(173b) Localization Model of Relaxation in Glass-Forming Liquids

By definition, solidifying glass-forming materials exhibit upon cooling a precipitous drop in the viscous and structural relaxation rates that govern deformation and flow. This solidification transition also reflects a particle localization transition, in which the material’s constituent particles cease to freely explore space and become locally entrapped. A fundamental understanding of deformation and flow in glass-forming materials would thus seem to require an understanding of the relationship between relaxation and particle localization, and achieving such an understanding has accordingly been a longstanding goal of soft matter physics.

In this talk, we present a new model for structural relaxation in glass-forming materials that accurately relates the alpha structural relaxation time to an experimentally accessible measure of localization – the Debye-Waller factor – in a variety of simulated and experimental glass-formers. This “localization model” follows from both free volume theory and elastically activated transport models of relaxation. It suggests that the growth in structural relaxation time is indeed directly related to particle localization, albeit in a way that depends both upon the anisotropy and anharmonicity of particle localization and upon the onset temperature of glass formation. Finally, the emphasizes the existence of a well-defined congested fluid regime, intermediate between a solid and liquid, that initiates with a localization onset condition at a temperature well above the glass transition.