Morphology Evolution of α Poly(Vinylidene Fluoride) Single Crystals in Its Blend with Poly(1,4‐Butylene Adipate)

The morphology evolution of α poly(vinylidene fluoride) (PVDF) crystals in blends with poly(1,4‐butylene adipate) (PBA) from single crystals to spherulites has been investigated. The crystals in approximately 5 nm‐thick films exhibit primarily two‐dimensional growth, due to the constraint of film thickness. When the PBA content is high, the lozenge‐shaped α‐PVDF single crystals appear. As the PBA content decreases, the single crystals bend into C‐shapes, and adjacent C‐shaped crystals grow side‐by‐side to form X‐shaped structures, eventually developing an eye‐like morphology. Branches preferentially grow on the convex side, resulting in dense proliferation. When the film thickness is increased to about 25 nm at a PVDF/PBA ratio of 20/80, in addition to branching within film surface, pronounced overgrowth on the crystal surface become visible, with growth displaying a certain degree of ordered alignment perpendicular to the b ‐axis. As the PBA content decreases, the overgrowth on the parent lamellae increases, exhibiting a more order arrangement and twisting. At a PVDF/PBA ratio of 70/30, a significant number of lamellae adopt an edge‐on alignment. Further increasing the film thickness can result in spherulites with banded structures. Through this study, we have gained a clear understanding of the development process of α‐PVDF, from single crystals to spherulites.