Atomistic mechanism of physical ageing in glassy materials

TL;DR

This study uses molecular simulations to uncover the microscopic relaxation mechanisms in aging glasses, revealing that subsequent relaxation times follow a history-independent power law and aligning with trap model predictions.

Contribution

It provides a detailed atomistic understanding of relaxation events and validates the trap model for aging in structural glasses.

Findings

Relaxation times follow a power law distribution independent of aging history.

Memory of the waiting time extends only up to the first relaxation event.

A CTRW model with atomistic data captures bulk diffusion and aging dynamics.

Abstract

Using molecular simulations, we identify microscopic relaxation events of individual particles in ageing structural glasses, and determine the full distribution of relaxation times. We find that the memory of the waiting time $t_w$ elapsed since the quench extends only up to the first relaxation event, while the distribution of all subsequent relaxation times (persistence times) follows a power law completely independent of history. Our results are in remarkable agreement with the well known phenomenological trap model of ageing. A continuous time random walk (CTRW) parametrized with the atomistic distributions captures the entire bulk diffusion behavior and explains the apparent scaling of the relaxation dynamics with $t_w$ during ageing, as well as observed deviations from perfect scaling.