Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J42: Focus Session: Physics of Glasses and Viscous Liquids II |
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Sponsoring Units: DCP Chair: Mark Ediger, University of Wisconsin Room: Hilton Baltimore Holiday Ballroom 3 |
Tuesday, March 19, 2013 2:30PM - 3:06PM |
J42.00001: Theoretical and Computational Studies of Dynamical Heterogeneity and Growing Length Scales in Supercooled Liquids Invited Speaker: David Reichman In this talk I review recent progress made by our group and collaborators in elucidating quantitative aspects connected to growing length and time scales in supercooled liquids. In particular, I focus on extraction of static length scales and the relationship between soft modes and dynamical heterogeneity. Connections to jamming are discussed. If time permits, I will discuss recent work on the mean-field theory of growing dynamical length scales in supercooled liquids with respect to critical fluctuations and the putative upper critical dimension. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:42PM |
J42.00002: Equilibrium study of a liquid-glass transition Invited Speaker: Ludovic Berthier The liquid-glass transition in dense fluids is characterized by several crossover temperatures, but glasses are obtained without crossing any sharp singularity. The existence of an underlying phase transition, predicted theoretically in some limiting cases, is therefore only supported by uncontrolled extrapolations of macroscopic observables. Here we use a specific random pinning field to induce a liquid-glass transition in a simulated fluid. We discover a range of control parameters for which the transition can be crossed at thermal equilibrium, which allows us to probe for the first time the microscopic nature of an equilibrium glass. Our results, obtained for a range of modest system sizes, suggest that the glass transition is of the random first order type. [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 4:18PM |
J42.00003: Static and dynamic length scales in glass-forming liquids Invited Speaker: Gilles Tarjus A recurring question about glass formation concerns the collective nature of the dynamics as one cools or compresses a liquid. If the phenomenon is indeed collective, it should be characterized by the development of nontrivial correlations to which one or several typical length scales might be associated. One source of growing correlations has been clearly identified in connection with the increasingly heterogeneous character of the dynamics as one approaches the glass transition. An associated length, commonly referred to as ``dynamic'', can be extracted from multi-point space-time correlation functions. In addition, several theories of the glass transition posit the existence of a growing ``static'' length accompanying a liquid's dynamical slowdown. This length is not detectable through standard measurements on pair density correlations, which have been shown to display only unremarkable behavior as the relaxation slows down. However, a number of proposals have been put forward for unveiling such a nontrivial static length. Through computer simulation of model glass-forming liquids, we address the two following central questions: (i) Are the variations with temperature or pressure of these various lengths correlated? (ii) Is the increase of the relaxation time due to the growth of any of the above lengths, or, with less compelling consequences, is it at least correlated to it? While our results rule out the existence of a general principle tying together the evolutions of dynamic and static lengths in glass-forming systems, we discuss how the answer to the above questions depends on the dynamic regime under consideration as well as on the type of material. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J42.00004: Correlations between Elementary Relaxation Steps in a Model Glass Former Dieter Bingemann, Nai Chien Yeat Despite decades of research the dramatic slowdown of the dynamics in glasses upon cooling remains a mystery. We identify individual, sudden, local, structural relaxation events in a deeply supercooled binary Lennard-Jones system through statistical analysis of the particle trajectories. Correlations between these events in space and time show that (a) relaxation events often occur in clusters (cooperatively rearranging regions), (b) events follow each other in space and time (facilitation), (c) regions with the longest waiting times between events are encapsulated in layers with increasingly shorter waiting times (dynamic heterogeneity), (d) the length scales of these fast and slow regions show very little temperature dependence. Focusing on individual relaxation events we find that large-amplitude vibrations of atoms surrounding each event open a gateway for structural relaxation, hinting at a potential molecular mechanism for the dramatic slowdown of glass dynamics. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J42.00005: Diffusion in Crowded Environments: Monte Carlo and Molecular Dynamics Studies Robin Selinger, Prithviraj Nandigrami, Andrew Konya, Jennifer Toth Anomalous diffusion is sometimes, but not always, observed in dense multicomponent mixtures, e.g. in diffusion of proteins in a lipid membrane [1]. To investigate this phenomenon, we carry out 2-d simulation studies using both on-lattice Monte Carlo and off-lattice Molecular Dynamics. ``Tracer'' particles are emitted from a source along one side of the simulation cell and absorbed by a sink along the other side, diffusing through a chamber containing ``crowder'' particles whose number remains constant. On-lattice Monte Carlo studies show that equilibrium tracer flux drops linearly with crowder density, showing non-Fickian behavior well below the percolation threshold. Molecular dynamics studies in the same geometry also show non-Fickian behavior, but tracer flux is a nonlinear function of crowder density. We compare our results with analytical calculations and experimental studies, and discuss implications for understanding diffusion-mediated processes in cell membranes.\\[4pt] [1] J. A. Dix and A. S. Verkman, Annu. Rev. Biophys. 37, 247 (2008). [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J42.00006: Crystallization and glass formation in multi-component liquids Kai Zhang, Minglei Wang, Stefanos Papanikolaou, Jan Schroers, Corey O'Hern When a liquid is cooled faster than the critical cooling rate, crystallization is avoided, and amorphous solids are formed. What sets the critical cooling rate? We perform molecular dynamics simulations of model metallic alloys---polydisperse spheres with hard-sphere and modified Lennard-Jones interactions---to study the critical cooling rate as a function of the particle size ratio, stoichiometry, and strength of the attractive interactions. We also characterize the structural properties of glassy and crystalline states that form at rapid and slow cooling/compression rates, respectively, using local order parameters, position correlation functions, and Voronoi and other tessellations. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:30PM |
J42.00007: What controls the relaxation time? Lessons learnt from simple liquids' quasiuniversality Invited Speaker: Jeppe Dyre The relaxation time of a supercooled liquid is extremely temperature and density dependent, approaching hours upon cooling or compression. Is this quantity controlled by the entropy, is it controlled by high-frequency elastic properties as assumed in the shoving and related elastic models, or by another physical property? It is far from certain that there is a simple and generally valid answer to this question for glass-forming liquids with quite different chemistry, but as physicists we like to think that this is the case. The talk summarizes recent results [1] on the quasiuniversality of simple liquids, where a simple liquid is defined as a system with strong virial / potential-energy correlations in the equilibrium NVT fluctuations. Such systems, which include e.g. the Lennard-Jones liquid, have good isomorphs. An isomorph is a curve in the phase diagram along which structure, dynamics, and some thermodynamic properties in reduced units are invariant to a good approximation [2-5]. It was recently conjectured [1] that simple liquids have almost the same isomorphs in the sense that these systems are characterized by a quasiuniversal one-parameter family of reduced-coordinate constant-potential-energy manifolds encoding all isomorph invariants. The entropy is the logarithm of the area of this manifold and the high-frequency elastic properties are basically the surface's curvature. Since the relaxation time is also encoded in the manifold, both quantities will appear to ``control'' the relaxation time, as will any isomorph invariant.\\[4pt] References: [1] J. C. Dyre, arXiv:1208.1748 (2012).\\[0pt] [2] N. Gnan et al., J. Chem. Phys. 131, 234504 (2009).\\[0pt] [3] N. Gnan et al., Phys. Rev. Lett. 104, 125902 (2010).\\[0pt] [4] U. R. Pedersen et al., Phys. Rev. Lett. 105, 157801 (2010).\\[0pt] [5] T. Ingebrigtsen et al., Phys. Rev. X 2, 011011 (2012). [Preview Abstract] |
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