Proliferation and Arrangement of Poly(vinylidene fluoride) Oval γ Single Crystals Grown in Its Poly(1,4-butylene adipate) Blends

Abstract

Blends of a small amount of poly(vinylidene fluoride) (PVDF) with miscible low-melting-point poly(1,4butylene adipate) (PBA) were prepared, and the structures of PVDF formed in the blend through isothermal crystallization were studied by optical, atomic force, and transmission electron microscopies. The results show that oval γ-PVDF basal single crystals with large number of overgrown crystals are produced in the thin blend films crystallized at various temperatures. The basal single crystal initially has a rectangular shape with three sectors showing different folding directions, resulting from a symmetrical growth along b-axis and an asymmetrical growth along [101]*. During the growth of the basal crystal, opposite rotations of growth axes about the film normal occur, leading to a final oval shape of the γ-PVDF basal single crystals. The over layer single crystals grow in the two [010] sectors following the crystallographic orientation of the basal one rather than in the [101]* sector. It is further confirmed that the completion of one ellipse-shaped basal crystal will initiate a continuous growth of another one, which produces a series of bent and connected ellipse-shaped basal single crystals. Moreover, the curvature radius of the crystal is bigger at higher temperatures. The scrolling of lamellae takes place in thicker films, which provide sufficient space for its growth.