Enhancement of polar crystalline phase formation in transparent PVDF-CaF 2 composite films

Abstract We consider the influence of calcium fluoride (CaF 2 ) nanoparticles on the crystalline phase formation of poly(vinylidene fluoride) (PVDF) for the first time. The transparent PVDF-CaF 2 composite films were prepared by casting on PET substrates using N,N -dimethylacetamide (DMAc) as a solvent. It was found that CaF 2 promoted the formation of polar crystalline phase of PVDF in composites, whereas nonpolar α-phase was dominant in the neat PVDF film prepared at the same condition. The portion of polar crystalline phase increased in proportional to the weight fraction of CaF 2 in the composite films up to 10 wt%. Further addition of CaF 2 suppressed completely the α-phase formation. Polar crystalline phase observed in as-cast composite films was a mixture of β- and γ-polymorph structures. It was also shown that much ordered γ-phase could be obtained through thermal treatment of as-cast PVDF-CaF 2 composite film at the temperatures above the melting temperature of the composite films, but below that of γ-phase.