30-170 nm which decrease with increasingconcentration of PIBS. Values of the Debye lengths were confirmed by performing independent measurements ofdouble-layer repulsion using TIRM. The charge carriers appear to be inverted PIBS micelles, having a diameter of 40nm, containing a substantial amount of solubilized water. About 25% of these micelles have a single plus or minuscharge, independent of concentration of PIBS.

232. Characterization of Nano- and Microdispersions using Multisample AnalyticalCentrifugation: Interparticle Forces, Deformability and Particle SizeTorsten Detloff, Titus Sobisch and Dietmar Lerche, L.U.M. GmbH, Berlin, Germany

The behavior of nano- and microdispersions, i.e. stability, flow, separation, packing behaviour, particle size distributionand particle deformability are of fundamental importance for the application of the dispersions in diverse fields. Thepresent work reports on the use of multisample analytical centrifugation for the investigation of packing, compression,demixing behavior and particle size distribution to characterize dispersed systems in the nanometer and micrometerrange. The new multisample approach uses the STEP-technology. Space and time resolved extinction profiles quantifythe alteration of particle concentration and packing behavior during centrifugation. The sedimentation kinetics of rigidnon-interacting particles (2 to 50 % v/v) can be exactly described by the phenomenological equations and thecorresponding flux density function, and exhibits the so-called type I and type II sedimentation. The packing density,obtained after compression, is related to the total interparticle potential energy. By using different additives interactionbetween particles can be shifted from nearly hard sphere behavior to strong attraction which results in flocculatedsystems. Additional information is obtained about the strength and elasticity of particle networks by analyzing therelative change in sediment volume after increasing/decreasing the excess pressure in multiple cycles. The paperfurther covers the determination of the particle size distribution from space and time extinction profiles for dispersions,with monomodal, multimodal and broad particle size distributions. An approach to account for effects of hinderedsettling and multiple scattering in concentrated dispersions is presented. Experimental results from concentratedsuspensions and emulsions will be compared with those of other measurement techniques.

233. NMR as a tool to measure directly the Surface Area of Nanoparticulate DispersionsDavid Fairhurst, Xigo Nanotools LLC, Morganville, NJ and Terence Cosgrove, University of Bristol, Bristol, UnitedKingdom

The need to determine the surface area of materials is well established; it influences many aspects of productperformance. The most widely employed technique is that of (BET) gas adsorption but it is only useful for analyzing drypowders. However, the overwhelming majority of manufactured products, including nanoparticulate systems, involvesuspensions of particulate materials in some fluid, either in the final state or at some stage of their production. Gasadsorption is not well suited to such systems; drying takes time and will promote aggregation. We describe arevolutionary instrument designed to measure the surface area of nanoscale particles or droplets dispersed in a liquid.This new (patent pending) technique is based on nuclear magnetic resonance (NMR) and it offers many advantages incomparison with conventional surface area instrumentation. The technique is based on the fact that liquid in contactwith, or “bound” to, the surface of a particle behaves differently from that of the bulk or “free” liquid. The NMR relaxationtime of bound versus bulk liquid is markedly different: the relaxation time of the latter is much longer. No assumptionsneed to be made about the sample particle (distribution) or shape in the determination of the surface area; it ismeasured directly. Suspensions and emulsions can be measured non-invasively, without dilution. The upper limit inconcentration is essentially unlimited; the lower limit is about 1-2%. The theory underpinning this new approach tosurface area measurement will be discussed and examples given to illustrate its wide applicability.

234. Keynote: Directional interactions with patchy colloidsABSTRACT WITHDRAWN



Abstract not available

33. Keynote: Self-assembly of soft spheresRandall D. Kamien, University of Pennsylvania, Philadelphia, PA

We propose a heuristic explanation for the numerous non-close-packed crystal structures observed in various colloidalsystems. By developing an analogy between soap froths and the soft coronas of fuzzy colloids, we provide ageometrical interpretation of the free energy of soft spheres. Within this picture, we show that the close-packing ruleassociated with hard-core interaction and positional entropy of particles is frustrated by a minimum-area principleassociated with the soft tail and internal entropy of the soft coronas. We find that the A15 lattice, known to be areaminimizing, is favored for a reasonable range of model parameters and so it is among the possible equilibrium statesfor a variety of colloidal systems. We extend these ideas to diblock copolymers and find new, stable sphere-likephases.

235. A surface resonance renders opaline photonic crystals ineffectiveFlorencio Garcia-Santamaria, Erik C. Nelson and Paul V. Braun, University of Illinois at Urbana-Champaign, Urbana,IL

In this work we identify and study the presence of extremely intense surface resonances that frustrate the coupling ofphotons to photonic crystals for crucial ranges of energy. The practical utility of photonic crystals demands the ability toexchange photons with the external medium, therefore, it is of paramount importance to acknowledge the presence ofthese surface resonances and eliminate them. Moreover, we demonstrate that these resonances lie in the regions ofphotonic band gaps for two important photonic crystal structures that include the widely used artificial opals. This hasled others to conclude that the structures they were investigating were functioning well as photonic crystals when infact the optical properties being measured were due to surface resonances and not the bulk photonic properties. Wedemonstrate that by modifying the surface geometry it is possible to tune the optical response or eliminate theresonances to enable full exploitation of the photonic crystal properties.

236. Fluid-bicontinuous emulsions stabilized by colloidal particlesEva M. Herzig, Paul S. Clegg, Andrew B. Schofield, Michael E. Cates and Wilson C.K. Poon, Edinburgh University,Edinburgh, United Kingdom

Using controlled spinodal decomposition, we have created bicontinuous emulsions stabilized by interfacially jammedcolloidal particles (Fig.1). The colloids, silica modified to yield partial wettability, are initially dispersed in the single-fluidphase. The sample is warmed (in the case of water-lutidine) into the two-fluid phase. The colloids become trapped onthe newly created interface; as the fluid domains coarsen the amount of interface decreases and the colloids jamtogether arresting phase separation. The arrangement of domains reflects the demixing kinetics: warming through thecritical point leads to a bicontinuous structure. (Structures can also be created via an upper critical point which weillustrate using silica colloids in alcohol-oil mixtures). We will present fluorescence confocal microscopy studies showingthe arrangement of domains, the stabilization by interfacial colloids over many weeks, and the changes in structure withboth sample composition and warming rate. We will give preliminary indications of the mechanical properties (Fig.2).Our results demonstrate that by varying the fluid composition systematically, and hence the demixing kinetics, anemulsion inversion occurs where the bicontinuous soft-solid is found at the inversion point.

Figure 1. A fluid-bicontinuous structure stabilized by silica colloids (white) imaged by fluorescence confocal microscopyat 40C. The two fluid domains (black) are water-rich and lutidine-rich respectively. The scale bar is 100mm.

Figure 2. An ~8mm long copper wire supported against gravity by a fluid-bicontinuous gel. The wire remained in placefor the duration of the study (several days); this demonstrates that the colloid-stabilized structure has a significant shearmodulus.



237. Segregation of Defects at Grain BoundariesAhmed M. Alsayed, University of Pennsylvania, Philadelphia, PA and Arjun G. Yodh, University of Pennsylvania,Philadelphia, PA

Interstitial impurity segregation at grain boundaries plays an important role in materials properties such as cohesion,grain growth kinetics, and transport. Unfortunately, direct measurement of grain boundary composition is difficult in bulkcrystals and polycrystals. In this contribution we directly study impurity segregation at grain boundaries using a modelcolloidal crystal. The polycrystals are made of temperature-sensitive micron size NIPA microgel particles. We add 100-200 nm fluorescent polystyrene particles to this system to model interstitial impurities. The impurities are then trackedusing video microscopy close to and far from the grain boundaries. We find that impurities hop from one position toanother and diffuse anisotropically when far from the grain boundaries and they diffuse isotropically in the grainboundaries. Upon increasing the temperature, the packing volume fraction of NIPA particles decreases and grainboundaries start to melt. We also explored the effects of the segregated impurities on grain boundary melting.

238. Segregation and Self-Assembly of a Polydisperse Suspension of Colloidal Particles viaDielectrophoresisPrasad S. Sarangapani and Y. Elaine Zhu, University of Notre Dame, Notre Dame, IN

Control of colloid segregation and self-assembly is important for inkjet printing, precision coating, synthesis ofnanoporous materials, and a variety of other modern technologies. We explore the method of dielectrophoresis tocontrol the interaction of micro/nano-colloids in AC electrical fields and assemble them from a suspension into newclasses of colloidal crystals and membranes. By tuning the frequencies of imposed AC fields on polydisperse silicamicro/nano-spheres, we are able to effectively segregate particles with a size ratio of 5:2:1 and tailor 3-D self-assembled structures, while monitoring the assembly process via confocal microscopy. Using high-speed fluorescenceimaging we also explore the mechanisms behind the AC colloid-dipole polarization and the multi-dipole interaction thatdrives the assembly of colloidal crystals.



239. Mechanics of deformable colloids: Elastic moduli of cross-linked Pickering emulsiondrops

James K. Ferri1, Nikolce Gorevski1, Andreas Fery2 and Philippe Carl2, (1)Lafayette College, Easton, PA, (2)MaxPlanck Institute for Collids and Interfaces, Golm, Germany

Growth in nanotechnology provides motivation for a comprehensive understanding of the strength of materials down tonanometer lengths.

We describe a new experimental technique, colloidal probe atomic force microscopy (AFM) combined with reflectioninterference contrast microscopy (RICM), and accompanying theoretical framework for the mechanical characterizationof soft materials with nanometer thickness; i.e. two dimensional continua. As a model system, a Pickering emulsiondroplet consisting of perfluorooctane/water/Cow pea mosaic virus nanoparticles.

The emulsion droplets are compressed via the colloidal probe tip of the AFM, the deformed drop shape is reconstructedby RICM. To determine the elastic behavior of the material, equations of equilibrium are used to describe the shape ofthe membrane in terms of the applied force, the contact radius and the membrane elastic parameters; the elasticparameters of the material are then found by adjusting their values in the model until a minimum in the error betweentheory and experiment is achieved.

Non-crosslinked nanoparticle monolayers display the behavior consistent with an aqueous/oil interface, i.e. constanttension with increasing strain. When nanoparticles cross-linking is introduced on the surface, the material displays aninitial region of linear elasticity for low deformation. For small surface strains, the surface elastic parameter is constantat approximately 0.7 N/m. As the strain increases further, the elastic parameter decreases, which indicates a loss ofstructure for higher, albeit small, deformations.

240. Keynote: Scattering from Colloidal Gels and MicrogelsDavid A. Weitz, Harvard University, Cambridge, MA

The results of light scattering measurements from colloidal gels and microgels will be reported. These measurementsprovide insight into the dynamics and structures of these systems. I will describe recent results that help determine thenature of the gelation process and the relationship of the properties of the gels to the control parameters used in theirformation. These stuctures are good models for stability of dispersions.

241. Probing Colloidal Dynamics with Diffuse LightFrank Scheffold, Fribourg University, Fribourg, Switzerland

We discuss some recent advances in multiple light scattering probes, or Diffusing Wave Spectroscopy, applied tocolloidal systems: the DWS Echo technique allows recording the full intensity autocorrelation function with a singleexperimental setup. This is achieved by putting a fast rotating diffuser in the optical path between laser and sample.We show that the recorded (multi-speckle) correlation echoes provide an ensemble averaged signal that does notrequire additional time averaging. We will further discuss applications of this technique in DWS microrheology and wewill present a new experiment that allows monitoring the drying of a colloidal thing film with high resolution.

242. Speckle-visibility spectroscopy study of bubble rearrangements in a coarsening foamDouglas J. Durian, University of Pennsylvania, Philadelphia, PA and Alex S. Gittings, UCLA, Los Angeles, CA

Speckle-Visibility Spectroscopy is a dynamic light scattering technique capable of resolving fluctuating or unsteadydynamics. Here we use it to study in detail the nature of bubble rearrangements in a coarsening foam. In particular wemeasure the statistical distribution of event durations, speeds, and time between events. By constrast, usual methodsyield only the average time between events.

243. Temporal heterogeneity and spatial correlation of the slow dynamics of soft glassymaterials



Luca Cipelletti1, Agnès Duri2, David Sessoms3 and Veronique Trappe3, (1)University of Montpellier 2 and CNRS,Montpellier, France, (2)Deutsches Elektronen-Synchrotron (Hasylab), Hambourg, Germany, (3)University of Fribourg,Fribourg, Switzerland

We investigate the dynamics of a variety of jammed soft materials, including strongly attractive colloidal gels,concentrated surfactant phases, and charged platelets (Laponite). By using Time Resolved Correlation, a time-resolveddynamics light scattering technique, we show that, quite generally, the dynamics of these systems are stronglyhetergogeneous in time, suggesting that they relax through discrete rearrangement events.. We measure the size of therearrangement events using a novel space- and time-resolved light scattering method: quite surprisingly, we find thateach event affects a volume much larger that the size of the system's constituent (particles or clusters). This finding isin stark contrast with simulations and experiments on supercooled fluids, where spatial correlations of the dynamicsextend over a few particles at most.

244. Time and space resolved measurements of dynamical heterogeneities in coarseningfoams

David Sessoms1, Hugo Bissig1, Veronique Trappe1, Agnes Duri2 and Luca Cipelletti2, (1)University of Fribourg,Fribourg, Switzerland, (2)University of Montpellier, Montpellier, France

We investigate heterogeneities in the dynamics of coarsening foams by performing both time and space resolveddiffusing wave spectroscopy experiments. In the transmission geometry, we record the speckle pattern in the far fieldusing a CCD-camera and process the images using the Time Resolved Correlation scheme [1]. In the backscatteringgeometry, we record the speckle pattern at the exit plane of our scattering cell and process the images by calculatingthe degree of correlation for different areas of the CCD-image. This latter technique allows us to construct spatiallyresolved maps of the instantaneous dynamical activity of our foam and to follow its temporal evolution. Our resultssuggest that the local intermittent rearrangements of bubbles typically observed in microscopy are not the only causefor dephasing the scattered light. When the internal stress imbalances, that gradually build up as the foam coarsens,become large enough, an event occurs that leads to a displacement of bubbles in a large portion of the sample. Thismajor event appears to effectively release the internal stress imbalances.

[1] L. Cipelletti, H. Bissig, V. Trappe, P. Ballesta, S. Mazoyer, J. Phys.: Condens. Matter 15, 257 (2003).

245. Time-resolved light scattering characterization of turbid colloidal suspensions and gelsChristian Moitzi, Hugo Bissig, Anna Stradner, Frank Scheffold and Peter Schurtenberger, University of Fribourg,Fribourg, Switzerland

To characterize the structural and dynamic properties of (soft) materials, information on the relevant mesoscopic lengthscales is required. Such information is often obtained from traditional static and dynamic light scattering (SLS/DLS)experiments in the single scattering regime [1]. In dense systems, such as colloidal suspensions and gels, however,these powerful techniques frequently fail due to strong multiple scattering of light. Here we review some of the recentadvances in light scattering from turbid fluid- and solid-like media that include 3D cross-correlation experiments tosuppress multiple scattering [2] and echo diffusing wave spectroscopy [3] to access dynamic and static properties ofextremely turbid media. We in particular focus on a novel multi-angle light scattering instrument that fully implementsthe 3D cross correlation scheme and thus allows for time-resolved measurements on turbid suspensions. We show thatthis technique provides access to the initial stage of aggregation and cluster formation in concentrated and turbiddestabilized colloidal suspensions.

References: [1] F. Scheffold and P. Schurtenberger, “Light scattering probes of viscoelastic fluids and solids”, SoftMaterials 1, 139-165, (2003) [2] Frank Scheffold, Andrey Shalkevich, Ronny Vavrin, Jérome Crassous, and PeterSchurtenberger, “PCS Particle Sizing in Turbid Suspensions: Scope and Limitations”, "Particle Sizing andCharacterization", ACS Symposium Series 881, T. Provder and . Texter, Eds., pp 3 - 32 (2004) [3] P. Zakharov, F.Cardinaux and F. Scheffold, "Multi-speckle diffusing wave spectroscopy with a single mode detection scheme", Phys.Rev. E, 73, 011413, 2006

246. Keynote: Polyelectrolyte-colloid coacervation: meso- and macro-phase separation in



polycation-micelle systems

Paul L. Dubin1, Anil Kumar1, Michael Hernon1, Yajuan Li1 and Werner Jaeger2, (1)University of Massachusetts,Amherst, MA, (2)Fraunhofer-Institut fur Angewandte Polymerforschung, Golm, Germany

Observable states for the polycation-anionic/nonionic mixed micelle system PDADMAC-SDS/TritonX-100 include:soluble complexes, liquid coacervates, and precipitates. The corresponding transitions were studied as a function of[SDS]/{[SDS]+[TX100]} = Y, temperature (T), ionic strength (I) and polycation MW. Phase separation (at Tφ) is inducedby an increase in T, a decrease or increase in Y or I, and is favored by high MW. At fixed I, the Tφ -Y boundarycomprises: (A) a coacervation domain exhibiting an LCST, and (B) a superimposed precipitation or high-densitycoacervation domain. Region A is symmetrical around 0.2<Y*<0.6 where charge-neutralized complexes/aggregates areat incipient phase separation. In region B (high Y) the dependence of the phase boundary on I, MW and Cp isconsistent with polycation collapse and counterion expulsion. Coacervates formed in region A, which were found toundergo further phase separation at Tφ' (> Tφ) , were characterized by turbidimetry, light scattering and rheology, withthe following results: (1) Microphase separation along elongational shear lines is seen at (Tφ'-T)=2oC - 8oC, wherecoacervates are shear-thinning. (2) Coacervates display a dominant slow mode in DLS which increases as temperaturerises above Tφ', along with a low-intensity temperature-independent fast mode corresponding to nearly free micellediffusivity. (3) At T ca. 2-3oC above Tφ', a plateau appears in shear stress vs. shear rate curves. The results areconsistent with mesophase separation within the coacervates driven by the entropy of counterion release. Theenhancement of this process by shear is not yet fully understood.

247. Interfacial polyelectrolyte structures for tunable high capacity protein uptake

Andy Kusumo1, Hongchen Dong1, Jinyu Huang1, Qiao Lin2, Krzysztof Matyjaszewski1, Tomek Kowalewski1, JamesW. Schneider1 and Robert D. Tilton1, (1)Carnegie Mellon University, Pittsburgh, PA, (2)Columbia University, New York,NY

Surface-bound polyelectrolyte structures are being designed for tunable protein uptake from solution. SPRmeasurements indicate at pH 6 poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes end-grafted from goldsurfaces by atom transfer radical polymerization (ATRP) adsorb net-negatively charged bovine serum albumin (BSA) toan extent equivalent to 10 BSA monolayers. The adsorbed BSA mass per unit volume in the brush is comparable to itsaqueous solubility limit in some cases. BSA uptake scales linearly with the surface concentration of grafted PDMAEMA,regardless of the degree of polymerization and grafting density for all brushes examined; BSA is bound at a constantratio of 120 DMAEMA monomer units per BSA molecule. The adsorption is electrostatically driven. Desorption ispossible only by manipulating the pH and/or ionic strength to weaken the electrostatic attraction. Net positively chargedlysozyme is completely rejected by the brush. Quantitative structure-activity relationships between protein size andelectrostatically driven uptake in PDMAEMA brushes will be discussed. If instead of a brush, a lightly crosslinkedPDMAEMA hydrogel is attached to the surface, both the binding kinetics and the extent of BSA uptake are diminished.BSA binding occurs at > 1000 DMAEMA units per BSA. This is attributed to the inability of crosslinked PDMAEMAchains to adequately reconfigure to accommodate bound BSA. Lastly, current efforts to copolymerize PDMAEMA withmore hydrophobic segments in order to achieve thermally programmable protein uptake will be described.

248. Solution behavior of rod-like polyelectrolyte-surfactant aggregates formed throughpolymerization of wormlike micellesDaniel M. Kuntz and Lynn M. Walker, Carnegie Mellon University, Pittsburgh, PA

The solution behavior of a rod-like, water-soluble, polyelectrolyte-surfactant aggregate system (pC16TVB) is detailed.These aggregates are generated by in situ polymerization of a cationic-hydrotrope wormlike micelle system. A featureof the system is the fact that the monomer groups and the surfactant are present in ion pairs in the absence of addedsalts or counterions, so the stoichiometry (with respect to charge) is 1:1 for the aggregates. Therefore, afterpolymerization the surfactant acts as the counterion for the polyelectrolyte chains as other counterions (salts) are notavailable. Despite being present in a 1:1 molar ratio, the aggregates are surprisingly stable in water (concentrations >600 mg/mL). Structural analysis shows that the polyelectrolyte chain is trapped in a cylindrical “tube” formed by thesurfactant. As such, the amount of surfactant present in the “tube” impacts the conformation adopted by the confined



polyelectrolyte chain and the aggregate as a whole. The aggregate length can be adjusted by removing or addingsurfactant and disrupting the 1:1 molar ratio. A simple model for the structure is presented and the ability to manipulatethe aggregate structure demonstrated.

249. Properties and applications of surfactant and polyelectrolyte gels

Yakov Lapitsky1, Tasneem Zahir1, Molly S. Shoichet1 and Eric W. Kaler2, (1)University of Toronto, Toronto, ON,Canada, (2)University of Delaware, Newark, DE

Oppositely charged surfactants and polyelectrolytes undergo associative phase separation when mixed in near-stoichiometric ratios. In recent years this phenomenon has been exploited to form ordered gel-like assemblies, whosestructure ranges from spherical particles (1 – 4000 µm in diameter) to cylindrical fibers and planar sheets. The stabilityof these materials depends on the equilibrium phase behavior of the surfactant and polyelectrolyte mixture, while theirstructure is governed by the method of their preparation. Here, we discuss the performance of these materials incontrolled release and tissue engineering applications: namely, the encapsulation of aromatic oil (cymene) for fragrancerelease and cell guidance for regenerative medicine. Surfactant and polyelectrolyte gel particles release aromatic oilsinto both aqueous and organic receiving solutions, with rates determined by the solubility and diffusivity of the oil in thegel matrix. Likewise, cylindrical surfactant and polyelectrolyte gel fibers prepared from biocompatible components canact as cell-adhesive scaffolds that guide cell growth.

250. Influence of protein on surfactant self-assembly in oil/water mixturesJun Y. Kim and Prof. Stephanie R. Dungan, University of California, Davis, CA

Proteins and surfactants coexist in biological and industrial systems, and have the potential to interact due toelectrostatic, steric and hydrophobic interactions. As a result, protein molecules may alter the interfacial energy ofsurfactant monolayers, and thereby modify the phase behavior of surfactants. It is particularly interesting to study self-assembly in equivolume mixtures of oil and water, in which the surfactant is free to form various nanostructures,depending on the spontaneous curvature of the monolayer. Using SAXS, we have found that small amounts of thewater-soluble, globular protein alpha-lactalbumin markedly alter phase morphologies of the surfactant AOT:transforming spherical water-in-oil (w/o) microemulsion droplets to large w/o ellipsoids, to inverted oil-in-water droplets,and to liquid crystalline and gel-forming structures. As the protein to surfactant ratio increases, the aspect ratio of thestructures also increases, and self-assembly shifts from the organic to aqueous phase. In the presence of the proteinthese morphologies are tuned by protein charge and ionic strength, with the protein/surfactant interaction nowapparently controlling the self-assembly. More subtle effects of protein on phospholipid self-assembly are alsoobserved, and suggest a significant role for molecular architecture.

251. Reversible aggregation of polyvinyl caprolactam in aqueous solutions above andbelow the lower consolute temperatureQiang Qiu, Unilever Research, Trumbull, CT, Larry Senak, International Specialty Products, Wayne, NJ and Brian A.Pethica Sr., Princeton University, Princeton, NJ

Poly vinylcaprolactam (PVCL) is completely soluble in water at temperatures below the lower consolute temperature(LCST) of ~32oC, above which a stable, non-sedimenting cloudy state is formed. Silica dispersions in PVCL solutionsare stable below the LCST, but rapid reversible flocculation and sedimentation occurs on raising the temperature abovethe LCST. Adsorption of PVCL to silica dispersions, as measured by the classical depletion method, is massivelyincreased above the LCST, rising steeply with polymer concentration. The large adsorption and associated flocculation(which appears as an adsorption from the depletion method) are both reversed on lowering the temperature below theLCST. PVCL is known to form aggregates above the LCST . A further study of PVCL in aqueous solution by GPC, DLSand MALLS over a range of temperatures across the LCST for two molecular weight PVCL preparations has beenmade. The results indicate some aggregation below the LCST, rapidly increasing with temperature as the phaseboundary is crossed . Above and near the boundary, the aggregates are polydisperse, becoming monodisperse as thetemperature is raised further. Aggregation reaches a maximum, falling off at the highest temperatures studied. Forexample, aggregates formed in a 3000ppm solution of a 70K PVCL preparation reach a maximum hydrodynamicdiameter of 1500nm at 40oC. The loss of PVCL from solution due to adsorption/flocculation observed with silicasuspensions above the LCST increases linearly with concentration with an approximately constant fraction of the added



polymer remaining in the supernatant.

252. Keynote: Particle-Assisted WettingWerner A. Goedel, Chemitz University of Technology, Chemnitz, Germany

In principle, one might easily prepare thin polymer membranes by copying the float glass process, but instead of moltenglass, one might wet a water surface with a polymerizable oil, solidify and lift it off the water as a thin freely suspendedmembrane. However, few oils wet a water surface. This inability can not be overcome by adding most amphiphiles, butcan be by adding particles. In general, placing a particle into a liquid/liquid or liquid/air interface gives rise to a gain inenergy, which is largest if the interface-particle contact angle is close to 90 degrees. If oil-particle mixtures are appliedto a water surface, the oil might form wetting layers in which the particles penetrate through at least one of theinterfaces of that layer. Depending on the interfacial tensions and contact angles of these interfaces with the particles,one can draw phase diagrams of particle assisted wetting. We developed a simple theory describing this phenomenonand correlated it to experimental observations. Cross-linking the oil within the mixed layers indeed gives rise tomembranes comprising enbedded particles. Especially of interest are those membranes prepared using a volume of oilsufficient to fill the space between the particles, but not fully cover them. If in these membranes the particles areselectively removed, one is left with a microsieve: a membrane bearing sub-microscopic holes of uniform diameter andthinner than the hole size; thus offering a minimum flow resistance and optimum selectivity in filtration applications.

253. Inversion of an Abnormal Emulsion produced by Continuous Stirring. Effect of theFormulation on the Evolution of the Double Emulsion

Marianna Rondón-González1, Véronique Sadtler1, Lionel Choplin1 and Jean-Louis Salager2, (1)GEMICO, ENSIC-INPL, Nancy, France, (2)FIRP, Universidad de los Andes, Mérida, Venezuela

Emulsion inversion, which is the change in emulsion morphology from oil-in-water (O/W) to water-in-oil (W/O) or viceversa, is a handy alternative to produce fine and concentrated emulsions. It could result from the continuous stirring ofan abnormal emulsion, in which case the external phase is not the one favored by the surfactant affinity but the one inhigher volume proportion.

The inversion mechanism associated with continuous stirring often involves the formation of a multiple emulsion(w/O/W), in which a portion of the (W) external phase is continuously included as (w) droplets in the dispersed (O)phase drops. This inclusion is eventually opposed by droplet escape from the drops. When both phenomena are indynamic equilibrium, the inversion cannot take place, but if the inclusion dominates over the escape, the apparentvolume of the dispersed phase increases until a critical value is reached and the inversion is triggered.

In the nonionic-brine-kerosene system studied, the balance between the inclusion and escape is found to be affectedby the formulation (as the hydrophilic-lipophilic-deviation HLD) and by the alcohol concentration. The interfacecomposition influences the stability of both inner w/O and outer O/W emulsions, thus determining the kinetics ofinclusion and the stirring time required to trigger the inversion into the W/O final morphology.

254. The Validity of the Ward-Tordai Model to Describe Dynamic Surfactant Transportthrough Fluid/Fluid InterfacesC. J. Radke, University of California, Berkeley, Berkeley, CA

We compare the classic Ward-Tordai and the microscopic Smoluchowski models for the dynamics of surfactanttransport through fluid/fluid interfaces. The Smoluchowski model treats the interface as a free-energy field, whereas theWard-Tordai model treats the interface as an infinitesimally thin plane exhibiting adsorption and desorption kinetics.Equivalence of the two models is established when the free-energy well underlying surfactant adsorption is flanked bybarriers that are larger than thermal energy. When energy barriers are non-existent, however, a finite interfacial widthmust be introduced into the Ward-Tordai analysis to obtain physically meaningful results, i.e. non-negative desorptionrate constants. Recenty, we presented an experimental investigation into the adsorption dynamics of diblock copolymersto a polymer/polymer interface and found them to be well described by the Smoluchowski model. Here, we show thatthe experimental sorption dynamics are also captured by a finite-interfacial-width extension of the Ward-Tordai model,whereas the classical model fails to predict the observed behavior.



255. Measurement and Interpretation of Line Tension in a Liquid Lens System

Robert David1, Stephanie M. Dobson1, Saiedeh Tavassoli1, M. Guadalupe Cabezas2 and A. Wilhelm Neumann1,(1)University of Toronto, Toronto, ON, Canada, (2)University of Extremadura

Widely varying measured values of three-phase line tension have been reported in the literature. Experiments in solid-liquid systems are subject to uncertainty caused by surface roughness and heterogeneity. These difficulties are avoidedin liquid-liquid systems.

We report new measurements of the line tension of the dodecane-water-air system in the liquid lens configuration. Improved experimental technique produced better axisymmetry and equilibrium of the lenses than in past experimentsin our group. Using a new image processing algorithm (TIFA-AI), the liquid-vapour interfaces were fit to solutions ofthe Laplace equation, rather than polynomials, as before. Line tension of +1.11 μN was obtained for lens radii in themillimetre range.

We will discuss the interpretation of the data in terms of both the Neumann quadrilateral relation and an alternative,empirical formulation, which was derived from trends observed in the literature data.

256. Cylindrical Particles at Fluid Interfaces: Controlling Orientation and AssemblyEric Lewandowksi, Kathleen J. Stebe and Peter C. Searson, Johns Hopkins University, Baltimore, MD

The configurations and interactions of anisotropic micro- or nanoparticles at fluid interfaces depend strongly on theparticle geometry and the contact angle of the three phase contact line in the zero Bond number limit. Here we explorecylindrical objects at fluid interfaces. First, the equilibrium configurations of an isolated cylindrical object at a fluidinterface are described. We identify conditions in which the particle can assume either an end-on or a side-onorientation depending on the aspect ratio of the particle and the contact angle. The predictions compare favorably toexperiments in which functionalized gold nanorods are spread at aqueous-gas interfaces, immobilized using a gel-fixation technique, and observed by scanning electron microscopy. Second, the directed assembly of cylindricalparticles in a side-on configuration is studied. Since fluid climbs the end faces of the cylinders, zero-mean curvaturemenisci form at each end face. When menisci from different particles overlap, attractive capillary interactions arecreated that drive end-to-end chaining. Experimental observations of this chaining are presented. Third, the orientationand translation of cylindrical objects on curved interfaces are described; forces driving translation and torques drivingorientation are established that depend on the local curvature of the fluid interface. Video microscopy experiments andanalytic arguments are presented in which cylindrical objects are placed on (macroscopic) menisci formed by capillaryrise on a bounding surface. Particles on convex interfaces align perpendicular to the bounding surface, while particleson concave interfaces align parallel to the bounding surface.

257. Thermodynamic understanding of alkanes' solubility in surfactant hydrocarbon layers

Jan van Stam1, Sara Briscoe1, Bengt Kronberg1, Gunilla Carlsson1 and Mikael Björling2, (1)Karlstad University,Karlstad, Sweden, (2)University of Gävle, Gävle, Sweden

A crucial question concerning interfacial wetting phenomena is how an organic solvent interacts with a surfactant layer'shydrocarbon chains. This interaction will, as an example, influence the swelling of the surfactant layer and, hence, thecurvature of inverted w/o micelles. We have chosen to use chromatographic measurements to study the interactionsbetween solvents and surfactants. The retention time, obtained by HPLC measurements, will be a measure on thesolubility of the solvent in the hydrocarbon chain layer. From measurements of the retention time's temperaturedependence and analyzing both the shift in retention time and peak tailing, an adsorption isotherm can be calculated.Combining the experimental results with thermodynamic modeling opens for a molecular understanding of solvent-surfactant interactions.

258. Molecular insights into self-perpetuating conformational changes of prions andamyloidsPeter M. Tessier and Susan Lindquist, Whitehead Institute for Biomedical Research, Cambridge, MA



Protein conformational changes drive many biological processes. Few are as dramatic in terms of the structuralchanges that occur, or the biological consequences they produce, as those governing the formation of amyloid fibers.These highly ordered, beta-sheet rich structures were initially linked to several neurodegenerative disorders such asAlzheimer's disease, but more recently they have also been linked to normal biological functions such as cell adhesionand skin pigmentation. Prions represent a unique class of amyloid-forming proteins capable of switching to self-perpetuating conformations that are infectious and can be transmitted between different organisms. Several prions inthe yeast S. cerevisiae have been identified, including Sup35, a protein involved in translation termination. Utilizingvariants of this protein we find that several outstanding questions related to prion biology and the formation of amyloidscan be investigated using arrays of short, surface-bound peptides. In this presentation I will discuss the use of peptidearrays to identify small elements of amino-acid sequence within several prions that govern their self-recognition andconformational conversion. Remarkably, we find that these same recognition sequences also govern the ability of theprions to adopt not just one amyloid conformation, but a suite of related yet structurally distinct conformations, known asprion strains. Further, our results suggest a mechanism that explains the previously perplexing relationship between theabilities of prions to form specific amyloid conformations and to cross species barriers. In the future, peptide arrays mayenable the rapid analysis of the conformational conversion and assembly of other amyloid-forming proteins.

259. Solution Structure of an Amyloid-Forming Protein During PhotoreversibleOligomerization Revealed Through SANSAndrea C. Hamill, Shao-Chun Wang and C. Ted Lee Jr., USC, Los Angeles, CA

Fibril formation in Alzheimer's disease is believed to result from the formation of unstable, slightly-unfolded proteinconformations, resulting in a cascading aggregation process from monomers to oligomers to short filaments andeventually fully-developed amyloid fibrils. Recently, the prefibrillar intermediates have become viewed as the primarypathogenic species. To investigate amyloid intermediates we have developed two complementary approaches: a meansto induce changes in protein folding and association in a controlled and photo-reversible manner, and a method todetermine the in vitro conformation of associated proteins at relatively high resolution. These methods utilize theinteraction of proteins with photosensitive surfactants that can be switched “on” or “off” with light. Light can be used toreversibly bind the surfactant to the protein, leading to photocontrol of protein conformation. Shape-reconstructionanalysis applied to small angle neutron scattering (SANS) data is then employed to determine the conformation ofprotein oligomers. With the photo-actived surfactant, expanded corkscrew-like hexamers are observed. Converting tophoto-passive surfactant causes hexamers to laterally aggregate, forming dodecamers with twisted conformations thateventually result in fully-developed fibrils. Together, these results provide the first direct observation of the mechanismof formation of the key intermediates in amyloid fibril formation, which could provide unique insight into the amyloidosisdisease pathway.

260. Fibrillation kinetics of recombinant human insulin with osmolytes: experiments andkinetic modeling

Arpan Nayak1, Chuang-Chung Lee2, Mirco Sorci1, Amit Dutta1, Robert Grassucci3, Ingrid Hahn3, Joachim Frank3,Gregory J. McRae2 and Georges Belfort1, (1)Rensselaer Polytechnic Institute, Troy, NY, (2)MIT, Cambridge, MA,(3)Wadsworth Center and Howard Hughes Medical Institute, Albany, NY

Amyloid fibrillation is the process of native soluble proteins misfolding into insoluble fibrils comprising of cross-â-sheetsand has received wide attention due to its substantial physiological relevance and the complexity of the underlyingphysical and chemical reactions. At present, more than 20 amyloidogenic diseases including Alzheimer's disease,Parkinson's disease, and prion–associated encephalopathies have been found to share fibril formation as the commoncause. Here, we investigate the influence of dissolved osmolytes (sugars) on the kinetics of insulin fibrillation. In thepresence of sugars, the fibrillation process (both the lag-time and the rate constant to form fibrils) is delayed andappears to correlate with the heats of solution at infinite dilution thereby supporting a preferential exclusion mechanism.With the recent focus on circular protofibrils and the suspicion that they may be toxic during amyloidosis, we haveconducted a series of exploratory experiments during the lag phase when protofibrils are thought to be formed. This hasincluded the use of small angle neutron scattering, sucrose gradient centrifugation, and cryo-electron microscopy toinvestigate the kinetics of protofibrils formation. We also present a mathematical mechanistic model that simulates thephenomena by incorporating the physical chemistry of nucleation and growth dynamics. Estimated by nonlinear leastsquare algorithms, we find rate constants that account for the ubiquitous sigmoidal responses of amyloidogenic proteins



when they misfold.

261. Structural characterization of polyelectrolyte-protein coacervates by DLS and neutronscattering

A. Basak Kayitmazer1, Paul L. Dubin1, H. Bohidar2, Yajuan Li1, Christophe Tribet3, Sergey Vasenkov4, ShengqinWang5 and Jiang Zhao5, (1)University of Massachusetts, Amherst, MA, (2)Jawaharlal Nehru University, New Delhi,India, (3)ESPCI, Paris, France, (4)University of Florida, Gainesville, FL, (5)Chinese Academy of Sciences, Beijing,China

Polyelectrolytes in the presence of oppositely charged small colloids may exhibit soluble complex formation orprecipitation, but an intermediate state of hydration involves the formation of a macroion-rich second liquid phase.These dense, optically clear and often viscous coacervates exhibit unusual rheological and transport properties, inparticular colloid translational diffusivities that are remarkably large given the large macroscopic viscosities. Forcoacervates of a protein (BSA) with polycations, dynamic light scattering and neutron scattering both provide evidenceof mesophase separation on the scale of a few hundred nm, a phenomenon also consistent with the results from anumber of other techniques (Cryo-TEM, rheology, FRAP, PFG-NMR and FCS). Marked differences between protein-polyelectrolyte coacervates and micelle-polyelectrolyte coacervates correspond to different types of mesophases. In thecase of polyelectrolyte-protein coacervates, coacervate properties and stability are strongly influenced when chitosanreplaces PDADMAC, a synthetic polycation with the same structural charge density but smaller persistence length. Forchitosan-BSA coacervates, SANS clearly indicated the presence of a fractal structure in the range q<0.06 (1/nm).Possible origins of mesophase structures will be discussed.

262. Development and evaluation of realistic microbioassays in freely suspended dropletson a chipVinayak Rastogi and Orlin D. Velev, North Carolina State University, Raleigh, NC

We present a new biomolecular detection technique performed in microliter droplets freely floating on the surface ofperfluorinated oil. The droplets are captured and transported by dielectrophoresis using an electrode chip submerged inthe oil. Each droplet serves as a container where microbioassays are performed using the process of agglutination ofantibody-coated particles in the presence of analyte. Evaporation leads to the rapid collection of particles in the topportion of droplets. The results are read out by the pattern of unaggregated gold nanoparticles collected on the dropletsurface (see Figure). We demonstrate and discuss two formats of microbioassays - GOAgg (Gold Only Agglutination)and GLAgg (Gold Latex Agglutination). The performance of these microbioassays was evaluated by varying analyteconcentration, particle concentration and size, number of antigen binding sites per particle, incubation time and rate ofparticle collection. Microbioassays for Ricin were designed and their performance was compared to the standard handheld assays employed in biological defense. Our droplet microbioassays were found to be 10 times more sensitive interms of analyte concentration while requiring 100 times less sample volume. We developed a model for theagglutination kinetics and mass transfer process taking place within the droplets, which correlates well with theexperimental data. These results could facilitate the development of immunoassays on a chip requiring even smallersample volumes.

263. Optimizing the dispersion of DNA-linked aggregates at a fixed temperatureChristopher K. Tison and Valeria T. Milam, Georgia Institute of Technology, Atlanta, GA

The controlled assembly of micron to nano-sized colloids using DNA has generated great interest in the past decade;however, dispersion of these aggregates is currently achieved using temperature changes. By controlling the numberand affinity of duplexes between surfaces, weak, but complete particle aggregation is induced through primary



hybridization events. This aggregated suspension can then be redispersed through the addition of longer, competitivesecondary targets with greater propensity for duplex formation than the primary target. The efficiency of competitivehybridization events is based upon the length of both the primary and competitive targets, the concentration of DNAlinkages between particle surfaces, and the accessibility of the surface duplexes to the competitive target. To minimizethe number of DNA linkages while simultaneously allowing competitive targets greater access, a system was developedwhereby restriction endonuclease AluI clips non-hybridizing or diluent strands immobilized to the surface. This approachallows precise control on the surface coverage of active hybridizing probe while still obtaining the benefits of shorterdiluent strands with less steric hindrance. To the best of our knowledge, this study is the first to examine using DNAhybridization events to both aggregate and disperse colloidal particles at a fixed temperature.

264. Amphiphilic block copolymer surface modification of nanoscale zero valent iron (NZVI)for source zone DNAPL remediationKevin M. Sirk, Navid B. Saleh, Tanapon Phenrat, Hye-Jin Kim, Gregory V. Lowry and Robert D. Tilton, CarnegieMellon University, Pittsburgh, PA

Dense non-aqueous phase liquids (DNAPLs), such as trichloroethylene (TCE), are a persistent source of mobilecontamination at thousands of sites in the U.S. Current remediation technologies such as “pump and treat” only targetthe dissolved phase plume, leaving the majority of the source pollutant intact. Nanoscale zero valent iron (NZVI)particles have been shown to effectively dechlorinate TCE, but their poor colloidal stability and transport properties limittheir effectiveness as in situ treatment agents. Modifying the surfaces of these nano-iron particles could allow for anaggressive source-zone targeting approach that should expedite site clean and lower cleanup costs. Using atomtransfer radical polymerization (ATRP), we have synthesized poly(methacrylic acid)-b-poly(methyl or butylmethacrylate)-b-poly(styrene sulfonate) triblock copolymers as NZVI coatings. Adsorption of these triblock copolymeramphiphiles on NZVI significantly enhances NZVI colloidal stability. Using quartz crystal microgravimetry (QCM) andellipsometry, we monitor the adhesion of NZVI particles with several different block copolymer surface modifiers on tosilica under varying ionic strength conditions that mimic those found in groundwater. In addition to stabilizing colloidalsuspensions, the polymeric coatings effectively eliminate NZVI adhesion to silica. The effect of silica hydrophobizationon nano-iron adhesion will also be addressed to estimate the ability of the block copolymer coatings to promote NZVIadhesion on DNAPL (oil)/water interfaces.

265. Effects of the discrete Nature of Charge on the Behavior of Colloidal Particles inengineered and natural EnvironmentsPatricia L. Taboada-Serrano, Georgia Institute of Technology, Oak Ridge, TN, Sotira Yiacoumi, Georgia Institute ofTechnology, Atlanta, GA and Costas Tsouris, Oak Ridge National Laboratory, Oak Ridge, TN

Colloidal particles are ubiquitous in natural and engineered environments. Processes like filtration, deposition,aggregation, transport of colloidal particles and associated chemical species, phase behavior of colloidal suspensions,and organization of large biomolecules such as DNA are governed by colloidal interactions. Traditionally, theseinteractions have been described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. In the DLVO theory,colloidal particles are modeled as uniformly charged surfaces embedded in solutions containing non-interacting ions thatlack size. Although the DLVO theory can be applied to cases within certain restrictions, many deviations betweenexperimental observations and theoretical predictions have been reported in the literature. For example, it has beenreported that deposition and remobilization of colloidal particles takes place at conditions predicted as unfavorable bythe DLVO theory. The effects of lifting the DLVO theory assumption of continuous charge is examined via acombination of molecular modeling and atomic force microscopy in this work. The formation of the EDL, interactions ofapproaching EDLs, and development of surface charge in solutions containing symmetric and asymmetric electrolytesare investigated. Phenomena such as size exclusion effects, like-charge attraction, and surface charge heterogeneities,not predicted by the DLVO theory, were detected by just considering the discrete nature of surface charge and chargedistribution within the EDL. The occurrence of these phenomena provides a plausible explanation for the deviationsbetween theory and experiments reported in the literature.

266. Pore Scale Simulation of Colloid Transport in Porous Media with COMSOL Multiphysics

Mehmet E. Cakmak1, Yuniati Zevi1, Veronica L. Morales1, Daniel R. Fuka1, Bin Gao1, John L. Nieber2 and Tammo S.



Steenhuis1, (1)Cornell University, Ithaca, NY, (2)University of Minnesota, St Paul, MN

Governing mechanisms in immobilization and mobilization of colloids in the unsaturated zone are not well understood.Recent findings show that colloids attach to the air-water-solid (AWS) interface. The interaction of the various forcesand the flow field on colloids near the AWS interface is complex. In this presentation, we will determine the interactionforce conditions for attachment of colloids to the AWS for flow fields consisting of flow around solid grains in thepresence of and air-water system of fluids. The flow field is determined using COMSOL-MP to numerically solve theNavier-Stokes equations. The viscous drag force for the moving fluid on the colloids is then quantified from thisnumerical solution and the balance of this force with other field forces resulting from interfaces (solid-liquid and liquid-air) is computed to determine the potential for attachment of colloids to the AWS interface. For the present studyspherical solid grains are considered, while in future studies we will consider solids grains of more realistic shape.

268. Influence of Humic Acid on the Aggregation Kinetics of Fullerene (C60) Nanoparticles

Kai Loon Chen and Menachem Elimelech, Yale University, New Haven, CT

Buckminsterfullerene C60 is a nanomaterial with potential applications in the fields of optics, electronics, and biomedicalengineering. With the impending widespread utilization of fullerene in industrial and consumer products, fullerenepollution of natural aquatic systems may become a major concern. Under aqueous conditions, hydrophobic fullerenemolecules bind strongly together to form negatively charged fullerene nanoparticles. To better understand the fate andtransport of these nanoparticles in natural aquatic systems, we investigate their aggregation kinetics in the presence ofSuwannee River humic acid and common monovalent and divalent electrolytes. In the absence of humic acid, theaggregation behavior of the fullerene nanoparticles in the presence of sodium, magnesium, and calcium ions wasconsistent with the classic DLVO theory. In the presence of humic acid and sodium or magnesium ions, humic acidadsorbed onto the fullerene nanoparticles resulting in steric repulsion, which stabilized the nanoparticle suspension.This increase in the nanoparticle stability was similarly observed in the presence of humic acid at low calcium ionconcentrations. However, enhanced aggregation occurred at higher calcium concentrations. Light scatteringmeasurements and TEM imaging of the fullerene aggregate structures indicated that bridging of the fullerenenanoparticles and aggregates by the humic acid aggregates was the likely mechanism for the enhanced aggregation.

267. The role of colloids on the migration of air bubbles in porous mediaABSTRACT WITHDRAWN

The transport of colloids in subsurface environments has been investigated extensively in the last decade. Suspendedcolloids in soil water or groundwater can be contaminants themselves and/or can serve as carriers of sorbedcontaminants on them. The presence of air-water interface in porous media can be an additional consideration whenthe porous media is unsaturated. Therefore, the understanding the effect of air phase and colloid/air-water interfaceinteraction is needed to predict the movement of air phase and colloid transport in unsaturated porous media.

The movement of air phase in porous media can take place either as a continuous air phase or discrete air bubbles.However, the present research focused on continuous air phase assumption and mass balance equations of individualphases rather than taking into account the movement of air bubbles and colloid capture on discrete air-water interfaces.This study presents a pore-scale study to model the migration of discrete air phase in the presence of bio/solid colloidscaptured on air-water interface. The model is based on the pore-scale balance equation for forces acting on a bubblerising in a porous medium in the presence of colloids. A dimensional analysis of the phenomenon is also conducted toprovide a more generalized methodology to evaluate the effect of individual forces acting on an air bubble. Theresulting governing equation is solved to predict the rise velocity of bubbles under a variety conditions.

269. Precipitation and aggregation of ZnS nanoparticles in the presence of thiol ligandsHeileen Hsu-Kim, Duke University, Durham, NC

ZnS and other metal-sulfide nanoparticles are known to persist as intermediates during precipitation and dissolution oftheir respective mineral phases. However, the mechanisms that enable these nanoparticles to persist in surface watersand sediment porewaters are unknown. Humic substances and other hydrophilic organics can stabilize ZnSnanoparticles by adsorbing to particle surfaces and preventing aggregation. In this study, the stability of aqueous ZnS



nanoparticles was investigated by assessing the role of low-molecular weight organic ligands (oxalate, serine, cysteine,and mercaptoacetate) during precipitation of ZnS. Zn(NO3)2 and Na2S were dissolved (2 uM each) in laboratoryaqueous solutions buffered at pH 7.5 and containing organic ligands. Particle formation and size was monitored overtime by dynamic light scattering. Zn speciation was measured by anodic stripping voltammetry to confirm that Zn wascoordinated to sulfide during the aggregation experiments and was not in the form of dissolved Zn-organic complexes.The ZnS aggregate growth rates varied by orders of magnitude, depending on the type and concentration of organicligand in solution. Growth rates were slowest in the presence of thiol-containing ligands, cysteine and mercaptoacetate.In contrast, ZnS aggregation rates were generally not affected by oxalate and serine, which contain carboxylate andamine functional groups. Thermodynamic stability constants for Zn-thiol complexes are greater that those for the otherZn-organic complexes. Thus, slow aggregation of ZnS nanoparticles may be caused by specific attachment of the thiolon surface Zn sites. These results indicate that thiol-containing organics are important for stabilizing metal-sulfidenanoparticles in the aquatic environment.

270. Influence of surface oxides on the aquatic stability, mobility and sorption properties ofcarbon nanotubesBilly Smith Jr., Hyun Hee Cho, Mi Shin, Matthew Hickin, William Ball and Howard Fairbrother, Johns HopkinsUniversity, Baltimore, MD

Surface oxides may become incorporated onto the surface of a carbon nanotube (CNT) following exposure to oxidizingagents used in routine laboratory modification/purification strategies and water treatment processes. In aquaticenvironments, surface oxides are expected to alter not only the CNT's sorption characteristics towards organic andheavy metal contaminants but also the CNT's aquatic stability and transport properties. Oxidized CNTs may in fact actas a Trojan horse, facilitating the unwanted transport of priority contaminate species. Consequently, the effect ofsurface oxidation has potentially important environmental health and safety implications for carbon based nanomaterials.To investigate these issues, a suite of CNTs with different levels of surface oxidation were prepared by refluxing CNTsin HNO3 solutions of various concentrations; X-ray photoelectron spectroscopy (XPS) showed that the surface oxideconcentration increased from 3% for the pristine nanomaterials to 12.5% for CNTs treated in ~16M HNO3. Studiesconducted over a wide range of aquatic conditions have shown that well-defined relationships exist between the level ofCNT surface oxidation and their aquatic stability; specifically, more highly oxidized CNTs remain stable over a widerrange of aquatic conditions. As the level of surface oxidation increases, the sorption properties of CNTs also displayedsystematic variations: adsorption of 14C labeled-naphthalene decreased linearly while divalent heavy metalcontaminates like Zn2+ showed an increasing affinity towards more highly oxidized CNTs. Preliminary results will alsobe presented on the influence that surface oxides exert on the transport properties of CNTs.

271. Influence of Grain Size and Flow Rate on the Transport and Retention of C-60 Fullerenein Water-Saturated Soils

Yusong Li1, Yonggang Wang2, Linda Abriola1 and Kurt D. Pennell2, (1)Tufts University, Medford, MA, (2)GeorgiaInstitute of Technology, Atlanta, GA

Widespread production and application of manufactured nanomaterials will inevitably lead to the release ofnanoparticles into the environment. The current understanding of nanoparticle fate and transport in subsurfaceenvironments, however, is quite limited. In this work, we seek to advance our understanding of the transport andretention of C-60 fullerene (95 nm dia.) in water-saturated soils through a combination of experimental andmathematical modeling studies. A series of transport experiments was conducted at several pore-water velocities inglass columns packed with various size fractions of Ottawa sand. Effluent concentration and particle retention datawere simulated using a mathematical model that incorporated traditional filtration theory with rate-limited, nonlinearsurface blocking behavior. The numerical model successfully captured the characteristics of both the effluentconcentration and particle retention profiles. The experimental and simulation results suggest that C-60 fullerene particleattachment is strongly dependent on porous media surface area and flow rate. Simulated attachment capacityincreased with increasing specific surface area, and for a given sand size fraction, simulated n-C60 attachment rateswere greater at higher flow rates. Extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, incorporating van derWaals, electro-static repulsion, and hydrophobic interaction forces, was used to evaluate potential mechanismsgoverning C-60 attachment. This analysis suggests that a sizable energy barrier of about 22 kT exists between C-60fullerene particles and Ottawa sand surfaces and that there is a very small secondary minimum attraction region with



depth of 0.12 kT. Additional studies are being conducted to further elucidate the forces responsible for n-C60 particleretention.

272. Slow Dynamics in Biphasic Colloidal Glasses and GelsDouglas C. Viehman and Kenneth S. Schweizer, University of Illinois, Urbana, IL

Integral equation, simple mode coupling, and activated barrier hopping theories have been combined to study slowdynamics in “biphasic” binary mixtures composed of hard and sticky spheres of identical diameters. Under structuralequilibrium conditions the theory has been employed to investigate how the addition of repulsive particles modifies theideal gelation transition and elastic modulus, and how attractive particles perturb the vitrification of hard spheres. Thetotal volume fraction dependence of the shear modulus is significantly changed relative to its analogous one-componentbehavior. A two-dimensional nonequilibrium free energy controls particle displacements, and the associated transientlocalization lengths and barrier hopping processes have been studied as a function of mixture composition and stickycolloid adhesion strength and spatial range. Barriers for activated transport of the attractive and repulsive particles aregenerally very different, implying a strong dynamical asymmetry. The corresponding quenched porous media problemshave also been studied. Ideal colloidal glasses in porous media form at much lower total volume fraction than for theone-component hard sphere fluid. If the sticky particles are mobile in the quenched media, then very rich dynamicalbehavior is found. For example, mobile colloids may undergo an ideal glass transition, an ideal gel transition, or both.The signature of the latter behavior is a nonequilbrium free energy that acquires two local minima.

273. Cracking and collapse of vesicle depletion gelsMatthew L. Lynch and Tom Kodger, Procter & Gamble Company, Cincinnati, OH

The addition of polymer to a dispersion of vesicles can result in the formation of space spanning depletion gels.However, the density mismatch between the vesicles and the polymer solution results in a gravitational stress thatleads to the collapse (or compression) of the gels. We have created kinetic phase diagrams in which the rate ofcollapse was measured as a function of volume fraction of vesicles, polymer concentration and particle-polymerasymmetry. At short times, the rate of collapse is framed in terms of the linear poroelasticity which balances viscous,elastic and gravitational forces on the gel structure. Many of these gels, however, exhibit a curious “cracking” behaviorin which the gel structure fractures into layers, changing the paradigm altogether.

274. Highly oil-swollen Vesicle Gels with elastic Properties

Michael Gradzielski1, Claudia Oppel1, Jens Poppig1, Sylvain Prévost1 and Laurence Noirez2, (1)TechnischeUniversität Berlin, Berlin, Germany, (2)Laboratoire Léon Brillouin, Gif-sur-Yvette, France

Vesicle gels have been investigated that are based on mixtures of classical nonionic surfactants with small amounts ofionic surfactants. Their rheological properties are largely controlled by the relative content of ionic surfactant in themixture and the elastic properties go through a pronounced maximum for relatively low amounts of ionic surfactantcontent and depend in a systematic way on the total surfactant concentration. Depending on their composition theirelastic moduli are typically in the range of 50-500 Pa and they have a yield stress of 1-20 Pa. The vesicle gels studiedare able to solubilise large amounts of oils (up to more than 3 times the amount by mass of the surfactant) where thesolubility depends to a large extent on the polarity of the oil and on the relative charge density of the surfactant mixture.We varied systematically the polarity of the solubilised oil and it is interesting to note that the maximum solubility occursfor the most hydrophobic oils while it is much less pronounced for more polar oils. The structural characterisation ofthese oil-swollen vesicle gels was done by means of static and dynamic light scattering, small-angle neutron scattering,electric conductivity, NMR self-diffusivity and electron microscopy. The vesicles bilayers are first swollen but for higheroil content the structure of individual vesicles is transformed into a bicontinuous structure. It is interesting to note that inthat process no macroscopic phase separation takes place and also that the elastic properties are retained.

275. Characterization of a model van der Waals gel systemRyan C. Kramb and Charles F. Zukoski, University of Illinois Urbana-Champaign, Urbana, IL

Model colloidal systems in which the phenomenon of gelation can be studied by characterizing and varying the strength



and range of the interaction between the particles are not common. Those model systems that are well studied typicallyfall into one of three categories – 1) proteins, especially lysozyme, 2) particles experiencing depletion interactions, 3)and thermal gels composed of ocadecyl coated silica particles. However, in the vast majority of these systems the mostcommonly found force resulting in gelation – van der Waals forces, is typically negligible. Our objective is to create afourth model system to characterize the phase behavior, microstructure, and gel mechanics in which van der Waalsforces are the dominant cause of the gel formation. In our system, monodispersed polystyrene latex particles 200-600nm in diameter coated with the surfactant hexaethylene glycol monododecyl ether (C12E6) form gels throughreversible aggregation. Using these particles, we investigate the phase diagram as the back ground ionic strength israised. At very low ionic strengths the suspensions crystallize due to electrostatic repulsions. At intermediate ionicstrengths, the suspensions are fluids. At higher ionic strengths, the suspensions gel. The gels are reversible in that ifdiluted with an electrolyte solution of the same ionic strength and same surfactant concentration, the gels fall apart andsingle particles are observed. We report on the ionic strength-volume fraction gel line and the flow properties of thesuspensions approaching and within the gels. In addition we report on microstructures of the gels determined by smallangle neutron scattering.

276. Nanoparticle-Crosslinked Hydrogels as Separation and Ion Exchange MediaBani Cipriano, Peter Thomas and Srinivasa R. Raghavan, University of Maryland, College Park, MD

A study of the absorption of ionic solutes using a new class of polymeric hydrogels is reported here. These hydrogelsare crosslinked using clay nanoparticles instead of the traditional crosslinking molecules. Some unique features of theseclay crosslinked gels that distinguish them from their conventional counterparts include larger pore sizes and increasedmechanical integrity. In addition, these particle crosslinked gels can be used as ion exchange resins since theincorporation of clay nanoparticles introduces charges into the otherwise neutral polymer gel. In particular, these gelshave an extraordinary ability to soak up cationic solutes from solution due to the anionic surface of the clay platelets.Furthermore, the absorbed molecules bind preferentially around the surface of the gel, leaving the rest of the gel free ofbound species. In contrast to covalently crosslinked gels, these particle crosslinked gels can be disassembled in thepresence of certain organic solvents due to the non-covalent interaction between polymer and particles. Upondisassembly, these gels release the bound species which can be subsequently recovered. Finally, we describe ourefforts towards the separation of particles such as carbon nanotubes and colloidal silica by size. These separationscannot be achieved using covalently crosslinked gels since their pore size is much smaller than the size of the particlesof interest.

277. Applications of Scaling Theories and Exact Results to Colloids and PolyelectrolytesLesser Blum, Rutgers University, Piscataway, NJ and Melvin Arias, University of Puerto Rico, Rio Piedras, PR

Charged systems obey exact asymptotic relations. Excluded volume for each ion is needed. These are included in theMean Spherical Approximation, thus this theory is exact for dense systems. A method that interpolates between theMSA and the PY equation and is amazingly accurate for many systems (Blum Narten, J. Chem. Phys. 56, 5197(1972)). The switching was done at a distance s such that all distribution functions were continuous everywhere. In thepresent work we extend this theory to the general case of an arbitrary mixture of charged hard spheres, and obtain anexplicit analytical solution in terms of a few scaling parameters G : We use the new extended soft mean sphericalapproximation (ESMSA). (Blum Arias, J. Phys. Cond. Matt. 18, S2437,(2006), Mol. Phys. 104,3801,(2006) that alsosatisfies the low temperature and low density association limits.

In the ESMSA the closure of the Ornstein Zernike (OZ) equation near the excluded core region is divided in tworegions: For the inner region we can use an exponential closure, for example the Percus-Yevick (PY) or the contactpair correlation function as derived in the BIMSA-EXP approximation ( Bernard and Blum,J. Chem. Phys. 104,4746,(1996)). This leads to the correct exact limits of zero temperature and zero density. In the outer region far fromthe central ion we use the Mean Spherical Approximation (MSA) closure. An explicit solution is obtained from thecontinuity of the pair correlation function when the distances are additive. The thermodynamics and structure functionsare also discussed.

278. Mechanisms of assembly in nanoparticle based materialsFrancis W. Starr, Wesleyan University, Middletown, CT



The formation of clusters or specifically ordered structures is common to many materials. We will focus on someexample systems where simulations are able to help elucidate ordering mechanisms. First, we will discuss the origins ofparticle clustering in polymer-nanoparticle composites with highly symmetric nanoparticles. Our simulations emphasizethe importance of effective long-ranged polymer mediated interactions between nanoparticles that promote particleclustering without the intervention of phase separation. Next we discuss how a recent model for assembly of DNA-dendrimer molecules can be adapted to mimic the behavior of DNA-coated colloids that cluster due to "linker" DNA thatselectively binds the colloids. In this case, the concentration of linker DNA controls the number of bonds that a particlecan form, thereby offering the possibility to form clusters with a low coordination that inhibits phase separation. Lastly,we will discuss how the interactions between patchy colloidal particles can be modified to promoted the formation of gelstructures on heating.

279. Self-Assembled moth-eye antireflection coatings

Nicholas Linn1, Chih-hung Sun1, Bin Jiang2 and Peng Jiang1, (1)University of Florida, Gainesville, FL, (2)PortlandState University, Portland, OR

Part of the light incident on all transparent materials is reflected. This reflection arises from the abrupt change in therefractive index at the interface of two media. The cornea of some nocturnal moths has a structure with a repeatingpattern of less than 250 nm and a physical depth of less than 200 nm. These submicrostructured surfaces can greatlyreduce reflection, helping conceal the inset from hungry predators. We report a simple bio-inspired self-assemblytechnique for fabricating artificial moth-eye antireflective coatings. Non-close-packed colloidal crystals with remarkablelarge hexagonal domains are created by a spin-coating technology, which is based on shear-aligning colloidal silicaparticles suspended in non-volatile triacrylate monomers. The resulting polymer-embedded colloidal crystals exhibithighly ordered surface modulation and can be used directly as templates to cast poly(dimethylsiloxane) (PDMS) molds.Polymer (e.g., PMMA and polystyrene) and glass antireflective coatings can then be molded against PDMS usingtraditional polymerization and sol-gel technologies. The depth of the micropatterns can be adjusted by plasma-etchingof the original colloidal crystal-polymer nanocomposite. Using the above colloidal self-assembly and micromoldingtechniques, large-area (up to 8-inch diameter, limited only by the substrate size) moth-eye antireflective coatings havebeen created on both planar and curved substrates. The microstructured coatings exhibit much lower reflectivity thanbare films and the optical reflection matches with the theoretical prediction using effective medium theory.

280. Crystalline monolayers from convectively self-assembled non-spherical colloidsIan D. Hosein and Chekesha M. Liddell, Cornell University, Ithaca, NY

Self-assembly of submicron particles into colloidal crystal structures offers a rapid, tunable and scalable process forcreating spatially periodic templates for nano-fabrication, micro-lens arrays and photonic crystals. Theoreticalcalculations have shown that colloidal crystals from non-spherical particles could allow robust and complete photonicbandgaps to open at lower refractive index contrasts, allowing a wider range of materials to be accessible forfabrication. In the present work, 2D structures with a high degree of positional and orientational order from mushroom-cap, pear and peanut shaped colloids were fabricated via convective assembly. Structure-optical property correlationswere made using SEM and optical diffraction spectroscopy. The ordered assembly process will be explained withrespect to particle concentration, solvent surface tension at the drying front, and geometric packing efficiency. Thestructures were modeled using the diffraction grating equation. Structural phases were examined with thermodynamicmodels from Monte Carlo simulations. Transitions between isotropic and ordered phases were followed using thesimulated osmotic pressure versus density curve and by visualization of the equilibrated system from the simulations.

281. Shape Selectivity in the Assembly of Lithographically-Designed Colloidal Particles

Stephane Badaire1, Cecile Cottin-Bizonne2, Joseph W. Woody1, Allen Yang1 and Abraham D. Stroock1, (1)CornellUniversity, Ithaca, NY, (2)Université Claude Bernard Lyon 1, Villeurbanne, France

The formation of a diversity of structures via the assembly of colloidal particles is hindered by the paucity of availableparticles, the difficulty of attaining monodisperse samples, and the lack of tunable and selective interactions. We willpresent the development of a controlled colloidal system based on photolithographically-designed particles of well-defined size and non-spherical shape. We will discuss the fabrication and characterization of these particles and theformation of controlled dispersions. With state diagrams (see figure - volume fraction of depletant vs. ionic strength) we



will elucidate the role of DLVO and depletion interactions in defining a diversity of assemblies. Finally, we will presentcomparisons to theory and comment on the influence of surface roughness and steric stabilization in controlling theobserved phenomena.

282. Molecular Dynamics Simulation of Nanoparticle Self-Assembly at a Liquid-LiquidInterface

Mingxiang Luo1, Oleg A. Mazyar2, Qing Zhu2, Mark W. Vaughn2, William L. Hase2 and Lenore L. Dai2, (1)TexasTech Umiversity, Lubbock, TX, (2)Texas Tech University, Lubbock, TX

We have used molecular dynamics simulations to investigate the in-situ self-assembly of modified hydrocarbonnanoparticles (mean diameter of 1.2 nm) at a water-trichloroethylene (TCE) interface. The nanoparticles were firstdistributed randomly in the water phase. The MD simulation shows the in-situ formation of nanoparticle clusters and themigration of both single particles and clusters from the water phase to the trichloroethylene phase, possibly due to thehydrophobic nature of the nanoparticles. Eventually, the single nanoparticles or clusters equilibrate at the water-TCEinterface, and the surrounding liquid molecules pack randomly when in contact with the nanoparticle surfaces. Inaddition, the simulations show that the water-TCE interfacial thickness analyzed from density profiles is influenced bythe presence of nanoparticles either near or in contact with the interface but is independent of the number ofnanoparticles present. The nanoparticles, water molecules, and TCE molecules all exhibit diffusion anisotropy.

283. Co-Assembly of non-spherical colloids and nanoparticle depletantsTrina Ghosh Dastidar, Ian D. Hosein, Poorna Rajendran, Ulrich Wiesner and Chekesha M. Liddell, Cornell University,Ithaca, NY

Several frontiers in photon-atom interaction require the development of inexpensive fine-scale and structurally complexperiodic materials. For example, the crystal structure and shape/complexity of photonic crystal bases greatly influencesthe capability of the materials to exhibit superior electro-optic properties. The potential to alter the dynamics ofspontaneous emission processes has implications for the enhancement of photocatalytic reactions, which play animportant role in environmental remediation strategies, as well as for more efficient photovoltaic and solar cell devices.Here, we study self-assembly of non-spherical mushroom-cap shaped colloids into ordered photonic crystal structures,aided by fluorescent nanoparticle depletants. Core-shell nanoparticles (~30 nm in diameter) consisting of the organicfluorophore tetramethylrhodamine isothiocyanate (TRITC) encapsulated in a silica shell were co-assembled withpolystyrene non-spherical particles using a convective approach. Colloidal phases were determined as a function of theconcentration ratio of nanoparticles to non-spherical colloids. The modification of dye emission characteristics due tochanges in the local density of photon states was explored in the reduced symmetry photonic crystal system (based onmushroom-cap basis) and compared with similar effects in a simple sphere based photonic crystal.

284. Shear-aligned assembly of colloidal photonic crystalsPeng Jiang, University of Florida, Gainesville, FL



A versatile spin-coating technique for assembling wafer-scale colloidal photonic crystals, along with a large variety offunctional nanostructured materials has been developed. The methodology is based on shear-aligning concentratedcolloidal suspensions using standard spin-coating equipment. It enables large-scale production of both 3D and 2D non-close-packed colloidal crystals as well as a wide range of nanostructured materials including 3D ordered polymernanocomposites, macroporous polymers, nanohole arrays, metallic surface gratings, attoliter microvial arrays, 2Dmagnetic nanodots, metallic pyramid arrays, and more. The spin-coating platform is compatible with standardsemiconductor microfabrication, enabling parallel production of micropatterns for potential device applications. The spin-coating process also provides a new route to study the fundamental aspects of shear-induced crystallization, meltingand relaxation. Different from simple shear flows in conventional shear cells, the flow in the spin-coating process isinherently non-uniform. The application of assembled periodic nanostructures as surface-enhanced Raman scattering(SERS) substrates will also be discussed.

285. Stability characterisation of nanoparticles DispersionHelene Dihang, Formulaction, L'Union, France and Jim Munhall, Sci Tec, Worthington, OH

The applications of nanoparticles in the industry are getting more and more important and concern many different fields(drug delivery, nanotubes, screen technologies, etc.). In the last decades a vast amount of scientific research has beendeveloped to improve the understanding of these complex dispersions. Using a scientific approach and new analyticaltechniques, it is now possible to control and tailor properties of suspensions and to get a better understanding of timebehaviour. Following this idea, stability measurements, which were commonly done by simple visual observations, cannow be performed automatically via an optical device.

This instrument is based on Multiple Light Scattering (MLS) and is associated to a vertical scanning of the sample. It islike a high resolution electronic eye, enabling to identify and quantify instability phenomena before they are visible tothe operator (5 to 50 times earlier than the naked eye). Physical parameters and kinetics can be computed in order tofacilitate and improve comparisons between formulations. Moreover, it is possible to use the information contained inthe MLS signal to extract parameters such as particle mean diameter without the need of dilution, as often required withdiffraction techniques based on single scattering models. This measurement can be done on the finished product or, inreal time, during the process.

286. Trichloroethylene remediation using nanoscale Fe/silica aerosol particlesTonghua Zheng, Jingjing Zhan, Jibao He, Gerhard Piringer, Gary L. McPherson, Yunfeng Lu and Vijay T. John,Tulane University, New Orleans, LA

We describe a novel assisted aerosol process to prepare porous silica particles containing nanoscale zerovalent ironwhich is a reactive species for the reduction of trichloroethylene (TCE). The environmentally benign silica particlesserve as effective carriers for nanoiron transport through soil. Encapsulation of iron into submicron silica particlesprotects ferromagnetic iron nanoparticles from aggregation, and increases their mobility through sediments. Additionally,the presence of surface silanol groups on silica particles makes it possible to control surface properties via silanolmodification using organic functional groups. Aerosol silica particles with functional groups such as ethyl tails on thesurface preferentially absorb hydrophobic TCE during environmental remediation. This increases the local concentrationof TCE in the vicinity of iron nanoparticles, thus promoting the degradation of TCE by iron. These nanoscale iron/silicaaerosol particles with controlled surface properties can be efficiently applied for in-situ remediation and permeablereactive barriers construction.

287. Nano-emulsion preparation by low energy methods: studies on optimization and scale-up

E. Beltran1, C. Pey1, A. Maestro1, C. Gonzalez1, Conxita Solans2 and J.M. Gutierrez1, (1)University of Barcelona,Barcelona, Spain, (2)IIQAB, CSIC, Barcelona, Spain

Nano-emulsions are a class of emulsions with fine droplet size. Nano-emulsions with smaller droplet size can presentan aspect similar to microemulsions, but, as fundamental difference, nano-emulsions are not thermodynamically stable,and, because that, their characteristics will depend on preparation method. In the so called low energy methods, finedispersion is obtained by chemical energy resulting of phase transitions taking place through emulsification path. The



adequate phase transitions are produced by varying the composition at constant temperature or by varying thetemperature at constant composition, phase inversion temperature method (PIT). In present work, an experimentalstudy about the influence of preparation variables, addition rate and agitation velocity, on nano-emulsions obtained byvarying composition method by water addition is carried on. The study is applied to two different systems with water ascontinuous phase: Brij30/Brij97 as surfactants and isopropylmiyristate as oil; and span20/tween20 as surfactants andliquid pararaffin as oil. Mean diameter of droplets is determined by dynamic light scattering. Preparation is carried out attwo different scales, 0.1 a 1.0 L, and in each experiment water addition rate and agitation velocity are fixed followingexperimental designs. Results are fitted to give mean diameter of nano-emulsion droplets as a function of significantterms of preparation variables. For small scale there is an optimum agitation velocity, while the lower the addition ratethe smaller droplet diameter. For 1.0 L scale droplet diameter is smaller than for smalls scale and does not presentsignificant variations with preparation variables.

288. Surface forces measured between gold surfaces coated with self-assembledmonolayers of thiols and xanthates in waterRoe-Hoan Yoon, Jan Christer Eriksson and Jialin Wang, Virginia Tech, Blacksburg, VA

Many investigators measured the forces between two hydrophobic surfaces in water, and observed long-rangeattractions that were stronger and longer-ranged than the van der Waals attractions. Some believe that the strongerattractions are due to structuring of water in the vicinity of hydrophobic surfaces, while others believe that they arecaused by nano-bubbles or by the correlation of mobile charged patches (or domains). The latter mechanism is possiblewhen using ionic surfactants that can physisorb and form mobile patches of self-assembled monolayers. In the presentwork, AFM force measurements were conducted between gold surfaces coated with chemisorbing hydrophobizingreagents such as n-alkane thiols and n-alkane xanthates. The equilibrium water contact angles of the treated surfaceswere in the range of 66 and 105o. In most cases, the force vs. distance curves exhibited long-range attractions withdecay lengths in the range of 16.5 and 26.0 nm. The force curves were smooth and showed no discontinuities (orsteps), excluding the possibility of nano-bubbles being responsible for the long-range attractions observed in thepresent work. Based on the results obtained in the present work, possible origins of the long-range attractions will bediscussed.

289. Nano-emulsion preparation by the phase inversion composition method (PIC) in thecationic system W / oleylammonium chloride - oleylamine - C12E10 / hexadecane

Isabel Solè1, Carmen Gonzalez1, Alicia Maestro1, J.M. Gutierrez1 and Conxita Solans2, (1)University of Barcelona,Barcelona, Spain, (2)IIQAB, CSIC, Barcelona, Spain

Nano-emulsions are a type of emulsions with droplets of very small diameter (20-500 nm). They are used in manydifferent applications related to chemical, pharmaceutical, and cosmetic fields. Their preparation methods can beclassified in two types: the dispersion or high-energy methods, in which mechanical energy is required to form them;and the condensation or low-energy methods, which make use of the phase transitions that take place during theemulsification process. In the present study, the low-energy emulsification method phase inversion composition (PIC)has been used to prepare nano-emulsions in the system W / oleylammonium chloride - oleylamine - C12E10 /hexadecane by addition of chlorhidric acid solutions in the mixtures formed by water, oleylamine, C12E10 andhexadecane. In this way, the oleylammonium formed along the emulsification path acts as the cationic surfactant. Theresults obtained, in terms of phase diagrams and nano-emulsion characteristics, are compared with those obtained inthe system with oleate as anionic surfactant and oleic acid as a cosurfactant. This study has been done in order toextend the application range of the ionic nano-emulsions, not only in anionic systems, but also in cationic ones.

290. Effects of Aggregate Structure on Gelation and Mechanical Properties of Silane-basedSol-gel CoatingsSaran Poovarodom, Jiong Liu and John Berg, University of Washington, Seattle, WA

Silane-based sol-gel coatings are commonly used as adhesion promoters. It is desirable to enhance the mechanicalproperties of these materials by reinforcing them with nanoparticulates, particularly oxide particles. Aggregation of thereinforcing particles is often associated with poor mechanical properties of the material. In this study, we evaluate the



effect of the degree of aggregation of reinforcing oxide particles on the mechanical properties ofglycidoxypropyltrimethyloxysilane (GPS) sol-gel coatings. The degree of aggregation is controlled by adjusting thesurface electronic properties of the particles using tetrasodium pyrophosphate (TSPP), which specifically adsorbs to theparticle surfaces. It is found that at small degree of aggregation (naggregate < 50 primary particles), there is only anegligible effect on the gel mechanical properties. However, large, loose aggregates caused by a more rapidaggregation leads to incoherent coatings with numerous cracks. This is a result of the participation of the oxideparticles in the GPS gel network. Therefore, the structure of the gel formed is regulated by the structure of the oxideaggregates present. Large, loose aggregates lead to a formation of a weak, low-density gel that is susceptible tocracking during the drying process and poor mechanical properties.

291. A mathematical approach to calculate the precision and relative differences of variousrelationships available to determine the surface tension of polymeric materialsSamad Ahadian, Siamak Moradian and Mohammad Amani Tehran, Amirkabir University of Technology, Tehran, Iran

The surface tension of polymeric materials commonly varies in the range 20-50 mJ/m2. Knowing this fact, the contactangles of 31 polymeric materials were varied with four probe liquids (i.e. diiodomethane, formamide, glycerine andwater) in 1 mJ/m2 increment in the mentioned range by the aid of the equation of state (i.e. Neumann's equation). Allthe 11 possible 2, 3 and 4 combinations of the liquid mixtures were used. The obtained contact angles were thenemployed to calculate the corresponding surface tensions using different approaches such as the Owens/Wendt, theharmonic mean, the van Oss et al. and the combined mean relationships. Additionally, the differential forms of thementioned relationships were used to rank the precision of each approach. The results illustrated that the relativedifferences between the predicted surface tensions obtained from each approach as compared to the equation of statewere strongly dependant on the liquid system used. The predicted surface tensions calculated by the Owens/Wendt,the harmonic mean, the van Oss et al. and the combined mean relationships were generally lower than thecorresponding values as calculated by the equation of state for low values of surface tension. This behavior wasinversed for the upper range of surface tension. Furthermore, the precision ranking of these relationships were in theorder of the equation of state> the harmonic mean> the combined mean> the Owens/Wendt> the van Oss et al.

292. NanoTextured Surfaces for the Sensing and Manipulation of Colloidal Scale Objects inMicroscale Flow

Ranojoy Dipak Duffadar1, Jeffrey M. Davis1 and Maria Santore2, (1)University Of Massachusetts, Amherst, Amherst,MA, (2)University of Massachusetts,, Amherst, MA

Selective tuning of the sizes, surface densities, and chemistries of 10-nanometer scale heterogeneities on planarsurfaces that interact with colloidal objects in shear flow allows control of the adhesion of the colloidal particles.Motivated by the need to develop artificial pattern recognition constructs for microfluidic sensor applications, systemshave been developed that exhibit tunable dynamic behavior on renewable surfaces, which allows colloidal objects to bedistinguished by their characteristic adhesion signatures and rates. Adhesion is reversible in a substantial portion ofparameter space, and surface features can give rise to particle skipping and rolling on the surfaces. These dynamicsare captured by a new model that incorporates both hydrodynamic forces on the particles and the spatially varyingphysicochemical interactions between the particles and heterogeneous surfaces. The adhesion is governed by thematching of the length scales of the patch spacing and the interactive surface area between the particle and surface,which is reminiscent of pattern recognition, although the patch distribution on the collector is random. Spatialfluctuations in the patch density are shown to play a critical role in the dynamic adhesion and rolling behavior (e.g.,allowing adhesion on a net-repulsive surface), which prevents this behavior from being predicted by a mean-fieldapproach. This talk highlights new developments in the experimental and modeling efforts and focuses on thefundamental dynamics of particle interaction with these sensing surface features in shear flow at low Reynolds number.

293. Imaging Energy Landscapes with Concentrated Diffusing Colloidal ProbesPradipkumar Bahukudumbi, Gregory E. Fernandes and Michael A. Bevan, Texas A&M University, College Station, TX

The ability to locally interrogate interactions between colloidal particles and energetically patterned surfaces providesessential information to design, control, and optimize template directed self-assembly processes. Although numerous



techniques are capable of characterizing local physicochemical surface properties, no current method resolvesinteractions between colloids and patterned surfaces on the order of the thermal energy kT, which is the inherentenergy scale of equilibrium self-assembly processes. In this talk, we describe video microscopy measurements and aninverse Monte Carlo analysis of diffusing colloidal probes as a means to image three dimensional free energy andpotential energy landscapes due to physically patterned surfaces. In addition, we also develop a consistent analysis ofself-diffusion in inhomogeneous fluids of concentrated diffusing colloidal probes on energy landscapes, which isimportant to the temporal imaging process and to self-assembly kinetics. Results of Monte Carlo and BrownianDynamics simulations will also be reported to verify the analysis and interpretation of experimental findings. Extensionof the concepts developed in this work suggest a general strategy to image multi-dimensional and multi-scale physical,chemical, and biological surfaces using a variety of diffusing probes (i.e. molecules, macromolecules, nanoparticles,colloids).

294. Coulomb Interactions in a Non-Polar ColloidSunil K. Sainis and Eric R. Dufresne, Yale Univeristy, New Haven, CT

We directly measure the electrostatic interaction between isolated pairs of microspheres (PMMA-PHSA) in solutions ofsurfactant (NaAOT) in oil(hexadecane). At high surfactant concentrations, we find the familiar screened Debye-Huckelform. However, at low concentrations of surfactant, we see an unscreened Coulomb potential. Our measurementsextract the particle charge and solvent ionic strength. We also study the particle charge as a function of bead size.

295. Effective interactions between like-charged colloidsErik Luijten, University of Illinois at Urbana-Champaign, Urbana, IL

The effective attraction between like-charged colloids, as induced by multivalent counterions, has been the subject of avariety of computational and theoretical investigations. Nevertheless, the topic is far from controversial, withcontradictory predictions and limited experimental observations. A major numerical complication is the dynamicslowdown resulting from the large size asymmetry between the colloids and their counterions. We overcome thisproblem by extending the generalized geometric cluster algorithm for colloidal suspensions to systems with electrostaticinteractions. Using this highly efficient method, we are able to study the onset of like-charged attraction as a function ofcolloid size. Theoretical considerations for planar geometries predict that the minimum required colloidal chargeincreases quadratically with colloid size, whereas strong-coupling theory predicts a linear relation. We resolve thiscontroversy by spanning a sufficiently large range in colloidal diameter. Furthermore, we demonstrate importantqualitative changes in the potential of mean force as the colloid size is increased.

296. Direct measurements of the effects of surfactant on interaction forces betweencolloidal particles at the decane-water interface

Bum Jun Park1, Jan Vermant2 and Eric M. Furst1, (1)University of Delaware, Newark, DE, (2)Katholieke Universiteit,Leuven, Belgium

The pair interactions of polystyrene particles were measured at the decane-water interface using laser tweezers. In theabsence of sodium dodecylsulfate (SDS) in the aqueous subphase, the particle interactions show a long-rangerepulsion, consistent with models proposed by Hurd [1] and Aveyard et al. [2, 3]. As SDS is added to the sub-phase,the repulsive force between particles decreases. Surprisingly, we find that the repulsive interactions also decrease withtime at fixed surfactant concentrations. This provides a possible mechanism for the reported flocculation behavior of 2Dsuspensions [4]. Finally, as the repulsion decreases, a long-range attractive force emerges, creating a secondaryminimum in the potential. The attractive interaction is consistent with attractive capillary forces between particles.Overall, our experiments demonstrate the richness of particle interactions at the oil-water interface, which can betailored to alter the stability and interfacial rheology of 2D systems.

[1] A. J. Hurd, J. Phys. A: Math. Gen. 1985, 18, L1055. [2] R. Aveyard et al. Langmuir, 2000, 16, 1969. [3] R. Aveyardet al. Phys. Rev. Lett. 2002, 88, 246102-1. [4] S. Reynaert et al. Langmuir, 2006, 22, 4936.

297. Interactions between star polymers: Microspheres grafted with filamentous phage virus



Phil F. Huang1, Seth Fraden1, Karim Addas2 and Zvonimir Dogic2, (1)Brandeis University, Waltham, MA, (2)RowlandInstitute of Harvard, Cambridge, MA

We genetically engineered M13 bacteriophage, a long filamentous particle that forms liquid crystalline phases, andcoupled biotin groups to one end of the virus. Biotinylated virus particles were then conjugated to streptavidin-coatedpolysterene spheres to form star complexes. The interparticle potential was measured between pairs of polystyrenebeads grafted with phage particles using an optical tweezer, and their behaviour in nematic M13 virus suspensions wasalso studied.

298. Melting and Fluctuations in Two-dimensional Colloid Crystals and Colloidal ‘Anti-Ferromagnets'Yilong Han, University of Pennsylvania, Philadelphia, PA

We use digital video microscopy to investigate melting of colloidal crystals under strong 2-dimensional (2D) confinementand frustrated colloidal ‘anti-ferromagnets' in weak 2D confinement. Our samples are composed of NIPA (N-isopropylacrylamide) microgel spheres whose diameter can be temperature-tuned, and whose pair potentials were measured tobe short-ranged and repulsive. The melting experiments revealed two first-order-like transitions from crystal to hexaticphase and hexatic to liquid phase as a function of temperature-tunable volume fraction. The divergences oftranslational and orientational susceptibilities were used to determine the phase transition points. This approach avoidsambiguities inherent in other analyses and resolved a novel premelting stage in the crystal that traditional analysesincorrectly associate with the hexatic phase. We will also show how these novel microgel spheres can be made tomimic the behavior of frustrated anti-ferromagnets. In this case, we measured statistics of frustrated bonds andcollective fluctuations of the degenerate system in space and time. This work was carried out in collaboration withAhmed Alsayed, Na Young Ha and Arjun Yodh with support from the NSF (MRSEC DMR-0520020 and DMR-0505048). I also thank Tom Lubensky and Yair Shokef for helpful discussions.

299. Keynote: Microscopic Theory of the Rheology of Colloid and Nanoparticle Glasses andGelsKenneth S. Schweizer, University of Illinois, Urbana, IL

A microscopic statistical dynamical theory for the effect of deformation on the transient localization, shear modulus,relaxation time, viscosity and other dynamic properties of glassy colloidal suspensions and entropic depletion gels hasbeen developed. The approach is built on single particle activated barrier hopping on a nonequilibrium free energyprofile as the elementary physical process in quiescent systems. External deformation distorts the confining free energy,weakens the caging constraints, and accelerates dynamics. The roles of mechanically driven motion and thermallyactivated flow have been studied. For glassy hard sphere suspensions power law and/or exponential dependences ofthe modulus and yield stress on colloid volume fraction are predicted. For polymer-particle suspensions the cagingconstraints and physical bond strength are quantified using PRISM integral equation theory. The absolute yield stresscollapses onto a universal master curve as a function of polymer concentration when scaled by its value at the idealmode-coupling theory nonergodicity transition, and sufficiently deep in the gel is of a power-law form with a universalexponent. The volume fraction dependence also exhibits such scaling but with a nonuniversal exponent. The theory hasalso been applied to thermal gels composed of colloids with sticky brush layers. Generalization of the approach tosuspensions of nonspherical colloidal molecules has been initiated. Distinctive changes in the location of ideal glass andgel boundaries, barriers and yield stresses with particle shape are found. This work was done in collaboration withY.L.Chen. V.Kobelev, E.J.Saltzman and G.Yatsenko.

300. Rheology and microstructure of a concentrated, near hard-sphere, colloidalsuspensions using 1-2 plane flow-SANS

Dennis P. Kalman1, Lionel Porcar2 and Norman J. Wagner1, (1)University of Delaware, Newark, DE, (2)NationalInstitute of Standards and Technology, Gaithersburg, MD

Colloidal suspensions of hard-spheres show significant shear thinning and shear thickening at volume fractions aboveabout Φ=0.20; these suspensions show progressively more shear thinning and shear thickening with increasing volume



fraction. Shear thickening is known to occur via the formation of load bearing hydroclusters from theory, simulations,flow-SANS experiments, and indirect rheological measurements, but there are no previous SANS measurements of thestructural rearrangements that accompany shear thinning or thickening directly in the plane of shear (the 1-2 or flow-gradient plane). Here, we study model suspensions of near hard-sphere silica particles, approximately 100nm indiameter in a near contrast-matching Newtonian solvent mixture of deuterated ethylene glycol and polyethylene glycolvia rheo-SANS in the radial and tangential direction (1-3 and 2-3 shear planes) and flow-SANS down the gap (in the1-2 plane). Volume fractions of Φ=0.52 and 0.40 are examined in the 1-2 plane. Significant anisotropic structure isevident around the peak in the structure factor in the shear thickened state, which is compared with theory andsimulations for the structure of the hydroclustered state. The microstructure results are compared to the measuredrheology to develop structure-property relations for colloidal suspensions.

301. Rheology of two dimensional weakly aggregated suspensionsSven Reynaert, Paula Moldenaers and Jan Vermant, Katholieke Universiteit, Leuven, Belgium

Two-dimensional suspensions are interesting both for a fundamental study of suspension dynamics and mechanics, aswell as for the applications in the stabililization of high interface systems such as foams and emulsions. Control overthe suspension structure of a planar particle monolayer can be achieved by destabilizing an initially crystallinemonolayer of colloidal particles. This requires adequate combinations of salt and surfactant in order to tailor theinteraction potential. A magnetic rod interfacial stress rheometer is used to characterize the dynamic rheologicalbehaviour of particle monolayers with a controlled aggregate structure. The linear viscoelastic properties and some non-linear rheological features will be shown. Also the compressional rheology is characterised using a Langmuir trough. Itwill be shown that interfaces with both high elastic shear and compressional moduli can be obtained. As allmicrostructural information can be readily accessed, direct comparison between structural and mechanical properties ispossible, providing mechanistic insight in the yielding and flow behaviour of these systems. The role of controlledsurface rheology in emulsion and foam formulation will be briefly addressed.

302. Keynote: Orientational transitions in supensions of ellipsoidal non-spherical particlesin sheared viscoelastic liquidsJan Vermant, D. Gunes and J. Mewis, Katholieke Universiteit, Leuven, Belgium

TBA

303. Influence of process variables on the rheological properties of highly concentratedwater-in-oil emulsions

Oscar A. Alvarez1, Lionel Choplin2, Veronique Sadtler2, Philippe Marchal2 and Marie-José Stébé3, (1)Universidad delos Andes, Bogotá, Colombia, (2)Laboratoire GEMICO, ENSIC - INPL, Nancy, France, (3)Equipe Physico-chimie descolloïdes UMR SRSMC N°7565 Nancy Université/CNRS Faculté des Sciences BP 239, Nancy, France

Concentrated emulsions are mixtures of two immiscible liquids (water and oil, generally), in which the volume fraction(Fv) of the dispersed phase is higher than 0.74. If Fv is higher than 0.90, these emulsions are defined as highlyconcentrated emulsions.

Semi-batch process is the main protocol used to obtain this kind of products. It consists of two steps, the first one isaqueous phase incorporation into the surfactant-oil mixture phase under given mixing conditions, and the second one isthe homogenization step in the same equipment (with possible modifications in the mixing conditions).

We studied process variables influence on rheological characteristics of highly concentrated water-in-oil emulsions.Thestudied mixing variables were: aqueous phase mass flow rate (Qw) and agitation speed (N) during the incorporationstep, and homogenization speed (N') and homogenization time (th) in the second step. The system under study iscomposed of n-dodecane as oily phase, deionized water as aqueous phase and sorbitan monooleate (Span 80) asemulsifying agent. The rheological behavior of highly concentrated water-in-oil emulsions was evaluated, one hour aftertheir preparation at room temperature, through mechanical spectrometry in the linear viscoelastic domain.

Results show a relationship between the rheological characteristics of highly concentrated water-in-oil emulsions



(elastic modulus (G')) and energy consumption during emulsification process (E). This relationship can be described byGaE0.6. In addition, we observed that energy consumption in homogenization step was higher that in incorporationstep.

304. Applications of Ultra Small Angle Neutron Scattering (USANS) to the Coatings Industry

Alan I. Nakatani1, Antony VanDyk1, Lionel Porcar2 and John G. Barker2, (1)Rohm and Haas Company, SpringHouse, PA, (2)National Institute of Standards and Technology, Gaithersburg, MD

Commercial coatings formulations are complex mixtures of inorganic pigments, dispersants, colorants, rheologymodifiers, and polymeric binders. The ability to understand and control the interplay of interactions between thesevarious components is critical to obtaining a high quality coating. Many published studies have been conducted onmodel polymer latex systems or model pigments and the relationship to commercial materials is often difficult to assess.The size scale of many of the commercially used latices and pigments is too large for the angular scattering rangecovered by traditional small angle neutron scattering instrumentation and the opacity of the samples prevents opticalscattering measurements at the concentrations of interest. Ultra Small Angle Neutron Scattering (USANS) provides anangular range uniquely suited for studies on materials of interest to the coatings industry. In this presentation, we haveused the contrast matching formalism on two different sample systems of interest. The first system is a mixture ofpigment (TiO2) and polymeric dispersants. The second system is a mixture of a polymer latex and pigment. For eachsystem samples were prepared where each component was independently contrast matched by preparing samples inthe appropriate ratio of H2O to D2O. The studies were performed as a function of shear rate to investigate the impactof shear on each of the components in these samples. The results provide new insight into the underlying structures inthese samples which could not be measured directly by other techniques.

305. A study of the Nanostructure and Material Properties in beta-Hairpin Peptide Hydrogelsby SANS

Rohan A. Hule1, Radhika P. Nagarkar1, Boualem Hammouda2, Joel P. Schneider1 and Darrin Pochan1, (1)Universityof Delaware, Newark, DE, (2)National Institute of Standards and Technology, Gaithersburg, MD

Hydrogels have been established as promising biomaterials for applications such as tissue engineering, controlledrelease of drugs and cell encapsulation. De novo designed beta hairpin peptides, capable of undergoing intramolecularfolding and consequent intermolecular self assembly and hydrogel formation, were investigated containing asymmetricbeta strand arms surrounding a turn sequence. The stimuli responsive self assembly of the hydrogels occurs via astrand interdigitation mechanism, resulting in a fibrillar nanostructure. Fibril dimensions as measured by TEM and AFMcorroborate the interdigitated assembly. Bulk material properties studied using oscillatory rheology vary significantly forthe different morphologies. Hydrogels consisting of laminated fibrils exhibited enhanced moduli over non-twisting ortwisting fibrils and yielded at lower strain values. A lag in the G' increase during the initial period in time sweeps hintsat slower assembly kinetics that can be related to higher number of monomers involved in the interdigitated assembly.SANS provides direct evidence of different fibril morphologies in terms of higher scattering intensities and lowercorrelation lengths for laminating fibrils vs. twisting or non-twisting structures. Inter and intramolecular associationsduring the self assembly process can also be related to Porod exponents indicative of mass fractals at high Q values.The formation of fibrils as a result of the self-assembly can be precisely tracked by changes in the Porod exponentsand correlation lengths. Differences in the peptide registry that drive hydrogel nanostructure and properties can bepotentially utilized in specific biomaterial applications.

306. Polymer brushes in restricted geometriesDennis Mulder and Tonya Kuhl, University of California, Davis, Davis, CA

The structure and dynamics of polymer brushes have been the subject of considerable theoretical and experimentalactivity. Experimental measurements of the steric forces between grafted brushes and the structure of a single brush atthe solid-solution interface are in good agreement with theoretical predictions. Yet, the structure that brush layers adoptduring compression has remained elusive. We report experimental density distribution measurements of two polymerbrushes as a function of compression. We find a significant increase in brush concentration at the interface as thelayers are compressed in contrast to the smoothly increasing concentration that has been predicted. The



interpenetration of the brushes has also been determined. These results demonstrate that high-density brushescollapse under confinement and explain why polymer brushes under good solvent conditions are so effective indecreasing the friction between surfaces.

307. Structural Origins for the Superior Toughness of Double-Network Hydrogels

Taiki Tominaga1, Vijay R. Tirumala2, Eric K. Lin2, Jian Ping Gong1, Hidemitsu Furukawa1, Yoshihito Osada1 andWen-li Wu2, (1)Hokkaido University, Sapporo, Japan, (2)National Institute of Standards and Technology, Gaithersburg,MD

Double network hydrogels (DN-gels) are the toughest of crosslinked polymer networks which contain 90% water byvolume. The fracture toughness of a highly swollen but brittle polyelectrolyte network increases by an order-of-magnitude from the in situ polymerization of neutral, linear chains. The order-of-magnitude increase in fracturetoughness is intriguing and has not been previously observed in other conventional interpenetrating polymer networks.Here, we present insights into the structure and dynamics of DN-gels studied using recent neutron scatteringmeasurements. The scattering from individual components within the DN-gels was obtained by using a deuterium-labeled monomer in conjunction with contrast-matched water. The highlights of our results are: (i) The two componentsare not isolated and instead form a stable associative complex in water, and (ii) Compositional fluctuations, probablyassociated with complex formation, correlated over large length scales (≈ 1.5 um) stabilize the structure of DN-gelsunder deformation. The possible role of the observed complexation in the toughening mechanism will be discussedbased on the scattering data and other supporting measurements.

308. Thin polymer film structure using resonant soft X-ray scattering and reflectometry

Cynthia F. Welch1, Rex P. Hjelm1, Joseph T. Mang1, Marilyn E. Hawley1, Debra A. Wrobleski1, E. Bruce Orler1 andJeffrey B. Kortright2, (1)Los Alamos National Laboratory, Los Alamos, NM, (2)Lawrence Berkeley National Laboratory,Berkeley, CA

Thin films of carbon-containing materials are found in a pervasive number of applications, ranging from well-establishedindustrial binders and coatings to novel biomedical and optoelectronic devices based on recent advances innanotechnology. Phase separation through self-assembly gives these films their desirable properties; thus, determiningthe film structure and understanding its formation are key to unravelling the structure-property relationships. However,determining the morphology of thin, carbon-based films via traditional x-ray and neutron scattering techniques is oftendifficult due to weak contrast between phases and small scattering volumes. Consequently, standard scatteringtechniques often require either heavy atom, for x-rays, or deuterium labelling, for neutrons, to locate the variouschemical constituents in the structure. Here we develop soft x-ray scattering and reflectometry techniques that allow usto analyze the morphology of thin polymer films whose phase-separated domains are distinguishable without resortingto chemical modification or isotopic labelling. With these techniques, we achieve significant, x-ray energy-dependentcontrast between carbon atoms in different chemical environments using soft x-ray resonance at the carbon edge. Wedemonstrate the use of this contrast mechanism on the phase-separated structure of a model thin polymer film. Whilethe realization of these methods represents a significant advance in our ability to probe the morphology of thin polymerfilms, we expect that they will also find extensive use in the analysis of other thin, carbon-containing films often found inbiological systems and new nanocomposite devices.

309. On the determination of liquid mixture free energies from light scattering data

David S. Ross1, Carl V. Lutzer1, Seth Fraden2 and George M. Thurston1, (1)Rochester Institute of Technology,



Rochester, NY, (2)Brandeis University, Waltham, MA

We are developing a method that uses static light scattering as a non-invasive means for determining intensive freeenergies of n-component liquid mixtures, by solving a second-order nonlinear partial differential equation appropriate forsingle isotropic liquid phases. Forward light scattering efficiency data permit integration of this equation withoutchoosing parametric free energy models in advance. With prior information about phase boundary locations, the methodalso accommodates phase separation. We address statistical and practical issues relevant for applying the method toexperimental data.

310. Relationship between “strain-hardening” and the structure of fibrin clotsLionel Porcar, National Institute of Standards and Technology, Gaithersburg, MD and Danilo C. Pozzo, University ofMaryland / NIST, Gaithersburg, MD

Bio-polymer networks have mechanical properties that can be remarkably different from those of most syntheticmaterials. One such property is the strain-hardening response that is exhibited by most biological tissues. Strain-hardening allows tissues to be soft and malleable during small perturbations while being hard and stiff when they aredeformed beyond a certain limit, thus allowing them to maintain their structural integrity under large loads. Despite theirmanifest importance, basic questions related to the structure of these biopolymer networks, such as how they deformunder stress, still remain unanswered. We have used “artificial” blood clots (fibrin networks) as a model system toinvestigate the structure of these bio-networks under stress deformation throughout the strain-hardening regime. Bycombining simultaneously rheology and Small Angle Neutron Scattering measurements (Rheo-SANS) we were able tocorrelate the internal structural changes occurring in the material to the macroscopic mechanical response. Our resultswill be discussed with respect to two recent theoretical models that have been proposed to explain strain-hardening.

311. Advance in structural complexity of block copolymer assembly via kinetics controlDarrin Pochan, University of Delaware, Newark, DE

Self-assembly of molecules is an attractive materials construction strategy due to its simplicity in application. Byconsidering peptidic or charged synthetic polymer molecules in the bottom-up materials self-assembly design process,one can take advantage of inherently biomolecular attributes; intramolecular folding events, secondary structure, andelectrostatic interactions; in addition to more traditional self-assembling molecular attributes such as amphiphilicty, todefine hierarchical material structure and consequent properties. Synthetic block copolymers with charged coronablocks can be assembled in dilute solution containing multivalent organic counterions to produce micelle structures suchas toroids. These ring-like micelles are similar to the toroidal bundling of charged semiflexible biopolymers like DNA inthe presence of multivalent counterions. Micelle structure can be tuned between toroids, cylinders, and disks simply byusing different concentrations or molecular volumes of organic counterion. Not only can novel micelle geometries beconstructed by taking advantage of charged corona-multivalent counterion complexations, but also completely newassembly strategies have been observed that can create complex, one-dimensional nanostructures throughmanipulation of charged, amphiphilic block copolymer kinetics in solution. One result of this new assembly strategy isforced spherical micelle aggregation along a preferred direction leading to formation of cylindrical nanostructures withalternating stripes of block copolymer chemistry perpendicular to the primary cylinder axis. The resulting cylinders wereused to template gold nanoparticle assembly in a periodic fashion. The second example is the construction of cylindricalmicelles with multicompartment cores of phase separated block chemistries.

312. Characterization of self-assembled nanostructures with internal phase separation fromtriblock copolymers of PAA-b-PMA-b-PSKelly D. Hales and Darrin J. Pochan, University of Delaware, Newark, DE

The characterization and understanding of the structure of polymer nanoparticles and bulk-like phase behavior ofamphiphilic triblock copolymers of poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene in water/tetrahydrofuran(THF) solvent mixtures is strongly dependent on block composition as well as solvent composition. The blockcopolymers were dissolved in THF in the presence of an organic counterion. Upon the slow addition of water, a varietyof structures were observed including phase-separated nanoparticles, bulk-like lamellar phase separation, spherical,cylindrical, and disk-like micelles, as well as toroidal assemblies. The specific structure formed was dependent on the



architecture of the triblock copolymer, the amount of counterion present, and the water to THF volume ratio. This workfocuses on the structure of polymer nanoparticles and networks formed in low water content systems. The size of thenanoparticles and whether separated nanoparticles vs. an interconnected network was formed can be controlled viasolvent composition. Importantly, both the nanoparticles and network phases contain their own inherent nanostructuredue to local phase separation of the block copolymers. Cryo-transmission electron microscopy, traditional transmissionelectron microscopy, and neutron scattering were used to examine these samples.

313. Dynamics of amphiphilic block copolymer micellesRaoul Zana, Carlos Marques and Albert Johner, Institut C. Sadron (CNRS), Strasbourg, 67000, France

The Pluronics® (polyethyleneoxide-polypropyleneoxide-polyethyleneoxide, PEO-PPO-PEO) are the only amphiphilicblock copolymers for which results for the kinetics of the copolymer exchange between micelles have been reported forseveral copolymers. The rate constants k+ and k- for the copolymer entry/exit into/from micelles have been extractedfrom these results for 8 copolymers. Contrary to what is observed for conventional surfactants, k+ is smaller/muchsmaller than for a diffusion-controlled process. Both k+ and k- decrease significantly with increasing number of POunits, nPO, but vary relatively little with the number of EO units, nEO, in the copolymer. The plot of log k- vs t4/3nPO

2/3

(t is a factor correcting for temperature) is linear. This behavior suggests that the PO block is somewhat folded in thefree (unimer) state, with less contact with water than in the fully extended conformation. This behavior explains why, forother amphiphilic block copolymers, the reported values of k- show remarkably little dependence on the copolymerarchitecture. An extrapolation of the Pluronics® results on the basis of Aniansson's expression for k- suggests that forcopolymers with a more hydrophobic block (i.e., polybutyleneoxide or polystyrene) the exchange process may be tooslow for being detected on the laboratory time scale. The folding of the hydrophobic block in the unimer state precludesthe determination of the free energy increment for the transfer of a hydrophobic unit from water to micelle from the cmcdependence on the hydrophobic block polymerization degree. The micelle formation/breakdown of Pluronics® micellesappears to occur via fragmentation/coagulation reactions.

314. Self-assembly of amphiphilic proteins with redox cofactorsVidya Karunakaran, Paul A. O'Brien, Viraj Parekh, P. Leslie Dutton and Bohdana M. Discher, University ofPennsylvania, Philadelphia, PA

Redox-active nanoscale materials such as porphyrin binding proteins are of immense interest because of their potentialuse as catalysts in light-energy harvesting processes or as bioelectronic devices. To realize this potential, we havedesigned simple, robust peptides (maquettes) that assemble into four-helix bundles. The maquettes presented herepossess overall amphiphilic character that enables their complex multi-component assembly in detergents,phospholipids vesicles or at air-liquid interfaces. To enable electron transfer within the protein and subsequently acrossa membrane, we have incorporated multiple binding sites for redox-active cofactors. We have tested how the position ofthe binding site with respect to the membrane affects the assembly, affinity, and redox properties. Results reportedhere include AP maquettes with up to 6 binding sites for protoporphyrins.

315. Hierarchical Self-assembly Based on the Metal-bisligand Coordination Complexes anda Block CopolymerYun Yan, Nicolaas A. M. Besseling, Arie de Keizer and Martien A. Cohen Stuart, Wageningen University, Wageningen,Netherlands

Metal-bisligand coordination complexes are self-assembled supramolecules1. The water solvable metal-bisligandcoordination complexes with negative charges on coordination centre can be regarded as negatively chargedpolyelectrolytes. This polyanions are found to form hierarchical self-assemblies with polyneutral-polycations blockcopolymer2. In this research, we report (1): Formation of spherical and worm-like micelles in poly(2-vinyl-N-methyl-pyridium iodide)-polyethylene oxide (P2MVP41-PEO204) /Zn-L2EO4 coordination complexes. The latter is formed bymixing 1,11-bis(2,6-dicarbonate potassium-4-yloxy)-3,6,9-trioxaundecane, L2EO4, with zinc nitrate. (2) Formation ofcoacervate fibbers in the mixture of Zn-L2EO4 and A-B-A type polyaminoacid block copolymer, where A representsneutral block while B represents positively charged block. This new class of self-assemblies are very interesting



because of the existence of metal ions in the coacervate core, which enable carriage of metal ions with water solublenano vehicles, and also shed lights on other practical fields.

Figure 1. Cryo-TEM images of coacervate core micelles formed in the PMVP41-PEO204/ Zn-L2EO4 mixed system at f-= 0.5.

References: 1. Vermonden, T.; Van Steenbergen, M. J.; Besseling, N. A. M.; Marcelis, A. T. M.; Hennink, W. E.;Sudhölter, E. J. R.; Cohen Stuart, M. A. J. Am. Chem. Soc. 2004, 126, 15802-15808. 2. Yan, Y.; Besseling, N. A. M.;de Keizer, A.; Marcelis, A. T. M.; Drechsler, M.; Cohen Stuart, M. A. Angew. Chem. Int. Ed. 2007, 46,

316. Rational design of peptide assemblies for bio-separationsRaymond S. Tu, Vikas Jain and Angela Jimenez, The City College of The City University of New York, New York, NY

Our goal is to develop a novel technology for robust and sequence specific DNA separation. The approach is based onthe formation of a self-assembly composed of de novo designed amphiphilic peptides, where the specific bindingresults in secondary structure enhancement and self-assembled phase transformations. Peptides can be rationallydesigned with native configurational fluctuations, and this entropically favored state is only broken on binding to form awell-ordered state. This process has been coined fishing because the fluctuating linear chain is facilitating the captureand catalysis of target molecules. A common misconception that is prominent in our teaching of molecular biology is theparadigm that protein sequence (primary structure) defines a uniquely folded protein structure (tertiary structure) that, inturn, directly relates to the presentation of an active binding site. This paradigm has been frequently used to define thethermodynamics and kinetics of biological processes. Yet the model underestimates nature's versatility. This workdescribes the development of peptide-motifs where peptides can actively respond to specific sequences of DNA,resulting in enhanced amphiphilicity and self-assembly. The engineering of these natively disordered proteins isaccomplished by judiciously manipulating the topography of the folding energy landscape to control actively assemblyas a function of binding.

317. Engineering self-assembly between biological materials

Suzanne M. Barber1, Philip J. Costanzo2, Jaroslaw Majewski3, Chad E. Miller3, Vishal Trivedi4, Walter Stockinger4,Timothy E. Patten5, Axel Nohturfft4 and Tonya L. Kuhl1, (1)University of California Davis, Davis, CA, (2)Army ResearchLaboratory, Silver Springs, MD, (3)Los Alamos National Laboratory, Los Alamos, NM, (4)Harvard University, Cambridge,MA, (5)UC Davis, Davis, CA

Rarely in Nature are single molecule interactions used for cell adhesion. Rather, several different types of molecules orstructures interact in concert to build effective adhesion. To study how these multivalent adhesive interactions areutilized by biological systems, we are working to develop a tailorable, self-assembled biosensor that can probe therange of interactions from the single molecule level to the ensemble average of multiple interactions. We selectivelyself-assemble functionalized polymer linkers with complementary terminal groups onto patterned nanoparticles to probeligand-receptor interactions on the surface of the membrane. However, multivalent interactions, resulting from ligand-receptor pairs, must partner with the membrane properties to result in fusion. Therefore in parallel, we are studying thecomposition and behavior of cell membranes, both in vitro and in vivo. In particular, we study intracellular vesiclesproduced from particles phagocytosed by J774 cells. By studying the phase behavior, composition and interfacialbehavior of phagosomal extracts, we aim to devise an improved model cell membrane system. We propose that bydeveloping a more sophisticated model of a cell membrane, a wider range of techniques may be effectively used tostudy critical biological processes, such as adhesion and fusion.



318. Interfacial Solubilization Mechanisms in the Micellar Solubilization of Oils fromMonodisperse DropletsSuwimon Ariyaprakai and Prof. Stephanie R. Dungan, University of California, Davis, CA

The mechanism by which hydrophobic solutes such as oils move from emulsion droplets into surfactant aggregatessuch as micelles continues to be debated. Controlling roles of micelle adsorption, micelle pinch-off, molecular diffusionor of rapid micelle uptake have been proposed by various research groups. In this study, nearly monodisperse alkane-in-water emulsion droplets were mixed with aqueous micellar solutions, allowing solubilization to proceed. Becausethese emulsions were nearly monodisperse, we were able for the first time to observe, using static light scattering, theprogressive decrease in average droplet size due to solubilization, and to analyze the rate of this decrease using apopulation balance approach to calculate the mass transfer coefficient. We studied the effect of oil chain length,surfactant type and concentration, and the aqueous phase viscosity on the mass transfer kinetics. The influence ofviscosity and of surfactant concentration, in particular, provide insight into the role of molecular diffusive processesrelative to interfacial mechanisms. Understanding solubilization mechanisms is important in a host of natural andindustrial processes, including nutrient absorption and release of pharmaceutical agents.

319. Particle Stability in Semidilute and Concentrated Polymer SolutionsDavid L. Green and Nupur Dutta, University of Virginia, Charlottesville, VA

Engineered composites are often formulated by grafting polymer brushes to the surfaces of nanoparticles to dispersethem into polymer solutions and melts. In these suspensions it is well established that nanoparticles can exhibit a widevariety of phase behaviors through depletion flocculation at low-to-moderate free polymer concentrations. However, fewstudies fundamentally elucidate the fate of polymer-grafted particles in concentrated polymer solutions and melts.Researchers who have studied these systems predict that ungrafted and grafted nanoparticles, once destabilized bydepletion flocculation, should restabilize in concentrated polymer solutions. In contradiction, we will show the results ofrecent light scattering experiments on polydimethylsiloxane (PDMS)-grafted silica nanospheres in PDMS/cyclohexanemixtures which indicate that at high free polymer volume fractions (0.5 – 1.0 v/v) the interfacial wetting of the graftedbrush is needed to stabilize the nanoparticles against aggregation. We correlate this behavior to wetting phasediagrams that predict the regions of stability and instability for the PDMS-g-silica nanoparticles. Overall, these studiesrepresent new ways of quantifying the factors that control the dispersion of polymer-grafted nanoparticles inconcentrated polymer solutions and melts – systems that are ubiquitous in formulating engineered composites.

320. Effects of interfacial dynamics on bulk flow patterns: drop deformation in anextentional flowAndres Gonzalez-Mancera, Mustapha Jamal and Charles D. Eggleton, University of Maryland, Baltimore County,Baltimore, MD

We consider a multiphase system in which a liquid drop is suspended in a distinct fluid. Surface-active moleculesadsorb to the interface and are often use to stabilize the drop and to reduce surface tension. We also considerliposomes which are self-enclosed structures composed of curved lipid bilayer membranes located at the interfacebetween an internal liquid and a suspending liquid. Lipid bilayer membranes are predominantly made from amphiphilicmolecules, a special class of surface-active molecules.

When the suspending liquid is set in motion, viscous stresses dynamically alter the tension distribution at the interface.Our study focuses on understanding the role that interfacial dynamics play on the transfer of energy between theinterface and the bulk fluids. We simulate the deformation of a particle in an axisymmetric extensional flow andsubsequent relaxation using the boundary integral method.

We model the interface of a surfactant laden drop using the Frumkin surface equation of state and consider equilibriumsurfactant concentrations ranging from zero to a highly packed monolayer. The lipid bilayer membrane is modeled usingan elastic two-dimensional continuous isotropic material with a varying elastic material property that depends on localarea changes. The elastic model was derived considering the mechanical behavior of a highly concentrated surfactantmonolayer. We analyze flow field properties such as streamlines, stress field and energy dissipation and identifycharacteristic flow patterns as a function of interfacial properties.



321. Remotely powered distributed microfluidic pumps and mixers based on miniaturediodes

Suk Tai Chang1, Vesselin N. Paunov2, Dimiter N. Petsev3 and Orlin D. Velev1, (1)North Carolina State University,Raleigh, NC, (2)University of Hull, Hull, United Kingdom, (3)University of New Mexico, Albuquerque, NM

We demonstrated earlier how miniature semiconductor diodes could self-propel by harvesting electric energy fromexternal AC fields and converting it to mechanical propulsion on the microscale. Here we report how this mechanismcan be used in new types of microfluidic devices. Miniature diodes embedded into microfluidic channel walls could actas distributed pumps or mixers powered by a global external field. The millimeter-sized diodes generate DC fieldsacross their electrodes as a result of rectification of the external AC field. The resulting localized electroosmotic flux onthe surface of diodes evokes an overall flow in the microfluidic channel in the direction of either the cathode or theanode depending on their surface charge. The flow velocity linearly increases with applied voltage, but does notdepend on the frequency of the field, which could eliminate problems with vortices in areas of non-uniform field thatoften occur in other AC electrohydrodynamic pumps. The combined application of AC and DC fields in our microfluidicchip allows efficient separation of particles with small differences in their charges or size. This localized-electroosmoticflow between the diodes in the channel wall could also be used in efficient controllable microfluidic mixers. Thisresearch may establish the foundation of new actively controlled nanofluidic-electronic chips for manipulating liquids,solutes and analytes at the nanoscale.

322. Extending the Threads in Surfactant-Mediated Microscale TipstreamingWingki Lee, Shelley L. Anna and Lynn M. Walker, Carnegie Mellon University, Pittsburgh, PA

Microfluidic flow focusing devices have been used to synthesize micrometer-scale emulsion droplets via the threadformation mode of drop breakup. Thread formation occurs when surfactants are dissolved in one or both liquid phases.In a particular range of surfactant concentrations and flow rates, a thin thread is drawn between two primary droplets.As the thread elongates, it disintegrates into a stream of tiny droplets, whose sizes depend on the final thread diameterand the physical properties of the liquids. In the present work, we investigate the role of physical parameters on threadformation. In particular, we show that the thread length is extended when the downstream geometry is modified tostretch the thread more rapidly. In addition, we construct a phase diagram indicating that as the viscosity ratiodecreases, the range of capillary numbers in which threads form increases and the threads become longer and thinner.These results suggest ways of optimizing the thread formation process to form ever smaller droplets.

323. Surfactant Induced wettability alteration in fractured carbonate reservoirsRobin Gupta and Kishore K. Mohanty, U. of Houston, Houston, TX

The conventional water flooding recovers little oil from oil-wet fractured reservoirs. Most of the water passes throughthe factures and does not imbibe into the matrix due to negative capillary pressures. The goal of this work is to inducewettability alteration on carbonate rocks such that water would be imbibed resulting in oil production. Many anionicsurfactants and a few cationic surfactants have been studied. The salinity is adjusted by varying the concentration ofsodium carbonate which also increases the pH above the PZC for carbonates preventing adsorption of anionicsurfactants on surface. Interfacial tension (IFT) of the order of 10-2 mN/m are observed for anionic surfactants (of theorder 1 mN/m for cationic) at optimal salinity. Contact angle studies have been conducted on initially oil-wet calciteplates. Surfactants have been identified which alter the water-oil contact angle to below 90„a. Limited studies with anAFM indicate the removal of adsorbed organics by surfactants. The screened surfactants are used to imbibe the initiallyoil-wet carbonate cores. The oil recovery is monitored with time. A numerical simulator is developed to understand theprocess by analyzing in-situ distribution of IFT, flow, capillary pressure, relative permeability and surfactantconcentration. The surfactant molecules diffuse from fractures into the matrix and change wettability and IFT. This leads



to reduction in capillary pressure and aqueous phase invades from bottom of the core pushing oil out from the top. Thechange in wettability results in an increase in oil relative permeability which increases oil recovery rate.

324. Dynamic Wetting of Boger Fluids

Yuli Wei1, G. Seevaratnam1, S. Garoff1, E. Rame2 and Lynn M. Walker1, (1)Carnegie Mellon University, Pittsburgh,PA, (2)National Center for Space Exploration Research, Cleveland, OH

The impact of fluid elasticity on the dynamic wetting of polymer solutions is important because many polymer solutionsin technological use exhibit non-Newtonian behaviors in the high shear environment of the wedge-like flow near amoving contact line. Our former study showed that shear thinning induced by a semi-flexible high molecular weightpolymer reduces the viscous bending near a moving contact line as compared to a Newtonian fluid having the samezero-shear viscosity. This results in a dramatic reduction of the dependence of the effective dynamic contact angle oncontact line speed. In this talk, we discuss dynamic wetting of Boger fluids which exhibit elasticity dominated rheologywith minimal shear thinning. These fluids are prepared by dissolving a dilute concentration of high molecular weightpolymer in a “solvent” of the oligomer of the polymer. We demonstrate that elasticity in these fluids increases curvaturenear the contact line but that the enhancement arises mostly from the weakly non-Newtonian behavior already presentin the oligimeric solvent.

. Understanding and exploiting the surface chemistry of single walled carbon nanotubesMichael S. Strano, University of Illinois Urbana-Champaign, Urbana, IL

Recent advances in the spectroscopy of single walled carbon nanotubes have significantly enhanced our ability tounderstand and control their surface chemistry, both covalently and non-covalently. We have used this insight to studyhow this chemistry controls intermolecular interactions for several applications. Molecular detection using near-infraredlight between 0.9 and 1.3 eV has important biomedical applications because of greater tissue penetration and reducedauto-fluorescent background in thick tissue or whole-blood media. We have pioneered the use of carbon nanotubes astunable near-infrared fluorescent sensors that are highly photo-stable In one system1, the transition of DNA secondarystructure from an analogous B to Z conformation modulates the dielectric environment of the single-walled carbonnanotube (SWNT) around which it is adsorbed. The SWNT band-gap fluorescence undergoes a red shift when anencapsulating 30-nucleotide oligomer is exposed to counter ions that screen the charged backbone. We demonstratethe detection of the mercuric ions in whole blood, tissue, and from within living mammalian cells using this technology.Similar results are obtained for DNA hybridization and the detection of single nucleotide polymorphism. We also reportthe synthesis and successful testing of near-infrared ?-D-glucose sensors2 that utilize a different mechanism: aphotoluminescence modulation via charge transfer. The results demonstrate new opportunities for nanoparticle opticalsensors that operate in strongly absorbing media of relevance to medicine or biology.

Another problem we have focused on is how the electronic structure of a carbon nanotube influences its chemicalreactivity. For example, rate constants for electron transfer reactions involving single walled carbon nanotubes shouldvary with their chirality vector (n,m), a measure of the helical ‘twisting' of the graphene lattice in the nanotube. To date,the functional form of this relationship has proven elusive. We have performed completely automated reactions of singlewalled carbon nanotubes (SWNT) with 4-hydroxybenzene diazonium salt under various experimental conditions, andanalyzed their influence on the reaction selectivity using UV-vis-nIR absorption spectroscopy and a previouslypublished spectral deconvolution procedure. The selectivity of the reagent to metallic SWNT over semiconductingSWNT was greater at low salt concentrations (73%) and lower at high salt concentrations (54%). The activity ofdiazonium was increased upon illumination; however, similar rate constants for the SWNT (relative to the (11,5)nanotube) were computed for the light and dark reactions, indicating that the type of diazonium intermediate affects theextent of reaction and not the rate. The steady state data has been modeled using an adsorption-reaction scheme, andan electron transfer theory is developed to yield the first structure-reactivity relationship for SWNT.

325. Designing Novel Biosensors from the Nanoscale UpAmanda J. Haes, University of Iowa, Iowa City, IA

Miniature optical sensors that specifically identify low concentrations of biological and environmental substances are inhigh demand. Currently, there is no optical sensor that provides identification of the aforementioned species without



amplification techniques and at naturally occurring concentrations. Recently, it has been demonstrated that triangularsilver nanoparticles have remarkable optical properties and that their enhanced sensitivity to small changes in theirlocal environment can be used to develop a new class of optical sensors using localized surface plasmon resonance(LSPR) spectroscopy and optimized surface chemistry. The examination of both model and non-model biologicalassays will be presented. It will be demonstrated that the LSPR nanosensor rivals the sensitivity and selectivity of andprovides a low-cost alternative to commercially available sensors.

326. Keynote: Nonequilibrium statistical mechanics, proteins, and nucleic acidsJan Liphardt, University of California - Berkeley, Berkeley, CA

Tools such as counter-propagating optical tweezers are allowing researchers to manipulate single proteins and nucleicacids with ever higher spatial and temporal resolution. However, our ability to interpret the data collected from single-molecule experiments is still only rudimentary since many take place very far from equilibrium. Fortunately, severaltheoretical results from nonequilibrium thermodynamics that were long-held to be untestable curiosities make it possibleto extract thermodynamic parameters from nonequilibirum experiments. The aim of my talk is to provide an overview ofresearch at the intersection of nonequilibrium statistical mechanics and single molecule biophysics. I will conclude witha survey of open problems in the field.

327. Photo-control of the form-dynamics-function relationship of enzymesShao-Chun Wang, Andrea C. Hamill and C. Ted Lee Jr., USC, Los Angeles, CA

We have recently developed a novel method to reversibly control protein conformation with simple light illumination.This method relies on the interaction of proteins with photoresponsive “azoTAB” surfactants that can be switched fromthe photo-active to a photo-passive state with exposure to visible or UV light, respectively. The active surfactant bindsto and unfolds proteins, while the passive surfactant dissociates from proteins inducing refolding. To examine thepartially-folded structures that result, we have utilized small-angle neutron scattering (SANS) along with shape-reconstruction algorithms. Briefly, shape reconstruction involves optimizing the positions of the “scattering centers”within the protein to best fit the SANS data. With azoTAB under visible light, lysozyme unfolding is localized to aswelling of the hinge region connecting the alpha and beta domains, while UV illumination refolds lysozyme to a native-like conformation. To investigate the effects of hinge swelling on protein dynamics, we have performed neutron spinecho (NSE) experiments. NSE can access relaxational dynamics over time scales from 0.01–100 ns and length scalesfrom 10–150 Å, appropriate for the study of domain motions within proteins. Interestingly, NSE detects internal motionswithin lysozyme in the presence of active surfactant (visible light), while converting the surfactant to the passive formwith UV light results in a “dormant” protein in the nanosecond/nanometer regime, similar to native lysozyme. Notably,these internal motions are accompanied by a 7x “superactivity” of the enzyme versus the native state. AzoTAB inducesunique allosteric control of enzyme activity through hinge swelling and enhancing enzyme flexibility.

328. Probing SDS-PAGE protein separations using small angle neutron scatteringDanilo C. Pozzo, University of Maryland / NIST, Gaithersburg, MD

Sodium dodecyl sulfate polyacrylamide electrophoresis (SDS-PAGE) is the most widely used method to carry outanalytical separations of small poly-peptides and proteins. Despite its recognized importance, our understanding of thetransport of surfactant denatured proteins during electrophoresis is based greatly on assumptions of proteinconformation inside the gel and on macroscopic measurements of their mobility. We have recently designed and built anew cell that allows us to perform small angle neutron scattering (SANS) measurements during the process ofelectrophoresis. Contrast-variation SANS is used to provide, for the first time, a structural picture of the conformation ofprotein-surfactant complexes during this separation process. Our recent SANS observations are discussed and relatedto transport models (Ogston model and reptation model) that have been proposed to occur during SDS-PAGE.

329. Therapeutic Proteins Encapsulated in PEG-based PolymersomesDavid A. Christian, Diana M. Bowen and Dennis E. Discher, University of Pennsylvania, Philadelphia, PA

Therapeutic proteins are generally potent but their effect in vivo is short-lived. The extension of this therapeutic



timescale has motivated recent work on protein encapsulation in drug delivery devices (i.e. liposomes, microparticles,hydrogels) or modification by polyethylene glycol (PEG). We are investigating the ability of PEG-based block copolymervesicles - or polymersomes - to encapsulate such proteins for controlled release, and in the process studying theinteractions between block copolymers and complex, aggregating proteins. We are using recombinant human insulin asone therapeutic protein for encapsulation and tuned release. Initial results indicate that the encapsulation of fluorescein-labeled insulin in polymersomes is possible. Insulin-loaded polymersomes can then be processed to a 100nm diameterand separated from unencapsulated insulin. These insulin-loaded nano-polymersomes are shown to be stable formonths at 4„aC as well as in whole blood in vitro. However, insulin is a complex protein that is readily capable ofaggregating to form dimers, hexamers, and higher molecular weight aggregates. This aggregation results from exposureto agitation, high temperature, and hydrophobic interfaces such as the air-water interface. Because high molecularweight PEG molecules have been shown to have little interaction with proteins or even to stabilize proteins in suchadverse conditions, it is thought that the 100% PEGylated surface of the polymersome membrane will have minimalinteraction with the proteins - making the aqueous lumen of the polymersome a stable environment for encapsulatedproteins. We intend to further examine the effect of polymersome encapsulation on the structure of insulin as a modelprotein therapeutic.

330. Targeted particulate binding to cellulose surfaces mediated by bifunctional fusionproteins

Gautam Pangu1, Eric Johnston1, Jordan Petkov2, Neil Parry2 and Daniel Hammer1, (1)University of Pennsylvania,Philadelphia, PA, (2)Unilever R&D, Bebington, United Kingdom

The targeted deposition and binding of particulates to cellulose mediated by a molecular family of heterobifunctionalfusion proteins is studied in this work. The fusion protein consists of a domain that binds to a particle either directly orthrough a model red dye, and a domain that binds to cellulose. The strength of adhesion of a single particle to acellulose fiber is measured by using micropipette aspiration as a function of its adhesive specificity, surface density andcontact time. In addition, the dynamics of adhesion of the functionalized particles to cellulose-coated glass slide undercontrolled hydrodynamic flow at various shear rates is explored using flow chamber assays for two scenarios:detachment of bound particles, and attachment of particles in suspension. Highly specific adhesion is observed in bothstudies. The force of adhesion was ~ 2 nN for the fully functionalized particles with the frequency of adhesion > 90% inmicropipette aspiration assay, while average force required to detach a bound particle was ~ 125 pN in flow chamberassay. The adhesive dynamics simulations of particle binding to cellulose coated substrate indicate that theexperimentally observed response of bound particles to the application of shear force can be simulated by combiningprobabilistic nature of receptor-ligand binding with heterogeneity in receptor density observed across particle population.

331. Influence of adsorbed fibrinogen on non-Specific micron-scale adhesionSurachate Kalasin and Maria Santore, University of Massachusetts,, Amherst, MA

Cell adhesion in biology is attributed to a handful of specific ligand-receptor interactions, or common motifs such asRGD. Conversely, bio-technical situations such as the interactions between the body and implanted materials, assaydevices contacting biological fluids, and even biomarine fouling will be largely influenced by nonspecific interactions.Indeed, some of the biological cell adhesive behavior may also be influenced by long range nonspecific interactionsbefore ligand-receptor binding comes to bear. To that end, we ask the question: how much adsorbed protein issufficient to produce adhesion at an interface which is otherwise substantially non-adhesive? Here we adsorbeddifferent amounts of fibrinogen (from 0.05 to 5 mg/m2) on a model surface which is non-adhesive or minimally-adhesive: silica. When a series of these surfaces are exposed to flowing suspensions, we find that even though the netlong range electrostatic field is negative, small amounts of fibrinogen, less than 0.5 mg/m2, are sufficient to giveadhesion, either through hydrophobic interactions or through the interaction of positive regions of the protein with theapproaching negative surface. We further observe that the adhesion “turns on” sharply at a distinct threshold,reminiscent of surface fluctuation studies with a purely electrostatic model. Hence this work not only answers thequestion “How much of a sticky protein can be tolerated before bioadhesion becomes a problem?”, it also demonstratesthe role of fluctuations in protein-driven non-specific adhesion.

332. Keynote: Drug Delivery and Imaging Using Nanoparticles Produced by Block-copolymer Directed Flash NanoPrecipitation



Robert K. Prud'homme, Walid Saad, Ying Liu, Marian Gindy and Margarita Herrera-Alonso, Princeton University,Princeton, NJ

Nanoparticle formulations of hydrophobic drugs present unique opportunities for treatment of solid tumor cancers, fordelivery of drugs by aerosol administration. The common requirements of these applications are precise control ofparticle size and surface functionality. We present our new process --Flash NanoPrecipitation – a controlledprecipitation process that produces stable nanoparticles at high concentrations using amphiphilic diblock copolymers todirect self-assembly. Uniform particles with tunable sizes from 50-500 nm can be prepared in an economical andscalable manner. The key to the process is the control of time scales for micromixing, polymer self-assembly, andparticle nucleation and growth. The diffusion-limited assembly enables particles of complex composition to be formed.The PEG protective layer creates long-circulating particles and the inclusion of PEG chains with terminal ligands allowsdrug targeting. Examples of particle formation for controlled delivery of multiple drugs from nanoparticles will bepresented. This enables the simultaneous, controlled release of multiple drug “cocktails” from nanoparticles for thetreatment of cancers and HIV. The incorporation of gold or magnetite nanoparticles or fluorophores with drugs into asingle nanoparticle enables simultaneous delivery and medical imaging.

333. Structure of “flexible” liposome formulations as probed by SANS

Oluwatosin A. Ogunsola1, Margaret E.K. Kraeling2, Matthew B. Dowling1, Robert L. Bronaugh2 and Srinivasa R.Raghavan1, (1)University of Maryland, College Park, MD, (2)Food and Drug Administration, College Park, MD

Recently, there has been much interest in creating liposomes that can penetrate skin and thereby deliver theirencapsulated contents for therapeutic (e.g., a drug or vaccine) or cosmetic purposes. Several studies have shown thatso-called “flexible” liposomes or transfersomesTM are indeed capable of penetrating skin. These liposomes are createdby mixing lipids with small amounts of a denaturing agent such as Tween 80 or an alcohol. The flexibility of theseliposomes has been quantified by permeability measurements, while their skin penetration has been evaluated byconfocal microscopy. In this study, we use small-angle neutron scattering (SANS) to further probe the structure informulations that are supposed to consist of flexible liposomes. Our studies suggest that the above solutions mayactually contain a combination of liposomes and micelles. In other words, the effect of adding detergent is not just tomake the liposomes flexible, but also to micellize a fraction of the lipids. To our knowledge, this aspect has not beenhighlighted in the literature thus far. Our findings suggest a different hypothesis for the skin-penetrating action of theseliposome formulations. We test this hypothesis further by examining the penetrating ability of new liposome-micellemixtures into hairless guinea pig skin using confocal microscopy.

334. Using Atomic Force Microscopy to investigate the interactions between living cells andparticles covered with RGD-containing proteins and the role of integrin bindingHiroyuki Shinto, Yuki Aso and Ko Higashitani, Kyoto University, Kyoto, Japan

The integrins are transmembrane adhesion molecules and act as cell-adhesion receptors that form contacts withextracellular matrix (ECM). They interact with one of many ECM components often by recognizing the tripeptidearginine-glycine-aspartic acid (RGD) in the substrate (e.g., laminin, fibronectin, or vitronectin).

In the present study, we have measured the interaction forces between living malignant melanoma B16F10 cells andthree types of polystyrene latex (PSL) spheres, using the Atomic Force Microscopy (AFM) with the colloid probemethod: (i) bare PSL (bare/PSL) spheres; (ii) carboxyl-coated PSL (COOH/PSL) spheres; (iii) RGD-coated PSL(RGD/PSL) spheres, which were modified by RGD-containing proteins, namely ProNectin® F Plus. The adhesion forcesof these PSL spheres with the surface of B16F10 cells give the order of (bare/PSL) < (COOH/PSL) < (RGD/PSL) inmagnitude. This strong adhesion of the RGD/PSL sphere to the cell surface is considered to originate from the integrin-RGD binding.

Also, we have measured the cell-particle adhesion forces in a culture medium including RGD tripeptides, which inhibitthe adhesive function of the cell integrins by binding with them. The adhesion of COOH/PSL and RGD/PSL spheresbecame weaker with increasing the concentration of the dosed inhibitors, while that of bare/PSL sphere remainedalmost constant. These results indicate that the integrins play an important role in cell-particle adhesion, depending onthe surface chemistry of particles. The possible mechanism of cell-particle adhesion will be given in our talk.



335. Deposition of biocomposite coatings from live cells and large particles by convective-sedimentation assemblyLindsey B. Jerrim and Orlin D. Velev, North Carolina State University, Raleigh, NC

We developed a method for depositing live cells and large particles in uniform, close-packed monolayers. It is based onconvective assembly at high volume fractions in the presence of sedimentation ("convective-sedimentation" assembly),and allows rapid deposition of uniform, close-packed coatings of yeast cells onto a glass plate (see figure). Acomputational model was developed to calculate the thickness profile of a coating by breaking the depositionmechanism into three discrete components: convection, evaporation, and sedimentation. The use of this model, inconjunction with parametric experiments, determined that both increasing the forward angle of the device anddecreasing the angle between the slides in the device increase the uniformity of the coatings deposited. In the nextstep of this work, the convective-sedimentation assembly was used to deposit composite coatings of live cells and largelatex particles as prototypes of self-cleaning materials. The latex particles form a protective, porous cover over theyeast cells, which cluster around the bottom parts of the microspheres. When exposed to growth media, the cellsproliferate and form a layer over the latex particles. When this coating is exposed to fluid flow, the overlaying cell layeris sloughed off, along with any debris that collects on the layer of cells. The cells remaining with the latex particles inthe coating will then continue to proliferate, thereby regenerating the coating.

336. Multi-Compartment Carriers for Enhanced Drug DeliveryGuohui Wu, university of california, santa barbara, santa barbara, CA, Rachel Freund, Santa Barbara City College,Santa Barbara, CA and Joseph Anthony Zasadzinski, University of California, Santa Barbara, CA

Vesosomes, a multi-compartment structure consisting of drug-loaded liposomes encapsulated within another bilayer, isa promising drug carrier with improved drug retention and stability compared with unilamellar liposomes. The vesosomepreparation takes advantage of the interdigitated phase of saturated lipids, which causes lipid bilayers to form flat, opensheets at low temperature, that close to form large unilamellar vesicles at higher temperatures. During this closure, theinterdigitated sheets encapsulate other lipid vesicles or colloidal particles to form and thereby become the outermembrane of the vesosome. However, vesosomes exterior shells made from a single lipid component, such asdipalmitoylphosphatidylcholine (DPPC), has an average diameter of 1.3 µm, too large for optimal intravenous use. Theaddition of poloxamer 188 (P188) at low concentrations preserves the interdigitated phase transition and can effectivelydecrease the vesosome diameter. Freeze-fracture TEM and light scattering were used to evaluate the size distributionand polydispersity of the vesosomes formed; poloxamer led to a decrease in the average diameter to about 0.6 µm.The polymer may also provide an extra steric layer protection of vesosomes against flocculation or recognition by theimmune system. Applying osmotic pressure by diluting the vesosomes with buffer of increased salt concentration canfurther decrease the vesosome diameter.

337. Impact of surfactant in solid oral dosage forms for small moleculesCraig A. McKelvey, Merck & Co., Inc., West Point, PA

Surfactant is used in oral dosage forms as a solubilizer and/or wetting agent. Applications including liquid filledcapsules, conventional dry tablets, and less conventional dry amorphous formulations employ surfactant for differentpurposes. This talk will discuss the impact of surfactant in these dosage forms, including (1) partial binary and ternaryphase behavior of common pharmaceutical liquid filled capsule formulation components (corn oil, Polysorbate 80,fractionated mono-,di-, and triglycerides, water etc.), (2) the synergistic effect of a bile salt on microemulsificationefficiency, and (3) the impact of surfactant during the dissolution and subsequent recrystallization of an insoluble drugin a conventional dosage form.



338. Interfacial Colloidal Sedimentation Equilibrium MicrostructuresMichael A. Bevan and Richar E. Beckham, Texas A&M University, College Station, TX

To intelligently design, control, and optimize self-assembly of three-dimensional colloidal structures on substrates (e.g.photonic crystals), it is necessary to understand how interactions between colloids, surfaces, and external fields lead tovarious interfacial microstructures. In this talk, we present confocal microscopy measurements and statistical mechanicalanalyses of the sedimentation equilibrium of inhomogeneous colloidal fluids coexisting with crystals above macroscopicplanar surfaces. In contrast to most previous sedimentation equilibrium studies, the present work focuses on relativelycompact microstructures over 10-100 particle diameters due to the similarity of particle dimensions and thecharacteristic gravitational lengthscale (mgd/kT~1). A new method is reported to obtain sedimentation equilibriumprofiles of sub-micron fluorescent silica core-shell colloids by deconvoluting intensity profiles as density distributionswithout locating particle centers. This approach overcomes limitations on accurately locating very large numbers of 3Dparticle centers in the presence of significant Brownian motion, but still allows real-space visualization of equilibriumfluid and crystal phase microstructures. Inverse analyses of the resulting sedimentation equilibrium profiles usingperturbation theory (based on the local density approximation), Monte Carlo, and a new density functional theoryformulation are used to extract particle pair potentials in excellent agreement with independent measurements.

339. Dynamics and Collapses of Two-Dimensional Colloidal LatticesSowmitri Tarimala, Chihyuan Wu and Lenore L. Dai, Texas Tech University, Lubbock, TX

One interesting aspect of colloidal particles is the formation of colloidal crystals at the two-dimensional and three-dimensional level. Here we report the dynamics and collapses of colloidal lattices at liquid-liquid interfaces usingPickering emulsions as an experimental template. The colloidal particles oscillate around their equilibrium positions. Theshort-time diffusion constant of single particles increases with increasing the lattice spacing; the oil phase viscosity onlyhas an effect on diffusion at large inter-particle distances. Strikingly, we observe that the equilibrium structure can bedisturbed when increasing the output laser intensity in a confocal laser scanning microscope which leads to thecollapse of colloidal lattices under small radiation pressure forces.

340. Spontaneous pattern formation by dip coating of colloidal suspensions onhomogeneous surfacesMoniraj Ghosh, johns Hopkins University, Baltimore, MD, Fengqiu Fan, Saoirse Corporation, Cambridge, MA andKathleen J. Stebe, Johns Hopkins University, Baltimore, MD

A partially wet, energetically homogeneous plate is withdrawn vertically at velocity U from a suspension of well-wetcolloidal particles. Periodic horizontal striped assemblies form at the three phase contact line, with stripe width andspacing depending on the withdrawal velocity U relative to a transition velocity Ut. Thick stripes separated by largespaces form for U < Ut. For U > Ut, thin stripes separated by small spaces form. Stripe spacing is reduced by an orderof magnitude and varies weakly with U until a maximum velocity is reached at which the stripes fail to form. A partiallywet surface can entrain a meniscus. For U < Ut, the meniscus forms with a pinned contact line. As the plate movesupward, it stretches the meniscus until it becomes too heavy to be retained by the wet, porous network provided by theparticles at the contact line. The contact line then jumps backwards to find a new equilibrium location, and the processbegins anew. For U>Ut, a film of thickness h is entrained above the meniscus. For h smaller than the particle diameterD, particles aggregate where the entrained film thickens to match up to the wetting meniscus. When an entrainedparticle becomes exposed to air by evaporation, it becomes the new pinning site. h increases with U; at some velocity,h becomes comparable to D. Particles flow into the film and deposit there in a disordered manner. A diagramsummarizing particle deposition is developed as a function of D, U and h.

341. Dipole interactions between dielectric spheres in AC electric fields

Manish Mittal1, Eric W. Kaler2 and Eric M. Furst2, (1)University Of Delaware, Newark, DE, (2)University of Delaware,Newark, DE

Micron-sized dielectric spheres aggregate to form linear chains on application of an AC electric field. The dipole-dipole



attraction is the dominant force in this process. The potential energy of a pair of polystyrene spheres has beenexperimentally measured. This is done by observing the equilibrium separation between particles held in static opticaltraps of known trap strength at various electric field intensities. The potential is evaluated for a range of saltconcentrations and electric field frequencies. Subsequently the kinetics of “pearl-chain” growth has also been studiedunder the same conditions. The potential calculated for a pair is then used to predict the aggregation kinetics andcomparisons are made with those obtained by solving the Smoluchowski equation. This study helps in validating thepotential calculated for a pair and extending the results from pair interaction to those for an ensemble of particles.

342. Electrokinetically-driven Capture of Colloidal Particles within Media of High IonicStrengthMatthew R. Tomkins, Jeffery A. Wood and Aristides Docoslis, Queen's University at Kingston, Kingston, ON, Canada

Experiments and numerical simulations are combined in an attempt to elucidate the mechanism by which colloidalparticles suspended in physiologically relevant (i.e., high ionic strength) media can be electrokinetically sampled on asurface. Results are reported for the trapping of 210 nm fluorescently labeled polystyrene spheres under the influenceof a high frequency non-uniform electric field created by planar quadrupolar microelectrodes deposited on an oxidizedsilicon chip. 3D computer modeling is subsequently used to yield the spatial profiles of electric field intensity,temperature, fluid velocity and force balance on the particles. The results suggest that the experimentally observedrapid particle trapping is achieved by the synergistic action of dielectrophoresis and electrothermal fluid flow.Specifically, electrothermal fluid flow was found responsible for the transport of the particles from the bulk of asuspension to the surface, where dielectrophoretic forces, which become significant only at very small length scalesfrom the surface, cause their stable capture. The calculations show that the time scales associated with the transportand capture of particles when a non-uniform AC field is used are smaller by at least one order of magnitude whencompared with those corresponding to a diffusion-limited system. This study can provide valuable insights in the designand operation of biosensors for rapid and in-situ detection of pathogens from small sample volumes, or thedevelopment of point-of-care diagnostic devices and micro-total analysis systems (micro-TAS) that operate on ACelectrokinetic principles.

343. Aggregation: how does a doublet of spheres interact with other particles?ABSTRACT WITHDRAWN

The dynamics of aggregation in colloidal systems are often described in terms of collision efficiencies: the ratio of actualaggregation to that caused by only the external forces on the individual particles. A standard way to calculate theseefficiencies is to consider the effects of hydrodynamics, Brownian motion, and other colloid-scale forces on theinteraction of two spheres. However, a particle formed from two aggregated spheres is far from spherical, and theaccuracy of this approximation remains open.

In this paper we use an "exact" method to investigate the interaction between an aggregated doublet of spheres and athird sphere, under the action of hydrodynamic forces. We show how this interaction depends on the orientation of thedoublet, compare the overall mobility of the system with that predicted more quickly by the Stokesian Dynamicsapproximation, and give some engineering approximations for the radius which should be chosen for the new sphererepresenting the doublet, in order to make best use of the spherical approximation.

This is work carried out in part by Anushi Weliwita, a summer project student from Sri Lanka.

344. Ionically self-assembled thin films for second-order nonlinear opticsAkhilesh Garg, Cemil Durak, Richey M. Davis and Randy Heflin, Virginia Polytechnic Institute and State University,Blacksburg, VA

Organic materials exhibiting second-order non-linear optical (NLO) properties are a key to the development of advancedelectro-optic modulators used in fiber-optic communications system. This research concerns a layer-by-layer techniqueused to fabricate films with useful second order NLO properties. A polycation - poly(allylamine) hydrochloride (PAH) -and a polyanion, poly{1-[4-(3-carboxy-4-hydroxyphenylazo)-benzenesulfonamido]-1,2ethandiyl} (PCBS) are self-assembled on a substrate by alternately adsorbing the two polymers. We study the film deposition process using a



Quartz Crystal Microbalance (QCM), ellipsometry, and absorbance measurements.

The deposition of multiple layers of PAH and PCBS adsorption were studied at different concentrations using a silicondioxide-coated substrate in a QCM. The results show a linear decrease in frequency with increasing number ofadsorbed layer signifying a homogeneous growth of the self-assembled films. Data obtained from QCM were comparedwith thickness measurements from ellipsometric data and absorbance measurements to estimate the water content inthese films. These findings will help us to understand this self-assembly at the molecular level in order to make apractical electro-optic modulation device.

345. Effects of ion size and charge on the electrical double layer formation in nanopores

Chia-Hung Hou1, Patricia L. Taboada-Serrano2, Sotira Yiacoumi1 and Costas Tsouris3, (1)Georgia Institute ofTechnology, Atlanta, GA, (2)Georgia Institute of Technology, Oak Ridge, TN, (3)Oak Ridge National Laboratory, OakRidge, TN

Electrical double layer (EDL) formation in nanoporous materials is important to many physicochemical processes ofpractical significance, including energy storage in super-capacitors and water purification. The effects of ion size andcharge of electrolytes confined in charged nanopores are simulated here by Monte Carlo techniques, includingCanonical Monte Carlo and Grand Canonical Monte Carlo. Simulation results show that multivalent and monovalentions present different characteristics under an electrostatic field in nanopores. When the pore size approaches to thedimension of ionic species, EDL overlapping occurs, which limits participation of ions in EDL formation. The distributionof ionic species is also very sensitive to the ion size. Furthermore, charge inversion may occur under certain conditionsof high electrolyte concentration and high surface charge. This phenomenon is more evident in the presence ofmultivalent counterions of a larger diameter. Three competitive factors can explain the fundamental mechanisms behindthe EDL behavior: (i) ion displacement due to ion-excluded volume, (ii) asymmetry in ion charge, and (iii) occurrence ofEDL overlapping. Besides the modeling work, electrochemical characteristics are revealed by cyclic voltammetry,demonstrating that the relationship between the pore size and ion size can determine the EDL capacitance ofnanoporous electrodes. This study concludes that the consideration of ion size, in both experimental and theoreticalstudies, is essential to our understanding of the EDL behavior of nanoporous materials, as well as to applications ofpractical significance.

346. Synthesis of Gas-Hydrate Aggregates for Applications in Energy Systems

Patricia L. Taboada-Serrano1, Phillip Szymcek2, Shannon Ulrich2, Megan E. Madden2, Tommy J. Phelps2 andCostas Tsouris2, (1)Georgia Institute of Technology, Oak Ridge, TN, (2)Oak Ridge National Laboratory, Oak Ridge, TN

Gas hydrates are solid crystalline structures in which water cages enclose gas molecules in a unit volume equivalent toat least a hundred unit volumes of gas under the same conditions. Naturally occurring gas hydrates can be found inocean sediments or the permafrost, and their existence constitutes an attractive future source of energy. Industrially,gas hydrates offer promising means for safe storage and transport of large volumes of gas, as well as produced waterpurification at the wellhead during natural gas production operations. Additionally, the utilization of gas hydrates is beingexplored as a feasible method for direct carbon sequestration. In this work, we report on the investigation of strategiesfor the synthesis of gas hydrate aggregates intended for applications as mentioned above. Gas hydrate aggregates ofvarying degree of consistency are synthesized in a two-phase, micro-emulsion injector reactor. Degrees ofcohesiveness desired for specific applications can be controlled by the choice of guest gas and its composition in the



hydrocarbon phase, and by the regulation of such operating parameters as pressure, temperature, reactant ratios anddegree of emulsification. Results on hydrate synthesis dealing with ocean carbon sequestration and coal-bed methaneproduced water treatment at the wellhead are discussed.

347. Influence of Synthesis Technique on Electrokinetic Properties of Fullerene (C60)Nanoparticles in Aqueous SolutionsKai Loon Chen and Menachem Elimelech, Yale University, New Haven, CT

Buckminsterfullerene C60 is an emerging nanomaterial that has attracted interest for its diversity of potentialapplications. Since fullerene C60 is only soluble in some organic solvents and is almost insoluble in water, recentefforts have been made to synthesize fullerene nanoparticles suspended in water suitable for use in aqueous andbiological systems. Currently, there are two techniques employed to synthesize these nanoparticles. One techniqueinvolves first dissolving fullerene in an organic solvent before ultrasonicating the mixture in water to remove the organicsolvent. Another technique simply requires the prolonged stirring of fullerene in water. Past studies have shown thatfullerene nanoparticles synthesized through both techniques exhibit a negative electrophoretic mobility, the source ofwhich is still unclear. In this study, we compare the electrokinetic properties and stability ratios of fullerene nanoparticlessynthesized through both techniques with the objective of understanding the source of their surface charge.Electrophoretic mobility measurements showed that both nanoparticles remained negatively charged over the pH rangeof 2–12, and that the electrophoretic mobility became less negative towards the lower pH. The aggregation kinetics ofthese nanoparticles were derived through time-resolved dynamic light scattering over a range of sodium and calciumchloride concentrations. The nanoparticles synthesized through prolonged stirring proved to be more stable toaggregation than the other, implying that the synthesis technique plays an important influence over their surfacecharacteristics. Spectroscopic study will be conducted to detect the formation of charged functional groups on thenanoparticles through the synthesis procedures.

348. The Effect of Filler-Polymer Interfacial Interactions on the Mechanical and RheologicalPerformance of Automotive Topcoats

Dariush Hosseinpour1, James T. Guthrie2 and John C Berg1, (1)University of Washington, Seattle, WA, (2)Universityof Leeds, Leeds, United Kingdom

Abstract:

The nature of interactions in assembled coatings containing an alumina filler that has been coated with differentchemical agents was investigated. The continuous medium was an automotive acrylic-melamine topcoat. The aluminaparticle was incorporated into the polymer solution with the aid of wetting and dispersing agent over a range of particleloading levels up to a particle volume concentration (pvc) of 50%. The approach taken involved ultimate tensile strengthevaluations and rheology studies. In general, it was found that there is a strong correlation between the ultimate tensileproperties and both the alumina loading level and the nature of the surface treatment given to the alumina particles.Functionalization of the alumina with agents, to give apolar characteristics resulted in deterioration of the compositetensile strength. Alumina particles with polar surface treatments gave an interaction with the matrix that improved themechanical performance of the system. This improvement was attributed to the role of the Lewis acid–baseinteractions. The rheological studies and subsequent calculations show that, at the dispersion stage, the apparentthickness of adsorbed polymer layer varied with the nature of the surface of the alumina. The adsorbed layer had anintermediate thickness for the dispersions containing the polar alumina. This thickness for the systems containingapolar alumina and untreated alumina was the greatest and the least, respectively.

349. Estimation of Hamaker coefficients for PEM fuel cell supported catalystsRam Subbaraman, Thomas Zawodzinski, Jr. and J. Adin Mann, Case Western Reserve University, Cleveland, OH

Supported Platinum electrocatalysts are used in Polymer electrolyte membrane fuel cells (PEMFC) to catalyze thehydrogen oxidation and oxygen reduction reactions. The high surface to volume ratios of supported catalysts maximizesthe area of catalytic surfaces available for reactions. A proper distribution of platinum nanoparticles on the carbonsupport minimizes the loss in activity due to agglomeration of the nanoparticles. Since colloidal interaction forces drive



the deposition process, it is imperative to understand the interactions between the support and the catalystnanoparticles. This interaction is used as the basis of our modeling of electrode structure using a hierarchical scheme ofsuccessively more complex structures. The free energy of interaction we measure is scaled by the Hamaker coefficientsfor the materials. We estimate these coefficients from optical spectra using Lifshitz theory; optical spectra for the carbonsupport and catalyst particles are measured. The Hamaker coefficients we compute are used in computer simulationsof the formation of particle ensembles using a stochastic model reported earlier that takes into account near neighborinteractions. The sensitivity to the values of the Hamaker coefficient on the processes of nanoparticle aggregation,dispersion on the surface and loading of catalysts will be discussed. Kinetic Monte Carlo calculations are performed toobtain nanoparticle cluster structure with and without the effect of the support interaction. We will discuss theimplications of the strength of the various interactions on the expected durability of fuel cell electrocatalyst structures.

350. Numerical simulation of nanocrystal formation in solution by burst nucleation anddiffusional growthD.T. Robb and V. Privman, Clarkson University, Potsdam, NY

The mechanism of "burst nucleation" of crystals from a supersaturated solution, as first put forward by LaMer andDinegar (J. Amer. Chem. Soc. 72, 4847 (1950)), has been widely used in explaining the chemical synthesis of bothmono- and poly-crystalline colloidal particles from solution. However, to our knowledge, the proposed kinetics of theburst nucleation mechanism have not been fully verified. Here we report the results of numerical simulations of a modelof the burst nucleation process, in which instant rethermalization of sub-critical embryos and irreversible diffusive growthof super-critical clusters is assumed. We present approximate analytical results for the long-time behavior of thecluster-size distribution in the model, and discuss the applicability of the model and numerical results to experimentalcolloidal systems.

351. The Balanced Nucleation and Growth Model for Controlled Crystal Nucleation and SizeDistribution – I. The ModelIngo Leubner, Crystallization Consulting, Penfield, NY

The Balanced Nucleation and Growth (BNG) Model was first proposed and experimentally supported in 1980(1-4). TheBNG model has correctly predicted previously unknown nucleation behaviors.

The present derivation of the BNG model is based on the classical concepts of Becker and Doering, but replaces thekinetic nucleation rate with the introduction of crystal growth processes during the nucleation phase.

The BNG model predicts the experimental result that many crystallization processes lead to a limited number of crystalsduring a nucleation period which is followed by growth only. Further, the model predicts the crystal formation during thenucleation phase, the crystal size distribution, maximum crystal size, number of crystals, nucleation rate and time.Model variables are the molar reactant addition rate during the nucleation phase, nucleation efficiency, critical nucleussize,and maximum crystal growth rate. These are related to experimental parameters. Without growth, the crystalnumber is proportional to addition rate and nucleation occurs continuously during the time of reactant addition.

The BNG model was originally derived for balanced double-jet batch precipitation, and later extended andexperimentally confirmed for controlled double-jet continuous crystallizations. (5)

1. Leubner, I. H., et al, Photogr. Sci. Eng., 24:268 (1980); 2.Leubner, I. H., J. Phys. Chem., 91:6069 - 6073 (1987; 3.Leubner, I. H., J. Disp. Sci. Technol., 22 :125 – 138 (2001); 4. Leubner, I. H., J. Disp. Sci. Technol., 23:577 – 590(2002); 5. Leubner, I. H., J. Imaging Sci. Technol., 42:357(1998)

352. The osmotic motorJohn F. Brady and Ubaldo Cordova-Figueroa, California Institute of Technology, Pasadena, CA

We propose a model for self-propulsion of a colloidal particle – the osmotic motor – immersed in a dispersion ofcolloidal ‘bath' particles. The osmotic motor is propelled by a chemical reaction that consumes bath particles over aportion of its surface. The non-equilibrium microstructure of bath particles induced by the surface reaction creates an



‘osmotic pressure' imbalance on the motor's surface causing it to move to regions of lower bath particle concentration.The osmotic motor's behavior is calculated for two scenarios: one in which the motor is held fixed and a second whereit is free to move. The departure of the bath particle concentration from equilibrium is characterized by the Damköhlernumber Da: the ratio between the surface reaction velocity and the diffusion velocity. The computed microstructure isemployed to calculate the driving force of the motor, from which the self-induced osmotic velocity is determined viaapplication of Stokes drag law. For small departures from equilibrium (Da << 1), the self-propulsion is determined bythe reaction velocity. In the large Da limit the surface reaction dominates over diffusion and the osmotic velocity cannotbe greater than the speed of bath particles that are about to react. The implications of these features for different bathparticle volume fractions and particle sizes are discussed. Theoretical predictions are compared with BrownianDynamics simulations.

353. Diffusion in charge-stabilized colloidal suspensions: Theory, simulation andexperiment

Gerhard Naegele1, Adolfo J. Banchio2, Adam Patkowski3 and Jacek Gapinski3, (1)Research Centre Juelich, Juelich,Germany, (2)Universidad Nacional de Cordoba, Cordoba, Argentina, (3)A. Mickiewicz University, Poznan, Poland

We report on a joint experimental-theoretical study of diffusion processes in dense suspensions of charge-stabilizedcolloidal spheres. Numerous transport properties have been calculated by means of a recently developed acceleratedStokesian dynamics simulation tool, and using methods of many-body theory adapted to colloidal soft matter systems.The simulation and theoretical methods describe quantitatively our static and dynamic synchrotron radiation scatteringexperiments on colloidal particles, globular proteins and DNA fragments. Salient results of this study comprise theabsence of screening of hydrodynamic flow in salt-free suspensions, and a hydrodynamic explanation for theunexpected non-monotonic concentration dependence of self-diffusion in suspensions of moderately charged particles.

354. Colloidal traffic through static and dynamic optical latticesGabriel C. Spalding, Illinois Wesleyan University, Bloomington, IL

Twenty years ago Arthur Ashkin, Steve Chu, and co-workers published the first paper using the single-beam opticalgradient trap, now known as Optical Tweezers. Recently, in the near field, we have successfully demonstrated anapproach that allows optical forces alone to assemble thousands of microparticles over macroscopic areas. Separately,the addition of simple holographic techniques has extended the basic capabilities of optical tweezing, making it a moreviable tool for the assembly of micro-systems and the organization of specimens into user-defined structures. Our earlyefforts at filling a 3D lattice of optical traps led to an appreciation for the dynamics of injected microparticle streams,which yield a surprisingly successful method of sorting or re-routing within microfludic environments. Here, we presentreal-space studies of Brownian hard sphere transport though externally defined potential energy landscapes.

355. Direct visualization of rod dynamics in three dimensions using confocal microscopyDeshpremy Mukhija and Michael J. Solomon, University of Michigan, Ann Arbor, MI

The dynamics of suspensions of anisometric colloids are of both fundamental and technological interest because of theireffect on liquid crystal phase transitions, rod-jamming and the transport of rigid, anisotropic bacteria, viruses andpolymers. Here, we develop and test an experimental method to investigate the dynamics of rod particles by measuringtheir rotation and translation in three dimensions. The method relies on solvent viscosification to retard dynamics toscales that are compatible with 3D confocal laser scanning microscopy. We demonstrate the performance of themethod by tracking the Brownian motion of fluorescent poly (methyl methacrylate) rods (aspect ratio, L/D = 3.1 and 7)grafted with poly (dimethylsiloxane). The rods are dispersed at dilute concentration in a solvent mixture of viscosity2000 cp. Rod translational and rotational diffusivities are extracted from the measured translational mean squaredisplacement and time correlation functions of the rod director, respectively. The orientational dynamics of the rods arecharacterized relative to both their azimuthal and polar angles. Experimental values obtained agree well with theory. Asan example of the future utility of this method, we investigate the rotational dynamics of depletion induced colloidal rod-gels.

356. Shear-induced migration of suspensions in 3D microfluidic geometries



Changbao Gao and James F. Gilchrist, Lehigh University, Bethlehem, PA

We investigated shear-induced migration of 1 micron Brownian particles in 1D, 2D, 3D steady microfluidic flowsgenerated in straight, herringbone, and staggered herringbone channels respectively. The transverse flows induced byrecessed herringbone structures in the top of the channels interplay with particle migration to the low shear regions ofthe pressure-driven flow. Using high-speed confocal laser scanning microscopy, we were able to image directly flowingparticles inside the channels. Moreover, we located the 3D positions for each particle and obtained 2D concentrationand 2D velocity profiles to better understand of the effects from the underlying flow topology, colloidal hydrodynamics,and Reynolds and Péclet number on particle migration.

357. Dynamics of suspensions of pH-responsive hydrogel colloidsJae Kyu Cho, L. Andrew Lyon and Victor Breedveld, Georgia Institute of Technology, Atlanta, GA

Colloidal hydrogel particles have attracted interest as building blocks for chemical sensors, photonic crystals and asdrug delivery vehicles. In addition, they are interesting model systems to study the phase behavior of colloidaldispersions with soft interaction potentials. The most commonly used pNIPAm hydrogels are temperature sensitive,showing a swelling-deswelling transition around 30 degrees Celcius; by including acrylic acid copolymer, one can obtainpNIPAm-co-AAc hydrogels that are also pH responsive.

For this work, we have investigated the dynamics of swelling and deswelling of these stimuli-responsive colloids in bothdilute and concentrated suspensions via particle tracking video-microscopy in a transparent microdialysis cell. Thedevice allows us to change the solvent composition (e.g. pH) in a controlled manner while simultaneously tracking themotion of hydrogel particles.

In dilute suspensions, we have studied the swelling-deswelling response of hydrogels of different sizes and varying AAccontents to elucidate the kinetics of the microstructural rearrangements of the hydrogel. In concentrated suspensions,the pH-induced particle expansion causes transitions between fluid, glassy and crystalline phases. Data will bepresented on the dynamics of the observed phase behavior, in particular crystal growth and jamming.

358. Microfluidic Assembly and Packing of Colloidal Granules

Robert F. Shepherd1, Jacinta C. Conrad1, Summer K. Rhodes1, Darren R. Link2, David A. Weitz3, Manuel Marquez4

and Jennifer A. Lewis1, (1)University of Illinois, Urbana-Champaign, Urbana, IL, (2)RainDance Technologies, Inc.,Guilford, CT, (3)Harvard University, Cambridge, MA, (4)Phillip Morris USA, Richmond, VA

The microfluidic assembly and packing of colloid-filled hydrogel drops and dried granules of varying shape andcomposition is investigated. Drops are formed by shearing a concentrated colloidal microsphere-acrylamide suspensionin a continuous oil phase using a sheath-flow or a double emulsion capillary device. Silica microspheres aresynthesized with different fluorescent cores to allow direct visualization of the process. Homogenous and Janus(hemispherically distinct) spheres and disks are produced by confining the assembled drops in microchannels ofprescribed geometry. To preserve their drop structure, photopolymerization of an acrylamide-based hydrogel solution iscarried out immediately after drop-breakup. Representative drops and dried granules are imaged using fluorescenceand scanning electron microscopy to probe their structural evolution during assembly and drying, while micro-CT isused to probe granular packing. Our approach opens up new opportunities for precision engineering of colloidal granulesize, shape, and composition.

359. A Generalized Hertzian Model for the Cracking of Thin Latex Films Saturated With FluidWilliam B. Russel and Ning Wu, Princeton University, Princeton, NJ

The concentration of a thin film of a stable colloidal dispersion increases as water evaporates until the particleseventually reach a random or ordered close packing. Further water evaporation generates a negative capillary pressurethat puts the film in tension. If the process temperature is below the glass transition temperature of the elastic particles,the latex film beyond a critical thickness will eventually crack. We develop a generalized model to understand thisquestion of cracking. We first construct a constitutive equation relating the stress to the strain with the assumption ofHertzian contact between colloidal particles. Then, employing a thin film approximation, we are able to reduce the



three-dimensional problem into two dimensions and calculate the relaxation of stress fields upon opening of a crack.Based on the well-known Griffith's energy criterion (by equating the recovery of elastic energy to surface energy), thetheory predicts critical capillary pressures necessary for opening of a single infinite crack, a finite isolated crack, parallelcracks, and intersecting cracks, respectively. The accompanying crack spacings are also predicted and they decreasewith increasing capillary pressures. Coupling the critical capillary pressure for cracking with the maximum capillarypressure sustainable with the air-water interface at the surface of the film then yields a critical film thickness belowwhich cracking will not occur. Finally, the comparison between our theoretical predictions and experimental results willbe discussed briefly.

360. Rheological probes of the relaxation dynamics of densely packed drops and bubbles

Hans M. Wyss1, Johan Mattsson2, Kunimasa Miyazaki3, David R. Reichman3 and David A. Weitz1, (1)HarvardUniversity, Cambridge, MA, (2)Chalmers University of Technology, Göteborg, Sweden, (3)Columbia University, NewYork, NY

Foams and compressed emulsions exhibit a fascinating mechanial behavior; while they consist entirely of fluids, theirmacroscopic rheological behavior is elastic-like within the time scales accessible to oscillatory rheology. They show theviscoelastic behavior typical for soft glassy materials, which suggests that a slow structural relaxation should dominatetheir rheology at low frequencies. In this talk we will present experimental results on these systems and discussdifferences to the behavior of suspensions of hard particles. We combine linear and nonlinear viscoelasticmeasurements by performing constant-rate sweeps, keeping the strain rate constant as the oscillation frequency isvaried. The viscoelastic response of these systems at different extents of oscillatory strain rate supports the validity ofStrain-Rate Frequency Superposition (SRFS) [*] for these systems; the shape of the structural relaxation remainsunchanged within a wide range of applied strain rates. However, the same techniques also allow us to detect asecondary relaxation process that appears to be intimately linked to the main structural relaxation itself, with a timescale that shows the same strain rate dependent scaling behavior. We present a simple model description thatqualitatively accounts for the observed behavior.

[*] see /cond-mat/0608151

361. Yield stress and thixotropy: on the difficulty of measuring yield stressesDaniel Bonn, University of Amsterdam and Ecole Normale Superieure, Amsterdam, Netherlands

The yield stress of many yield stress fluids has turned out to be difficult to determine experimentally. This has led tovarious discussions in the literature about those experimental difficulties, and the usefulness and pertinence of theconcept of yield stress fluids. We argue here that most of the difficulties disappear when taking the thixotropy of yieldstress fluids into account, and will demonstrate an experimental protocol that allows reproducible data to be obtainedfor the critical stress necessary for flow of these fluids. As a bonus, we will show that the interplay of yield stress andthixotropy allows one to account for the ubiquitous shear localization observed in these materials. However, due to thethixotropy the yield stress is no longer a material property, since it depends on the (shear) history of the sample.

362. DWS-based micro-rheology on vesicle depletion gelsMatthew L. Lynch and Tom Kodger, Procter & Gamble Company, Cincinnati, OH

Traditional DWS-based micro-rheology measures the high-frequency moduli of viscoelastic fluids by tracking the motionof particle tracers. We extended this concept to vesicle depletion gels where the viscoelasticity arises not only from theinterstitial viscoelastic fluid but also from the microstructure of the dispersion. Importantly, DWS measurements allow thedirect measure of vesicle motion (bypassing the need for tracers) with essentially no applied stress. There is a broadagreement between the magnitude of the moduli measured with oscillatory rheology and DWS-based micro-rheologydemonstrating the general application of this combined technique for studying particle gels. This approach is beingused to study collapse rates, aging and delayed collapse of these gels.

363. Nonlinear microrheology of a wormlike micelle solution using ferromagnetic nanowireprobes



Nathan Cappallo, Clayton Lapointe, Robert L. Leheny and Daniel H. Reich, Johns Hopkins University, Baltimore, MD

We describe the application of high-aspect-ratio ferromagnetic nanowires as microrheological probes of wormlikemicelle solutions composed of equimolar cetylpyridinium chloride/sodium salicylate (CPCl/NaSal). Employing high-speedvideo microscopy to track the rotation of suspended nanowires in response to external magnetic fields we access boththe linear and nonlinear rheology of the fluid. The linear viscosity at low rotation rates is strongly temperaturedependent as expected from macroscopic rheometry. At high rotation rates the viscosity exhibits pronounced shearthinning that is surprisingly independent of temperature. The onset of the nonlinear response is characterized by ashear thickening that has no apparent counterpart in the macroscopic rheometry. Measurements involving step changesin rotation rate reveal that, once the fluid has been prepared into a shear-induced state, it exhibits nonlinear behaviorfar within the expected linear regime. Further, the shear-thinned fluid generates an out-of-plane torque on the wirewhose magnitude varies as a power law with the rotation rate, with a power-law exponent of approximately 0.4. Fromtime-resolved measurements tracking the motion of the wire in response to this torque we extract an effective viscosityfor drag perpendicular to the nonlinear shear flow. This viscosity reveals insight into the anisotropic behavior of theshear induced state.

364. Active Laser Tweezer Microrheology of a Colloidal SuspensionIndira Gopal and Eric M. Furst, University of Delaware, Newark, DE

We investigate the behavior of a colloidal suspension using active, oscillatory microrheology. The experimental systemis an aqueous suspension of index matched fluorinated ethylene propylene (FEP) particles embedded with either 2 umsilica or 3 um polystyrene probe particles. The probes are trapped and oscillated using laser tweezers at frequencies of5-1000 Hz and at amplitudes of 25-400 nm. The oscillation amplitude and phase of the probe are measured using aphoto diode and lock-in amplifier, which are used to compute the frequency dependent microviscosity of thesuspension. Frequency thinning is observed at all concentrations and is most significant for volume fractions above 0.3.The results are in quantitative agreement with both previous measurements of the suspension microviscosity [1] andrecently developed theory [2].

[1] Meyer, A., et al., Journal of Rheology. 50(1), 77-92, (2006). [2] Khair, A. S., and J. F. Brady, Journal of Rheology.49(6), 1449-1481, (2005).

365. Apparent Microrheology of Oil-Water Interfaces by Single Particle TrackingJian Wu and Lenore L. Dai, Texas Tech University, Lubbock, TX

We investigate the dynamics of charged microparticles at polydimethylsiloxane (oil) - water interfaces using Pickeringemulsions as an experimental template. The mobility of the charged particles depends largely on the viscoelasticproperties of the oil phase and the wettability of the solid particles. More importantly, we have explored the potential ofdeveloping one-particle microrheology at liquid-liquid interfaces. The complex, loss, and storage moduli of oil-waterinterfaces as a function of frequency measured from microrheology are compared with those of bulk oils measured froma conventional rheometer and developed bulk microrheology. The nature of the tracer particles plays an important rolein one-particle microrheology at liquid-liquid interfaces, especially when the oil phase is viscoelastic.

366. Dissolution of concentrated surfactant systems: convection and microstructuraleffectsMarco Caggioni, Christopher Stoltz and Pat Spicer, Procter and Gamble Company, West Chester, OH

We utilize a combination of millifluidic and particle tracking microrheology experiments to study dissolution dynamics inconcentrated surfactant systems. Previous work conducted demonstrated the diffusion-limited nature of this processand highlighted the need for a better understanding of mesophase formation and convective effects on dissolutiondynamics [1,2]. Our experiments enable us to measure diffusivity in the different meshophases formed duringdissolution by combining results obtained with different boundary conditions. The use of millifluidic devices allows us toinvestigate the role of convection on dissolution dynamics while microrheology provides information on the evolution oflocal viscoelastic properties.



1 Lim, J. C., Miller, C. A., "Dynamic Behavior and Detergency in Systems Containing Nonionic Surfactants and Mixturesof Polar and Nonpolar Oils," Langmuir, 7, 2021-7 (1991).

2 Chen, B.-H., Miller, C. A., Walsh, J. M., Warren, P. B., Ruddock, J. N., Garrett, P. R., Argoul, F., Leger, C.,"Dissolution Rates of Pure Nonionic Surfactants," Langmuir, 16, 5276-83 (2000).

367. Co-assembly of Alkylated DNA Oligomers and Nonionic SurfactantsShane T. Grosser, Jeffrey M. Savard and James W. Schneider, Carnegie Mellon University, Pittsburgh, PA

Electrokinetic separation of DNA oligomers is a fundamental procedure in bioanalytical chemistry. While lengthresolution is typically achieved by the use of polymer gels as sieving matrices, a faster alternative is to end-labeloligomers with uncharged objects so that the charge-to-mass ratio varies with oligomer length. With this goal in mind,we have been exploring the use of nonionic micelles as end-labels for DNA in capillary electophoresis. DNA oligomersof interest are end-alkylated (either covalently or by hybridization of an alkylated probe) to provide for interaction withmicelles. Unlike covalently attached polymers or proteins, nonionic micelles transiently attach to alkylated DNA by a co-assembly mechanism, and this provides important advantages in bioanalytical applications. One is that the mobility ofthe alkylated DNA can be tuned to prevent co-migration of oligomers. Using open-channel capillary electrophoresis inthe presence of Triton X-100, we demonstrate that DNA mobility is a very strong function of the attached alkane lengthin the range of C12 to C18. A phase partitioning model is presented that fully accounts for the effect of alkane length,DNA oligomer length, micelle size, and micelle concentration on the observed mobility. The model can be used tomeasure the length of alkylated DNA, and model parameters can be predicted by thermodynamics of the co-assemblyprocess. Bi-alkylated DNA oligomers have also been synthesized. The combined effect of micelles at each end on isfound to be additive for long oligomers, but is attenuated for short ones due to hydrodynamic communication betweenthe micelles.

368. Reversible heteroaggregation of lipid vesicles using DNA as biomolecular combinationlocksPaul A. Beales and T. Kyle Vanderlick, Princeton University, Princeton, NJ

Besides being model systems for studying biological processes in cell membranes, lipid vesicles offer promise ascontainers for use in technological applications. Gaining control of the interactions between vesicles of differentpopulations will enable vesicles with different chemical contents to be brought together into higher order structures formanipulation: potentially their cargo could be mixed in small volumes by inducing fusion events between the vesicles insuch conglomerates. We use single-stranded DNA (ssDNA) anchored to the vesicle membrane to bind to vesicles of asecond population with the complementary ssDNA anchored to their membranes. The vesicles self-assemble intosuperstructures of bound vesicles directed by the specificity of the interaction between complementary ssDNA strands.We find three regimes of aggregation behaviour: no aggregation, stable aggregates and aggregates that grow untilflocculates are visible in solution. The rate of aggregation is determined by the vesicle collision rate and the probabilityof hybridisation of complementary ssDNA strands during a collision. Vesicle binding is found to be reversible by heatingabove a melting temperature for the DNA duplex. The thermal stability of the DNA duplex is found to be greatlyenhanced when anchored to the vesicles compared with the stability in free solution. This is caused by the enhancedlocal concentration and reduced conformational entropy of the DNA due to being anchored to the lipid vesicles.

369. Numerical study on the self-assembling of DNA-dendrimersJulio Largo, University of Rome La Sapienza, Roma, Italy, Francis W. Starr, Wesleyan University, Middletown, CT andFrancesco Sciortino, Universita' di Roma La Sapienza, Roma, Italy

The synthesis of nanoparticle building blocks functionalized with specifically designed oligonucleotides [1] has openednew possibilities for the assembly of networked materials. The DNA-type interactions offer selectivity and sensitivity thatwill play an important role in the self-assembly of these particles. These properties allow us to control the inter-particleinteractions that will lead to the construction of the desired supra-molecular structures. We present a moleculardynamics simulation study of a simple DNA-dendrimer model designed [2] to capture the basic characteristics of thebiological interactions. Exploring a large set of state points [3], we follow the progressive formation of a percolatinglarge-scale network whose connectivity can be described by random percolation theory. We identify the relative regions



of network formation and kinetic arrest versus phase separation. The location of the two-phase region can beinterpreted in the same framework as reduced valency models. This correspondence provides guidelines for designingstable, equilibrium self-assembled low-density networks. Finally, we demonstrate a relation between bonding anddynamics, by showing that the temperature dependence of the diffusion constant is controlled by the number of fullyun-bonded dendrimers.

The design of an effective inter-particle potential for this family of dendrimers is discussed. The results obtained withthis effective potential are compared with the results of the full-system.

[1] Mirkin C A, Letsinger R L, Mucic R C and Storhoff J J Nature 382 607–9 (2006)

[2] Starr F.W. and Sciortino F.,J. Phys.: Condens. Matter 18 L347–L353 (2006).

[3] Largo J., Starr F.W. and Sciortino F. Langmuir (2007).

370. Phase behavior and surface anchoring of an isomeric monolayer at a nemtic liquidcrystal/aqueous interfaceAndrew D. Price and Daniel K. Schwartz, University of Colorado, Boulder, Boulder, CO

In the absence of an external field, the long-range alignment of a nematic liquid crystal (NLC) layer depends on surfaceanchoring by the bounding surfaces. A dynamic surface composed of an adsorbed amphiphilic monolayer at thenematic/aqueous interface anchors the nematic in both a temperature and surface pressure-dependent manner inresponse to the molecular organization of the monolayer. When composed of the azobenzene derivative 8Az3COOHanchoring is also shown to significantly depend on the isomeric (cis-trans) composition of the monolayer. Long-rangealignment of the NLC layer is characterized by both the birefringence and director azimuth. Exhibited are isotropic 2Dvapor and liquid phases, primarily dependent on surface pressure, and condensed mesophase domains with defineddirector azimuths at temperatures below 8-10 oC. Isomeric mixtures additionally exhibit a smectic C-like phase thatanchors the NLC with varying degrees of birefringence and no set director azimuth. The phase diagram of an8Az3COOH monolayer adsorbed at a nematic/aqueous interface is plotted as a function of the control parameters(temperature, surface concentration, and irradiation).

371. Single-molecule studies of surfactant adsorption, desorption, and surface diffusionDaniel K. Schwartz, Andrei Honciuc and Adam Harant, University of Colorado, Boulder, Boulder, CO

We report single-molecule observations of surfactant adsorption, desorption, and surface diffusion at the solid/solutioninterface using total internal reflection fluorescence microscopy (TIRFM). Typical surfactants used include carboxylic andphosphatidic acids; substrates include fused silica and single crystal sapphire. The observation of individual adsorptionand desorption events permits the calculation of molecular "on rates" and "off rates" as a function of concentration, andtheir comparison to the net adsorption rate as measured by laterally-averaging techniques. The surface residence timedistribution is also determined, and is consistent with first-order desorption kinetics. Surface trajectories of individualmolecules are analyzed as a function of surface crowding, and analyzed with respect to two-dimensional Brownianmotion. Typical surface diffusivities are in the range 0.01-0.1 square microns/second. Some interesting anomalies fromideal Brownian behavior are observed at long diffusion times.

372. Structural Transition of Polyelectrolyte Brush at the Air/Water InterfaceHideki Matsuoka, Ploysai Kaewsaiha, Yoshiko Suetomi and Tasuku Yamada, Kyoto University, Kyoto, Japan

The nanostructure and its transition of polyelectrolyte brushes in the amphiphilic diblock copolymer monolayers on thewater surface were investigated by X-ray and neutron reflectivity techniques. The critical brush density (cbd), where thetransition between carpet-only/carpet+brush structures occurs, was quantitatively determined and its dependencies onthe hydrophilic chain length and salt concentration were examined. The cbd for polymethacrylic acid (PMA) brushdecreased with increasing PMA chain length. The cbd for polystyrenesulfonate (PSS) showed no chain lengthdependence but increased beyond the critical salt concentration. The cbd for polyacrylic acid (PAA) showed no chainlength and no salt concentration dependencies. Hence the brush formation mechanism is suggested to be different from



each other for these three polyelectrolyte brushes. The salt effect on PSS brush and small ion transportation from/tothe PSS brush layer were also discussed. Ref. P.Kaewsaiha, K.Matsumoto, H.Matsuoka, Langmuir, 23(1), 20-24(2007).

373. Self-assembly of multilayer structures at the air-water and silicon-water interfaces

Mauro Moglianetti1, Simon Titmuss1, S.P. Armes2 and Robert K. Thomas1, (1)Oxford University, Oxford, UnitedKingdom, (2)University of Sheffield, Sheffield, United Kingdom

The self-assembly of multilayer structures has been observed for two different polymer/surfactant systems at the air-water and at silicon-water interfaces through neutron reflectivity measurements.

At the air-water interface, poly(dimethyl aminoethylmethacrylate) (poly(DMAEMA)) and sodium dodecyl sulphate (SDS)form multilayer structures at different surfactant concentrations at high and low pH. The use of different isotopiccompositions, in particular a perdeuterated polymer in combination with both hydrogenated and perdeuteratedsurfactant, have allowed a complete characterization of the distribution of the polymer and surfactant across themultilayer structure.

At the silicon-water interface, a high charge density polyelectrolyte incorporating poly(ethylene oxide) side chains(poly(PEOyMEMA:METACx)) forms a multilayer structure at a bulk concentration of SDS that is below the CMC. Theposition of the characteristic Bragg peak in the reflectivity profile, suggests the presence of surface micelles. The use ofmultiple isotopic compositions allows us to propose a multilayer structure in which layers that are predominantlycomposed of SDS micelles and water alternate with layers that are predominantly polymer and water. The micellarlayers do include some polymer, which suggests that a cooperative binding mechanism is responsible for the multilayerstructure.

374. Underwater Contact Angle Hysteresis of Superhydrophobic Polymer SurfacesH. Yildirim Erbil, Gebze Institute of Technology, Kocaeli, Turkey

Surfaces that would decrease marine biofouling attract considerable theoretical and practical interest in the last decade.Recently, it was demonstrated that engineered topographically corrugated surfaces are capable of reducing biofoulingbecause the fouling organisms that are larger than the primary length scale of the surface texture would exhibit reducedadhesion strength as there would be fewer attachment points. However, when roughness and chemical heterogeneity isintroduced to a surface, then usually a large contact angle hysteresis, (H = θ adv - θ rec) is found showing thedeviation from the ideal flat and homogeneous surfaces. There are reports that H of the substrate has some effect onbiofouling and coatings having the lowest H show the best biorelease properties. In all of these publications, H and thecritical surface tension (γc) values of substrates were measured under air. Relating these values to the underwaterbiofouling process is an indirect method and unjustified because low-energy surfaces in air tend to form high-energyinterface in aqueous solutions, and vice versa. Thus, there is a need to determine (Hunderwater) values for bettercorrelation to bioadhesion. Underwater contact angle measurement can be done by applying the two-liquids contactangle method and its combination with the one-liquid method have been discussed. In this work, we show thedetermination of underwater contact angle hysteresis of rough, hydrophobic polymer surfaces using two-liquids and airbubble in water methods and discuss its possible implications on biofouling.

375. Lotus Inspired Superhydrophobic Coating using a Simple Single-step Sol-gelApproach

Eric D. Branson1, C. Jeffery Brinker1, Frank B. van Swol1 and Seema Singh2, (1)Sandia National Labs / University ofNew Mexico, Albuquerque, NM, (2)Sandia National Laboratories, Albuquerque, NM

Over the last decade there has been a growing interest in creating superhydrophobic (SH) surfaces stimulated by awide range of potential applications. Superhydrophobicity is loosely defined as contact angles of water exceeding 150º.It has been suggested that contamination, corrosion, oxidation, current conduction and flow resistance can all bereduced on superhydrophobic surfaces. Wenzel and Cassie - Baxter have established equations relating surfaceroughness and contact angle. Both natural and synthetic SH materials show that both micro and nano scale roughnessare needed to achieve superhydrophobicity. Using our simple silica based aerogel procedure, SH films with contact



angles greater than 165º have been achieved with minimal roughness (~ 40nm). Using AFM, NMR, and scattering(GISAXS/light), we are correlating pore size and surface roughness to superhydrophobicity. Furthermore we havedeveloped a procedure to optically control wetting of our SH surfaces. Exposure to UV light causes the macroscopiccontact angle to vary continuously from about 165º to 0º depending on exposure time. The result is a UV dose-dependent decrease in contact angle. Spatial patterning is achieved by UV exposure through a mask as withconventional lithography. This treatment changes the surface energy without affecting the surface structure. Vaporphase exposure to a trimethylsilane restores the contact angle to nearly its original value. We present our simple singlestep procedure for creating optically transparent SH coatings with minimal surface roughness and show the optimumconditions needed for droplet rolling while also including some potential applications of these coatings.

376. Retention forces of a liquid slug in a rough capillary with symmetric or asymmetricfeaturesC. W. Extrand, Entegris, Chaska, MN

On surfaces with asymmetric or “saw tooth” features, liquid slugs or drops tend to move preferentially in one direction.In these systems, capillarity manifests itself as a retention force that holds back the movement of liquids againstexternally applied forces, such as gravity or pressure. In this theoretical study, the imbalance of capillary forces thatleads to directionally-biased wetting is examined. Capillary tubes with symmetric and asymmetric saw tooth featureswere used to estimate the ratios of retention forces in opposing directions. Our analysis suggests that the differencebetween the retention force in one direction versus the other can be maximized by increasing feature asymmetry andminimizing inherent hysteresis (liquid-solid adhesion) of the materials of construction. This work has implications forsmall channels or surfaces of fluid handling components found in microfluidic devices and fuel cells.

377. DNA Multi-Ring Formation Via Evaporation ProcessLu Zhang, Siddharth Maheshwari, Hsueh-Chia Chang and Y. Elaine Zhu, University of Notre Dame, Notre Dame, IN

The evaporation of a droplet often leads to the formation of a ‘coffee ring' pattern due to the outward evaporative fluxwhich carries the nonvolatile solute to the edge of the contact line. In this talk, we present an interesting observation ofmulti-ring formation of DNA stain and elucidate the mechanism responsible for this unique multi-ring pattern formationupon drying DNA droplets. A high-speed fluorescence microscope is used to visualize the structure and dynamics of themulti-ring formation, which results from a pinning-depinning dynamics in contact line. At high concentrations, weobserve viscous figuring as a result of the stagnation flow, which is responsible for the formation of periodic multi-rings.At lower concentration, we observe film rupture accompanied by contact-angle changes in a saw-tooth pattern, whichsuggests rapid contact-line receding and results in the formation of aperiodic rings. We further examine the effects ofDNA concentration, droplet size and evaporation temperature on the spontaneous emergence of multi-ring patterns.

378. Phase separation in mixed Langmuir monolayers of n-pentadecanoic acid andperfluoroundecanoic acidSiwar Trabelsi and Daniel.K Schwartz, university of Colorado, Boulder, CO

Micro-phase separation in mixed Langmuir monolayers of n-pentadecanoic acid and perfluoroundecanoic acid isobserved due to chemical dissimilarity between the hydrogenated and fluorinated alkyl chains. We studied the influenceof various experimental parameters - including mixing ratio, n-alkyl chain length and temperature - on the morphologyof the mixed monolayer using Brewster angle microscopy and atomic force microscopy. In addition, we characterizedthe role played by a third line-active molecular component, i.e. "linactant". A linactant molecule plays an analogous roleto that played by a surfactant in 3D. Linactants tested include partially-fluorinated molecules and two-tailed molecules.We observe that the presence of linactant at very low concentrations systematically reduces characteristic domainsizes, consistent with a decrease in line tension. A quantitative characterization of the fundamental line activity of thelinactant is performed by measuring line tension isotherms in the mixed monolayer. The measurement involves theobservation of relaxation dynamics of the domains, initially deformed from their equilibrium shape by surface shear.

379. Effect of wetting and interfacial properties on crystallization pattern of saturated saltsolutions during drying



Noushine Shahidzadeh-Bonn, Salima Rafai and Gerard Wegdam, Universiteit van Amsterdam, Amsterdam,Netherlands

Salt weathering is an important cause of damage in building materials (stones, bricks, etc..) and threatens our culturalheritage (statues, fresco, monuments..). However, there is still a lack of fundamental understanding of the difference incrystallization damage between different salts such as sodium sulfate and sodium chloride. We study, using directimaging and optical microscopy, the growth of salt patterns during evaporation of saturated salt solutions on flatsurfaces with well controlled wetting properties. The results show the importance of wetting properties of the wall andthe presence or absence of a liquid film on the place where crystallization takes place (preference for liquid/air,solid/liquid interfaces or solid/liquid/air contact line) and the crystallization pattern. These results were completed by theexperimental studies of crystal growth in capillary tubes with different geometries (circular and square cross section) assimple model systems for a single pore within a porous medium. For the square capillary tube, the presence of thickliquid films in the corners strongly affects the drying rate, ion transport and the onset of crystallization. Consequently,the crystallization patterns are found to be very different even for a single salt in the two types of capillaries.

380. Determination of the basal and edge surface free energies of talc using the acid-basetheoryJinhong Zhang and Roe-Hoan Yoon, Virginia Tech, Blacksburg, VA

The thin-layer wicking technique was employed to determine the contact angles (q) of different liquids on powdered talcsamples. The measured contact angles were then used to calculate the surface free energy (gS) of a talc sample,including its dispersion (gS

d), acidic (gS+), basic (gS

-), and acid-base (gSAB) free energy components, using the van

Oss-Chaudhury-Good (OCG) equation. By conducting the measurements at two different particle sizes, it was alsopossible to determine the free energies of the edge and basal surfaces of the layer-structured mineral. The resultsshow that the basal surfaces are basic and the edges surfaces are acidic. By determining the surface free energiesbefore and after treating a talc sample with a polymer, it was possible to determine if the reagent adsorbs preferentiallyon the basal or edge surfaces of the mineral and with what possible mode of orientation. The method developed in thepresent work can also determine the particle size at which fracture begins to occur along the edge surfaces of themineral.

*Corresponding author: Tel. (540)231-7056; e-mail: [email protected]

1Present address: Department of Mining and Geological Engineering The University of Arizona,Tucson,Arizona 85721

381. Surfactant effects on the activity and structure of the human adenosine A2a G-proteincoupled receptorMichelle A. O'Malley and Anne Skaja Robinson, University of Delaware, Newark, DE

G-protein coupled receptors (GPCRs) represent the largest group of integral membrane proteins, accounting for over50% of all pharmaceuticals targets. However, GPCRs prove difficult to study due to problems with their expression,purification, and stability outside of the membrane environment. GPCRs, as with all membrane proteins, requiresurfactants to stabilize their conformation outside the plasma membrane. High-level expression and purification of thehuman adenosine A2a (hA2aR) receptor in a heterologous yeast system has enabled the characterization of thisreceptor through biophysical techniques. Here, we assess the ability of different surfactants to stabilize the humanadenosine A2a (A2aR) receptor, as measured through ligand binding and biophysical methods. After solubilization fromthe yeast membrane in n-dodecyl-beta-D-maltoside, different surfactants including maltosides, thiomaltosides, andglucosides were exchanged and the effects of this exchange on the protein detergent complex (PDC) were carefullymonitored. The addition of a mammalian cholesterol analog (CHS) to the PDC is found to be crucial to the maintenanceof proper structure of A2aR. This interaction may hold the 7-alpha helical domains of the GPCR more rigid, in an activeconformation within the micelle. Furthermore, surfactants which share common structure and differ only by one carbonlength show marked differences in the ability to stabilize hA2aR. We will further explore the effects of surfactant type,chain length, and other parameters on the activity of purified A2aR and on the protein detergent complex.

382. Diffusing Colloidal Probes of Calcium Mediated Cadherin Interactions



W. Neil Everett and Michael A. Bevan, Texas A&M University, College Station, TX

The ability to measure kT- and nanometer-scale potentials of mean force between proteins provides a fundamentalbasis to understand many problems in biology and medicine. Yet, the current state-of-the-art in measuring proteininteractions is generally limited to mechano-chemical measurements of binding pair off-rates or spectroscopicinterrogation of ensemble dissociation constants. In this talk, we describe the use of freely diffusing colloids as probesof thermally accessible, equilibrium interactions between cadherin fragments (cell-cell adhesion protein superfamily)covalently attached and oriented on lipid bilayers supported on colloid and wall surfaces. In particular, two separatemethods involving diffusing colloidal probes are employed to measure the Ca2+ dependence of homophilic cadherininteractions. In the first method, video microscopy is used to measure particle pair distribution functions from whichparticle pair potentials are obtained via inverse Monte Carlo analyses. In the second method, integrated evanescentwave scattering and video microscopy are used to simultaneously measure single and ensemble particle-wallinteractions to yield both equilibrium potentials and association dynamics. All measurements are performed inphysiological ionic strength buffers with varying [Ca2+] to obtain information on short-range, protein-protein potentials.The use of different particles sizes and supported lipid bilayers is exploited in this work to provide flexible control overprotein surface density, lateral mobility, and number of parallel association events. Ongoing work is extending theseapproaches to sensitively interrogate heterophilic cadherin interactions using homophilic interactions from the presentwork as a baseline.

383. Interactions Between Nucleoporins and Karyopherins Using a Quartz CrystalMicrobalance with Dissipation Monitoring with Relevance to Transport Across the NuclearPore Complex

Amit K. Dutta1, Jacklyn Novatt2, Tijana Jovanovic2, Antoine Bouchoux1, Anna S. McKenney2, Mike P. Rout2, Brian T.Chait2 and Georges Belfort1, (1)Rensselaer Polytechnic Institute, Troy, NY, (2)The Rockefeller University, New York,NY

The Nuclear Pore Complex (NPC) is the sole mediator of exchange between the nucleus and the cytoplasm in alleukaryotic cells. While small molecules pass through the NPCs unchallenged, large macromolecules are excludedunless chaperoned across by transport factors collectively termed Karyopherins (Kaps). The translocation of thecomplexes of Kaps and their cargo proteins occurs through the specific affinity and binding between Kaps andparticular nuclear pore complex proteins (nucleoporins) called FG-Nups, that share a degenerate multiple-repeated “Phe-Gly” motif. Our approach has been to form self-assembled monolayers (SAMs) of the FG-Nups bound directlyonto a gold surface via a cysteine-tag. The SAMs obtained were characterized using a quartz crystal microbalance withdissipation monitoring (QCM-D) by observing the change in frequency and dissipation during adsorption. Kaps wereadsorbed onto an FG-NUP SAM to study the binding between FG-Nups and Kaps. A change in the slope of thefrequency versus dissipation plot confirmed the binding between FG-Nup and Kap. The relative floppiness of theseproteins was estimated from the specific dissipation during adsorption of these proteins onto gold. These results helpelucidate the binding mechanisms involved during the transport of large proteins through the NPC.

384. Sphingomyelinase-induced aggregation of low density lipoproteinMichael J. Walters and Steven P. Wrenn, Drexel University, Philadelphia, PA

Cardiovascular disease (CVD) is the leading cause of human death in the US. Despite decades of intensive research,the formation of atherosclerotic lesions is not fully understood. Aggregation of low density lipoprotein (LDL) is believedto enhance the initiation of atherosclerosis. We are interested in sphingomyelinase (Smase)-induced aggregation ofLDL - as it relates to uptake by macrophages – which we demonstrated previously abides by colloidal principles ofmass action. Here we address the relative rates (kinetics of enzyme hydrolysis versus particle aggregation dynamics) tosuppress time as an independent variable and view LDL aggregation in ceramide space. Ceramide formation wasmeasured as a function of time for enzyme concentrations in the range 0-0.24 units Smase/mL at a fixed substrateconcentration 0.33 mg LDL/mL. LDL aggregate sizes were measured (dynamic light scattering, method of cumulants) asa function of time for the same enzyme concentrations. Trends are shown between ceramide concentrations andresulting aggregate sizes, giving more information on the relationships between these two values both during and aftercompletion of the enzymatic reaction and the aggregation process. We will present our results and discuss the findingsfrom a colloidal perspective. This work demonstrates the role that colloidal science can play in better understanding



human disease.

385. Engineering αL I Domain using Yeast Display to Modulate Adhesive BehaviorLauren R. Pepper, Eric T. Boder and Daniel A. Hammer, University of Pennsylvania, Philadelphia, PA

Activated lymphocyte function-associated antigen-1 (LFA-1, αLβ2 integrin) found on leukocytes facilitates firm adhesionto endothelial cells by binding to intercellular adhesion molecule-1 (ICAM-1), which is upregulated on the endotheliumat sites of inflammation. Recent work shows that LFA-1 in a preactivation, low-affinity state may also be involved in theinitial tethering and rolling phase of the adhesion cascade. The ligand binding epitope of LFA-1 is contained in theinserted (I) domain, and a conformational change in this region during activation increases ligand affinity. We havedisplayed wild-type I domain on the surface of yeast and validated expression using I domain specific antibodies andflow cytometry. Surface display of I domain supports yeast rolling on ICAM-1-coated surfaces under shear flow. Idomain mutants were also expressed, and soluble ICAM-1 binding studies validated that these mutants have a rangeof affinities for the ligand. Expression of the locked open, high-affinity I domain mutant supports firm adhesion of yeastunder shear flow, while yeast displaying intermediate-affinity I domain mutants exhibit a range of rolling phenotypes.Rolling behavior for these mutants fails to correlate with ligand binding affinity. These results indicate that unstressedbinding affinity is not the only molecular property that determines adhesive behavior under shear flow. Work to validatethis observation on a larger scale is underway utilizing I domain mutant libraries to characterize the molecular structure-function relationship via directed evolution. Understanding of adhesive behavior of particles on ICAM-1 surfaces willfacilitate further engineering of LFA-1 I domain for inflammatory targeting applications.

386. The structure, stability, and curvature of protein-coated lipid bilayer interfaces

Margaret Horton1, Christian Reich1, Suliana Manley2, Bert Nickel1, Alice P. Gast3 and Joachim O. Rädler1,(1)Ludwig-Maximilians-Universität, Munich, Germany, (2)National Institutes of Health, Washington, DC, (3)LehighUniversity, Bethlehem, PA

Proteins bound to lipid bilayer membranes provide a physical model for macromolecular complexes on cellularmembranes, and a template for immobilizing molecules at biocompatible surfaces. We study the proteins streptavidinand avidin self-assembled on the surfaces of supported lipid bilayers (SLBs) and fluid lipid bilayer vesicles. Proteinsbind to the lipid bilayers through biotin-functionalized lipids, and streptavidin interacts laterally to form two-dimensionalprotein crystals. We systematically vary the relative amounts of streptavidin and avidin at the lipid bilayer surface toinvestigate how crystalline proteins influence the structure, fluidity and curvature of lipid bilayers. Our experimentalapproach combines fluorescence microscopy and X-ray reflectivity, allowing us to determine the molecular structure ofthe protein/lipid interface, and the influence of microscopic protein crystals on the physical properties of the interface.Using synchrotron X-ray reflectivity, we measure the dimensions of the bound protein layer, as well as the thin hydratedlayer separating the proteins from the lipid bilayer. We compare the stability of our protein-coated lipid bilayer interfacesto previous studies of protein-coated lipid monolayers. With fluorescence microscopy, we demonstrate how proteinsconfer stability to lipid bilayers subjected to mechanical stress and slightly decrease lipid diffusion constants. Theexperimental framework that we present can be extended to study more complex protein-lipid interactions at a singlelipid bilayer interface.

387. Steric stabilization of magnetite nanoparticles with charged, water-soluble triblockcopolymers with polyether end groupsRichey Davis, Qian Zhang and Judy Riffle, Virginia Tech, Blacksburg, VA

Novel triblock copolymers consisting of end blocks of polyethylene oxide (PEO) and a center block consisting ofurethane and carboxylic acid groups have been shown to sterically stabilize magnetite nanoparticles that have potentialdrug delivery applications.(1) For these applications, it is essential to control the state of dispersion of the magnetitenanoparticles, especially with a coating of a biocompatible polymer such as PEO which can inhibit protein binding.These block copolymers adsorb on particles of magnetite, Fe3O4 approximately 10 nm in diameter via the carboxylicacid-containing center block. This leads to the formation of a PEO brush layer that sterically stabilizes the particles inan aqueous buffer solution for periods of weeks. Critical parameters that were measured included particle size with theadsorbed triblock stabilizer, the number of polymer chains/unit area bound to the particles, and the zeta potential of theparticles. The hydrodynamic diameter of the polymer-magnetite complexes can be predicted using the Density



Distribution model by Vagberg, et.al., that was based on the blob model for star polymers. The observed colloid stabilitycan be related to the interparticle pair potential that governs particle dispersion by the modified Deryaguin-Landau-Verwey-Overbeek (DLVO) theory in which the steric pair interaction is modeled with a theory developed by Likos et al.,based on interactions between star polymers.

(1)L. A. Harris, J. D. Goff, A. Y. Carmichael, J. S. Riffle, J. J. Harburn, T. G. St. Pierre, M. Saunders, MagnetiteNanoparticle Dispersions Stabilized with Triblock Copolymers, Chemistry of Materials, 15, 1367-1377 (2003).

388. Multicolor Quantum Dot Encoded Polystyrene Beads for Use in an Ultra-miniaturizedMicroarray PlatformShyam V. Vaidya, Charles Maldarelli, M. Lane Gilchrist and Alexander Couzis, City College and the Graduate Centerof the City University of New York, New York, NY

Focus of this paper is the development of optically barcoded polymer beads for use in high throughput multiplexedscreening applications such as protein microarrays. Luminescent semiconductor nanocrystals (or quantum dots (QDs))with different emission wavelengths (colors), and encapsulated in different compositions in polystyrene (PS) beads areused to define an optical barcode. The encapsulation is undertaken by copolymerizing the PS beads with the QDsusing a spraying suspension polymerization procedure. A mechanism is detailed by which these QDs are incorporatedin the bead matrix allowing for a controlled distribution of colors and compositions. QD embedded PS beads ofapproximately 50 microns in diameter are obtained. Confocal laser scanning microscopy (CLSM) and fluorometryresults for the PS beads embedded with three color CdSe/ZnS core-shell QDs in varying concentrations are reported.Distinguishable optical barcodes derived from the spectral scans of these QD loaded PS beads are reported. Theseoptically bar-coded PS beads arrayed in a square grid of microwells on a substrate will play host for biologicalreceptors such as cell surface membrane proteins, whose interactions with target molecules in analyte solutions wouldbe detected in high-throughput screening of drug molecules or pathogens.

389. Phospholipid membranes and ultrasound

Mona Pong1, Sumet Umchid1, Peter Lewin1, Jerzy Litniewski2, Andrzej Nowicki2 and Steven P. Wrenn1, (1)DrexelUniversity, Philadelphia, PA, (2)Polish Academy of Sciences, Poland

“Stealth” liposomes containing poly(ethylene glycol) (PEG) are good candidates for drug delivery due to theirbiocompatibility. Additionally, interest in using ultrasound energy in intracellular drug delivery has been growing rapidly.Combining the technology of ultrasound and the science of lipids will lead to advancements in the field of targeted drugdelivery. Development and treatment optimization of such non-diagnostic applications of ultrasound requires afundamental understanding of interactions between the acoustic wave and phospholipid membranes, be they cellmembranes or liposome bilayers. This work investigates the changes in membrane permeation (leakage mimickingdrug release) in vitro during exposure to ultrasound applied in two frequency ranges: “conventional” (1 MHz and 1.6MHz) therapeutic ultrasound range and low (20 kHz) frequency range. Phospholipids vesicles were used as controllablebiological membrane models. Membrane properties were modified by changes in vesicle dimensions and incorporationof PEGylated lipids. The results of this work might be helpful to optimize acoustic field and membrane parameters forgene or drug delivery.

390. Diffusive transport in nanostructured hollow colloidal capsulesJames K. Ferri and Rufaro Mukogo, Lafayette College, Easton, PA

Novel diffusion controlled delivery vehicles are among a host of recent developments in the micro and nano-encapsulation active ingredients in nutrition and biomedicine. Recently a technique for the synthesis of hollowbiocompatible nanocapsules using layer-by-layer adsorption of oppositely charged polyelectrolytes was introduced.Here a method is presented to characterize the transport properties in these nanostructured materials and developstructure-property relationships between the membrane thickness, composition (i.e. chemical constituency), andsynthesis conditions on the transport coefficients of the resulting nanocapsules. These variables are related to thetransport properties via the mesh size of the polyelectrolyte membrane. Solute transport in the capsule membrane ismeasured via fluorescence recovery after photobleaching (FRAP). Coupled conservation equations are written in thenanomembrane and the capsule interior. The diffusion coefficient in capsule interior, D1, is measured by PFG-NMR.



Data are presented for capsules synthesized from the polyanion poly-sodium 4-styrene sulfonate (PSS) and polycationpoly-allylamine hydrochloride (PAH) that are 30nm and 50nm thick. For these capsules, unsteady transport of 66kDaTRITC-Dextran, which has a hydrodynamic radius of about 10 nm in solution, is measured. It is demonstrated thattransport in both the capsule wall and interior must be considered, and that the value for D2, the transport coefficient inthe capsule wall, is bounded between 1x10-15 m2/s and 1x10-14 m2/s.

391. Targeting integrins with surface-bound ligands: Specifity & affinity of bindinginteractionsMark H. Lee, Marla McConnell, David Boettiger and Russell J. Composto, University of Pennsylvania, Philadelphia, PA

Text Not Available.

392. Lipid Based Liquid Filled Capsule Formulations as Enabling Technology for RapidDevelopment of Poorly Soluble Compounds

Eleni Dokou1, Michael Lowinger1, Craig A. McKelvey1, Andrey Peresypkin2, Anand Balakrishnan1 and W. PeterWuelfing1, (1)Merck & Co, Inc., West Point, PA, (2)Merck & Co, Inc., Rahway, NJ

As the number of hydrophobic drug development candidates in the pharmaceutical pipeline increases, it is particularlychallenging to deliver effective formulations for poorly soluble compounds. Lipid based Liquid Filled CapsuleFormulations, and in particular Self-Emulsifying (or Self-Microemulsifying) Drug Delivery Systems (SEDDS/SMEDDS)have been used to enhance the bioavailability of poorly soluble compounds.

These systems typically contain an oil (lipid), surfactants and in some cases a co-solvent. Upon dispersion in anaqueous environment similar to that encountered in the gastrointestinal tract, these systems emulsify under conditionsof mild agitation. The primary mechanism of action that leads to higher bioavailability for these formulations issolubilization of the drug (by means of emulsion formation, micellar solubilization or via cosolvency), thus avoiding slowdissolution from the crystalline state, which is frequently the rate limiting step for the absorption of hydrophobic drugs.This leads to overall higher bioavailability, and often reduces variability in absorption.

This presentation will discuss some of the key features of lipid based formulations, considerations for material selection(oils, surfactants, etc.), and the in vitro tools used for formulation characterization, such as phase behavior studies andemulsification tests. Furthermore, comparisons of the in vitro screening tools, such as dispersibility and the in vivoperformance of self emulsifying drug delivery systems will be discussed. Examples will be provided to illustrate theeffective use of lipid based liquid formulations to support the successful development of challenging poorly water solublecompounds.

393. Modulating Lipid Self-Assembly in Skin Microstructures with Implications to theEnhanced Transdermal Delivery of BiomacromoleculesVijay T. John, Grace Tan, Peng Xu, Louise B. Lawson, Jibao He, John D. Clements and Lucia C. Freytag, TulaneUniversity, New Orleans, LA

We describe methods of modulating skin lipid conformation especially through hydration, to enhance penetration ofvaccine antigens. Hydration of porcine skin tissue for a period of 4-8 hours causes a 3-4-fold expansion in the stratumcorneum. Significant structural alterations are observed, such as swollen corneocytes, separation of lipid bilayers in thestratum corneum intercellular space, formation of spindle-shaped dilations, and the disruption of lipid membranes. Clearconformational changes of intercellular lipids from lamellar bilayers to rolled-up structures resembling multilamellarvesicles are observed in high clarity. Confocal microscopy studies show distinct enhancement in penetration of a largebiomacromolecule, fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) through the skin when hydrated for 4hours or greater. The fluorescent protein permeates the dermis region of highly hydrated skin, whereas in native skin, itmainly accumulates at the surface of the skin. When the highly hydrated skin is exposed to the environment for anhour, the skin is restored to its former compact structure. The results point towards the development of novel patchtechnologies for vaccine delivery.



394. Investigating Molecular Interactions between Drug and Polymer Molecules in SolidAmorphous DispersionsMichael Lowinger, Hsien-Hsin Tung, C. A. McKelvey, Zhen Liu and Wei Xu, Merck & Co, Inc., West Point, PA

In an era of increasing need to develop drug candidates with tightening timelines and resources, the pharmaceuticalindustry is facing an ever more challenging pipeline with >50% poorly water soluble chemical entities. Solid dispersionformulations, an emerging field addressing some of these issues, enable the rapid development of poorly water solublecompounds by placing the drug in a physically stabilized amorphous state capable of increasing its apparent solubility.

A solid dispersion necessitates the inclusion of a drug molecule and supersaturation-enhancing polymer in a stable,homogeneous solid mixture produced by melt extrusion, solvent evaporation, or analogous processes. Predictivethermodynamic models, such as Flory-Huggins, aid in the selection of a suitable polymer or mixture of polymers havingfavorable interactions with the drug candidate. Inclusion of surfactants often enhances the compatibility of hydrophobicdrug with hydrophilic polymer, providing improved bioavailability over the binary system alone. By exploring themolecular level interactions between drug and polymer candidates, we can understand the influence of structure on invivo performance.

395. Nano- and micro-particle two-dimensional self-assembled structures in a wedge filmAlex D. Nikolov and Darsh T. Wasan, Illinois Institute of Technology, Chicago, IL

Suspensions of nanometer to micrometer sized particles are spread over solid surfaces to develop nano- and micro-sized structured materials with desirable structural and optical properties. A wedge film is formed by placing a droplet ofan aqueous suspension of latex particles on a smooth solid surface. The drop dries and the evaporation flux drives thelatex particles into the wedge film. The particle structuring phenomenon in the wedge film was directly observed usingreflected light microinterferometry. Both the contact angle dynamics and the particle trajectories inside the wedge filmwere monitored. A sensitive infrared camera is used to monitor the temperature gradient over the droplet surface. Theevaporation flux creates the temperature gradient over the drop surface, thereby inducing the Marangoni flow. TheMarangoni flow drives particles outward from the central part of the region of the drop into the drop periphery. Theeffect of surfactants on the particle flow was investigated. Under the confinement effect of the wedge film, the flowassembles the particles into a 2-D array structure. The experimental results were rationalized in terms of a theoreticalmodel.

396. Microemulsions: From Science to ApplicationsThomas Sottmann and Reinhard Strey, University of Cologne, Cologne, Germany

Although thermodynamically stable mixtures of at least a hydrophilic -, a hydrophobic - and an amphiphilic component,i.e. microemulsions, gain an increasing interest in technical applications, their manifold use failed up to now. Onereason is the poor transfer of the scientific results to application. In this contribution examples will be given where thistransfer (almost) succeeded. It will be shown that the ultra-low interfacial tension in microemulsions can be used for theefficient degreasing of animal skins. Using microemulsions as reaction media it is found that the large specific internalinterface leads to a drastic enhancement of epoxidation rates. In another application microemulsions are used for cleancombustion in motors, like e.g. diesel engines. It is known for a long time that the presence of liquid water in thecompressed, hot combustible air-fuel mixture reduces the emission of pollutants like soot and nitrogen oxides. Oftenwater-fuel emulsions are injected. Emulsions are thermodynamically unstable and therefore tend to separate.Microemulsions, on the contrary, do not separate because they are thermodynamically stable. We mademicroemulsions of water and diesel and tested these in truck engines. Soot was reduced by more than 90 % in steadystate operation and about 97 % in dynamic (i.e. accelerating) operation. Nitrogen oxides were 40 to 70 % lowercompared to the reference diesel. In certain modes of operation fuel consumption was reduced. Explanations andimplications of these favourable findings will be discussed.

397. Phase diagram approach to emulsion evaporationStig E. Friberg, University of Virginia, Cahrlottesville, VA



The evaporation from emulsions is of vital importance for a large number of industrial and technical applications andhas, hence, been studied extensively with the recent contributions from University of Hull as leading. The fundamentaltreatment has evaluated different factors, which influence the evaporation rate for emulsions with sufficiently smallsurfactant content to retain the 2-phase structure during the evaporation. However, a large number of emulsions havesufficiently high concentrations of surfactant for phase changes to occur within a limited time after the evaporation isinitiated. For such systems the phase diagram approach provides a unique opportunity to describe not only theevaporation path and the variation of amount of the compounds in the process, but, more essentially, the changes inthe number and amount of different phases. The lecture will introduce this approach and give an example describing atypical emulsion system.

398. Antioxidant Distributions between Oil, Water and Interfacial Regions in Model FoodEmulsions

Krishnan Gunaseelan1, Laurence S. Romsted1 and Carlos Bravo-Días2, (1)Rutgers University, Piscataway, NJ,(2)Universidad de Vigo, 36200 Vigo-Pontevedra, Spain

We developed a new method for estimating antioxidant (AO) distributions in emulsions based on pseudophase modelsfor chemical reactivity in micelles and microemulsions. AO distributions are expressed in terms of two partitionconstants between oil-interface (PO

I) and water-interface (PWI) regions within the emulsions. To estimate values of

POI and PW

I requires two independent data sets described by mathematical relations (models) that are dependent onthese parameters and solving two equations in two unknowns. One data set is obtained from the observed rateconstant (kobs) measured electrochemically for reaction of the AO with an arenediazonium ion with increasing nonionicsurfactant in a stirred tributyrin-water emulsion. The other data set is obtained by measuring the distribution constant ofthe AO between tributyrin and water in the absence of emulsifier by UV-Visible spectrometry. The distribution of t-butylhydroquinone (TBHQ) was determined in a simple model food emulsion - hexaethyleneglycol monododecyl ether(C12E6)/water/tributyrin at 25 °C. From the PO

I and PWI values, we estimate that about 65% of TBHQ is located in the

interfacial region at about 2% of C12E6 with significant percentage of TBHQ in the tributyrin region. The distributionconstant (K) of TBHQ between water and tributyrin in the absence of C12E6 is 0.015.

399. Supercritical carbon dioxide - microemulsions as precursors for nanofoams: Study ofmicrostructure

Lorenz G. A. Kramer1, Thomas Sottmann1, Peter Lindner2, Ralf Schweins2 and Reinhard Strey1, (1)University ofCologne, Cologne, Germany, (2)Institut Laue – Langevin, Grenoble CEDEX 9, France

For the production of nanofoams, which have very small heat conductivity and special optical properties, Strey et aldeveloped the new procedure: Principle Of Supercritical Microemulsion Expansion (POSME). The principle is based onthe formulation of supercritical microemulsions containing nano-sized spherical micelles swollen by a supercritical fluid.In this study we used the non-toxic and non-flammable carbon dioxide. Staying above the critical parameters, Tc = 31°C and pc = 72 bar, allows to continuously expand the CO2-swollen micelles in a supercritical state. This work examineswhether the well-known properties of microemulsions at atmospheric pressure are also found at increased pressure. Westudied the temperature dependent phase behaviour of systems of the type H2O/NaCl - CO2 - technical non-ionicsurfactant at a pressure of p = 220 bar. For the first time the typical phase inversion of a non-ionic surfactant systemfrom a CO2 - in - water to a water - in - CO2 microemulsion is found. It turned out that a hydrocarbon-type surfactantcould solubilize supercritical CO2 only inefficiently. The addition of a perfluorinated surfactant led to an improvedefficiency and could be the key for an efficient solubilisation of supercritical CO2. Having determined the phasebehaviour systematically, we performed small angle neutron scattering (SANS) experiments on these scCO2-microemulsions to elucidate the microstructure and their variation with pressure. To this end we built a new highpressure cell with variable volume which is suitable for SANS experiments under pressures up to p = 250 bar. Firstresults are presented.

400. Study of foam film drainage in relation to self-assembled nanostructures



Plamen Tchoukov, Dimitrinka Arabadzhieva, Elena Mileva and Dotchi Exerowa, Institute of Physical Chemistry,Bulgarian Academy of Sciences, Sofia, Bulgaria

Studies on foam films formed from aqueous surfactant solutions in broad concentration interval (below and above thecritical micelle concentration) are performed. Anionic, cationic and nonionic surfactants in presence of electrolyte areinvestigated. Foam film results are juxtaposed to adsorption properties of the solutions at the same conditions. Theresults show that film drainage behavior deviate significantly from the predictions of the theoretical models. Filmdrainage parameters, velocity of thinning and drainage time, change sharply within a relatively narrow interval ofconcentrations. A distinct correlation between the run of the film kinetic parameters and observed peculiarities in theadsorption isotherms is established. The proposed explanation of the experimental results outlines the impact of theexisting self-assembled nanostructures on the tangential mobility of foam film surfaces. We suggest an explanationrelating the specific hydrodynamics of the film, the mass transfer of amphiphilic molecules and the presence of self-assembled structures.

401. Surfactant phase behavior and nano-emulsion formation by low-energy methods

Jordi Nolla1, Daniel Morales1, J. M. Gutierrez2, Jordi Esquena1, Maria Jose Garcia-Celma3 and Conxita Solans1,(1)Institut d' Investigacions Químiques i Ambientals de Barcelona (IIQAB). Consell Superior d' InvestigacionsCientífiques (CSIC)., Barcelona, Spain, (2)Universitat de Barcelona, Departament d'Enginyeria Quimica, Barcelona,Spain, (3)Universitat de Barcelona, Departament de Farmacia i Tecnologia Farmaceutica, Barcelona, Spain

Nano-emulsions are emulsions with droplet size in the nanometer scale (typically in the range 20-200 nm). Due to theextremely small droplet size, nano-emulsions appear transparent or translucent (resembling microemulsions) andpossess stability against sedimentation or creaming. The formation of kinetically stable liquid/liquid dispersions of suchsmall sizes is of great interest from fundamental and applied viewpoints. Nano-emulsions are generally prepared bydispersion or high-energy emulsification methods. However, condensation or low-energy methods, which make use ofthe phase transitions taking place during the emulsification process, are receiving an increasing attention in thiscontext. This communication will focus on the potential of surfactant phase behavior information for the preparation ofcontrolled size nano-emulsions by low-energy methods. Phase behavior studies in water/polyethoxylated nonionicsurfactant/oil systems have shown that phase transitions during the emulsification process involving lamellar liquidcrystalline and/or bicontinuous microemulsions phases are required to achieve minimum droplet size. Examples will begiven on the formation of O/W nano- emulsions with droplet sizes as low as 20 nm, low polydispersity and high kineticstability. In addition, the use of nano-emulsion droplets as templates for the preparation of nanoparticles will be alsodescribed.

402. Stop-flow photolithography to create custom anisotropic colloidsPatrick S. Doyle, Dhananjay Dendukuri, Shelley Gu, Daniel Pregibon and T. Alan Hatton, Massachusetts Institute ofTechnology, Cambridge, MA

Polymeric particles in custom designed geometries and with tunable chemical anisotropy are expected to enable avariety of new technologies in diverse areas such as photonics, diagnostics and functional materials. We present asimple, high throughput and high resolution microfluidic method to synthesize such polymeric particles. Building offearlier work that we have done on continuous flow lithography, CFL (Dendukuri et al., Nat. Mat. 2006), we have devisedand implemented a new setup that uses pressure driven flows to synthesize particles using a technique that we callstop-flow lithography (SFL). A flowing stream of oligomer is stopped before polymerizing an array of particles into it,providing for much improved resolution (down to 1 micron) over particles synthesized in flow. The formed particles arethen flushed out at high flow rates before the cycle of stop-polymerize-flow is repeated. The high flow rates enableorders-of-magnitude improvements in particle throughput over CFL. However, the deformation of the PDMS elastomerdue to the imposed pressure restricts how quickly the flow can be stopped before each polymerization event. We havedeveloped a simple model that captures the dependence of the time required to stop the flow, on geometric parametersof the microchannel such as height, length and width, as well as on the externally imposed pressure. Further, we showthat SFL proves to be superior to CFL even for the synthesis of chemically anisotropic particles with sharp interfacesbetween distinct sections.

403. Effect of suspended clay particles on isotropic–nematic phase transition of liquidcrystal



Zexin Zhang, University of Pennsylvania, Philadelphia, PA and Jeroen S. Van Duijneveldt, University of Bristol, Bristol,United Kingdom

Sterically stabilized nano-platelets were prepared by treating montmorillonite clay with both a surfactant and apolymeric stabilizer. These nano-platelets, for the first time, formed stable suspensions in a thermotropic liquidcrystal(LC), 5CB. In the isotropic state of the LC, static light scattering confirmed that the clay nano-platelets werefreely suspended, with no aggregation detected even after repeated temperature cycling. Small-angle X-ray scatteringrevealed that the clay was nearly completely delaminated in the LC, with some stacks of a few clay nano-plateletshaving formed. Differential scanning calorimetry of the LC/clay suspensions showed a small but non-monotonic shift ofthe I-N transition temperature. This behavior is similar to that of LC confined in porous media, with an initial increase ofthe transition temperature on adding clay being ascribed to the effect of surface anchoring facilitating the formation ofthe nematic phase; whereas a decrease at higher clay concentrations (or equivalently, for smaller pores) is ascribed toconfinement effects frustrating the formation of the nematic phase. This interpretation is supported by polarizing lightmicroscopy which showed the nematic domain size becoming smaller on increasing the clay concentration.

41044 modified by 158.130.30.30 on 2-15-2007-->

404. Adhesion, self assembly and structure of actin filamentsZvonimir Dogic and Ashok Prasad, Brandeis University, Waltham, MA

Direct measurement of the intermolecular potential between a pair of charged actin filaments is essential forunderstanding their pathways of self-assembly. We have developed two methods that allow us to directly measure theadhesion energy between a pair of filaments held together by the depletion or any other attractive interaction. Thesensitivity of our force measurement is in a picoNewton to femtoNewton range. Our data indicate that thermalfluctuations renormalize the adhesion strength in the weak binding limit. We are able to correlate changes in theadhesion strength with changes in the structure of actin bundle.

405. Effect of double layer polarization on particle interactions in AC electric fieldsPushkar Lele, Eric M. Furst and Eric W. Kaler, University of Delaware, Newark, DE

We studied the effect of AC electric fields on pair-wise and many-body colloidal interactions. In the absence of anelectric field, the interactions for three particles in triangular and linear configuration were in good agreement with thepredicted results from Stokesian dynamics simulations, which account for the hydrodynamic interactions betweenparticles. In addition, we carried out a systematic experimental characterization of pair interactions under an applied ACelectric field. The electrolyte concentration in the medium and the frequency of the electric field had a strong effect onthe particle interactions. Our results suggest that the dipole-dipole interactions are dominated by the double layerpolarization around the particles. This interaction is an order of magnitude larger than the dipole-dipole force expectedfrom the particle polarization, as calculated by the Claussius-Mossotti factor. These effects need to be accounted forwhen considering the field-induced assembly of particles in AC electric fields

406. Hydrodynamic interactions between a silica particle and a deformable droplet – effectof particle/droplet size ratio and bulk phase viscosityGrant B. Webber, Rogerio Manica, Scott Edwards, Geoff Stevens, Derek Y.C. Chan, Raymond R. Dagastine and FranzGrieser, The University of Melbourne, Melbourne, Australia

In many industrial applications such as froth flotation, foams and emulsions, the interactions between solid and



deformable interfaces, or two deformable interfaces, is of critical importance. Understanding these micro-scaleinteractions is vital for the prediction and control of the macro-scale behaviour. The understanding of the dynamicinteractions when one or more surfaces is “soft”, and thus the overall interaction may be dominated by surfacedeformations, is of particular interest. Recent advances within the Particulate Fluids Processing Centre has enabled themodeling of atomic force microscope (AFM) force data collected for the static1 and dynamic interactions2,3 between asolid sphere and a deformable interface, or two liquid droplets. Here we present data examining the effect of theparticle/droplet size ratio and the bulk phase solution viscosity on the interaction between silica spheres and sodiumdodecyl sulfate (SDS) stabilised tetradecane droplets. In particular, this data enables us to probe the existence, orotherwise, of a slip boundary between the two interacting surfaces. Force-distance profiles collected from AFMexperiments are compared to theoretical profiles in which different slip lengths are incorporated.

References

(1) Dagastine, R. R.; Stevens, G. W.; Chan, D. Y. C.; Grieser, F. Journal of Colloid and Interface Science 2004,273, 339-342.

(2) Carnie, S. L.; Chan, D. Y. C.; Lewis, C.; Manica, R.; Dagastine, R. R. Langmuir 2005, 21, 2912-2922.

(3) Dagastine, R. R.; Manica, R.; Carnie, S. L.; Chan, D. Y. C.; Stevens, G. W.; Grieser, F. Science (Washington,DC, United States) 2006, 313, 210-213.

408. Deposition of microsphere monolayers for microlens arraysPisist Kumnorkaew, Yik-Khoon Ee, Nelson Tansu and James F. Gilchrist, Lehigh University, Bethlehem, PA

Colloidal silica microspheres of 0.5 and 1 micron were deposited into thin films on a glass substrate via a rapidconvective deposition method. By varying deposition rate and contact angle, the optimal operating ranges in which 2Dclosed-pack of silica existed were obtained. Using a confocal laser scanning microscope, dynamic self assembly ofcolloidal particles under capillary force during solvent evaporation was revealed. In addition, interaction betweensubstrate and colloidal particles played an important role in formation of ordered crystalline arrays. The interaction wasaltered by varying pH (2-11) and salt concentration of either substrate rinsing solution or colloidal suspension. Using thesame technique, stacked layers of 1 micron silica monolayer on top of 1.1 micron polystyrene monolayers andsubsequent melting of the polystyrene to partially wet the silica microspheres were deposited on GaN layer. Thisprocess was implemented on the top p-GaN layer of InGaN quantum wells light emitting diode (LEDs) device structure,resulting in the formation of a microlens array for enhancing its light extraction efficiency. This approach led to ~230%increase of the LEDs output power.

407. Long-range hydrodynamic response of particulate liquidsABSTRACT WITHDRAWN

In viscous particulate liquids, such as colloidal suspensions and polymer solutions, the large-distance steady-state flowdue to a local disturbance is commonly described in terms of hydrodynamic screening — beyond a correlation length ξthe response drops from that of the pure solvent, characterized by its viscosity η0, to that of the macroscopic liquid withviscosity η>η0. For cases where η>>η0 we show that this screening picture, while being asymptotically correct, shouldbe refined in an essential way. The crossover between the microscopic and macroscopic behaviors occurs graduallyover a wide range of distances, ξ<r<(η/η0)1/2ξ. In liquid-laden solids, such as colloidal glasses, gels, and liquid-filledporous media, where η→∞, this intermediate behavior takes over the entire large-distance response. The intermediateflow field has several unique characteristics relating to its distance dependence, concentration dependence, and



temporal buildup, which are demonstrated in several model systems.

409. The viscoelastic properties of interfacial lung surfactant filmsSiegfried Steltenkamp, University of California, Santa Barbara, CA and Joseph A. Zasadzinski, University of CaliforniaSanta Barbara, Santa Barbara, CA

Lung surfactant (LS) is a complex mixture of lipids and proteins originating from the type II cells that line the alveolarepithelial walls. LS reduces surface tension in the alveolar spaces, which minimizes the work of breathing and preventsthe alveolar collapse. A lack of functional surfactant due to premature birth leads to neonatal Respiratory DistressSyndrome (nRDS) which is routinely treated in developed countries with animal derived replacement surfactant. One ofthe essential features of good LS is to reduce the surface tension at the alveolus air-water interface to near zero.Presently, there is no simple theory relating chemical or physical properties of a monolayer with its ability to lowersurface tension in the dynamic process of breathing. Monitoring the viscoelastic properties of interfacial films allowshypothesizing how surface viscosity depends on lipid and protein composition, packing properties and other variables atdifferent states of the breathing process. Our viscometer consists of a Langmuir trough equipped with Helmholz coilswhich generate a controlled magnetic force to move a magnetic needle floating on the monolayer. If the applied force isoscillatatory, the complex shear modulus is determined from measurements of the in-phase and out-phase of theresulting strain. If the force is constant, the shear viscosity can be extracted from the terminal velocity of the needle.Here we present the behavior of LS monolayer concerning surface viscosity at different surface pressure, compositionand phase in order to make a prediction about the optimal composition of LS.

410. Non-Aqueous Photorheological Fluids Based on Reverse Wormlike MicellesAimee Ketner, Patrick W. Elder and Srinivasa R. Raghavan, University of Maryland, College Park, MD

Our lab has been investigating surfactant fluids with light-tunable rheological properties (i.e., “photorheological” or PRfluids). We recently reported a class of PR fluids based on wormlike micelles in water (JACS 129, 1553 (2007)). In thissystem, light caused a well-defined drop in viscosity due to a transition from long to short micelles. Here, we report anincrease in viscosity due to light in a non-aqueous reverse micellar fluid. It is well-known that the phospholipid, lecithincan form reverse wormlike micelles in organic solvents like cyclohexane, upon addition of a small amount of water.These solutions consequently have a high viscosity. However, when we add a photoresponsive stilbene compound intothe water phase the solution viscosity drops. When this sample is then irradiated with UV light, the stilbene undergoesa photoisomerization, and we observe that the viscosity reverts to a high value. These results are evidently due to theinterplay between molecular geometry and reverse micellar structure. We will present results from a variety ofspectroscopic, analytical and scattering techniques to elucidate the molecular and microstructural mechanism for ourresults.

411. Photogelling fluids: Micellar solutions whose viscosity can be increased by lightRakesh Kumar and Srinivasa R. Raghavan, University of Maryland, College Park, MD

Fluids with photoresponsive rheological properties can be useful in a variety of applications, such as in sensors,dampers, and valves for microfluidic or MEMS devices. Currently, such fluid formulations are available only to a fewresearch groups since they tend to be based on specialized photosensitive molecules (e.g. a photosensitive surfactantor polymer). Here, we describe formulations based on a commercially available zwitterionic surfactant and aphotosensitive cinnamic acid derivative. These fluids exhibit a rapid and controllable increase in viscosity (gelling) uponexposure to UV radiation. Initially, the fluid has a low viscosity, indicating the presence of small micelles. Uponirradiation in the UV range, the cinnamic acid derivative undergoes a trans to cis photoisomerization. This change ingeometry alters the molecular packing of surfactant/acid complex, transforming spherical micelles into long wormlikemicelles. In turn, the solution viscosity is increased by more than five orders of magnitude. Small-angle neutronscattering (SANS) is used to confirm the dramatic increase in micellar length.

412. A Novel Associative Polymer Network with Tunable Rheological Properties

Lin Fu1, Xuhong Guo2, Stephen Lincoln3 and Robert Prudhomme1, (1)Princeton University, Princeton, NJ, (2)EastChina University of Science and Technology, Shanghai, China, (3)University of Adelaide, Australia



Water soluble associative polymers, which are usually composed of hydrophilic backbones and hydrophobic sidechains, are widely used as rheology modifiers in coating, painting, cosmetics and pharmaceutics. In this study, a novelassociative polymer network with tunable rheological properties is developed based on cyclodextrin-hydrophobeinclusion complex. Mixtures of two polyacrylic acid backbone polymers: cyclodextrin attached to PAA andhydrophobically modified PAA are used. With cyclodextrin host-guest inclusion as the associative sites, this novelpolymer network is able to provide more controllable rheological properties than traditional associative polymers,because: first, the lifetime of this host-guest association can be well controlled by the length of alkyl chain inserted intothe cyclodextrin; second, the binary nature of cyclodextrin-hydrophobe inclusion prevents hydrophobes from multipleassociation. At the same time, this system can serve as a model associative polymer network for understandingpolymer association theory. Dynamic rheological properties of this mixture solution can be quantitatively controlled byadding free cyclodextrin or sodium dodecylsulfate (SDS). Dynamic modulus could change up to several orders ofmagnitude, even from gel state to sol state. The phase behavior of this mixture solution is experimentally studied byturbidity measurement and rheological approach. The thermodynamic behavior is found to show good consistency withassociative gelation theory. Further, we studied the life time of cyclodextrin-hydrophobe interaction independently fromisothermal titration calorimeter and surface plasmon resonance study. Both thermodynamics and dynamics of thiscyclodextrin inclusion process are explored for better controlling rheological properties of this model system.

413. Particle effects on an ordered cylindrical micelle gel of block copolymer solutionsTheresa A. LaFollette and Lynn M. Walker, Carnegie Mellon University, Pittsburgh, PA

Recent efforts to template hydrophilic nanoparticles in the interstitial spaces of the thermoreversible close-packedmicellar structure seen in Pluronic block copolymers has been shown successful. Previous work focused on systemsforming cubic soft crystals of spherical micelles and is currently being extended to cylindrical micelles. The pluroniccopolymer P123 (PEO20-PPO70-PEO20) forms both an ordered cubic micelle gel and packed cylindrical micelle gel.Phase transitions are determined from rheology and birefringence and verified with small-angle scattering. Proteins areused as monodisperse nanoparticles; two different sizes of particle, bovine serum albumin (BSA) and lysozyme areadded to the P123 system forming a nanocomposite. We observe an apparent hysterisis during the transition betweenthe cubic and cylindrical micelle gel during heating and cooling in the nanocomposites, while no hysterisis is observedin the neat system. BSA at 2-3 wt% disrupts the formation of the packed cylindrical micelle gel while the smallerlysozyme does not. This indicates formation of a weaker gel and is caused by the size of the particles relative tointerstitial spaces. A mechanical protocol for studying the nanocomposites has been developed and limits for placingparticles in the nanocomposite have been established.

414. Ring shaped structure in free surface flow of non-Newtonian liquidsNilesh H. Parmar and Mahesh S. Tirumkudulu, IIT Bombay, Mumbai, India

We report the formation of a ring like structure (donut shaped) in the flow of particular non-Newtonian liquids coating arotating vertical disc. Experiments were performed with a known volume of the liquid and at varying rotation rates suchthat inertial and centrifugal effects were negligible. Liquid injected on to the rotating disc initially coats the surfaceuniformly, which then redistributes itself such that at steady state a significant amount collected into a circular ring, offcenter with the axis of rotation. The ring formation was not observed in the case of Newtonian liquids. Theseexperiments motivated a study on the liquid of Newtonian viscous liquids on the same geometry. A lubrication analysisfor Newtonian liquid resulted in a time evolution for the film thickness that accounted for gravity, surface tension andviscous forces. The predicted thickness profiles are in excellent quantitative agreement with those obtainedexperimentally for moderate volumes of silicone oil. Shear rate calculation for the Newtonian liquid suggests that theshear thinning nature of the non-Newtonian liquid may be the cause for the observed ring formation.

415. Liquefaction of quicksand under stressAsmae Khaldoun, University of Amsterdam, Amsterdam, Netherlands

Quicksand is the generic name for unstable soils reputed to trap anyone who treads on it. Popular wisdom has it thatone should not move when trapped in quicksand, as motion makes one sink in even deeper and that once trapped, itis difficult to escape1. Here we provide an explanation for these observations by studying the most commonlyencountered form of natural quicksand. We show that a spectacular liquefaction of the material occurs when a stress is



applied to the material: the liquefaction is the reason why one sinks away, and it is more pronounced for largerstresses. By constructing 'laboratory quicksand', we demonstrate that the liquefaction is due to the structure: quicksandis a loose granular packing of sand particles stabilized by a clay matrix that forms a particulate gel. The stress liquefiesthe clay matrix, and the granular assembly collapses, expulsing water. This results in a densely packed system thatpractically impossible to dilate: it is for this reason that once trapped it is difficult to get out of quicksand. A sinking testdemonstrates that, due to buoyancy, it is impossible to drown in the quicksand.

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