A GEOMETRIC AND ANALYTIC APPROACH TO THE PROCESS OF VITRIFICATION .2.KINETIC TREATMENT

The processes of evolution of the frozen non-equilibrium structure of a glass to the equilibrium state of an undercooled liquid are consider ed in terms of the thermodynamics of irreversible processes. An improv ed rate equation is derived which accounts for the non-symmetric cours e of the thermodynamic driving force of the stabilization process as w ell as for possible memory effects. An atomistic model of a simple sin gle-component vitrifying liquid is employed in order to establish a re alistic temperature dependence of the structural parameter, xi, and of the time of molecular relaxation, tau(T). By using simple analytic co nsiderations and geometric concepts, memory effects in the kinetics of vitrification are demonstrated and expressions for the kinetic stabil ity of superheated and supercooled glasses are derived. An extended de finition of the vitreous state, including supercooled and superheated glasses, is given.