Hybrid BaTiO 3 -PVDF Piezoelectric Composites for Vibration Energy Harvesting Applications
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Hybrid BaTiO3-PVDF Piezoelectric Composites for Vibration Energy Harvesting Applications Veronica Corral-Flores, Dario Bueno-Baqués, Ronald F. Ziolo Research Center for Applied Chemistry, Enrique Reyna 140, Saltillo, 25253, Mexico ABSTRACT Hybrid piezoelectric composites were obtained by embedding barium titanate (BTO) nanofibers into a polyvinylidene fluoride (PVDF) matrix. Green BTO fibers were obtained by electrospinning a precursor polymeric solution under an electric field of 1 kV/cm. A network of non-woven ceramic BTO fibers was obtained after calcination of the green fibers. A PVDF solution was deposited over the ceramic fibers by spin-coating and then subjected to a low temperature heat treatment, to evaporate the solvent and promote the crystallization of the polar beta phase of PVDF. In average, the diameter of the ceramic fibers ranged from 105 to 225 nm, presenting ribbon-like shape in some cases. Crystalline phases of BTO and PVDF were confirmed by X-ray diffraction and infrared spectroscopy, respectively. Polarization hysteresis curves revealed a ferroelectric behavior in all samples. INTRODUCTION Energy harvesting, as an emerging multidisciplinary area, involves design of complex systems capable of harness ambient energy and transform it to electric energy. The full development of this technology requires a deep understanding of the transduction fenomena, as well as conversion and administration of energy depending on the required application. Hybrid ceramic-polymeric composites offer the possibility to tune both mechanical and electrical properties. In this respect, several systems have been already developed, such as CCTO - poly(vinylidene fluoride – trifluoroethylene) [P(VDF-TrFE)] [1], BTO – PVDF [2], MWCNTs – BTO – PVDF [3], Sm/Mn doped PbTiO3 - epoxy [4], and PZT – Rubber [5]. Composites are complex, heterogeneous and usually anisotropic systems. Its properties are affected by many variables, including constituent material properties, geometry, volumetric fraction, interface properties, coupling properties between the phases, porosity, etc. In this work we discuss the preparation and ferroelectric properties of composites obtained from BaTiO3 fibers embedded in a PVDF matrix. EXPERIMENT BTO nanofibers were obtained by electrospinning technique. A 1 M precursor solution containing titanium butoxide and barium acetate at a 1:1 molar ratio in methoxyethanol and acetic acid was mixed with a poly(vinyl pyrrolidone) solution. The resulting solution was electrospun at the following conditions: feed rate of 0.5 ml/hr, 15 kV and tip-to-collector distance of 15 cm. The electrospun nanofibrous membranes were sintered at 800°C for 2 hours to obtain the ceramic phase. Then the BTO nanofibrous membranes were embedded in a PVDF matrix by spin-coating a 14 wt.% PVDF (Kynar 761, supplied by Arkema) solution over the membranes in a conductive Pt-Si substrate. After deposition, samples were heat-treated at 60°C
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for 1 hour to crystallize the beta phase of the polymer. All chemicals used in this study were rea
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