Crystalline transformations in spherulites of poly(vinylidene fluoride)

Abstract

Parts of poly(vinylidene fluoride) spherulites of the α-phase undergo a transformation to the higher-melting γ-form when crystallized at high temperatures. As a rule, this transformation originates at the periphery of α-spherulites where their lamellae are in contact with, and oppositely directed to, lamellae of γ-spherulites; the latter are formed only at high temperatures. The transformation on then retreats towards the nuclei of α-spherulites at a slow (∼10 −4 μm s −1), linear rate, which increases with temperature. At very high temperatures, this transformation is also initiated at some α-nuclei; a few of the α-spherulites also exhibit areas of the high-melting phase irregularly dispersed within their interiors. In samples crystallized below ∼154°C, the transformation is of very limited extent, even after prolonged annealing at higher temperatures.