Ionic liquid modified poly(vinylidene fluoride): crystalline structures, miscibility, and physical properties

A room temperature ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], has been used to modify poly(vinylidene fluoride) (PVDF). The crystalline structures, miscibility, and physical properties of PVDF/IL blends were investigated systematically. It was found that the incorporation of IL into the PVDF leads to drastically increased γ crystal forms of PVDF by the interaction between the >CF2 and cationic ions. Moreover, IL is fully miscible with PVDF with the interaction parameter (χ12) of −2.84 calculated by the revised Nishi–Wang equation due to the drastic equilibrium melting temperature depression. Dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS) results indicate that the IL molecules are inserted into the gallery of PVDF lamellae. A small amount of IL induces the appearance of the crystal-amorphous interface relaxation of PVDF, originating from the enrichment of IL distribution near the crystal-amorphous interface. The obtained PVDF/IL blends exhibit excellent mechanical performance with significantly increased ductility and good optical transmittance. In addition, the incorporation of IL into PVDF enhances the electrical conductivity of PVDF films greatly. Therefore, novel PVDF films with high transparency, excellent antistatic properties, and a highly polar crystal form fraction were successfully achieved.