Accueil >
Production scientifique
(307) Production(s) de BERTHIER L.

Dense assemblies of
selfpropelled particle systems
Auteur(s): Berthier L.
(Séminaires)
Cavendish Laboratory (Cambridge, FR), 20140612 


A novel approach to numerical measurements of the configurational entropy in supercooled liquids
Auteur(s): Berthier L., Coslovich D.
(Article) Publié:
Proceedings Of The National Academy Of Sciences Of The United States Of America, vol. 111 p.11668 (2014)
Texte intégral en Openaccess :
Ref HAL: hal01060372_v1
Ref Arxiv: 1401.5260
DOI: 10.1073/pnas.1407934111
WoS: 000340097900033
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
39 Citations
Résumé: The configurational entropy is among the key observables to characterize experimentally the formation of a glass. Physically, it quantifies the multiplicity of metastable states in which an amorphous material can be found at a given temperature, and its temperature dependence provides a major thermodynamic signature of the glass transition, which is experimentally accessible. Measurements of the configurational entropy require, however, some approximations which have often led to ambiguities and contradictory results. Here we implement a novel numerical scheme to measure the configurational entropy Sigma(T) in supercooled liquids, using a direct determination of the free energy cost to localize the system within a single metastable state at temperature T. For two prototypical glassforming liquids, we find that Sigma(T) disappears discontinuously above a temperature T_c, which is slightly lower than the usual estimate of the onset temperature for glassy dynamics. This observation is in good agreement with theoretical expectations, but contrasts sharply with alternative numerical methods. While the temperature dependence of Sigma(T) correlates with the glass fragility, we show that the validity of the AdamGibbs relation (relating configurational entropy to structural relaxation time) established in earlier numerical studies is smaller than previously thought, potentially resolving an important conflict between experiments and simulations.
Commentaires: 9 pages; v2 accepted to PNAS Journal: Proc. Natl. Acad. Sci. USA 111, 11668 (2014)



Thinning or thickening? Multiple rheological regimes in dense suspensions of soft particles
Auteur(s): Kawasaki T., Ikeda A., Berthier L.
(Article) Publié:
Europhysics Letters (Epl), vol. 107 p.28009 (2014)
Texte intégral en Openaccess :
Ref HAL: hal01053378_v1
Ref Arxiv: 1404.4778
DOI: 10.1209/02955075/107/28009
WoS: 000340779900036
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
32 Citations
Résumé: The shear rheology of dense colloidal and granular suspensions is strongly nonlinear, as these materials exhibit shearthinning and shearthickening, depending on multiple physical parameters. We numerically study the rheology of a simple model of soft repulsive particles at large densities, and show that nonlinear flow curves reminiscent of experiments on real suspensions can be obtained. By using dimensional analysis and basic elements of kinetic theory, we rationalize these multiple rheological regimes and disentangle the relative impact of thermal fluctuations, glass and jamming transitions, inertia and particle softness on the flow curves. We characterize more specifically the shearthickening regime and show that both particle softness and the emergence of a yield stress at the jamming transition compete with the inertial effects responsible for the observed thickening behaviour. This allows us to construct a dynamic state diagram, which can be used to analyze experiments.
Commentaires: 6 pages, 3 figures



Clustering and heterogeneous dynamics in a kinetic MonteCarlo model of selfpropelled hard disks
Auteur(s): Levis D., Berthier L.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 89 p.062301 (2014)
Texte intégral en Openaccess :
Ref HAL: hal01025923_v1
Ref Arxiv: 1403.3410
DOI: 10.1103/PhysRevE.89.062301
WoS: 000336979500008
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
67 Citations
Résumé: We introduce a kinetic MonteCarlo model for selfpropelled hard disks to capture with minimal ingredients the interplay between thermal fluctuations, excluded volume and selfpropulsion in large assemblies of active particles. We analyze in detail the resulting (density, selfpropulsion) nonequilibrium phase diagram over a broad range of parameters. We find that purely repulsive hard disks spontaneously aggregate into fractal clusters as selfpropulsion is increased, and rationalize the evolution of the average cluster size by developing a kinetic model of reversible aggregation. As density is increased, the nonequilibrium clusters percolate to form a ramified structure reminiscent of a physical gel. We show that the addition of a finite amount of noise is needed to trigger a nonequilibrium phase separation, showing that demixing in active Brownian particles results from a delicate balance between noise, interparticle interactions and selfpropulsion. We show that selfpropulsion has a profound influence on the dynamics of the active fluid. We find that the diffusion constant has a nonmonotonic behaviour as selfpropulsion is increased at finite density and that activity produces strong deviations from Fickian diffusion that persist over large time scales and length scales, suggesting that systems of active particles generically behave as dynamically heterogeneous systems.
Commentaires: 17 pages, 13 figures Journal: Phys. Rev. E 89, 062301 (2014)



Nonequilibrium glassy dynamics of selfpropelled hard disks
Auteur(s): Berthier L.
(Article) Publié:
Physical Review Letters, vol. 112 p.220602 (2014)
Texte intégral en Openaccess :
Ref HAL: hal01010555_v1
Ref Arxiv: 1307.0704
DOI: 10.1103/PhysRevLett.112.220602
WoS: 000336920800002
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
96 Citations
Résumé: We analyse the collective dynamics of selfpropelled particles in the large density regime where passive particles undergo a kinetic arrest to an amorphous glassy state. We capture the competition between selfpropulsion and crowding effects using a twodimensional model of selfpropelled hard disks, which we study using MonteCarlo simulations. Although the activity drives the system far from equilibrium, selfpropelled particles undergo a kinetic arrest, which we characterize in detail and compare with its equilibrium counterpart. In particular, the critical density for dynamic arrest continuously shifts to larger density with increasing activity, and the relaxation time is surprisingly well described by an algebraic divergence resulting from the emergence of highly collective dynamics. These results show that dense assemblies of active particles undergo a nonequilibrium glass transition which is profoundly affected by selfpropulsion mechanisms.
Commentaires: 5 pages Journal: Phys. Rev. Lett. 112, 220602 (2014)



Crossovers in the dynamics of supercooled liquids probed by an amorphous wall
Auteur(s): Hocky Glen M, Berthier L., Kob W., Reichman David R.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 89 p.052311 (2014)
Texte intégral en Openaccess :
Ref HAL: hal00998409_v1
Ref Arxiv: 1402.5974
DOI: 10.1103/PhysRevE.89.052311
WoS: 000336765000003
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
30 Citations
Résumé: We study the relaxation dynamics of a binary LennardJones liquid in the presence of an amorphous wall generated from equilibrium particle configurations. In qualitative agreement with the results presented in Nature Phys. {\bf 8}, 164 (2012) for a liquid of harmonic spheres, we find that our binary mixture shows a saturation of the dynamical length scale close to the modecoupling temperature $T_c$. Furthermore we show that, due to the broken symmetry imposed by the wall, signatures of an additional change in dynamics become apparent at a temperature well above $T_c$. We provide evidence that this modification in the relaxation dynamics occurs at a recently proposed dynamical crossover temperature $T_s > T_c$, which is related to the breakdown of the StokesEinstein relation. We find that this dynamical crossover at $T_s$ is also observed for a system of harmonic spheres as well as a WCA liquid, showing that it may be a general feature of glassforming systems.
Commentaires: 9 pages, 7 figures



Intermittent dynamics and logarithmic domain growth during the spinodal decomposition of a glassforming liquid
Auteur(s): Testard V., Berthier L., Kob W.
(Article) Publié:
The Journal Of Chemical Physics, vol. 140 p.164502 (2014)
Texte intégral en Openaccess :
Ref HAL: hal00991464_v1
Ref Arxiv: 1309.1587
DOI: 10.1063/1.4871624
WoS: 000336047700043
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
44 Citations
Résumé: We use largescale molecular dynamics simulations of a simple glassforming system to investigate how its liquidgas phase separation kinetics depends on temperature. A shallow quench leads to a fully demixed liquidgas system whereas a deep quench makes the dense phase undergo a glass transition and become an amorphous solid. This glass has a gellike bicontinuous structure that evolves very slowly with time and becomes fully arrested in the limit where thermal fluctuations become negligible. We show that the phase separation kinetics changes qualitatively with temperature, the microscopic dynamics evolving from a surface tensiondriven diffusive motion at high temperature to a strongly intermittent, heterogeneous and thermally activated dynamics at low temperature, with a logarithmically slow growth of the typical domain size. These results shed light on recent experimental observations of various porous materials produced by arrested spinodal decomposition, such as nonequilibrium colloidal gels and bicontinuous polymeric structures, and they elucidate the microscopic mechanisms underlying a specific class of viscoelastic phase separation.
Commentaires: 18 pages
