Ferroelectricity of polymers based on vinylidene fluoride

Abstract

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.