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Characteristics of the ferroelectricity in polyvinylidene fluoride (PVDF) and copolymers based on vinylidene fluoride (VDF) with different previous thermomechanical histories are analysed. Switching of polarisation and the fluctuation mechanism of formation of new nuclei upon the appearance of conformation defects such as kink bonds are considered. The role of the space charge, which stabilises the new polarisation position, is noted. It is shown that the Curie transition can be either a first-or second-order phase transition depending on the copolymer composition. The influence of the morphology of PVDF on some ferroelectric characteristics is found. In particular, the morphology of thick lamellar crystals is favourable for enhanced spontaneous polarisation. It is shown that a ferroelectric structure approaching the texture of an ideal single crystal can be created in Langmuir ± Blodgett films. As the number of unimolecular layers decreases, the concentration of conformational defects in these films increases and the crystallographic order in the lattice is violated. This intensifies the low-temperature Curie transition. The bibliography includes 247 references.

The molecular mobility in copolymers of vinylidene fluoride-hexafluoropropylene VDF/HFP of 93/7 and 86/14 ratios has been investigated by means of broadband dielectric relaxation spectroscopy (10 À1 -10 7 Hz), differential scanning calorimetry DSC (À100 to 1508C), and of wide angle X-ray diffraction WAXS. Four relaxation processes and one ferroelectric-paraelectric phase transition have been detected. The process of the local mobility b-(at temperatures below glass transition point) is not affected by chemical composition of the copolymer and the formed structure. Parameters of segmental mobility in the region of glass transition (a a -relaxation) depend on the ratio of comonomer with lower kinetic flexibility. a c -relaxation is clearly observed only in VDF/HFP 93/7 copolymer, which is characterized by a higher crystallinity and a higher perfection of crystals of a-(a p -) phase. Diffuse order-disorder relaxor type ferroelectric transition connected with the destruction of the domains in low-perfect ferroelectric phase in the amorphous regions has been detected for both copolymers. An intensive relaxation process (a-process) was observed for both copolymers in high-temperature region. DSC data shows that it falls on the broad temperature region of aphase crystals melting. It is considered to be connected with the space charge relaxation.