A Thermodynamical Criterion for the Glass-Transition Temperature.

摘要

A study, based upon the Gibbs free energy, is made of the thermodynamical behaviour of dissipative and memory-dependent materials. The creep-function mechanical properties involved are generalizations of the usual volumetric ompressibility, the coefficient of thermal expansion, and the specific heat at constant pressure. It is found that under a certain special equilibrium condition, a transition behaviour occurs in the material whereby the mechanical and thermal properties change with time. The criterion for its occurrence is that of a certain proportionality between the volumetric, thermal expansion and specific-heat creep functions. This criterion is interpreted as that of the glass-transition temperature, the resulting forms bear some resemblance to those of an Ehrenfest second-order transition. However, the similarity is only superficial since herein full account is taken of time-dependent memory effects. The application of the present criterion suggests a specific and new means of unambiguously determining the glass-transition temperature for polymers.