Single-Molecule Probing of Dynamical Heterogeneity in Molecular Glass Formers

T. Xia, R. Zondervan, F. Kulzer,M. Orrit

Molecular Nano-Optics and Spins

C. Storm, W. van Saarloos

Instituut Lorentz

M. Möbius, M. van Hecke

Kamerlingh Onnes Laboratory

LION, Leiden University (NL)

Dr. Rob Zondervan

Ted Xia

Dr. Florian Kulzer

• Introduction- single-molecule microscopy- rotational diffusion, previous work

• Local viscosity measurements- supercooled glycerol- heterogeneity

• Rheology- home-built Couette cell- plate-plate geometry

• Discussion and Outlook

Outline

Spatial selection

Collection Excitation

Confocal microscope

3. 1 mVillum

Color scale:

1500 to 20000 counts/s

with 750 W/cm2

exc. 514.5 nm

(R. Zondervan, 2003)

m10

Room Temperature

DiI

in Zeonex®

Probing viscosity with fluorescence

• Fluorescence Anisotropy (during emission)

• Polarization fluctuations (small ensembles)

• Single-molecule orientation

Rotational diffusion time:( )

B

TV

k T

Previous Work

Tg+10 K

Tg+5 K

Tg+2 K

Deschenes et al. JPC 106 (2002) 11438

Environmental exchanges

Spread of diffusion rates

Schob et al., Eur. Polym. J. 40 (2004) 1019

Similar results inpolymers, with rareenvironmentalexchanges.

- Very small samples (1 fL) quick heating and cooling (1 s).- Many repeated cycles possible

Zondervan et al., Biophys. J. 90 (2006) 2956.

Thermal Cycles for Single Protein Dynamics

Rotational diffusion of single fluorescent dyes

Perylene-di-imide (a) in glycerol (b)R. Zondervan et al., P. N. A. S. 104 (2007) 12628

Viscosity of supercooled glycerol

from: Schröter & Donth, J. Chem. Phys. 113 (2000) 9101

Agreement with rheology

Polarized single-molecule fluorescence

Anticorrelation of polarization channels

Single-molecule tumbling at variable T

T-dep. of tumbling rates for 69 molecules

Long memory time of local tumbling rate

Seen already for colloidalsuspensions in the glassphase:E. R. Weeks et al.,Science 287(2000) 627

A solid matrix should beelastic : rheology?

Extremely long memory of diffusion rate: evidence for solid walls? (foam)

Rheology of Super-Cooled Glycerol

R. Edgeworth et al., Eur. J. Phys. (1984) 198

The Pitch-Drop Experiment (Ig-Nobel 2005)

Optical probing of shear deformation

R. Zondervan et al., P. N. A. S. 105 (2008) 4993

Bulk viscosity values:

Glycerol:Schröter & DonthJCP 113 (2000) 9101

o-TerphenylLaughlin & UhlmanJPC 76 (1972) 2317

Symbols: data from Zondervan et al., PNAS 105 (2008) 4993

Shear strain traces upon sudden load

Thermal histories yielding solid-like rheology

Model of mixed response

M

10

102

10

1

100

,,

1)(

k

v

k

M

tM

ett

Exponential jump and viscous drift

: liquid’s viscosity

: network’s spring constant

: effective viscosity (creep)

0

k

1

Shear modulus and viscosities from fits

0 100 200 300 400 500 600

14

16

18

20

22

time (s)

An

gle

(m

rad

)

Better fit with a stretched exponential(measurement with commercial rheometer)

0 1 exp /t a t

0.65

36

2.25 /a

s

rad s

Aging and hardening (over 2 weeks)

Ortho-Terphenyl

Shear rejuvenation

180 200 220 240 260 280 300 32010-1

100

101

102

103

104

105

106

107

108

109

1010

Schroeter and Donth

(P

a s)

T (K)

Tg

Viscosity with Couette cell (1mm gap) in rheometer (by M. Möbius)

Thermal History

Slow cooling from 260 K to 195 K at 5 K/hour, anneal at 195 K for 2 hour, warmup to aging temperature at 1 K/min

Monitor G’,G’’ at f =0.1 Hz at low strain γ=0.0005

0 10 20 30 40 50 60 70 80180

200

220

240

260

280

300

warming rate:12K/h

T (

K)

tabs

(h)

TG

Tm

T=220K

cooling rate:5K/h

1K/min

(dips are dewar changes)

15 20 25 30 35 40 45 50 55 60100

101

102

103

104

105

106

107

108

G'' G'

G',

G''

(Pa)

tabs

(h)

changed dewar

15 20 25 30 35 40 45 50 55 60105

106

107

108

* (P

a s)

tabs

(h)

d

Aging at T=220K

Solid response sets in after 25.8 hour of aging (growth)

Aging at T=240K

0 1 2 3 4 5 6 7105

106

107

108

G' (

Pa

)

Aging Time (hr)

“Slushy” appearance

- Importance of free volume; captured in liquid lakes, fenced in by solid walls?

- Mobility as a function of effective pressure(Reiser et al. Europhys. Lett. 76 (2006) 1137)

- Convergence of temperature dependences to about 230 K, Tg + 40 K; MCT?

Discussion

(ln )0.2

1 g

p MPaT

mT p

- Relation to Fischer clusters?

- Crystallization? Characterize at various stages…

- Relation to glacial phase?

Images of structure growth in triphenylphosphite:from H. Tanaka, R. Kurita, H. Mataki, PRL 92 (2004) 025701

Tg+ 15 KTg+ 8 K

Glacial phase

- Influence of thermal history on microstructure?

- Size and shape of lakes?

To do:

Relevance to glass transition?

- General for several molecular glass formers

- Seen also in colloidal models

Conclusions• Inhomogeneity and spread of local

viscosity

• Soft Glassy Rheology of supercooled glycerol and o-TP. General for glass formers?

• Relation to glacial phases and microscopic picture?

Outlook: SM’s and nano-probing for soft matter studies

Rob Zondervan

Meindert van Dijk

Florian Kulzer

ClemensHofman

n

AurélienNicolet

Kramers theory for bond breaking

• Closed Broken

F : applied force

• Effective viscosity (plastic deformation)

K : spring constant of bond

11 2 ( )

R

B B R

kKk k k

Rk

Bk0 0exp( / )Bk k F F

• according to model, the force on the spring is

the effective viscosity decreases much slower at high forces(as 1/F only)

Applied force is reduced by liquid shear

11

1 0

F F

k1

0F

Shear thinning

«… glassy dynamics is a natural consequence of two properties shared by all [Foams, emulsions, pastes,

slurries, quicksand, dense suspensions, …] soft materials: structural disorder and metastability. »

P. Sollich et al., Phys. Rev. Lett. 78 (1997) 2020

Also supercooled liquids!

Soft Glassy Rheology

220 230 240 2500.1

1

10

100

On

set

of

solid

ific

atio

n (

hr)

220 230 240 250102

103

104

105

106

(P

a s

)

T (K)

0 10 20 30 40 50 60 70

104

105

106

107

108

109

1010

1011

0 200 400 600 800 1000 1200 1400

(ks)

(s)

T = 292K ~ (Tm+1K)

Time

Ap

par

ent

Vis

cosi

ty (

Pa.

S)

T = 293K ~ (Tm+2K)

Crossing the Melting Temperature

Slow warming (12K/hr).Melting around 291K – melting point of glycerol

220 230 240 250 260 270 280 290 300 31010-3

10-2

10-1

100

101

102

103

104

105

106

107

108

220 230 240 250 260 270 280 290 300 31010-2

10-1

100

101

102

103

104

105

106

107

108

loss storage

G',

G''

(Pa

)

T (K)

* (P

a s

)

T (K)

shear

from Literature

stayed therefor 1 hr

-Friction: local pressure and temperature, third body,...

- Adhesion: role of a soft layer in between two solids, probed with different dyes

Solid-solid interaction with SM’s