Engineered PVDF-BaTiO3 composites as efficient dielectric materials for energy storage

BaTiO3 nanoparticles (100÷150 nm), prepared in-house by a hydrothermal-like method starting from BaCl2 and TiCl4 precursors, were dispersed into a matrix of poly(vinylidene fluoride) (PVDF, Solef 6008 Solvay). 0-3 connectivity composites containing up to 35 vol% of ceramic inclusions were obtained either by solution casting or melt blending in a Brabender type batch-mixer; a compression moulding step was performed to obtain sheets 0.5-1 mm thick enriched in the electro-active ? polymorph of PVDF. Bare and surface-modified BaTiO3 particles were used, modification included functionalization with silane-based coupling molecules and/or coating with a thin shell of TiO2 (k ? 100). Such engineered polymer/ceramic interfaces should facilitate a fine dispersion of the inclusions by realizing, from the particle core to its surface, a gradient of the dielectric constant giving a more homogeneous distribution of the electric field in the resulting composites. Morphological and microstructural features of particles and composites were investigated by TEM and SEM-EDX microscopy, respectively. The amount of the ferroelectric crystalline ? phase in the PVDF matrix was determined by ATR-FTIR spectroscopy and X-ray diffraction. The dielectric constant and the loss tangent of the composites were measured at different frequencies by impedance spectroscopy. Simulations of electric field distribution performed by 3D finite element modelling were correlated with the experimental evidences.