General Two-Parameter Model of Alpha-Relaxation in Glasses

TL;DR

This paper introduces a universal two-parameter model for alpha-relaxation in glasses near the glass transition, unifying diverse glass-formers with a simple scaling law.

Contribution

It demonstrates that many glass-formers follow a universal two-parameter scaling described by the TS2 theory, linking relaxation times to universal constants.

Findings

Many glass-formers exhibit a universal scaling with two material-specific parameters.

The master curve of alpha-relaxation can be described by the TS2 theory.

The TS2 model connects to the Hall-Wolynes elastic relaxation theory.

Abstract

In the vicinity of the glass transition, the characteristic relaxation time (e.g., the alpha-relaxation time in dielectric spectroscopy) of a glass-former exhibits a strongly super-Arrhenius temperature dependence, as compared to the classical Arrhenius behavior at high temperatures. A comprehensive description of both regions thus requires five parameters. Here, we demonstrate that many glass-formers exhibit a universal scaling, with only two material-specific parameters setting the timescale and the temperature scale; the other three being universal constants. Furthermore, we show that the master curve can be described by the recently developed two-state, two-(time) scale (TS2) theory (Soft Matter 2020, 16, 810) and regress the universal TS2 parameters. We also show the connection between the TS2 model and the Hall-Wolynes elastic relaxation theory.