Fragilities of Liquids Predicted from the Random First Order Transition Theory of Glasses

TL;DR

This paper develops a microscopic theory based on the random first order transition to explain liquid fragility and glassy dynamics, quantitatively linking empirical correlations to underlying energy landscape features.

Contribution

It introduces a model that quantitatively explains liquid fragility and relaxation behaviors based on an underlying random first order transition framework.

Findings

Empirical correlations of fragility are quantitatively explained by the model.

The universality of the Lindemann ratio accounts for variations in fragility.

The size of reconfiguring regions and relaxation nonexponentiality are qualitatively linked to fragility.

Abstract

A microscopically motivated theory of glassy dynamics based on an underlying random first order transition is developed to explain the magnitude of free energy barriers for glassy relaxation. A variety of empirical correlations embodied in the concept of liquid "fragility" are shown to be quantitatively explained by such a model. The near universality of a Lindemann ratio characterizing the maximal amplitude of thermal vibrations within an amorphous minimum explains the variation of fragility with a liquid's configurational heat capacity density. Furthermore the numerical prefactor of this correlation is well approximated by the microscopic calculation. The size of heterogeneous reconfiguring regions in a viscous liquid is inferred and the correlation of nonexponentiality of relaxation with fragility is qualitatively explained. Thus the wide variety of kinetic behavior in liquids of quite disparate chemical nature reflects quantitative rather than qualitative differences in their energy landscapes.