Ref HAL: hal-00667220_v1
DOI: 10.1038/NPHYS2133
WoS: 000300403700023
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183 Citations
Résumé:

The viscosity of glass-forming liquids increases by many orders of magnitude if their temperature is lowered by a mere factor of 2-3. Recent studies suggest that this widespread phenomenon is accompanied by spatially heterogeneous dynamics, and a growing dynamic correlation length quantifying the extent of correlated particle motion. Here we use a novel numerical method to detect and quantify spatial correlations that reveal a surprising non-monotonic temperature evolution of spatial dynamical correlations, accompanied by a second length scale that grows monotonically and has a very different nature. Our results directly unveil a dramatic qualitative change in atomic motions near the mode-coupling crossover temperature, which involves no fitting or indirect theoretical interpretation. These findings impose severe new constraints on the theoretical description of the glass transition, and open several research perspectives, in particular for experiments, to confirm and quantify our observations in real materials.

Ref HAL: hal-00808514_v1
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Point to set correlations in supercooled liquids

Commentaires: , DOI = 10.1093/acprof:oso/9780199691470.001.0001

Ref HAL: hal-00685186_v1
PMID 22463215
Ref Arxiv: 1111.5957
DOI: 10.1103/PhysRevE.85.021503
WoS: 000300572000009
Ref. & Cit.: NASA ADS
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53 Citations
Résumé:

We perform molecular dynamics simulations to characterize the occurrence of inhomogeneous shear flows in soft jammed materials. We use rough walls to impose a simple shear flow and study the athermal motion of jammed assemblies of soft particles, both for purely repulsive interactions and in the presence of an additional short-range attraction of varying strength. In steady state, pronounced flow inhomogeneities emerge for all systems when the shear rate becomes small. Deviations from linear flow are stronger in magnitude and become very long-lived when the strength of the attraction increases, but differ from permanent shear-bands. Flow inhomogeneities occur in a stress window bounded by the dynamic and static yield stress values. Attractive forces enhance the flow heterogeneities because they accelerate stress relaxation, thus effectively moving the system closer to the yield stress regime where inhomogeneities are most pronounced. The present scenario for understanding the effect of particle adhesion on shear localization, which is based on detailed molecular dynamics simulations with realistic particle interactions, differs qualitatively from previous qualitative explanations and ad-hoc theoretical modelling.

Commentaires: 12 pages, 12 figures Journal: Phys. Rev. E 85, 021503 (2012)

Ref HAL: hal-00653735_v1
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Point to set correlations in supercooled liquids

Ref HAL: hal-00653734_v1
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Lengthscales in amorphous materials

Ref HAL: hal-00643045_v1
PMID 22181365
Ref Arxiv: 1106.4663
DOI: 10.1103/PhysRevE.84.051103
WoS: 000296958700001
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64 Citations
Résumé:

We develop a microscopic theory to analyze the phase behaviour and compute correlation functions of dense assemblies of soft repulsive particles both at finite temperature, as in colloidal materials, and at vanishing temperature, a situation relevant for granular materials and emulsions. We use a mean-field statistical mechanical approach which combines elements of liquid state theory to replica calculations to obtain quantitative predictions for the location of phase boundaries, macroscopic thermodynamic properties and microstructure of the system. We focus in particular on the derivation of scaling properties emerging in the vicinity of the jamming transition occurring at large density and zero temperature. The new predictions we obtain for pair correlation functions near contact are tested using computer simulations. Our work also clarifies the conceptual nature of the jamming transition, and its relation to the phenomenon of the glass transition observed in atomic liquids.

Commentaires: 31 pages, 18 figures; long version of arXiv:1011.5638 Journal: Phys. Rev. E 84, 051103 (2011)