APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010;
Portland, Oregon
Session V2: Relaxation and Dynamic Heterogeneity and Glass
8:00 AM–11:00 AM,
Thursday, March 18, 2010
Room: Oregon Ballroom 202
Sponsoring
Unit:
DCMP
Chair: Zexin Zhang, University of Pennsylvania
Abstract ID: BAPS.2010.MAR.V2.2
Abstract: V2.00002 : Dynamic Heterogeneity and Relaxation Time Very Close to Dynamic Arrest
8:36 AM–9:12 AM
Preview Abstract
Abstract
Author:
Luca Cipelletti
(University Montpellier 2 and CNRS)
In supercooled molecular fluids or concentrated colloids and
grains, the dynamics slow down markedly with no distinct
structural changes as the glass and jamming transitions are
approached. There is now ample evidence that structural
relaxation in glassy systems can only occur through correlated
rearrangements of particles, leading to dynamics that are
heterogeneous both in time and in space. On approaching
these transitions, the size of these rearranging domains grows in
glass-formers, colloids, and driven granular materials alike,
providing a possible explanation for kinetic slowing. However,
little is known yet on the behavior of dynamical heterogeneity
and relaxation time very close to dynamical arrest.
In this talk, I'll present recent results from our group for a
simples model sustem --colloidal hard spheres--, as well as for
other glassy and jammed soft materials.
By extending previous data [1] by at least 2 orders of magnitude
in time, we established that the volume fraction dependence of
relaxation time and dynamic heterogeneity in colloidal hard
spheres follow mode coupling theory (MCT) [2] predictions
only in a restricted density range [3]. Unlike previous studies,
we provide equilibrium measurements above the MCT critical
packing fraction, thereby proving unambiguously that in our
samples the algebraic divergence is absent at the predicted
packing fraction.
The behavior of dynamical heterogeneity is even more surprising.
While in supercooled hard spheres the size of domains undergoing
cooperative rearrangements is limited to a few particles at
most, closer to jamming the correlation length of the dynamics
increases dramatically, approaching the system size in a variety
of systems [4,5]. In this regime, spatial and temporal
fluctuations of the dynamics may decouple, as observed
for near hard sphere particles: while the range of spatial
correlations continuously increase on approaching jamming, the
temporal fluctuations of the dynamics initially increase with
particle volume fraction, but drop markedly very close to jamming
[5], unveiling a richer-than-expected scenario.
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[1] W. van Megen et al., Phys. Rev. E 58, 6073 (1998);
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[2] W. G\"otze, J. Phys. Condens. Matter 11, A1 (1999);
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[3] G. Brambilla et al., ``Probing the Equilibrium Dynamics of
Colloidal Hard Spheres above the Mode-Coupling Glass
Transition,'' Phys. Rev. Lett. 102, 085703 (2009);
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[4] A. Duri et al., ``Resolving long-range spatial correlations
in jammed colloidal systems using photon correlation imaging,''
Phys. Rev. Lett. 102 085702 (2009);
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[5] Pierre Ballesta, Agn\`es Duri, \& Luca Cipelletti,
``Unexpected drop of dynamical heterogeneities in colloidal
suspensions approaching the jamming transition,'' Nature Physics
4, 550 - 554 (2008)
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2010.MAR.V2.2