A unified molecular level mechanism for the universal alpha- and Johari-Goldstein beta-relaxations in glassformers

TL;DR

This paper proposes a unified molecular mechanism explaining both alpha- and Johari-Goldstein beta-relaxations in glassformers, based on the behavior of relaxation modes in molecular strings across temperature ranges.

Contribution

It introduces a string model that accounts for the transition from a single to two relaxation species, unifying the understanding of alpha- and JG beta-relaxations.

Findings

The model predicts n relaxation modes for n coupled molecules.

At high temperatures, relaxation modes behave as a single relaxation.

At low temperatures, two distinct relaxation species emerge, matching experimental observations.

Abstract

We presented that the relaxation of n coupling molecules in a molecular string exhibits n individual relaxation modes (RMs), each mode being characterized by a definite relaxation time and amplitude according to the string model. The n RMs behaving a single relaxation at high temperature, evolves to two relaxation species, at low temperature, with different temperature dependences for the respective relaxation times and amplitudes. Since the characteristics of the two relaxation species are in agreement with those exhibited by the universal alpha- and Johari-Goldstein (JG) beta-relaxations in glass dynamics, we provided a unified molecular level mechanism for these two processes.