New electrostrictive PVDF copolymers for large-strain actuator application

A new class of ferroelectric polymeric material was developed by using the copolymers of polyvinylidene fluoride and trifluoroethylene, P(VDF-TrFE). Copolymer samples were subjected to high-energy electron irradiation, and the material appeared to be converted into a relaxor ferroelectric. The polarization hysteresis loop near the dielectric peak temperature became nearly non-hysteric, but gradually broadened and evolved into a normal ferroelectric hysteresis loop as the temperature was reduced. The dielectric constant as a function of temperature showed a broad dispersive peak in frequency, with the dispersion obeying the Vogel-Fulcher law. The dielectric constant was greatly increased with electron bombardment and a massive electrostriction was observed. Accompanying these changes were the resulting large electrically induced strain and high elastic energy density. The cause of these changes is presently believed to be the breakup of the coherent macro-polar regions containing the all-trans molecular conformation into micro-polar regions with increasing amorphous-crystalline interface as the sample was exposed to electron irradiation.