Determination of β Phase Crystalline Fraction in Electrospun Poly(vinylidene fluoride) Fibers

The β-crystallographic phase of poly(vinylidene fluoride), PVDF, is often used in fabricating piezoelectric and pyroelectric materials. However, the specific equilibrium heat of fusion of β-PVDF has not yet been definitively determined. The difficulty in this measurement arises from the necessity of obtaining solely beta phase crystals, as well as quantifying the overall degree of crystallinity. Here, we investigate the crystalline fraction of β-PVDF in fibers prepared by electrospinning from solutions of 12.5 wt% and 15.0 wt%. Scanning electron microscopy images show that the fiber diameters range from 0.2 µm to 10 µm. This preparation produces dominantly beta phase crystals by using the simultaneous application of mechanical and electrical forces to stretch the polymer fibers thus favoring the all-trans chain conformation. The crystalline fraction of a specific crystallographic phase was determined by wide-angle X-ray scattering and Fourier-transform infrared spectroscopy peak deconvolution. Melting enthalpy of the crystals was determined by the differential scanning calorimetry. A preliminary estimate of the equilibrium heat of fusion of beta-PVDF will be presented.