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Shear Alignment and Mechanical Properties of Nanostructured Hydrogels
Lynn M. WalkerDepartment of Chemical Engineering
Carnegie Mellon UniversityCarnegie Mellon UniversityPittsburgh PA 15217
IMA Special WorkshopFlowing Complex Fluids: Fluid Mechanics‐Interaction of
Microstructure and FlowOctober 12‐16, 2009
One person that would be happy…
Chevy Chase as Gerald FordS t d Ni ht Li
Th ill b th
Saturday Night Live
There will be no math…
Nanostructured Block Copolymer SolutionsBlock copolymers – covalently linked blocks ofBlock copolymers covalently linked blocks of chemically dissimilar chains.
In a “selective” solvent
Lyophobic
Lyophiliccorona Block copolymer micelles – associated
structures held together by intermolecularcore structures held together by intermolecular forces. Nagg ~ 100
At high enough concentrations
Block copolymer “crystal” – intermicellar interactions will lead to long range ordering.
Nanostructured HydrogelsF (PEO) (PPO) (PEO) t ibl k l t b l ti l t t• For (PEO)-(PPO)-(PEO) triblock copolymers, water becomes a selective solvent at temperatures > 10 – 15oC.
Temperature
Nanostructured Hydrogels
T 5⁰C T = 25⁰CT = 5⁰C Liquid
T = 25 CGel
• Increase in temperature results in a spontaneous transition from a liquid (polymer solution) to a gel (close packed micelle “crystal”).
Nanostructured HydrogelsCl k d i ll f h t d t i l ith l t t• Close-packed micelles form a phase separated material with nanoscale structure. The transition is entropic, so likely dominated by the change in volume fraction.
~ 10 nmInterstitial spaces form water filled “pockets”. versus
PPO cores – dehydrated melt.PEO corona – hydrated.
Features of “pocket”:• Mainly solvent (water).• Dense hydrated PEO “boundaries”.• Dimensions on the order of 10 nm.• Thermoreversible.
Templating ApproachApplications in:Applications in:• Nanoparticle storage.• Protein protection/storage.• Nanomaterial design.
Requirements of Dispersed Particles:• Colloidally stable.y• Minimal adsorption of polymer.• Dimensions coincident with crystal.• Stoichiometry.
Series of papers by D. C. Pozzo and L. M. Walker
Mechanical Properties - Thermoreversibility
~ 0o
17o ~ 0o
~ 17o
Wanka, G., Hoffmann, H., and Ulbricht, W. “Phase Diagrams and Aggregation Behavior of Poly(oxyethylene)-Poly(oxypropylene)-Poly(oxyethylene) Triblock Copolymers in Aqueous Solutions” Macromolecules 27 (1994), 4145-4159.
Mechanical Behavior - Composites
101
102
20% F127 Matrix
105F127 25% + BSA
Loading Level Gel Stiffness
/s 10-3
10-2
10-1
100
10
rad/s
103
104
10 F127 25% + BSA 0 w% 1 w% 3 w% 4 w% 5 w%
% C l
101
102
(kP
a) @
1 ra
d/
10-5
10-4
10 3
25% F127 Matrix
(kPa) @
1 r
101
102
G*
(Pa)
6 w% Crystal
3
10-2
10-1
100
10
G*
G* (
10-1
100
5550454035302520151050Fluid
10-5
10-4
10-3
6560555045403530252015105T t (C)
No Silica 5% Silica 7 nm 10% Silica 7 nm
5550454035302520151050Temperature (°C)
Used rheology as a tool to map out the Temperature (C)operating space.
Series of papers by D. C. Pozzo and L. M. Walker
How do we measure structure directly? - SANSV ti f H O t D O t “ t h” ti f it t i l• Vary ratio of H2O to D2O to “match” portions of a nanocomposite material.
10
8
Polymer Micelles
8
6
I1/2
4
2
Dispersed Phase
0
100806040200D2O (mol/mol %)
Proteins – Templating of BSA
• C t t i ti SANS h th t th ti l h th ti l t t• Contrast variation SANS shows that the particle have the same spatial structure as the template.
Templating of protein – Different templates
• Two different block copolymer templates but a similar templating observed.p y p p g
Shear Alignment of Crystal DomainsShear→
“Powder” Macro‐domain Shear →
Couette shear
Typical ScatteringProfiles
Alignment to Single CrystalShear Rate: 1 s-1Powder Scattering Shear Rate: 10 s-1 Shear Rate: 100 s-1Shear Rate: 1 sPowder Scattering Shear Rate: 10 s Shear Rate: 100 s
Simple Shear
VorticityVorticity
Shear
• Alignment does not require large deformation rates (G* ~ O(10 – 100 kPa)
• Quantify the level of domain alignment:
bkg)q(I
bkg)q(S)q(P)N,(C)(I q
bkg)q(IPP )q(S)(S)1()(S PPAP qq
Aligned Un‐aligned
Shear Alignment with Dispersed ParticlesNeat Micelle Crystal (Pluronic F127 20%)
Φ
1.0
0.8
F127 25 wt% at 25 °C
Neat Polymer Shearing Neat Polymer Rest after Shear3 % Sili Sh i
y ( )
1.2
1.0 First Ring
ΦPowder ≈
0.6
Frac
tion
3 wt% 7nm Silica Shearing 2 wt% BSA Shearing 2 wt% BSA Rest after Shear
1.0
0.8log
0.4P
owde
r 0.6
0.4 P
0.2
0.0
0.2
• Addition of particles to interstitial spaces does not stop ability to align crystal
100806040200Shear Rate (s-1)
0.0
1 10 100 1000Shear Rate
Addition of particles to interstitial spaces does not stop ability to align crystal.• Alignment is initially “easier”; detailed nature of particles impacts alignment at higher rates.
Alignment to Single CrystalShear Rate: 1 s-1Powder Scattering Shear Rate: 10 s-1 Shear Rate: 100 s-1Shear Rate: 1 sPowder Scattering Shear Rate: 10 s Shear Rate: 100 s
Simple Shear
VorticityVorticity
Shear
5 Hz, 1000% Strain 50 Hz, 1000% Strain Powder Scattering
O ill tOscillatory Shear
• Significant difference between simple and oscillatory shear flow• Significant difference between simple and oscillatory shear flow.• Structures are more aligned in oscillation.
Oscillatory Shear – Linear?5 Hz 1000% Strain
10000
1000001 rad/s5 rad/s10 rad/s15 rad/s20 d/
Region probed with SANS
5 Hz, 1000% Strain
100
1000
%
20 rad/s25 rad/s
5 Hz 100% Strain
1
10Stra
in % 5 Hz, 100% Strain
0.1
1
0 200 400 600 800 10000 200 400 600 800 1000Stress (Pa)
• SANS performed under nonlinear conditions.SANS performed under nonlinear conditions.• Appears that we need nonlinear levels of strain to align the powder.
Persistence of Structure
25wt% F127; 5 Hz, 500% strain
Sample at rest (15 min)Under shear Sample at rest (15 min)Under shear
F127 30 wt% + Silica 3 wt%;Sili S iSilica Scattering;Simple shear 10s‐1
Sample at rest (1 month)Under shear
• Once aligned, samples remain ordered over time.
Flow mechanism?Equilibrium
HCP {1010}
HCP {3210}
Equilibrium
HCP {1010}
HCP {3210}
Sliding
FCC {220}HCP {1210}FCC {220}HCP {1210}
Zig‐zagZig-Zag SlidingZig-Zag Sliding
Loose W. and Ackerson B.J., JCP 1994
Flow mechanism of BCP crystal
0.04
0.06
0.08
0.04
0.06
0.08Rest
0.04
0.06
0.08100 s-
110 s-
1
25% F127 in 100% D2O
-0.04
-0.02
0.00
0.02
QV
ort (
A-1)
-0.04
-0.02
0.00
0.02
QV
ort (
A-1)
-0.04
-0.02
0.00
0.02
QV
ort (
A-1)
-0.08
-0.06
-0.08 -0.04 0.00 0.04QVel (A
-1)
-0.08
-0.06
-0.08 -0.04 0.00 0.04QVel (A
-1)
R-0.08
-0.06
-0.08 -0.04 0.00 0.04QVel (A
-1)
R
10 s-
1
R
Zig-Zag SlidingZig-Zag Sliding
To quantify:
A = (Itop – Isides)/Ipowder
• Does not agree with either simple flow mechanism.C i f h l h ?
T
• Coexistence of another crystal phase?
Anisotropy of Bragg spots
1.0
1.5
owde
r
0.0
0.5
- Isi
des)
/ I p
o
Equilibrium
HCP {1010}
HCP {3210}
FCC {220}
Equilibrium
HCP {1010}
HCP {3210}
FCC {220}
-1.0
-0.5(I t
op-b
otto
m
F127 25 wt% at 25 °C
Neat Polymer Shearing Neat Polymer Rest after Shear 2 wt% BSA Shearing2 t% BSA R t ft Sh
FCC {220}HCP {1210}FCC {220}HCP {1210}
-1.5
300250200150100500Shear Rate (s-1)
2 wt% BSA Rest after Shear 3 wt% 7nm Silica Shearing
• Again, the nature of the particles matter.• Flo mechanism is complicated in all cases
Shear Rate (s )
• Flow mechanism is complicated in all cases.
Conclusions
• Thermoreversible block copolymer gels are able to spatially template nanoparticulate material.
• Templating is controlled primarily by particle size.
• Shear allows soft gels to be aligned which persists• Shear allows soft gels to be aligned which persists.
• Flow mechanisms are complex and depend on details of particulate material (and gel?)particulate material (and gel?)
F127_25_03 (40.7) BSA 25ºC
AcknowledgementsGraduate Students May 2006Graduate Students• Brian Priore• Brian Thebaud• My Hang Truong
May 2006
• Yenny Christanti• Michael Gerber• Danilo Pozzo
Git S tJune 2008
• Gita Seevaratnam• Marshall Lindsey• Jeff Shaheen• Danny Kuntz
Funding• National Science Foundation• National Energy Tech Lab.
P t & G blDanny Kuntz• Eric Miller• Yuli Wei• Theresa LaFollette
• Proctor & Gamble• ACS – PRF• NASA
• Wingki Lee• Nick Alvarez• Viet Lam
M tt R i h t
A Gordon Conference to consider (www.grc.org):
Colloidal, Macromolecular & Polyelectrolyte Solutions Gordon Research Conference• Matt Reichert
• Vicki Cheng
Research Conference Four Points Sheraton in Ventura, CA ; February 21‐26, 2010