Structural relaxation of glass and its influence on other dynamic processes

Abstract

Glasses are thermodynamically unstable materials. Hence, they spontaneously relax towards the supercooled liquid state. The structural relaxation process is an irreversible, time-dependent phenomenon, which may be experimentally detected by measuring some property over time at temperatures close to the glass transition. Although it is already reasonably known, glass relaxation still has many unknown features. Therefore, this doctoral project aims at a detailed study of relaxation regarding some open scientific problems. We plan to focus on the following topics: structural relaxation via three different properties (refractive index, ionic conductivity and density), analyzing whether the relaxation kinetics depends on the property; the influence of relaxation on crystallization; in-situ and ex-situ relaxation, comparing the kinetics when the property is measured directly at the heat treatment temperature (in-situ) versus room temperature after heat treatment (ex-situ); possible structural changes of the glasses after complete relaxation; relationship between the relaxation times measured experimentally with those calculated via Maxwell equation by shear modulus measurements; temperature dependence of experimental relaxation times versus those calculated via Maxwell equation; and, finally, the influence of structural relaxation and residual stresses in the chemical strengthening process via ion exchange (the same process used in the famous Gorilla glass of smartphones). This doctoral project is original at the international level, with a deepening of some themes that we studied previously, as well as discussed in an interview for Agência FAPESP about the international award of this work initial part. In addition, we will cover several other problems that have not yet been studied. (AU)