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