Isoconfigurational state dependent molecular mobility in the glass temperature range

A method of analysis of calorimetric data has been applied to various glasses to study the molecular mobility in different isoconfigurational states (T < T-g). A so-called Arrhenian temperature dependence is observed but the slopes appear to be dependent on those states i.e., on the physical aging conditions. All the experimental results are explained in the framework of a theory based on (i) occurrence of density fluctuations on a nanometer scale (or quasi-point defects) and (ii) hierarchically correlated motions of molecular species with a correlation parameter being related to the disorder (concentration of quasi-point defects). The theory previously used for interpretation of the different features resulting from liquid-glass transition, physical ageing and structural relaxation far from equilibrium, appears to be self-consistent with the properties of the material in either the frozen state or the metastable equilibrium (supercooled liquid) state. Moreover, calorimetric data are shown to be in agreement with data obtained from mechanical spectroscopy. (C) 1998 Elsevier Science B.V. All rights reserved.