An explanation of the large peak of activation energy observed by TSDC at Tg: a simple model of entropy relaxation

When investigating amorphous materials, i.e. polymers and glasses, by Thermally Stimulated Depolarization Current (TSDC), strong changes in relaxation rates at the glass transition T_g are frequently explained in terms of a physical singularity of the molecular motions. We show that the unexpected values for activation energy and pre-exponential factor obtained around T_g from the analysis of TSDC signal, result from the misuse of the Arrhenius law for treating the experimental data obtained in non-stationary experimental conditions. A simple model based on a time dependent configurational entropy is therefore proposed to explain the experimental behavior. Then, the pronounced variation of the effective activation energy appears as a dynamic signature of a simple entropy relaxation associated to non-stationary conditions.