Effect of stretching rate on charge relaxation in PVDF films.

It is known that the piezoelectric properties of vinylidene fluoride-tetrafluoroethylene copolymer (P(VDF-TFE)) appear after their pre-stretching. In this paper, we carry out a comparative analysis of the effect of the film stretching rate on the stability of the electret, and, therefore, piezoelectric state. The thermally stimulated depolarization currents (TSC) data for the corona-charged electret state in P(VDF-TFE) films showed the presence of two processes, which showed as two peaks – high-temperature and low-temperature. The high-temperature peak is associated with the relaxation of the homocharge, the value of which depends on the stretching rate. The activation energy of traps (homocharge) increases with the increase of stretching rate from 0.92 eV to 0.96 eV. The low-temperature peak can be associated with the reorientation of polar structures present in the amorphous phase. The fraction of reoriented polar structures increases with an increase of the homocharge, i.e. with increasing stretching rate. It is the presence of the component associated with the reorientation of polar structures that determines the stability of the electret state and, therefore, the stability of the piezoelectric state. In the case of a thermoelectric state in films, the curves of thermally stimulated depolarization currents show only a low-temperature peak associated with depolarization processes in the amorphous phase, which has nothing to do with the piezo activity of the material. [ABSTRACT FROM AUTHOR]