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In this paper, poly(vinylidene fluoride)-based dielectric composite films with graphite micro-sheet as fillers were prepared by solution casting method. Graphite micro-sheet was first heated to thermal expansion and was then allowed to experience the surface chemical etching (hydroxyl modification) to improve its' surface hydroxyl contents. This hydro-xyl-modified graphite micro-sheet was added to the poly(vinylidene fluoride) matrix to prepare the poly(vinylidene fluoride)/graphite micro-sheet composite films. The microstructures, crystallization, thermodynamic stabilities and dielectric properties of the composite films were tested, and the effects of graphite microchip on the structures and properties of the films were analyzed. Scanning electron microscope results showed that the prepared graphite sheets were well dispersed in poly(vinylidene fluoride) matrix. X-ray powder diffraction spectrum indicated that the introduction of graphite micro-sheets has little effect on the phases' change of poly (vinylidene fluoride) films. Thermal analysis showed that the addition of graphite micro-sheets slightly decreased the thermal stability of the composite films. Broadband dielectric spectroscopy test results showed that with the increase of the content of graphite micro-sheet, the dielectric constant of the composite films increased continuously. The dielectric constant of composite films increases as high as 6.5 x 105 under 100 Hz test frequency at the case of graphite micro-sheets' content is 6wt%. The results also indicated that the highest breakdown field strength of this composite film is 0.63 kV/mm and its specific energy storage is 2.07J/cm[sup 3] which is over 120 times than that of pure poly(vinylidene fluoride) film. [ABSTRACT FROM AUTHOR]

In this study polyimide/inorganic silica-alumina nanoparticle hybrid films are first prepared by sol-gel method to find a promising method for enhancing thermal property and other properties. Silica sol and alumina sol starting from tetraethoxysilicane (TEOS) and aluminum isopropylate (ALP) are doped in a solution of poly (amic acid). The hybrid films are obtained by a stepwise heating method. The structure, micro-morphology, and thermal properties of the films are characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The micrographs show uniform distribution of club shaped particles in the films containing silica and alumina. The micrographs of polyimide/silica hybrid films revealed sphericity and uniform distribution of particles. Al2O3 particles are poorly dispersed and are prone to agglomerate in the polyimide/alumina hybrid films. Moreover, there are chemical bonds between inorganic and organic phases in the hybrid films. The thermo-decomposition temperature of the hybrid films is also improved markedly after the addition of silica and alumina nanoparticles. [ABSTRACT FROM AUTHOR]