Controlled Preparation And Properties Of Polymer-based Graphene Composites

Graphene has gained tremendous attention owing to its excellent physical propertiesand potential applications in electronic devices, energy storage, oil cleanup, and biologysupporter. One important and effective route to employ graphene sheets for the aboveapplications is to harness its properties to enhance physical performances of polymercomposites. However, the fabrication of polymer-based graphene composites with highphysical performances suffers from many challenging difficulties such as easyaggregation, high leakage current, weak interfacial interaction, and high inter-sheetresistance. For these problems, we have designed and synthesized two dimensional (2D)functional graphene sheets and three dimensional (3D) graphene networks for thepolymer composites with high performance. The research contents are mainly dividedinto the following three aspects.First, we design and synthesize2D sandwich-like graphene-TiO2hybrid sheets andgraphene oxide-encapsulated carbon nanotubes (GO-e-CNTs) hybrid sheets forenhancing dielectric properties of polymers. The resulting graphene-TiO2hybrid sheetspossess graphene substrates and morphology-controllable TiO2nanorod decoration.Graphene provides superior electrode materials for constructing microcapacitor network.TiO2decorations not only provide dielectrics for these microcapacitors, but also suppressthe leakage current through preventing connections between graphene sheets. Moreover,the TiO2layers are introduced to achieve a gradient of the dielectric constant for thecomposite components. Therefore, the obtaining graphene-TiO2/polymer compositesshow high dielectric performances including high dielectric constant and low dielectric loss. In addition, the dielectric constant of the composites can be tuned by controllingTiO2decoration amount. The resulting GO-e-CNTs show highly stable solution-likedispersion. GO-e-CNTs hybrid sheets also possess highly conductive CNT cores andelectrical-insulating GO shells, thus its polymer composites show high dielectric constant,low dielectric loss, enhanced breakdown strength, and enhanced maximum energystorage density.Second, we design and synthesize2D hyperbranched aromatic polyamidefunctionalized graphene sheets (GS-HBA) for enhancing mechanical performances. HBAfunctionalization not only improves the dispersion of graphene in polymer matrix, butalso reinforces the interfacial adhesion between graphene and matrix, leading to efficientload transfer from the matrix to graphene. The GS-HBA/polymer composites showhigher modulus, higher tensile strength and higher yield strength, and remain a nearlysame strain at break when compared with the composites with graphene oxide, ethylenediamine-modified graphene, and hydrazine reduced graphene. Additionly, themechanical properties of the composites are dependent on not only the interfacialinteraction but also the oritention of graphene sheets. For insistence, the Ca2+crosslinkedgraphene oxide/polymer composites show high modulus, tensile strength and yieldstrength, along with a high strain at break.Third, we design and fabricate foams with3D interconnected graphene networks forenhancing electrical performances of the polymer-based composites. The obtainedcomposites with4.8vol%graphene shows a high electrical conductivity of1024.8S/m,which is superior to that of the graphene composites prepared by an organic solventmixing method. After annealing the composites at high temperature, a3D porousgraphene framework is collected, and shows a higher electrical conductivity, possiblyhaving potential applications as electrode materials for lithium ion batteries andsupercapacitors. Polymer-based graphene foams possess a3D binary structure, and thegraphene sheets are uniformly assembles on a3D polymer skeletons. The unique binary structure combines the advantages of both polymer and graphene materials, as aconsequence, the as-prepared foams exhibit high conductivity, high hydrophobicity, andoutstanding mechanical properties including compression, bend and twist. The3D binarystructure design expands the research thought of graphene-based foams, and alsoprovides a new pathway for designing graphene-based foams with high performances.Moreover, graphene-Ag nanowire hybrid foams can be fabricated by adding Agnanowires as building block during the assembly process. Importantly, the assemblytechniques for the polymer-based composites and foams with3D graphene networks areconducted in aqueous solution, which have shows many advantages such asenvironmental protection, low cost, and scalable production.