Magnetic Nanofluids for Chemical and Biological Processing Andre Ditsch, Bernat Olle, Harpreet Singh, Lino Gonzalez, Marco Lattuada, Lev Bromberg, Daniel I.C. Wang, Kenneth A. Smith & T. Alan Hatton Department of Chemical Engineering Massachusetts institute of Technology Cambridge MA 02139
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Magnetic Nanofluids for Chemical and Biological Processing
Andre Ditsch, Bernat Olle, Harpreet Singh,Lino Gonzalez, Marco Lattuada, Lev Bromberg,
Daniel I.C. Wang, Kenneth A. Smith & T. Alan Hatton
Department of Chemical EngineeringMassachusetts institute of Technology
Cambridge MA 02139
Magnetic Nanoparticles
Magnetic CoreSuperparamagneticApplications
Magnetic storage mediaMagnetic drug targetingProtein/Cells separationRNA/DNA purificationMagnetic resonance ImagingCatalystsMR FluidsMass and heat transfer enhancement
8 nm
15-20 nm
Polymer ShellColloidal stability
Functionality
Functionalised Magnetic Nanoparticles
Coating Material FunctionMagneticparticle Perfluorocarbons O2Transfer Enrichment
• Modified with moieties containing highly nucleophilic groups• Selectively attack electrophilic groups such as P-O bonds
found in toxic organophosphates• Contain charged group on the surface: colloidally stable in
water
Fe3O4
Stabilizing polymers
Oxime
α-nucleophile: a heteroatom with an unshared electron pair adjacent to the nucleophilic center
α-nucelophiles: oximates, phenolates, etc.
C=N-OHH
Nucleophiles Thus Far Tested
PAM: 2-pyridinealdoxime(common antidotal drug)
p(VPOx-AA): Copolymer of oximatedpoly(4-vinylpyridine) and polyacrylic acid(novel polymeric nucleophile)
N
CH3
HC N OH
CH2
HC C
H2
HC
N
COOH
CH2
C N OH
Decomposition of Organophosphates
O
P(H3C)2HCO
OCH(CH3)2
F
O
PH3C
OCH(CH3)2
F
DFPSarin
O
PH3C F
Soman
OCH(CH3)CH2(CH3)3
Diisopropyl fluorophosphate: model nerve gas
OP+ Nanoparticle gives water-soluble phosphoric acid + fluoride ionNanoparticles are recyclable by HGMS
Method of analysis: continuous detection of F-
Kinetics of Hydrolysis
0.0001
0.001
0.01
0.1
1
10
0.01 0.1 1 10
k obsx1
03 (s-1
)
Concentration (mg/mL)
PAM/M
PAM
p(VPOx-AA)/M
M p(VP-AA)/M
Spontaneous Hydrolysis
Rapid hydrolysis in presence of oximated species
Recycling
0.00
0.10
0.20
0.30
0 1000 2000 3000
-ln(1
-Ct/[D
FP] o)
Time (s)
PAM/M
p(VPOx-AA)/M
1
2
3
1
2
3
Particles can be recovered and recycled with no loss of catalytic effectiveness
Applications
Catalytic decomposition of organophosphates:Numerous OP pesticides and insecticides Warfare agents such as sarin, soman, and VX
Drainwaters, industrial runoffs and spillsProtective clothingFilters, membranes, gas masks
Brownian: rotation of particle in fluid
Neel: rotation of magnetic vector within particle
10-810-710-610-5
0.00010.001
0.010.1
1
6 8 10 12 14 16 18
Rel
axat
ion
Tim
e, s
Particle Size, �
Neel
Brownian
τ B =
3Vη0
KT
τ N =
1f0
exp KVkT
⎛⎝⎜
⎞⎠⎟
Relaxation Processes
Magnetic Response of Nanoparticles
λ =µ0 M 2V14kT
≈µ0 χ 2 H0
2V14kT
? 1
20 nm
+ Fe3+ + Fe3+
χshell ≈ 1.3χdist
Magnetite NanoparticlePreparations
Aqueous RouteNucleation of magnetite nanocrystals from a solution of FeCl3 & FeCl2, NH4OH, 80°C. Various stabilizersPros: Cheap, fast, variety of stabilizersCons: broad nanoparticledistribution, irregular shape, average crystallite size fixed
Organic RouteIron-triacetylacetonate reduction by 1-2 hexadecanediol, at 300°C in benzylether,oleic acid+oleyl aminePros: narrow crystallites distribution, regular (controlled) shape, tunable sizeCons: expensive, works only with some organic stabilizers, chemistry poorly understood
20 nm
+ Fe3+ + Fe3+
Magnetophoretic Separation of Nanoparticles in Microfluidic Systems
Decreasing H
Fmag + Fdrag = −µ0Vp M f ∇H − 6πηRU p = 0
Fmag = µ0Vp ( M p − M f )∇H
= −µ0Vp M f ∇H
Fdrag = −6πηRU p
U p = −
µ0Vp M f ∇H6πηR
Magnetic Fluid
Flow Magnetophoresis for Nanoparticle Separations
Nanoparticle Separation and Focusing
Particle Resolution is affected byConvective dispersion (non-uniform velocity profiles)Non-uniform lateral field distributions
Magnetic Shells
Use layer-by-layer technique to coat polystyrene beads with polyelectrolytes and then adsorb magnetic nanoparticles.
Polymer core can be dissolved out using solvent.
Applications of Magnetic Chains and Rods
Fundamental studies on behavior under fixed and rotating magnetic field
Magneto-rheological effectsMagnetic actuators and valves Micromixers, pumps, etc. under a rotating magnetic fieldMagnetic nanowires (Bibette &Vivoy) Magnetic pillars can be used for separations (currently used in
separation of DNA (Doyle's research))Functionalized chains can be used for separations
Molecular movement of a molecule through the maze of chains onlygoverned by size and interactions with chains...
Separation of paramagnetic species
Bead Alignment and Coupling
Beads can be aligned in microchannel under magnetic field and joined together either using sol-gel chemistry or
chemical coupling with appropriate linker.
Rigid Magnetic Chains
Sol Gel kinetics (Titanium isopropoxide as precursor)
Extremely fast hydrolysis reactionLinking requires preferential nucleation on the bead surface
Magnetite beads coated with PDAMAC and resuspended in anhydrous ethanol; Kpw = 60
Water of hydration in the PDAMAC shell ensures reaction on the bead surface onlyPositively charged bead captures negatively charged nucleated titania efficiently