Perspective: The glass transition

Abstract

We provide here a brief perspective on the glass transition field. It is an assessment, written from the point of view of theory, of where the field is and where it seems to be heading. We first give an overview of the main phenomenological characteristics, or "stylised facts," of the glass transition problem, i.e., the central observations that a theory of the physics of glass formation should aim to explain in a unified manner. We describe recent developments, with a particular focus on real space properties, including dynamical heterogeneity and facilitation, the search for underlying spatial or structural correlations, and the relation between the thermal glass transition and athermal jamming. We then discuss briefly how competing theories of the glass transition have adapted and evolved to account for such real space issues. We consider in detail two conceptual and methodological approaches put forward recently, that aim to access the fundamental critical phenomenon underlying the glass transition, be it thermodynamic or dynamic in origin, by means of biasing of ensembles, of configurations in the thermodynamic case, or of trajectories in the dynamic case. We end with a short outlook.

Viscosity of deeply supercooled water and its coupling to molecular diffusion

“…Such a large jump is usually the signature of a strong glass, i.e., one in which relaxation times or viscosity follow an Arrhenius law upon cooling. However, pioneering measurements on bulk supercooled water by NMR (11) and quasi-elastic neutron scattering (12), as well as recent ones by optical Kerr effect (8, 9), reveal a large super-Arrhenius behavior between 340 and 240 K, similar to what is observed in fragile glassformers (13,14). The temperature dependence of the relaxation time is well described by a power law (8, 9), as expected from mode-coupling theory (15, 16), which usually applies well to liquids with a small change of sound velocity upon vitrification.…”

Fluctuation analysis of time-averaged mean-square displacement for the Langevin equation with time-dependent and fluctuating diffusivity

“…In particular, the comparison of the crossover time determined from the RSD of the TAMSD with other characteristic times (such as the α-relaxation time) will be interesting. Garrahan, Chandler and coworkers [44][45][46] analyzed so-called the "activity" to study the dynamics of supercooled liquids. The activity is defined as:…”

Thermodynamic scaling of dynamics in polymer melts: Predictions from the generalized entropy theory

“…[1,2] The properties of supercooled liquids obviously vary strongly with thermodynamic state, which for a one-component system corresponds to systems with specified temperature T and pressure P (convenient when cooling at constant pressure) or specified temperature T and density ρ (convenient when cooling at constant volume). Since separate variations in density ρ or temperature T greatly affect the dramatic slowing down of dynamics of glassy materials, the observation that dynamical properties, such as the viscosity η, the structural relaxation time τ , and the diffusion constant D, depend only on a single control parameter, ρ γ /T , where γ depends on the material, is a quite remarkable finding that is important in guiding the design of new materials.…”