A PHENOMENOLOGICAL MODEL FOR THE ENTHALPY RELAXATION OF GLASSES .2. EFFECTS OF A CONTINUOUS DISTRIBUTION OF RELAXATION-TIMES

A multiordering parameter model for the relaxation behaviour of glasses around the glass-transition region is presented. This paper is intended as a generalization of the single order parameter models presented in the first part of this work. It is assumed that each order parameter is associated with a relaxation time of the form suggested by Narayanaswamy and we have adopted a continuous distribution of these relaxation times defined by a single Williams-Watts parameter beta. Computer simulations permit predictions of the fictive temperature evolution of glasses, subjected to arbitrary temperature-time histories, in terms of material constants and kinetic parameters such as the activation energy E(a), or the partition factor x. Furthermore, the present model adequately fits the available experimental data obtained from DSC experiments on amorphous selenium and allows us to analyse memory effects (i.e. crossover experiments).