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Dynamical heterogeneity at the jamming transition of concentrated colloidsPowerPoint Presentation

Dynamical heterogeneity at the jamming transition of concentrated colloids

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Dynamical heterogeneity at the jamming transition of concentrated colloids

P. Ballesta1, A. Duri1, Luca Cipelletti1,2

1LCVN UMR 5587

Université Montpellier 2 and CNRS, France

2Institut Universitaire de France

Heterogeneous dynamics

homogeneous

Dynamical susceptibility in glassy systems

Supercooled liquid (Lennard-Jones)

Lacevic et al., PRE 2002

c4~ var[Q(t)]

Outline

- Measuring average dynamics and c4 in colloidal suspensions
- c4 at very high j : surprising results!
- A simple model of heterogeneous dynamics

Experimental system & setup

PVC xenospheres in DOP

radius ~ 10 mm, polydisperse

j = 64% – 75%

Excluded volume interactions

Experimental system & setup

CCD-based (multispeckle)

Diffusing Wave Spectroscopy

CCD

Camera

Laser beam

Change in speckle field mirrors change in sample configuration

Probe d << Rparticle

lag t

time tw

fixed tw, vs.t

2-time intensity correlation function g2(tw,t) - 1

Time Resolved Correlationdegree of correlationcI(tw,t) = - 1

< Ip(tw) Ip(tw+t)>p

< Ip(tw)>p<Ip(tw+t)>p

2-time intensity correlation function

f = 66.4%

Fit: g2(tw,t) ~ exp[-(t /ts (tw))p(tw)]

- Initial regime: « simple aging » (ts ~ tw1.1 ± 0.1)
- Crossover to stationary dynamics, large fluctuations of ts

2-time intensity correlation function

f = 66.4%

Fit: g2(tw,t) ~ exp[-(t/ts(tw))p(tw)]

Average dynamics :

< ts >tw , < p >tw

Average dynamics vs j

Average relaxation time

lag t

time tw

fixed t, vs.tw

fluctuations of the dynamics

var(cI)(t)

c (t )

Fluctuations from TRC datadegree of correlationcI(tw,t) = - 1

< Ip(tw) Ip(tw+t)>p

< Ip(tw)>p<Ip(tw+t)>p

Fluctuations in the DWP model

Random number of rearrangements

g2(t,t) – 1 fluctuates

r

r increases

fluctuations increase

Fluctuations

r

Moderate j : large sf2 few events large flucutations

Near jamming : small sf2 many events small flucutations

Conclusions

Dynamics heterogeneous

Non-monotonic behavior of c*

Competition between

increasing size of dynamically

correlated regions ...

Conclusions

Dynamics heterogeneous

Non-monotonic behavior of c*

Competition between

increasing size of dynamically

correlated regions

and

decreasing effectiveness of

rearrangements

Conclusions

Dynamics heterogeneous

Non-monotonic behavior of c*

Competition between

increasing size of dynamically

correlated regions

and

decreasing effectiveness of

rearrangements

Dynamical heterogeneity dictated by the number of rearrangements

needed to decorrelate

A further test…

Single scattering, colloidal fractal gel (Agnès Duri)

sf2 ~q2d 2look at different q!

A further test…sf2 ~q2d 2look at different q!

A further test…sf2 ~q2d 2look at different q!

A further test…Average dynamics vs j

Average relaxation time

Dynamical hetereogeneity in glassy systems

Supercooled liquid (Lennard-Jones)

Glotzer et al.,

J. Chem. Phys. 2000

c4 increases when approaching Tg

Conclusions

Dynamics heterogeneous

Non-monotonic behavior of c*

Many localized, highly effective

rearrangements

Conclusions

Dynamics heterogeneous

Non-monotonic behavior of c*

Many localized, highly effective

rearrangements

Many extended, poorly effective

rearrangements

Conclusions

Dynamics heterogeneous

Non-monotonic behavior of c*

Many localized, highly effective

rearrangements

Many extended, poorly effective

rearrangements

Few extended, quite effective

rearrangements

General behavior

lag t

time tw

Time Resolved Correlationdegree of correlationcI(tw,t) = - 1

< Ip(tw) Ip(tw+t)>p

< Ip(tw)>p<Ip(tw+t)>p

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