ISSP soft matter 2010

Interfacial microrheologyof phospholipid monolayers
at the air/water Interface

Siyoung Choi
K. Kim, J. Zasadzinski, T. Squires
University of California, Santa Barbara

Motivation
Science !

Cell membrane

Engineering!

Foams

High Internal Phase Emulsion(PS-P2VP)!
Kramer group (2003)!

Shampoo, detergents, etc.

Coating Process

Lung surfactants
Zasadzinski group (2003)!

Interfacial viscoelasticity
A magnetic needle at the air/water Interface

Interfacial viscoelasticity
A magnetic needle at the air/water Interface

A few drops of water-insoluble surfactants

Systems we are working on

DPPC(phospholipid)

DPPC +Chol(60:40)

Colloidal crystal
at the oil/waterinterface

Systems we are working on

DPPC(phospholipid)

DPPC +Chol(60:40)

Colloidal crystal
at the oil/waterinterface

Systems we are working on

DPPC(phospholipid)

DPPC +Chol(60:40)

Colloidal crystal
at the oil/waterinterfaceSystems we are working on

DPPC(phospholipid)

DPPC +Chol(60:40)

Colloidal crystal
at the oil/waterinterface

Viscometry of 2D interfaces!s !: surface viscosity! ! : subphase viscositya!

!s!

a : disk radius!!

P : Contact perimeter to 2D surface
A : Contact Area to bulk phase“Boussinesq!
Number”

High perimeter/area ratio: higher sensitivity!
HighHigh
aspectratio(e.g.
needles
Fuller,Vermant,Vermant,Fischer,Zasadzinski
aspectratio(e.g.
needles–-Brooks,Brooks, Fuller,Fischer,Zasadzinski,...) …)!
Small probes(microrheology- Weeks,Sickert & Rondelez,Fischer,Dai, ...…)!
Small probes(microrheology– Sickert& Rondelez,Fischer, Dai,Weeks,

General Experimental Procedure
CameraImage analysis

Angular strain(t)!
(Red)

microscopeelectromagnets

interface!
subphase!

DATA acquisition board

Applied Torque ~ Stress!
Rotational displacement ~ Strain
Magnetic torque(t)!
(Green)Imposedoscillatory
Can compute
Record imposed
B-field and disk orientation simultaneously
magnetic fieldviscoelasticity(G’, G’’)

General Experimental Procedure
CameraImage analysis

Angular strain(t)!
(Red)

microscopeelectromagnets

interface!
subphase!

DATA acquisition board

Applied Torque ~ Stress!
Rotational displacement ~ Strain
Magnetic torque(t)!
(Green)CancomputemeasureImposedImposedoscillatory
constantCan
Record imposed
B-field and disk orientation simultaneously
Creepcompliance--J(t)magnetic
stress fieldviscoelasticity(G’,G’’)Janus ferromagnetic microprobes

Janus ferromagnetic microprobes
requirements• Small, yet visible• Ferromagnetic• AmphiphilicJanus ferromagnetic microprobes
Photolithographyrequirements• Small, yet visible• Ferromagnetic• AmphiphilicJanus ferromagnetic microprobes
Photolithographyrequirements• Small, yet visible• Ferromagnetic• Amphiphilic
Thiol monolayer
Au (~10 nm)
Ni/Co (~100 nm)
Photoresist (~ 1 um)

Janus ferromagnetic microprobes
Photolithographyrequirements• Small, yet visible• Ferromagnetic• Amphiphilic
Thiol monolayer

20μm diameter

1μm tallAu (~10 nm)
Ni/Co (~100 nm)
Photoresist (~ 1 um)

20µm

bright field image

Amphiphilic - Janus

Janus ferromagnetic microprobes
Photolithographyrequirements• Small, yet visible• Ferromagnetic• Amphiphilic
Thiol monolayer

20μm diameter

1μm tallAu (~10 nm)
Ni/Co (~100 nm)
Photoresist (~ 1 um)

Control overSize, Shape,
Magnetic and Surface
properties

20µm

bright field image

Amphiphilic - JanusHow the disk responds!!
!
I! + "# + k! = m $ B
Rotational drag!"

Oscillatory Magnetic Field!
Angular displacement!

Rotational !
elastic constant

Torque= mBsin(! " # )$ mB

m : magnetic moment!
B : magnetic field!
! : angle for magnetic field!
" : angle for magnetic moment!
! : drag coefficient!
k : spring constant!

From field, orientation
data!
From field vs. orientation:!
!
!
– measure ! (viscosity) and k (elasticity)

recover ς(~viscosity) and κ (~elasticity)Surface drag of the probe
Total dragBulk dragDhBo =ηs(surface viscosity)η(bulk viscosity)aApparatus

Allows interfacial visualization during measurement

DPPC and its isotherm
Surface Pressure / mN/m50•Major component of Lung surfactants and cell membranes•One of the most common phospholipids(Equilibrium properties are well known)

40
30
20
100
40

60

high conc.

80

100
2Area/molecule / Å120

low conc.

DPPC and its isotherm
Surface Pressure / mN/m50•Major component of Lung surfactants and cell membranes•One of the most common phospholipids(Equilibrium properties are well known)

40Inspired by Mcconnell
texas red DHPE(0.1mol%)

302010Liquid Expanded(LE)04060high conc.

80

100
2Area/molecule / Å120

low conc.

DPPC and its isotherm
Surface Pressure / mN/m50•Major component of Lung surfactants and cell membranes•One of the most common phospholipids(Equilibrium properties are well known)

40

Inspired by Mcconnell
texas red DHPE(0.1mol%)

3020LC+LE coexistence

1004060high conc.

80

Liquid Expanded(LE)1002Area/molecule / Å120

low conc.

DPPC and its isotherm
Surface Pressure / mN/m50•Major component of Lung surfactants and cell membranes•One of the most common phospholipids(Equilibrium properties are well known)

40

Inspired by Mcconnell
texas red DHPE(0.1mol%)3020
Liquid condensed(LC)

10040

60

high conc.

LC+LE coexistence80

Liquid Expanded(LE)100
2Area/molecule / Å120

low conc.

Linear viscoelasticity of LC phase

Elasticity - domain deformation
Viscosity - Slipping domains

Linear viscoelasticity of LC phase
Surface Dynamic Modulus / uN /m4

Viscous dominant

3G’

2Elastic dominantG’’

0.19880.1

2

46 8

2

1
Frequency / Hz

46 8

10Slow dynamics- does not flow for 10 sec

2Elasticity - domain deformation
Viscosity - Slipping domains

Linear viscoelasticity of LC phase
Surface Dynamic Modulus / uN /m4

Viscous dominant

3G’

2Elastic dominant

G’’

0.1
9880.1

2

46 8

2

1
Frequency / Hz

46 8

10Slow dynamics- does not flow for 10 sec

2Elasticity - domain deformation
Viscosity - Slipping domains

Incredibly long relaxation time for 2 nm thick film

Linear viscoelasticity of LC phase
Surface Dynamic Modulus / uN /m4

Viscous dominant

3G’

2Elastic dominantG’’0.1
98

80.1

2

46 8

21
Frequency / Hz

46 8

10Slow dynamics- does not flow for 10 sec

2

Elasticity - domain deformation
Viscosity - Slipping domains

Incredibly long relaxation time for 2 nm thick film

Linear viscoelasticity of LC phase
Surface Dynamic Modulus / uN /m4

Viscous dominant

3G’

2Elastic dominant

G’’

0.1
98

80.1

2

46 8

21
Frequency / Hz

46 8

10Slow dynamics- does not flow for 10 sec

2

Elasticity - domain deformation
Viscosity - Slipping domains

Incredibly long relaxation time for 2 nm thick film

Where does this G’ come from?
γa γ
G' ~ 2 ~aa

From emulsion theory

γ ~ G 'a ~ 10 (N / m) × 10 (m) ~ 1pN−7−5

Where does this G’ come from?
γa γ
G' ~ 2 ~aa

From emulsion theory

γ ~ G 'a ~ 10 (N / m) × 10 (m) ~ 1pN−7−5

Molecular argumentkT
adhesive energy~ 1 pNline tension ~~length
1 nm

Where does this G’ come from?
γa γ
G' ~ 2 ~aaFrom emulsion theory

γ ~ G 'a ~ 10 (N / m) × 10 (m) ~ 1pN−7−5

Molecular argumentkT
adhesive energy~ 1 pNline tension ~~length
1 nm
surface tension ~adhesive energy
areakT~~ 1 mN/m
1 nm2

Linear rheology after large shear

Linear rheology after large shear

Viscous dominant over frequencies

Linear rheology after large shear

Viscous dominant over frequencies

History dependent rheology

Visualization for large shear

Visualization for large shear• Domain deformation• Interface fractures(plastic)• Slip-line forms

Visualization for large shear

Does the interface heal?

• Domain deformation• Interface fractures(plastic)• Slip-line forms

Complete healing of the deformed domains
0 sec

0 sec

30 sec 60 sec

60 sec

Before deforming

30 secComplete healing of the deformed domains
0 sec

0 sec

30 sec 60 sec

60 sec

Before deforming

30 secComplete healing of the deformed domains
0 sec

0 sec

30 sec 60 sec

60 sec

Before deforming

30 sec20 times smaller moduli
after large stressComplete healing of the deformed domains
0 sec

0 sec

30 sec 60 sec

60 sec

Before deforming

30 sec20 times smaller moduli
after large stress
Viscous - Elastictransition

A few clues of yield stress
2 nm molecular Mayonnaise??

Surface Dynamic Modulus / uN /m4

Viscous dominant

3G’

2Elastic dominant

G’’

0.1
98

Amplitude sweep

80.1

2

4

6 8

2

1
Frequency / Hz

46 8

102

Surface Dynamic Modulus / uN /mFrequency sweep

Point that starts to yield

0.1
98
7
6543
3

4

5 6 7 89230.1
Amplitude / rad4

5 6 7 89

Steady rotation - yield stress

No yield stressSteady rotation - yield stress

No yield stressSteady rotation - yield stress

No yield stressSteady rotation - yield stress

No yield stressSteady rotation - yield stress• Evident yield stressτ  σ y rc (2π rc )applied stress~ yield stressσ y ~ 10 N / m−8higher stress
No yield stressSteady rotation - yield stress• Evident yield stressτ  σ y rc (2π rc )applied stress~ yield stressσ y ~ 10 N / m−8higher stress
No yield stressSteady rotation - yield stress• Evident yield stressτ  σ y rc (2π rc )applied stress~ yield stressσ y ~ 10 N / m−8higher stress
No yield stressSteady rotation - yield stress• Evident yield stressτ  σ y rc (2π rc )applied stress~ yield stressσ y ~ 10 N / m−8

higher stress
No yield stressYield stressThixotropic behavior(time dependent viscosity)

Theories and experiments by Daniel Bonn

Aging (system) vs Rejuvenation (applied stress)
Can we do analogous experiments after yielding the interface?

After ~ 5 minutes rotation
We turn off the field

25x real time

Healing by unwindingAfter ~ 5 minutes rotation
We turn off the field

25x real time

Healing by unwindingAfter ~ 5 minutes rotation
We turn off the field
Field off

25x real time

Healing by unwindingAfter ~ 5 minutes rotation
We turn off the field
Field off

25x real time

Healing by unwindingAfter ~ 5 minutes rotation
We turn off the field
Field off

25x real time

Healing by unwindingAfter ~ 5 minutes rotation
We turn off the field
Field off

25x real time

Strong memory
Slow recovery

Healing by unwindingWatching individual domains
Blue - T1 transition
Red - recoilingGreen - change
its neighborDomains don’t melt - they stretch!

Rayleigh - Plateau instability
3D

low P

high P

low P

Rayleigh - Plateau instability
3D2D

low P

high Phigh P

low P

low P

high P

Always stable without
fluctuation or defects

Rayleigh - Plateau instability
3D

2D

low P

high Phigh P

low P

low P

high P

Always stable without
fluctuation or defects
No Rayleigh-Plateau instability for 2D

Asymmetric stress response

Chirality of DPPC

20 um

20 um

Conclusion• Direct visualization of individual DPPC domains under stress• Shear banding, yield stress, history dependence and aging• 2D Soft glassy materials - 2D high internal phase emulsions