Free volume in the classical model of viscous flow during glass transition

A modification of the Eyring model is discussed, which takes into account free volume during viscous flow. It is proposed to include free volume directly in the structural model. In this model, repeated vacancies in the material are analogous to sets of edge dislocations on a single sliding plane. The displacement is a cooperative process involving successive “jumps” of groups of atoms (in the one-dimensional case, chains). An inverse proportionality between the Newtonian viscosity coefficient and vacancy concentration is determined. As temperature decreases, vacancy concentration decreases and kinetic unit size (or “structural”) increases. This can lead to increased potential barrier and further slowing of glass transition. Within the framework of the improved model, it has been shown that the frequency of asymmetric local oscillations at vacant positions should be considered as fluctuations of kinetic entities that determine viscosity and the glass transition process.