Annealing effects on the glass transition: Experiment and theory

Extensive experimental and theoretical studies have been performed in recent decades regarding the effect of the rates of change of temperature on the glass transition temperature, T-g, and the width of the glass transition interval, delta T-g. In this paper, we push forward the frontiers of knowledge obtained in this direction by performing a detailed analysis of the dependence of Tg and delta T-g obtained in subsequent heating on the initial glass densities, which were reached after prolonged preliminary sub-T-g annealing. Our experiments show that T-g increases and delta Tg decreases with increasing the initial glass density. By treating the structural relaxation time as a function of temperature and density, we develop a theoretical model that successfully describes both the density changes in annealing and the resulting variations of the glass transition temperature and the width of the glass transition interval in subsequent heating. These findings are relevant to understand glass annealing and its effect on devitrification in subsequent heating -two phenomena of major importance in glass science and technology.