The Dielectric Properties of Poly

The dielectric properties of poly(vinylidene fluoride) (PVF(,2)) are discussed in this work. A review of the literature concerning the five known dielectric relaxations of PVF(,2) is presented and the general theory of dielectric relaxations in polymers is summarized. The real and imaginary parts of the dielectric constant of several samples of PVF(,2) were measured as a function of frequency, temperature and pressure. In the temperature experiment covering the range from 5 K to 380 K at five audio frequencies (100 Hz to 10 KHz), four relaxations were found: (alpha), (beta), (delta) and (epsilon). The (alpha) relaxation at temperatures between 345 and 370 K at 1000 Hz, was found to be dependent on the history and preparation method of the sample and also to have a Debye like behavior. The (beta) relaxation around 250 K at 1000 Hz was found to be related to the glass transition of PVF(,2) and its behavior is parametrized by using the Williams-Landel-Ferry (WLF) model. The (delta) relaxation around 76 K at 1000 Hz was found to be Debye like and associated with the (alpha)-phase of PVF(,2). The (epsilon) relaxation was found in (beta)-phase PVF(,2) at 14.5 K at 1000 Hz. Evidence of the relaxation was found also in (alpha)-phase PVF(,2). In the pressure experiments the (beta) relaxation was studied in the temperature range from 240 to 360 K and at pressures from 0.0001 to 0.6 GPa. The behavior was explained by using the WLF free volume model and comparison between the calculated glass transition temperature parameter in the WLF equation and the experimental peak temperature is made. It was found that even though the WLF equation mathematically describes the (beta) relaxation, the T(,g) parameter does not represent the real transition temperature behavior with pressure. The peak temperature of the (beta) relaxation, was found to be a better guide to the behavior of the real T(,g).