Study On The Preparation And Dielectric Properties Of Graphene/Polyvinylidene Fluoride Composites

With the increase of energy requirement, the development of energy storagetechnology is urgently needed to improve the efficiency of energy utilization.Dielectric materials have caused wide concern because of its applicability used inenergy storage. As good processing property and low density, polymer-baseddielectric materials can promote the miniaturization and weight lightness of electronicdevices more efficiently. Graphene possesses perfect physical properties includinghigh specific area, high conductivity and good mechanical properties. The addition ofgraphene can enhance dielectric properties of the obtained polymer-based dielectricmaterials obviously. However, graphene sheets aggregrate easily, thus it is hard todistribute homogeneously in polymer matrix. This brings difficulties in the study. Inthis theis, graphene oxide was prepared with modified Hummers method. Thengraphene oxide was modified or coated followed by reduction with three differentmethods. The obtained graphene was added into the polyvinylidene fluoride toprepare graphene/polyvinylidene fluoride composites. The dielectric properties ofthese composites were studied.(1) Graphene modified with p-chlorophenyl isocyanate was prepared by the reactionwith hydroxyl and carboxyl followed by chemical reduction. Fourier transforminfrared (FT-IR) spectroscopy and UV-visual (UV-vis) spectroscopy revealed that thereaction between graphene and p-chlorophenyl isocyanate formed carbamate andamide. Graphene oxide was reduced well. Scanning electron microscopy (SEM) andtransmission electron microscopy (TEM) revealed that reduced graphene oxideexihibited favorable dispersibility in N, N-dimethyl formamide, most of which weresingle layer. Dielectric measurement indicated that dielectric constant of modifiedgraphene/polyvinylidene fluoride composite was78, which was8times larger thanthat of polyvinylidene fluoride, while dielectric loss was only0.25.(2) Graphene oxide was coated with Co3O4nanoparticles. Then graphene coatedwith Co3O4was prepared with thermal reduction. AFM and SEM observationdemonstrated that nanoparticles were coated on graphene sheets homogeneously. Thethickness of coated graphene was about15nm. FT-IR, UV-vis and TG revealed that thermal reduction exhibited the same result as chemical reduction. Dielectric constantof the composite was90and dielectric loss was0.39. Especially at high frequencydielectric loss maintained at a low level and increased little when the graphenecontent surpassed the percolation threshold. This provided access to the applicationof dielectric composites at high frequency.(3) Polydopamine was coated with graphene oxide by the self-polymerization ofdopamine. Then graphene coated with polydopamine was prepared by chemicalreduction. AFM and TEM observation demonstrated that relative homogenouspolydopamine was coated on the surface of graphene oxide. The thickness was about1.5nm-1.7nm. The coated graphene demonstrated favorable dispersibility in N,N-dimethyl formamide. Dielectric measurement demonstrated that dielectric constantof the composite reached278, which was enhanced obviously compared with PVDF.Dielectric loss was0.48, which was restrained to a certain degree.