Heat capacity at the glass transition

TL;DR

This paper explains the heat capacity jump at the glass transition as a consequence of changes in material properties when the liquid's relaxation halts at a specific temperature, linking it to relaxation dynamics and fragility.

Contribution

It introduces a new perspective that the heat capacity jump results from the cessation of relaxation at $T_g$, without requiring a distinct glass phase.

Findings

Heat capacity jump correlates with relaxation stopping at $T_g$.

Logarithmic increase of $T_g$ with quench rate explained.

Heat capacity jump linked to liquid fragility.

Abstract

A fundamental problem of glass transition is to explain the jump of heat capacity at the glass transition temperature $T_g$ without asserting the existence of a distinct solid glass phase. This problem is also common to other disordered systems, including spin glasses. We propose that if $T_g$ is defined as the temperature at which the liquid stops relaxing at the experimental time scale, the jump of heat capacity at $T_g$ follows as a necessary consequence due to the change of system's elastic, vibrational and thermal properties. In this picture, we discuss time-dependent effects of glass transition, and identify three distinct regimes of relaxation. Our approach explains widely observed logarithmic increase of $T_g$ with the quench rate and the correlation of heat capacity jump with liquid fragility.