Effect of crystallization, poling and ageing conditions on the FIR, dielectric and pyroelectric properties of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02)

Abstract

AbstractWe studied the influence of hot‐pressing temperature as well as poling and ageing conditions on the amount of polar phase of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02) foil. FIR transmission spectra of hot‐pressed homopolymer and copolymer films were measured in the 30‐450 cm—1 range as a function of hot‐pressing temperature Thp and poling temperature Tp. The FIR studies show that homopolymer and copolymer consist of both polar and nonpolar modifications of PVDF. The content of the polar phase tends to decrease with Thp and increase after poling. The FIR spectra of our samples exhibit a strong absorption peak near 100 cm—1 absent in the biaxially oriented Solef samples, which is believed to be due to the amorphous phase in our samples. Four thermally stimulated current (TSC) maxima are attributed to the relaxation in the amorphous region (∼40°C), to the dipolar relaxation in the nonpolar (∼60°C) and polar (∼80°C) phase, and the space charge relaxation (dependent on the poling temperature). The pyroelectric coefficient of the homopolymer and copolymer thermoelectret foil prepared by hot‐pressing is of the same order as that of the PVDF thermoelectret foil produced by Solvay and can be influenced by the hot‐pressing conditions. The dielectric response of the hot‐pressed PVDF‐type foils can be described by the Kohlrausch‐–Williams‐Watts function and is characteristic of a heterogeneous system.