Crystallization and morphology of melt‐solidified poly(vinylidene fluoride)

Abstract

Crystallization of poly(vinylidene fluoride) (PVF 2) from the melt yields two types of spherulites. The first consists of large, highly birefringent, and tightly banded spherulites of the α‐form, which are seen at all temperatures. The second type, termed mixed, crystallizes with a newly reported unit cell which appears to be the correct one for γ‐PVF 2, but may contain inclusions of a different form (probably α‐PVF 2); it is seen only at relatively high temperatures and frequently exhibits irregular or disorganized birefringent and morphological features. In thin films, some mixed spherulites contain regions of single‐crystal‐like aggregates which are grown parallel to the substrate and appear essentially nonbirefringent between crossed polars. Mixed spherulites frequently undergo transformations at their growth fronts leading to initiation of α‐growth. These transformations are associated with the generally higher growth rate of α‐spherulites which may exceed that of their mixed counterparts by almost seven times. However, with increasing temperature this difference in growth rates is progressively reduced and ultimately reversed.