2,374 research outputs found
Dynamic heterogeneity in amorphous materials
Amorphous solids are mechanically rigid while possessing a disordered
structure similar to that of dense liquids. Recent research indicates that
dynamical heterogeneity, spatio-temporal fluctuations in local dynamical
behavior, might help understanding the statistical mechanics of glassy states.Comment: 7 pages; 5 figures -- "Trends" article published by Physics at
http://physics.aps.org/articles/v4/4
Can the jamming transition be described using equilibrium statistical mechanics?
When materials such as foams or emulsions are compressed, they display solid
behaviour above the so-called `jamming' transition. Because compression is done
out-of-equilibrium in the absence of thermal fluctuations, jamming appears as a
new kind of a nonequilibrium phase transition. In this proceeding paper, we
suggest that tools from equilibrium statistical mechanics can in fact be used
to describe many specific features of the jamming transition. Our strategy is
to introduce thermal fluctuations and use statistical mechanics to describe the
complex phase behaviour of systems of soft repulsive particles, before sending
temperature to zero at the end of the calculation. We show that currently
available implementations of standard tools such as integral equations,
mode-coupling theory, or replica calculations all break down at low temperature
and large density, but we suggest that new analytical schemes can be developed
to provide a fully microscopic, quantitative description of the jamming
transition.Comment: 8 pages, 6 figs. Talk presented at Statphys24 (July 2010, Cairns,
Australia
Random pinning in glassy spin models with plaquette interactions
We use a random pinning procedure to study amorphous order in two glassy spin
models. On increasing the concentration of pinned spins at constant
temperature, we find a sharp crossover (but no thermodynamic phase transition)
from bulk relaxation to localisation in a single state. At low temperatures,
both models exhibit scaling behaviour. We discuss the growing length and time
scales associated with amorphous order, and the fraction of pinned spins
required to localize the system in a single state. These results, obtained for
finite dimensional interacting models, provide a theoretical scenario for the
effect of random pinning that differs qualitatively from previous approaches
based either on mean-field, mode-coupling, or renormalization group reatments.Comment: 15 pages, 9 fig
Evidence for a disordered critical point in a glass-forming liquid
Using computer simulations of an atomistic glass-forming liquid, we
investigate the fluctuations of the overlap between a fluid configuration and a
quenched reference system. We find that large fluctuations of the overlap
develop as temperature decreases, consistent with the existence of the random
critical point that is predicted by effective field theories. We discuss the
scaling of fluctuations near the presumed critical point, comparing the
observed behaviour with that of the random-field Ising model. We argue that
this critical point directly reveals the existence of an interfacial tension
between amorphous metastable states, a quantity relevant both for equilibrium
relaxation and for nonequilibrium melting of stable glass configurations.Comment: 4 figs, 5 page
A random walk description of the heterogeneous glassy dynamics of attracting colloids
We study the heterogeneous dynamics of attractive colloidal particles close
to the gel transition using confocal microscopy experiments combined with a
theoretical statistical analysis. We focus on single particle dynamics and show
that the self part of the van Hove distribution function is not the Gaussian
expected for a Fickian process, but that it reflects instead the existence, at
any given time, of colloids with widely different mobilities. Our confocal
microscopy measurements can be described well by a simple analytical model
based on a conventional continuous time random walk picture, as already found
in several other glassy materials. In particular, the theory successfully
accounts for the presence of broad tails in the van Hove distributions that
exhibit exponential, rather than Gaussian, decay at large distance.Comment: 13 pages, 5 figs. Submitted to special issue "Classical and Quantum
Glasses" of J. Phys.: Condens. Matter; v2: response to refere
Comment on "Constant stress and pressure rheology of colloidal suspensions"
This is a comment on the recent letter by Wang and Brady on "Constant stress
and pressure rheology of colloidal suspensions", Phys. Rev. Lett. 115, 158301
(2015).Comment: 1 page; under review -> v2: publishe
Characterizing dynamic length scales in glass-forming liquids
Reply to Comment by Flenner and Szamel on our paper in Nature Physics 8, 164
(2012).Comment: 1 pag
Shear localization in a model glass
Using molecular dynamics simulations, we show that a simple model of a glassy
material exhibits the shear localization phenomenon observed in many complex
fluids. At low shear rates, the system separates into a fluidized shear-band
and an unsheared part. The two bands are characterized by a very different
dynamics probed by a local intermediate scattering function. Furthermore, a
stick-slip motion is observed at very small shear rates. Our results, which
open the possibility of exploring complex rheological behavior using
simulations, are compared to recent experiments on various soft glasses.Comment: 4 pages, 4 figures (5 figure files
Static and dynamic lengthscales in a simple glassy plaquette model
We study static and dynamic spatial correlations in a two-dimensional spin
model with four-body plaquette interactions and standard Glauber dynamics by
means of analytic arguments and Monte Carlo simulations. We study in detail the
dynamical behaviour which becomes glassy at low temperatures due to the
emergence of effective kinetic constraints in a dual representation where spins
are mapped to plaquette variables. We study the interplay between non-trivial
static correlations of the spins and the dynamic `four-point' correlations
usually studied in the context of supercooled liquids. We show that slow
dynamics is spatially heterogeneous due to the presence of diverging
lengthscales and scaling, as is also found in kinetically constrained models.
This analogy is illustrated by a comparative study of a froth model where the
kinetic constraints are imposed.Comment: 12 pages, 13 figs; published versio
- …