Why are glass-forming liquids non-Arrhenius?

TL;DR

This paper reviews classical models explaining the non-Arrhenius behavior of glass-forming liquids' relaxation times and discusses a recent model linking activation energy to shear modulus increase upon cooling.

Contribution

It critically evaluates classical phenomenological models and introduces a recent model connecting activation energy to the shear modulus for explaining non-Arrhenius behavior.

Findings

Classical models like free-volume and entropy models are critiqued.

The recent model links activation energy to the work done in shoving aside the liquid.

Non-Arrhenius behavior arises from the increase in shear modulus upon cooling.

Abstract

A major mystery of glass-forming liquids is the non-Arrhenius temperature-dependence of the average relaxation time. This paper briefly reviews the classical phenomenological models for this phenomenon - the free-volume model and the entropy model - and critiques against these models. We then discuss a recent model [Dyre, Olsen, and Christensen, Phys. Rev. B 53, 2171 (1996)] according to which the activation energy for the average relaxation time is determined by the work done in shoving aside the surrounding liquid to create space needed for a flow event. In this model the non-Arrhenius temperature-dependence is a consequence of the fact that the instantaneous (infinite-frequency) shear modulus increases upon cooling.