Comparison between volume and enthalpy relaxations in non-crystalline solids based on the fictive relaxation rate

The volume and enthalpy relaxation rate of inorganic glasses and organic po lymeric materials subjected to temperature jump Delta T has been analyzed. It is shown that the relaxation behavior in isothermal conditions can be co mpared on the basis of the fictive relaxation rate defined as R-f=(dT(f)/dl ogt)(i). No significant difference between volume and enthalpy relaxation r ate has been found for all materials examined. A simple equation relating t he R-f and parameters of Tool-Naraynaswamy-Moynihan (TNM) phenomenological model has been derived. This equation predicts increasing R-f with the magn itude of temperature jump. It seems that correct determination of TNM param eters might be problematic for slowly relaxing polymers as the effect of th ese parameters becomes comparable with experimental uncertainty.