Preparation And Dielectric Properties Of Poly(vinylidene Fluoride) Composites Filled With Carbon Material

Carbon materials such as graphene,carbon nanotubes and graphite powders(GPs)aggregate easily in polymer and the combination between carbon materials and polymer is poor,so carbon materials could not dispersed well in polymer,which restrict the development of carbon-polymer composites with high dielectric properties.In order to solve this problem,we propose two modification methods to modify graphene nanosheets and GPs,and then fill them in poly(vinylidene fluoride)(PVDF)respectively,at last,carbon-polymer composites are prepared.By a facile and effective redox reaction,we obtain MnO2/graphene nanosheets/MnO2(MGM).The MGM is used as a dielectric filler to prepare MGM-PVDF composites by solution casting and hot pressing.In addition,we provide a one-step hydrothermal reaction to modify GPs and prepare hydroxyl modified GPs-PVDF composites using high conductivity,low cost GPs as raw material.Scanning electron microscopy and transmission electron microscopy showed that MGM and GPs do not generate agglomeration and combine well with polymer.Dielectric analyzer shows that the dielectric properties of MGM-PVDF and GPs-PVDF composites are better than the dielectric properties of most carbon-polymer composites.According to the theory of mini-capacitor,the dielectric constant depends on the numbers of mini-capacitor and the capacitance of every mini-capacitor,the dielectric loss depends on the extent of contact.The agglomeration of carbon materials largely reduce the number of mini-capacitor,and decrease the capacitance of every mini-capacitor,so the dielectric constant of carbon-polymer composites is decreased.In addition,the poor combination between carbon materials and polymer results that the carbon materials tend to contact with each other rather than disperse in polymer,so the dielectric loss of carbon-polymer composites is increased.We propose two modification methods to prevent the agglomeration of carbon materials and improve the combination between carbon materials and polymer.The modification can improve the number of mini-capacitor and increase the capacitance of every mini-capacitor,which results the increase of dielectric constant.Moreover,after modification,the carbon materials tend to disperse in polymer,so the dielectric loss is largely reduced.