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

Polyvinylidene fluoride (PVDF) is a known polymer with pronounced polymorphs. Among these polymorphs, the beta and gamma 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 gamma-phase-rich PVDF thin films through selective melting and subsequent recrystallization. The proposed approach comprises the selective melting of both the nonpolar alpha-PVDF and polar gamma-PVDF crystals but not the stable gamma'-PVDF ones and subsequent isothermal recrystallization at 160 degrees C. During the recrystallization process, the nonmelting stable gamma'-PVDF crystals can induce the direct gamma-PVDF crystallization of the melt. In contrast, locally ordered domains survived in the molten alpha-PVDF crystal regions also result in a direct formation of gamma-PVDF crystals. This is of great importance to fabricate high-quality thin films of gamma-PVDF crystals for advanced applications.