Polymer Compositional Ratio-Dependent Morphology, Crystallinity, Dielectric Dispersion, Structural Dynamics, and Electrical Conductivity of PVDF/PEO Blend Films

The polymer blend (PB) films consisted of poly(vinylidene fluoride) (PVDF) and poly(ethylene oxide) (PEO) with different compositional ratios (i.e., PVDF/PEO =100/0, 75/25, 50/50, 25/75, and 0/100 wt%) have been prepared by solution casting method. These PB films were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and dielectric relaxation spectroscopy (DRS). The pristine films of PVDF and PEO have spherulite morphologies, which change enormously with the variation of their compositions in blend films. The EDX spectra confirm the linear variation of the amount of respective polymer elements, with the change of its compositional ratio in the PB films. The XRD and FTIR results confirm that the semicrystalline PVDF film has predominantly alpha- and beta-phase crystals. The degree of crystallinity of these PB films exhibits non-linear increase, with increasing amount of PEO in the films. The relative fraction of the beta-phase crystal of the PVDF in these complex PB films has been determined from the fractional relations based on the areas and intensities of crystalline peaks, observed in their XRD patterns which is found the maximum (similar to 50%) for the 75 PVDF/25 PEO blend film. The dielectric dispersion of these PB films in the frequency window of 20 Hz-1MHz at 27 degrees C reveals that the real part of the complex permittivity is governed predominantly by the interfacial polarization effect at lower audio frequencies, whereas it mainly depends on the polymer compositional ratio at higher radio frequencies. The segmental relaxation process peak of the PEO chain observed in the loss part of the electric modulus spectra, shifts toward the lower frequency side with a significant suppression of intensity as the amount of PVDF enhances in the PB films. This result confirms that the PEO dynamics face considerable hindrance by the PVDF structures. The dc electrical conductivity of these PB films increases non-linearly with increasing amount of PEO in the films, and varies by more than an order of magnitude with the variation of the compositional ratio over the entire range. The temperature-dependent study of 50 PVDF/50 PEO blend film confirms its thermally activated dielectric properties and the structural dynamics with the relaxation activation energy of 0.23 eV. The compositional ratio-dependent dielectric properties of PVDF/PEO blend films offer a promising potential for their use as dielectric permittivity- and electrical conductivity-tunable insulating materials, with engineered functionality for flexible electronics and electrical devices.