Electrical properties of form III poly(vinylidene fluoride)

Abstract

Abstract Form III poly(vinylidene fluoride) crystals were easily obtained by an isothermal crystallization between 165 and 175°C. The dielectric relaxation for the form III crystal was observed at high temperatures, where values of dielectric constant ε′ and loss factor ε″ were very large. The ε′ underwent almost a tenfold increase when the temperature was raised from 150°C to the melting point (198°C) of the sample. The sharp drop in ε′ beyond the melting point was even more striking. Also, at 100 Hz, the ε″ reached a very sharp maximum at about 180°C. The relaxation strength was about 2.8 × 104. According to the results of mechanical and DSC measurements, it may be concluded that this high temperature relaxation is due to the form III crystallites. There are two possibilities for the mechanism responsible for the relaxation: (I) the orientational motion of crystallites accompanied by the applied ac electric field; (2) the motion of the domain boundaries of the form III polar crystallites which bring about a hysteresis on the polarization-electric field diagram. As large as 5 × 10−7 A cm−2 of thermal depolarization current was observed for the form III specimen between 150 and 200°C. This anomalously large current may be related to the form III polar crystallites.