Poly(vinylidene fluoride) single crystals

Abstract

Information about the structure and properties of bulk poly (vinylidence fluoride) PVF₂ has been previously obtained in this laboratory from X-ray diffraction [1], NMR spectra [1], and dielectric constant measurements [2, 3]. Depending on sample preparation, one finds two different types of orthorhomic unit cells (Table 1). Type II appears in samples crystallized from the melt either isothermally or at slow cooling. Drawing of bulk material at 50°C yields phase I, whereas drawing at higher temperatures, between 120 and 160°C, yields a mixture of phase I and II. The structure of phase I has been determined from X-ray data and confirmed by NMR investigation of the dependence of second moment on the angle between magnetic field and the draw direction. A tentative orthorhomic unit cell was also proposed for phase II, but no direct check was available at that time. Leshchenko et al. [4] have suggested a monoclinic unit cell (Table 1) which does not agree with the data of phase I or II. In addition, Galperin et al. [5] have suggested a different monoclinic cell (Table 1) for phase II.