Polarization reversal in homopolymer and copolymers of vinylidene fluoride at low electric field and high temperature

During the study of anomalous discharge current in copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE), polarization reversal was noticed for homopolymer VDF (PVDF) and copolymers of VDF at low electric field and at high temperature. A hysteresis loop was observed for PVDF for form II at an electric field of about 100 kV-m^-1 in a temperature region above 120°C, although the remanent polarization was only about 3 mC-m^-2. VDF/TrFE copolymers also exhibited a hysteresis loop above the Curie temperature at low electric field. The remanent polarization in the copolymers was the same order of magnitude as that in PVDF. In PVDF the polarization reversal is likely connected with change in conformation of the molecular chain between form II and III at high temperature