Relaxed enthalpy and volume during physical aging: Their interrelation

TL;DR

This paper investigates the relationship between relaxed enthalpy and volume during physical aging of glassy materials, proposing a model linking defect Gibbs energy to bulk properties to explain empirical observations.

Contribution

It introduces a model connecting defect Gibbs energy with bulk properties to explain the empirical relation between enthalpy and volume during aging.

Findings

The slope of relaxed enthalpy versus volume plots relates to inverse isothermal compressibility.

The model explains the empirical correlation observed near the glass transition.

Provides a theoretical basis for the interrelation of enthalpy and volume during aging.

Abstract

Several papers have recently presented results of measurements of physical aging by studying the behavior of glassy materials quenched from temperatures above their glass transition temperature $T_g$. The evolution of the aging process is usually followed by plotting the relaxed enthalpy versus the accompanying decrease in volume. Here, we focus on the slope of such plots, which are found to be similar to the inverse value of the isothermal compressibility close to $T_g$. An explanation of this empirical result is attempted in the frame of a model that interconnects the defect Gibbs energy with properties of the bulk material.