Crystal Structure Regulation of Ferroelectric Poly(vinylidene fluoride) via Controlled Melt–Recrystallization

Abstract

Polyvinylidene fluoride (PVDF) is a known polymer with pronounced polymorphs. Among these polymorphs, the β and γ form crystals with strongest piezo- and pyro-electric activities of polymeric materials have attracted much attention. We report here a simple melt–recrystallization approach for producing γ-phase-rich PVDF thin films through selective melting and subsequent recrystallization. The proposed approach comprises the selective melting of both the nonpolar α-PVDF and polar γ-PVDF crystals but not the stable γ′-PVDF ones and subsequent isothermal recrystallization at 160 °C. During the recrystallization process, the nonmelting stable γ′-PVDF crystals can induce the direct γ-PVDF crystallization of the melt. In contrast, locally ordered domains survived in the molten α-PVDF crystal regions also result in a direct formation of γ-PVDF crystals. This is of great importance to fabricate high-quality thin films of γ-PVDF crystals for advanced applications.