Theory of Aging in Structural Glasses

TL;DR

This paper extends the random first order transition theory to model aging in structural glasses, predicting relaxation behaviors, temperature dependencies, and spatial temperature fluctuations consistent with experimental observations.

Contribution

It introduces a unified microscopic theory of aging in glasses using local energy landscapes, connecting with existing models and predicting new phenomena.

Findings

Quantitative correlation between relaxation nonlinearity and liquid fragility.

Explanation of residual non-Arrhenius temperature dependence in quenched glasses.

Prediction of non-Gaussian spatial fluctuations of fictive temperatures leading to ultra-slow relaxations.

Abstract

The random first order transition theory of the dynamics of supercooled liquids is extended to treat aging phenomena in nonequilibrium structural glasses. A reformulation of the idea of ``entropic droplets'' in terms of libraries of local energy landscapes is introduced which treats in a uniform way the supercooled liquid (reproducing earlier results) and glassy regimes. The resulting microscopic theory of aging makes contact with the Nayaranaswamy-Moynihan-Tool nonlinear relaxation formalism and the Hodge-Scherer extrapolation of the Adam-Gibbs formula, but deviations from both approaches are predicted and shown to be consistent with experiment. The nonlinearity of glassy relaxation is shown to quantitatively correlate with liquid fragility. The residual nonArrhenius temperature dependence of relaxation observed in quenched glasses is explained. The broadening of relaxation spectra in the nonequilibrium glass with decreasing temperature is quantitatively predicted. The theory leads to the prediction of spatially fluctuating fictive temperatures in the long-aged glassy state, which have non-Gaussian statistics. This can give rise to ``ultra-slow'' relaxations in systems after deep quenches.