Dipole reorientation in polyvinylidene fluoride

Abstract

The thermally stimulated current (TSC) from polarized polyvinylidene fluoride is studied below room temperature. The experimental results indicate that the maximum of the TSC observed at ∼ −50°C is due to reorientation of dipoles in a process associated with the glass transition. The TSC peak is inhomogeneously broadened by a distribution in relaxation frequencies. The results are analyzed in terms of both Arrhenius, and Williams-Landel-Ferry descriptions of the temperature dependence of the relaxation processes and the distribution function for the relaxation frequencies is calculated from the temperature dependence of the TSC. It is shown that a distribution in preexponential factors or in activation energies can account for the observed width of the TSC peak. For the latter case a distribution varying exponentially with activation energy seems most likely. From the data we obtain (3.6±0.4)×104 °K for the apparent activation energy and ∼2×10−3 sec−1 for the relaxation frequency of the dominant realignment process. The glass transition temperature is determined as Tg ∼ −51°C.