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 isoconfigurationa l states (T < T-g). A so-called Arrhenian temperature dependence is ob served but the slopes appear to be dependent on those states i.e., on the physical aging conditions. All the experimental results are explai ned in the framework of a theory based on (i) occurrence of density fl uctuations on a nanometer scale (or quasi-point defects) and (ii) hier archically 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 differe nt features resulting from liquid-glass transition, physical ageing an d structural relaxation far from equilibrium, appears to be self-consi stent with the properties of the material in either the frozen state o r the metastable equilibrium (supercooled liquid) state. Moreover, cal orimetric data are shown to be in agreement with data obtained from me chanical spectroscopy. (C) 1998 Elsevier Science B.V. All rights reser ved.