Methods to characterize the crystal polymorphs of polyvinylidene fluoride using Fourier transform infrared spectroscopy

Polyvinylidene fluoride (PVDF), a polymer with three common crystal polymorphs (alpha, beta, gamma), has several practically useful properties, including piezoelectric properties. Accurate measurement of its crystalline polymorphs is important since only the beta phase has the desired piezo properties. PVDF was processed into isotropic samples having predominantly alpha, beta, and. crystalline phases. These samples were analyzed with Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and differential scanning calorimetry (DSC). FTIR spectra were fitted with the Gaussian peaks for quantitative analysis of the phases. Peaks exclusive to the amorphous phase were identified and used for the amorphous phase quantification, leading to the accurate determination of the crystalline fraction. IR absorption coefficients for their respective peaks were calculated to quantify individual crystalline polymorphs in the sample. Pure phase spectra were extracted, and a linear combination of the pure phase spectra was fitted to the spectrum of a sample with different phases to accurately obtain the values of the phase fraction and the thickness of the sample.