An explanation of the peculiar behavior of TSDC peaks at Tg: a simple model of entropy relaxation

Thermally stimulated depolarization current (TSDC) signals measured in polymers at the glass transition T_g often exhibit intricate shapes that much depend on the thermal history and on the non-stationary condition used during experiments. This peculiar behavior is frequently explained in terms of a physical singularity of the molecular motions. We show that this singularity, i.e. unexpected values for activation energy and pre-exponential factor, obtained around T_g, result from the misuse of the Arrhenius law for treating the experimental data obtained in non-stationary experimental conditions. A simple model using time dependent configurational entropy for the material evolution and using a single Debye relaxation for the dielectric relaxation process is therefore proposed to explain the experimental behavior. The influence of the heating rate and of a non-Debye relaxation on the TSDC signal is also studied and clearly shows that the peculiar behavior of TSDC peaks can originate from the conjugated effects of entropy relaxation and non-Debye response