Combined ac and dc thermocurrent measurements to study molecular relaxation and electrical phenomena in polyvinylidene fluoride films

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Abstract
Ac currents, measured at discrete bias frequency, and dc thermocurrents, measured at discrete heating rates, both experimentally recorded as a continuous function of temperature have been carried out in parallel on commerical polyvinylidene fluoride (PVF2) films. Combined analysis of these measurements in a framework which relates frequency in an ac experiment to heating rate in a TC measurement allows us to characterize both the αa and αc molecular relaxation processes over the nine orders in frequency extending down to 10−4 Hz. The relatively broad distribution of relaxation rates underlying the αa process, in particular, is shown to be manifest in the associated current peak linewidth. The electrical properties above 100 °C and the relative amplitudes of the current peaks associated with the αa and αc relaxations are shown to be sensitive to the film’s thermal and field exposure history in situ. The time‐dependent response of ac conductivity to applied electric field is described. Thermal cycling of films which had previously suffered a decrease in conductivity due to electric field exposure reveals the conditions under which that effect can be reversed.

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