THERMALLY STIMULATED DEPOLARIZATION CURRENTS - A NEW ANALYSIS AND SIGNIFICANCE OF THE COMPENSATION LAW

The model introduced by Ngai to predict the relaxation behavior of condensed matter is used here to derive the expression of thermally stimulated depolarization currents (TSDC). This is done via Ngai's second universality equation and by assuming that the stretching index beta is temperature dependent. The four parameters involved in the model can, in principle, be determined from TSDC data. Two parameters are determined for polyisoprene below its glass transition temperature Tg. Furthermore, expressing that a compensation law holds for the alpha relaxation of polymers around Tg, the variation of beta with T is given. This relation leads to a Williams-Landel-Ferry-type expression of the macroscopic relaxation time near and above Tg, a well-known experimental observation, and gives a strong support in favor of the model.