RATE-DETERMINING FACTORS FOR STRUCTURAL RELAXATION IN NONCRYSTALLINE MATERIALS II - NORMALIZED VOLUME AND ENTHALPY RELAXATION RATE

The rate-determining factors for isothermal structural relaxation in n on-crystalline materials are discussed. The normalized volume and enth alpy relaxation rate RF is defined and analyzed for the Tool-Narayanas wamy-Moynihan phenomenological model. It is shown that the temperature dependent RF is controlled mainly by the parameter (1-x)theta, where x is the nonlinearity parameter and theta = Delta h/RTg2. Materials w ith higher values of parameter (l-x)theta (e.g, vinylic polymers) exhi bit low relaxation rate. In contrast, high relaxation rate is expected for materials with low values of (l-x)theta (inorganic glasses). The applicability of this approach for the analysis of isothermal volume a nd enthalpy relaxation data is shown for arsenic sulfide glass, polyst yrene, poly(vinyl acetate), poly(methyl methacrylate) and poly(vinyl c hloride). The normalized enthalpy and volume relaxation rates for thes e materials agree well within the limits of experimental errors. (C) 1 998 Elsevier Science B.V.