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Direct-space investigation of the ultraslow ballistic dynamics of a soft glass
Auteur(s): Mazoyer Sylvain, Cipelletti L., Ramos L.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 79 p.011501 (2009)
Texte intégral en Openaccess :
Ref HAL: hal-00323837_v1
PMID 19257036
Ref Arxiv: 0809.3995
DOI: 10.1103/PhysRevE.79.011501
WoS: 000262976600049
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
10 Citations
Résumé: We use light microscopy to investigate the aging dynamics of a glass made of closely packed soft spheres, following a rapid transition from a fluid to a solid-like state. By measuring time-resolved, coarse-grained displacements fields, we identify two classes of dynamical events, corresponding to reversible and irreversible rearrangements, respectively. The reversible events are due to the small, experimentally unavoidable fluctuations of the temperature imposed to the sample, leading to transient thermal expansions and contractions that cause shear deformations. The irreversible events are plastic rearrangements, induced by the repeated shear cycles. We show that the displacement due to the irreversible rearrangements grows linearly with time, both on average and at a local level. The velocity associated with this ballistic motion decreases exponentially with sample age, accounting for the observed slowing down of the dynamics. The displacement field due to the irreversible rearrangements has a vortex-like structure and is spatially correlated over surprisingly long distances.
Commentaires: 10 pages, 7 figures, submitted to PRE
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Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition
Auteur(s): Brambilla G., El masri Djamel, Pierno Matteo, Berthier L., Cipelletti L., Petekidis George, B. Schofield Andrew
(Article) Publié:
Physical Review Letters, vol. 102 p.085703 (2009)
Texte intégral en Openaccess :
Ref HAL: hal-00323231_v2
PMID 19257755
Ref Arxiv: 0809.3401
DOI: 10.1103/PhysRevLett.102.085703
WoS: 000263816200034
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
290 Citations
Résumé: We use dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres. Our study covers an unprecedented density range and spans seven decades in structural relaxation time, $\ta$, including equilibrium easurements above $\phi_{\rm c}$, the location of the glass transition deduced from fitting our data to mode-coupling theory. Instead of falling out of equilibrium, the system remains ergodic above $\phi_{\rm c}$ and enters a new dynamical regime where $\ta$ increases with a functional form that was not anticipated by previous experiments, while the amplitude of dynamic heterogeneity grows slower than a power law with $\ta$, as found in molecular glass-formers close to the glass transition.
Commentaires: 4 pages, 3 figures, published in PRL 102 085703 (2009)
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Unexpected drop of dynamical heterogeneities in colloidal suspensions approaching the jamming transition
Auteur(s): Ballesta Pierre, Duri Agnès, Cipelletti L.
(Article) Publié:
Nature Physics, vol. 4 p.550-554 (2008)
Texte intégral en Openaccess :
Ref HAL: hal-00292570_v1
Ref Arxiv: 0807.0281
DOI: 10.1038/nphys1000
WoS: 000257984600015
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
78 Citations
Résumé: As the glass (in molecular fluids\cite{Donth}) or the jamming (in colloids and grains\cite{LiuNature1998}) transitions are approached, the dynamics slow down dramatically with no marked structural changes. Dynamical heterogeneity (DH) plays a crucial role: structural relaxation occurs through correlated rearrangements of particle ``blobs'' of size $\xi$\cite{WeeksScience2000,DauchotPRL2005,Glotzer,Ediger}. On approaching these transitions, $\xi$ grows in glass-formers\cite{Glotzer,Ediger}, colloids\cite{WeeksScience2000,BerthierScience2005}, and driven granular materials\cite{KeysNaturePhys2007} alike, strengthening the analogies between the glass and the jamming transitions. However, little is known yet on the behavior of DH very close to dynamical arrest. Here, we measure in colloids the maximum of a ``dynamical susceptibility'', $\chi^*$, whose growth is usually associated to that of $\xi$\cite{LacevicPRE}. $\chi^*$ initially increases with volume fraction $\varphi$, as in\cite{KeysNaturePhys2007}, but strikingly drops dramatically very close to jamming. We show that this unexpected behavior results from the competition between the growth of $\xi$ and the reduced particle displacements associated with rearrangements in very dense suspensions, unveiling a richer-than-expected scenario.
Commentaires: 1st version originally submitted to Nature Physics. See the Nature Physics website fro the final, published version
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