Ref HAL: hal-00514499_v1
PMID 20482065
Ref Arxiv: 0910.0364
DOI: 10.1103/PhysRevLett.104.165701
WoS: 000277007700037
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186 Citations
Résumé:

We numerically produce fully amorphous assemblies of frictionless spheres in three dimensions and study the jamming transition these packings undergo at large volume fractions. We specify four protocols yielding a critical value for the jamming volume fraction which is sharply defined in the limit of large system size, but is different for each protocol. Thus, we directly establish the existence of a continuous range of volume fraction where nonequilibrium jamming transitions occur. However, these jamming transitions share the same critical behaviour. Our results suggest that, even in the absence of partial crystalline ordering, a unique location of a random close packing does not exist, and that volume fraction alone is not sufficient to describe the properties of jammed states.

Commentaires: 5 pages, 3 figs Journal: Phys. Rev. Lett. 104, 165701 (2010)

PMID 20481669
Ref Arxiv: 0911.5269
DOI: 10.1103/PhysRevE.81.040502
WoS: 000277265700007
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25 Citations
Résumé:

We use computer simulations to study the dynamics of a physical gel at high densities where gelation and the glass transition interfere. We report and provide detailed physical understanding of complex relaxation patterns for time correlation functions which generically decay in a three-step process. For certain combinations of parameters we find logarithmic decays of the correlators and subdiffusive particle motion.

Commentaires: 4 pages, 5 figures Journal: Phys. Rev. E 81, 040502 (2010)

Ref HAL: hal-00597603_v1
PMID 20365738
Ref Arxiv: 0912.1738
DOI: 10.1103/PhysRevE.81.031505
WoS: 000276199300058
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25 Citations
Résumé:

We combine the hyper-netted chain approximation of liquid state theory with the mode-coupling theory of the glass transition to analyze the structure and dynamics of soft spheres interacting via harmonic repulsion. We determine the locus of the fluid-glass dynamic transition in a temperature -- volume fraction phase diagram. The zero-temperature (hard sphere) glass transition influences the dynamics at finite temperatures in its vicinity. This directly implies a form of dynamic scaling for both the average relaxation time and dynamic susceptibilities quantifying dynamic heterogeneity. We discuss several qualitative disagreements between theory and existing simulations at equilibrium. Our theoretical results are, however, very similar to numerical results for the driven athermal dynamics of repulsive spheres, suggesting that 'mean-field' mode-coupling approaches might be good starting points to describe these nonequilibrium dynamics.

Commentaires: 11 pages, 8 figures Journal: Phys. Rev. E 81, 031505 (2010)

Ref HAL: hal-00597618_v1
Ref Arxiv: 0912.2657
DOI: 10.1039/B926412D
WoS: 000279046300016
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38 Citations
Résumé:

We use the hyper-netted chain approximation of liquid state theory to analyze the evolution with density of the pair correlation function in a model of soft spheres with harmonic repulsion. As observed in recent experiments on jammed soft particles, theory predicts an 'anomalous' (nonmonotonic) evolution of the intensity of the first peak when density is increased at constant temperature. This structural anomaly is a direct consequence of particle softness, and can be explained from purely equilibrium considerations, emphasizing the generality of the phenomenon. This anomaly is also predicted to have a non-trivial, '${\cal S}$-shaped', evolution with temperature, as a result of a competition between three distinct effects, which we describe in detail. Computer simulations support our predictions.

Commentaires: 5 pages, 4 figures

Ref HAL: hal-00597624_v1
Ref Arxiv: 0810.4405
DOI: 10.1209/0295-5075/86/10001
WoS: 000266414000001
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98 Citations
Résumé:

We use molecular dynamics to investigate the glass transition occurring at large volume fraction, phi, and low temperature, T, in assemblies of soft repulsive particles. We find that equilibrium dynamics in the (phi, T) plane obey a form of dynamic scaling in the proximity of a critical point at T=0 and phi=phi_0, which should correspond to the ideal glass transition of hard spheres. This glass point, 'point G', is distinct from athermal jamming thresholds. A remarkable consequence of scaling behaviour is that the dynamics at fixed phi passes smoothly from that of a strong glass to that of a very fragile glass as phi increases beyond phi_0. Correlations between fragility and various physical properties are explored.

Commentaires: 5 pages, 3 figures; Version accepted at Europhys. Lett Journal: Europhys. Lett. 86, 10001 (2009)

Ref HAL: hal-00512107_v1
Ref Arxiv: 0903.1933
DOI: 10.1088/1742-5468/2009/07/P07015
WoS: 000269353300015
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42 Citations
Résumé:

We use dynamic light scattering and numerical simulations to study the approach to equilibrium and the equilibrium dynamics of systems of colloidal hard spheres over a broad range of density, from dilute systems up to very concentrated suspensions undergoing glassy dynamics. We discuss several experimental issues (sedimentation, thermal control, non-equilibrium aging effects, dynamic heterogeneity) arising when very large relaxation times are measured. When analyzed over more than seven decades in time, we find that the equilibrium relaxation time, tau_alpha, of our system is described by the algebraic divergence predicted by mode-coupling theory over a window of about three decades. At higher density, tau_alpha increases exponentially with distance to a critical volume fraction phi_0 which is much larger than the mode-coupling singularity. This is reminiscent of the behavior of molecular glass-formers in the activated regime. We compare these results to previous work, carefully discussing crystallization and size polydispersity effects. Our results suggest the absence of a genuine algebraic divergence of tau_alpha in colloidal hard spheres.

Commentaires: 16 pages; 12 figures

Résumé:

Résumé (à complèter)