X-ray high pressure study of polyvinylidene fluoride

Abstract

An X-ray high pressure study at room temperature of both phase I and phase II crystal structures of polyvinylidene fluoride has been carried out. At room temperature both phases are stable up to pressures greater than 14 kbar. The variation of lattice compressive strains with pressure could be fitted to the Tait equation with little scatter and the variation of the unit cell parameters with pressure computed. The bulk lattice compressibilities of both phase I and phase II was found to be considerably less than that of polyethylene with the lowest compressibility being found for the phase I structure. The linear lattice compressibilities are extremely anisotropic with the lowest compressibility being in the chain direction as expected. However, at the highest pressures, for the case of phase II it was observed that this anisotropy was greatly reduced. Applications of these data to the unique piezo-electric activity of PVF₂ are pointed out.