Relaxation aspects of the liquid–glass transition

Relaxation theories of the glass transition and viscous flow of glass-forming melts are presented. The focus is on modern representations of the glass transition equation $q \tau_{\rm g}$ = $\delta T_{\rm g}$ that describes the appearance of a glassy state during cooling. Here, $q$=d$T$/d$t$ is the temperature change rate during melt cooling and $\tau _{\rm g}$ is the relaxation time at the glass transition temperature ${T}_{g}$. Various methods for calculating the characteristic temperature band $\delta T_{\rm g}$ during the liquid–glass transition are considered. The generalized equation for the dependence of $T_{\rm g}$ on the melt cooling rate is derived. Based on the model of delocalized atoms, a modified kinetic glass transition criterion is discussed. A generalized viscosity equation for glass-forming liquids is derived.