PHENOMENOLOGICAL MODEL TO DESCRIBE THE GLASS-TRANSITION RELAXATION PEAKS FOR DEPOLARIZATION CURRENT EXPERIMENTS

A simple phenomenological pseudo-equilibrium dipolar model is presente d to characterize the dipolar relaxation related to the glass transiti on temperature of some polymers as measured by thermally stimulated de polarization current (TSDC) experiments. To characterize the normalize d TSDC relaxation current peak only three parameters are necessary. Th e first is the measured glass transition temperature of the relaxation . The second is related to the proposed phenomenological energy term a nd is linked to the behavior of the specific heat observed by differen tial scanning calorimetry experiments. The last is the zero order appr oximation near the glass transition temperature, T-g, of the Williams- Landel-Ferry expression describing the temperature dependence of the r elaxation time. A first order approximation for the relaxation rime gi ves a somewhat better description of the low-temperature side of the r elaxation peak. To take into account the nonequilibrium character of t his transition, the parameters in the model are functions of the cooli ng and heating rates used during the experiment. In general, they are functions of the thermal and electrical history of the sample. Some ac tual experimental data used to test this model will be presented and d iscussed.