Quantitative analysis of polar crystalline fractions in poly(vinylidene fluoride) electrospun fibers and electrosprayed films

Abstract

We have used a novel technique, Fourier self-deconvolution (FSD) of the infrared spectrum, to quantify the relative fractions of the electro-active (EA) crystal phases in poly(vinylidene fluoride), PVDF. Electrospinning and electrospraying are effective methods to obtain the EA phases which include the polar β (chain conformation, TTTT) and γ (TTTGTTTG’) crystallographic phases. In this work we studied electrospun fiber mats and electrosprayed non-fibrous mats of PVDF obtained from solutions of N,N-dimethylacetamide and acetone. Wide-angle X-ray scattering (WAXS) and Fourier-transform infrared (FTIR) spectra show that samples prepared by electrospinning/electrospraying contained only polar crystal phases, and no non-polar alpha phase crystals were present. Fourier Self Deconvolution is a method used to synthetically narrow broad and complex infrared absorbance spectra. Here we demonstrate this technique to determine the relative fractions of β- and γ-phase crystals by resolving the peak at 840 cm−1 in the IR absorbance spectra. When the overall level of crystallinity is known, as it is here from X-ray analysis, then FSD allows determination of the absolute content of the polar β and γ phases. Comparing results from wide-angle X-ray scattering and FTIR/FSD, we show that γ-phase dominates over β-phase in both electrospun and electrosprayed materials, with relative γ to β ratios of 55/45 and 81/19, respectively.