A study on the structure and properties of poly(vinylidene fluoride)/graphite micro-sheet composite films

Abstract

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 hydroxyl-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 × 105 under 100 Hz test frequency at the case of graphite micro-sheets’ content is 6 wt%. 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 2.07 J/cm3 which is over 120 times than that of pure poly(vinylidene fluoride) film.