Investigation of the properties of directionally solidified poly(vinylidene fluoride)

Abstract

Zone solidification at low growth rates succeeded in producing large films of oriented α-PVF 2 spherulites. The other polymorphs were either absent or unoriented due to their rapid encirclement by the much faster growing α-form. The high anisotropy of our samples was confirmed by optical microscopy, X-ray diffraction and polarized infra-red spectroscopy. It was found that unit cell orientation in spherulites of α-PVF 2 is such that the b-axis is radial. Dynamic mechanical behaviour of films both along the direction of solidification (longitudinally) and normal to it (transversely) is in qualitative agreement with a two-phase model proposed by Takayanagi. The behaviour of isothermally crystallized samples approaches that of longitudinal sections at high temperatures and that of transverse sections at low temperatures. Piezoelectric response of zone solified α-PVF 2 poled at low fields is similar to that of a random α-spherulitic sample and almost two orders of magnitude lower than that of a uniaxially drawn film.