Morphological Structure And Electric Properties Of Graphene/Polyvinylidene Fluoride Composites

In order to achieve higher conductivity at low conductive filler loadings, theelectrically conductive polymer composites with a segregated structure have beenextensively studied in recent years. In these composites, the fillers are located on thesurface of polymer matrix particles to form an interface conductive network, whichexhibits a lower percolation threshold, relative to the composites that contain uniformlydispersed fillers. Graphene has a high electrical conductivity and can transform aninsulating polymer into a conducting composite at very low loading because of theirextremely high aspect ratio。This simple method to prepare thermally reduced grapheneoxide/polymer composites was developed to enhance the electrical conductivity ofpolymer, which can effectively prevent the aggregation of graphene and improve theelectrical conductivity of the composites. In this work, the morphological structure,crystallization temperature and electrical properties of RGO/PVDF composites wereinvestigated by X-ray diffraction, scanning electron microscope, polarizing opticalmicroscope, differential scanning calorimeter, atomic force microscope and impedancespectroscopy. Graphene oxide sheets were coated on the surfaces of poly(vinylidenefluoride) powders and then hot pressed at200oC to form composites with a segregated structure. After hot-pressing, the thermally reduced graphene oxide sheets are located inthe interstices among the polymer domains and form a two-dimensional conductivenetwork. The resulting composites exhibit excellent electrical conductivity and a lowpercolation threshold (0.105vol.%). Graphene/PVDF composites with high dielectricpermittivity have been successfully prepared by this method. The dielectric propertiesshow a dramatic change as high as several orders of magnitude near the percolationthreshold， which can be well explained by interfacial polarization efect andmicrocapacitor model. The dielectric constants depended on the frequency should bemainly ascribed to the Maxwell Wagner Sillars (MWS) polarization in the lowfrequency range and thus lead to the dielectric constant increase. The RGO/PVDFcomposite (f=0.263vol.%) exhibits higher dielectric constants (225) and smaller lossfactor (7.9) at103Hz. This type of RGO/PVDF composites with a low percolationthreshold can be potentially applied in high energy density capacitors and hightechnology applications as novel dielectric materials. This method is simple,environmentally-friendly and suitable for industrial application, which provides a newroute to prepare electrical conductive TRGO/polymer composites with a segregatednetwork structure.