Thermal cycling of glasses: A theoretical and experimental approach

Abstract

A theoretical model for the response of glass-forming systems to three-step thermal cycles is reviewed, and is shown to predict two important features. First, under limiting conditions of rapid heating of well-stabilized glasses, a single (main) peak in the heat capacity occurs at a temperature which depends strongly on the experimental variables. This dependence is a unique function of the parameter x , controlling the relative contributions of temperature and structure to the retardation times, and provides a rational means of evaluating x which is shown to be experimentally feasible. Second, when these thermal cycles involve the opposite conditions of slow heating of poorly stabilized glasses, then either two peaks (a main peak and an upper peak) or a single upper peak may be observed. The main peak and the upper peak are quite different in nature, particularly in respect of the manner in which they depend on the experimental variables, and data in the literature are used to show that all reported observations of double peaks can be explained qualitatively on the basis of this theoretical model.