Excitation Chains at the Glass Transition

TL;DR

This paper discusses the excitation-chain theory of the glass transition, proposing that diverging relaxation times and length scales explain the dynamic and thermodynamic properties of glass-forming liquids, with large excitation chains inducing heterogeneities.

Contribution

It introduces the role of critically large excitation chains in understanding the glass transition, drawing analogies to critical clusters in droplet models and emphasizing heterogeneities.

Findings

Excitation chains lead to diverging relaxation times.

Large excitation chains induce spatial heterogeneities.

The glass transition may not be a conventional thermodynamic phase transition.

Abstract

The excitation-chain theory of the glass transition, proposed in an earlier publication, predicts diverging, super-Arrhenius relaxation times and, {\it via} a similarly diverging length scale, suggests a way of understanding the relations between dynamic and thermodynamic properties of glass-forming liquids. I argue here that critically large excitation chains play a role roughly analogous to that played by critical clusters in the droplet model of vapor condensation. The chains necessarily induce spatial heterogeneities in the equilibrium states of glassy systems; and these heterogeneities may be related to stretched-exponential relaxation. Unlike a first-order condensation point in a vapor, the glass transition is not a conventional phase transformation, and may not be a thermodynamic transition at all.