Enhancement of polar crystalline phase formation in transparent PVDF-CaF2 composite films

摘要

We consider the influence of calcium fluoride (CaF2) nanoparticles on the crystalline phase formation of poly(vinylidene fluoride) (PVDF) for the first time. The transparent PVDF-CaF2 composite films were prepared by casting on PET substrates using N,N-dimethylacetamide (DMAc) as a solvent. It was found that CaF2 promoted the formation of polar crystalline phase of PVDF in composites, whereas nonpolar 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 CaF2 in the composite films up to 10 wt%. Further addition of CaF2 suppressed completely the alpha-phase formation. Polar crystalline phase observed in as cast composite films was a mixture of beta- and gamma-polymorph structures. It was also shown that much ordered gamma-phase could be obtained through thermal treatment of as-cast PVDF-CaF2 composite film at the temperatures above the melting temperature of the composite films, but below that of gamma-phase. (C) 2016 Elsevier B.V. All rights reserved.