Dielectric Properties and Phase Stabilization of PVDF Polymer in (1-x)PVDF/xBCZT Composite Films

초록

Polyvinylidene fluoride (PVDF) is a semi-crystalline ferroelectric polymer which can be stabilized in its distinct electroactive polymorphs alpha and gamma by selective processing techniques. In this article, to study the effect of processing temperature and barium calcium zirconium titanate (BCZT) ceramic-doping on PVDF phase stabilization, the pure PVDF and PVDF/BCZT composite films were fabricated by solution-casting and melt-pressing. The Fourier-transform infrared spectroscopy and x-ray diffraction studies showed that the pure PVDF and PVDF/BCZT composite films fabricated by solution-casting possessed the characteristic gamma-PVDF peaks while melt-pressing stabilized PVDF mostly in the alpha-phase. The BCZT ceramic particles were found to have no significant effect on PVDF phase stabilization, but it enhanced the overall crystallinity of polymer matrix. The dielectric studies revealed that the relative permittivity (epsilon(r)) of gamma- and alpha-PVDF phases in pure PVDF film samples was approximate to 10 and 7.5 (at 120 Hz) respectively. The epsilon(r) of PVDF/BCZT composite films having 50 wt.% BCZT content synthesized by solution-casting and melt-pressing were estimated to be approximate to 31 and 20 (at 120 Hz), respectively, which was about three times that of pure PVDF film synthesized by the respective technique. The value of loss tangent (tan delta) for pure PVDF films synthesized by solution-cast and melt-press technique were approximate to 0.07 and 0.35 (at 120 Hz) respectively. In temperature-dependent dielectric studies, gamma-PVDF showed distinct alpha-relaxation peak at approximate to 120 degrees C and polymer melting at temperature > 130 degrees C. For alpha-PVDF, the increase in epsilon(r) and tan delta was observed during alpha-relaxation transition at higher temperatures. The dielectric studies indicated that the introduction of BCZT ceramic particles in PVDF matrix increased the epsilon(r)-value by enhancing the dipolar and interfacial polarizations in composites, while the decrease in tan delta-value was observed due to decrease in molecular dipoles with a decrease in wt.% of PVDF content. These phenomena collectively improved the overall electric properties of ceramic/polymer composites which makes them suitable candidates to explore for flexible electroactive material form.

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