ChemE 554 Nano Science I Rheology and Processes in Nanotechnology Instructor: René M. Overney [email protected] http://depts.washington.edu/nanolab/ Department of Chemical Engineering University of Washington Seattle, WA 98195
Dec 28, 2015
ChemE 554
Nano Science IRheology and Processes in
NanotechnologyInstructor: René M. Overney
http://depts.washington.edu/nanolab/
Department of Chemical EngineeringUniversity of Washington
Seattle, WA 98195
Introduction Mesoscale Research and Perception Novel Surface Technique: Scanning Force Microscopy (also
called: Atomic Force Microscopy) Motivation for Mesoscale Research:
- Confinement Effects in Thin Spincast Films Examples of Sensible Mesoscale Technologies:
- Thin Film Lubrication Mesoscale Kinetics
- Ultrathin LED Materials
Exciton Annihilation
- PEM Fuel Cell Proton Transport
Mesoscale Science and Technology
Applications:
- Lubrication
- Photonics
- Fuel Cells
- Data Storage
The realm of the Mesoscale fosters new perceptions and approaches.
Classical Sciences
Molecular SciencesAtomistic &
Illustration of a 2D PhenomenonA highly organized plastic deformation: often referred to as Schallamach Waves
a slow moving (~ m/s ) sliding contact (~10-5 m2) affects a scan area on the order of 103 m2 in an apparently coherent fashion.
AFM Scan:
Probe Width: ~ 10 nm
Line Separation: > 100 nm
(a)
(d)(c)
(b)
An entertaining satire by Edwin A. Abbott
A Sphere, an inhabitant from
Spaceland,
E.A. Abbott, Flatland, A Romance of Many Dimensions. Dover Publ. Inc., New York (1992) first published 1884 under the title “A. Square”
Flatland
a Square,an inhabitant from
Flatland
introducesto a higher
Dimensionality
Perception
• Objects are perceived in Flatland as lines or points.
Dimensionality nurtures perceptions and limits possibilities.
Flatland – An entertaining satire by Edwin A. Abbott
• To distinguish objects in Flatland the observer has to travel around the objects. A Circle is perceived as an
angularly length- invariant object.
A Sphere is reduced to its cross-sectional area with Flatland, and thus, perceived as a Circle.
Boundaries in lower dimensionalities are lifted from the perspective of a higher dimensionality
Flatland – Shrinking, Disappearing and Reappearing Act
DoorDoor
??
North
South
Direction of Rain
Flatland: “Physical Laws”Abbott spent a significant part for a his satire on developing the two-dimensional world of Flatland by introducing imaginary laws of nature that apply in one and 2-dimensions. Although these laws that for instance explain how rain is experienced in 2-dimensionsare unrealistic, they impressively illustrate the mystery of lower dimensionalities.
Huygens Body Waves (3D solution)A spatially localized initial disturbance gives rise to alimited and fast decaying disturbance only, at any accessible location away from the source of the disturbance.
Rayleigh Surface WavesWaves, propagating over the surface of a body with a smallpenetration distance into the interior of the body, acquireat a great distance from the source a continually increasingpreponderance.
--> important in the study of seismic phenomena
Illustration of Dimensionality:Acoustic Wave (3D vs. 2D)
SAMPLE
CANTILEVER
PIEZO
Atomic Force Microscopy (AFM)
Photodiode LASER
Topography
NanoScience ToolNanoScience Tool
AFM
Friction
Material Distinction
100 µm
0 µm
50 µm
100 µm0 µm 50 µm
A
B32.33 µm
0 µm
16.17 µm
32.33 µm0 µm 16.17 µm
ElasticityTg = 374K
Glass Transition
In environmental chamber with sample heating /cooling stage
SFM Setup
C
SFM/AFM Heating/Cooling Stage:Explorer (Topometrix) (MMR Techn.)
Confined Boundary Layer of Spincast Films
Mean field theories consider the effect of pinning at interfaces only within a pinning regime (0.6 – 1 nm « Rg)
BU
LK
SIC
Z
~ 1 nm
Lateral Force and Dewetting Studies suggest that the PEP phase is rheological modified within a 100 nm boundary region that exceeds by two orders of magnitude the theoretically predicted pinning regime of annealed elastomers at interfaces with negative spreading coefficient.
BU
LK
SIC
ZS
RZ
~ 100 nm
DisentangledSublayer
Diffusioninto
Classical Actual
Mean field theories consider the effect of pinning at interfaces only within a pinning regime (0.6 – 1 nm « Rg)
R.M. Overney et al., J. Thermal Analysis and Calorimetry, 59, 205-225 (2000).
S.Ge, et al. Phys. Rev. Lett., 85, 2340-2343 (2000)
Glass Transition Properties of Confined Films
Glass transition studies on polystyrene indicate confinement effects similar to those found in PEP shear studies.
85
90
95
100
105
0 50 100 150 200 250 300
FILM THICKNESS, ( nm )
Tg
( o
C )
12.0 kDa PS
FOX-FLORY (BULK)
BULKS ICZ SRZ
xmod
Shear Response
ShearDisplacement
Sample
CantileverTip
xL
Heating/Cooling Stage
xmodxmod
Shear Response
ShearDisplacement
Sample
CantileverTipCantileverTip
xL
Heating/Cooling Stage
Near-Surface Tg Measurements of “Thick” Films (t > 100 nm) are bulk-like.
Liquid Structuring: Entropic Cooling• Interfacial confinement leads to an entropically cooled boundary layer in simple fluids like hexadecane.
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-6 -5 -4 -3 -2 -1 0 1 2 3 4
DISPLACEMENT (nm)
NO
RM
AL
IZE
D V
AL
UE
(A
.U.)
MODULUS
CONTACT FORCE
I II III
I: BULK LIQUID
II: BOUNDARY LAYER
III: SOLID SUBSTRATE
Shear Modulated SFM approach curves indicate a hexadecane boundary layer thickness of ~2.5 nm on SiO2.
He, et al., Phys. Rev. Lett. 88, 15 (2002)
Molecular Dynamics simulations predict a boundary layer thickness of 1.5-1.8 nm.
Xia, et al., Phys. Rev. Lett. 69, 1967 (1992)
Lubrication
Examples of Sensible Mesoscale Technologies
- Thin Film Lubrication
Mesoscale Kinetics
- Thin Film LED Materials
Exciton Annihilation
- PEM Fuel Cell
Proton Transport
Mesoscale Kinetics -Fractal Bonding Kinetics and Lubrication
10 Å100 Å
400 Å
Si
Cr
CHxZdol
X - (CF2O)y (CF2CF2O)z CF2 – X
X CH2OH (functional group) y perfluoromethylene oxide groups (C1)z perfluoroethylene oxide groups (C2)
polargroup
polargroupbackbone
Monolayer Lubricant:Hydroxyl-terminated perfluoropolyether (PFPE-OH) film (Fomblin Zdol©)
Interaction: Hydroxylated chain ends form hydrogen bonds with carbon surface.
Lubrication Performance: Depends on the molecular mobility
Bonding Kinetics and Shear Mechanical Response
Kinetic Experiments 10.5 ± 0.5Å Zdol, 2500 CHx
0 20 40 60 80 100 120 140 1600.00
0.05
0.10
0.15
0.20
T = 54°C
T = 86°C
t-1. 0
= 0.8
t-
t -0. 5
k b
TEMPERATURE (°C)
LOW TEMPERATURE5.0)( tktk b
• “GLASS LIKE”• SHORTER RANGE INTERACTIONS• DIFFUSION LIMITED
HIGH TEMPERATURE0.1)( tktk b
• “LIQUID LIKE”• DISPERSIVE INTERACTIONS• ACTIVATION BARRIER LIMITED
Shear Modulated SFM
0 20 40 60 80 100 120 140 1600.010
0.015
0.020
0.025
0.030
0.035 T = 56°C
SH
EA
R R
ES
PO
NS
E (
a.u
.)
TEMPERATURE (°C)
T = 85°C
Monolayer Lubrication and Kinetics
i. The monolayer confined system exhibits a glass transition value of 52 oC that is significantly exceeding the bulk material value of -115 oC.
ii. The confined system exhibits a “Fractal Reaction Kinetics”.
iii. The rheological transition at 52 oC separates two fundamental kinetic bounding regimes:
- diffusion limited reaction- activation barrier limited reaction
iv. The shear rheological analysis with SM-SFM was found to provide valuable material information that explains the “exotic” reaction kinetics.
Photonics and Thin Semiconducting Polymer Films
Film preparation parameters have shown to effect significantly the optoelectronic properties (e.g, conversion temperature)
Ultrathin films have shown very exotic optoelectronic properties (bias-voltage dependent color emission)
Motivations for Mesoscopic Rheological Analysis:
Thickness dependent Luminescence
Bias-voltage dependent Reversible Color Emission
Zhang, X., S. A. Jenekhe, et al. (1996) Chem. Mater. 8: 1571-1574
tc 50 nm
67 nm40 nm
Aln-type (hole)
p-type (electron) ITO
PPQ
PPV tPVP
V (bias)tPPQ
PPQt)V(h
polyquinolines (PPQ)
p-phenylenes (PPV)
tPPQ = 67 nm; tPVP = 25 nm
10-30 V: orange-red
tPPQ = 67 nm; tPVP = 25 nm 8-10 V: orange13-20 V: green
PPV is not soluble in conventional solvents used for spin coating. A two-step process is needed, which involves a tetrahydrothiofenium (THT) precursor polymer, which is soluble (e.g., in methanol). After spin casting the film is converted by thermal annealing into PPV
- silicon substrates: cleaned sequentially with acetone and methanol
- THT films: spin coated at 1000 rpm onto Si (sulfonium precursor in a methanol solution, 1 wt%)
- Conversion in vacuum oven at 10°C/min starting from 100°C.
- Samples were cooled to room temperature at a rate of approximately 40°C/min
Film Preparation of PPV
nn
S+
n
Cl-
S+
n
Cl-
h
Conversion Temperature: 175 oC
SHEARDISPLACEMENT,
XMOD
SHEAR RESPONSE
XR
SAMPLE
CANTILEVER
TIP
NO-SLIPCONTACT
HEATING / COOLING STAGE
40 45 50 55 60 65 70 75 80 85 90 95 100
0.038
0.040
0.042
0.044
0.046
0.048
0.050
0.052
Tg = 66 oC
Shea
r R
espo
nse
x RTEMPERATURE (oC)
Rheological Transition Measurements
Qualitative comparison of
(a) the rheological transition temperature ■, (Tg ) (measured with the SM-SFM method) with
(b) the photo-luminescence (PL) efficiency ▲ Morgado, J., F. Cacialli, et al. (1999). J. Appl. Phys. 85(3): 1784-
1791. as function of the PPV conversion temperature.
55
60
65
70
75
80
85
90
140 160 180 200 220 240 260 280
Conversion Temperature (oC)
Tran
sitio
n Te
mpe
ratu
re
(oC
)
0.085
0.105
0.125
0.145
0.165
0.185 PL Q
uantum E
fficiency
Photoluminescence Efficiency vs. Glass Transition
Below 205 oC, the degree of conversion to PPV (which is increasing with temperature) is dominating both, the rheological transition properties and the EL efficiency.
Interpretation
55
60
65
70
75
80
85
90
140 160 180 200 220 240 260 280
Conversion Temperature (oC)
Tran
sitio
n Te
mpe
ratu
re
(oC
)
0.085
0.105
0.125
0.145
0.165
0.185 PL Q
uantum E
fficiency
Above 205 oC, polymer degradation is dominating. For instance, it is known that carbonyl groups are formed excessively (Morgado, J., F. Cacialli, et al. (1999). J. Appl. Phys. 85 (3): 1784-1791)
Effects on EL Intensity:
- (left) Degree of conversion to PPV increase EL intensity.
- (right) Residual byproducts from conversion and oxygen degradation act as exciton quenching sites (radiation-free annihi-lation), i.e., lower the EL intensity.
Effects on Rheological Transition:
- (left) Degree of conversion to PPV increases thermal transition values
- (right) Degradation lowers the transition values
Proton Exchange Membrane (PEM) Fuel Cell
R.M. Overney University of Washington
PEM
50-175m5-50m
ACTIVE LAYER
ANODE CATHODE
4H++4e-+O22H2OH+H22H+ + 2e-
PEM Fuel Cell
Nafion: Commercially available perfluorosulphonate cation exchange membrane SO3H form: Tg 376 K [S.C. Yeo, A. Eisenberg, J. Appl. Polym Sci. 21, 875 (1977)]
A. Sen, et al., Mat. Res. Soc. Symp. Proc. Vol. 393, 157 (1995)Temperature (oC)
Mem
bran
e R
esis
tivi
ty (
Ohm
-cm
)
Tc 80-90 oC
(CF2-CF2)x (CF2-CF)y
(O-CF2-CF)m O-CF2- CF2-SO3H
CF3
Nafion consists of a hydrophobic tetrafluoroethylene (TFE) backbone with pendant side chains of perfluorinated vinylethers terminated by ion-exchange groups. Ionic Cluster Model involving sulphonate groups.
Polymer relaxation properties affect the proton transport properties.
SM-SFM Rheological Response
Temperature (oC)
Mem
bran
e R
esis
tivi
ty (
Ohm
-cm
)
Tc 80-90 oC
A. Sen, et al., Mat. Res. Soc. Symp. Proc. Vol. 393, 157 (1995)
Transition
Regime
Low PEM
Efficiency
High PEM
Efficiency
60 70 80 90 100 110 120
0.009
0.010
0.011
0.012
0.013
12
14
16
18
20
Vis
cous
Res
pons
e
Mod
uli R
espo
nse
Temperature (oC)
~83 oCRheological transition at