Broadband dielectric relaxation spectra of PVDF copolymer films

The dielectric permittivity of polyvinylidenefluoride (PVDF) and its copolymer containing trifluoroethylene (TrFE) is investigated in the frequency domain with variation of the temperature. A pronounced relaxational behavior is observed in the films at high frequencies. In thick commercial PVDF films a Vogel-Tamman-Fulcher (VTF) dependence of the relaxation time versus the temperature is found yielding a thermally activated process. In thin Langmuir-Blodgett P(VDF-TrFE) films the relaxation times determined from the dielectric permittivity in the frequency range are not consistent with the relaxation times determined from the temperature range. The data extracted from the temperature domain also here show a VTF behavior. Nevertheless, the relaxation times calculated from the frequency domain cannot be fitted with the VTF formula. Thus, the time-temperature superposition principle is not valid in the thin films.