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

Abstract

Thermally stimulated depolarization current (TSDC) signals measured in polymers at the glass transition Tg 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 Tg, 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