| Graphene, a new one-atomically thick carbon nanostructure with sp2hybridized carbon atoms arranged in a honeycomb lattice, has attracted enormous attentions due to its unique structure and excellent physical, chemical, electrical, optical, thermodynamical and mechanical properties. However, graphene has poor dispersity in most common solvents because of its large specific surface area and easy aggregation. These properties have limited its application in most areas. This problem could be solved by modifying graphene with organic agents.In this work, for the purposes of bringing graphene superior performance into full display, three kinds of non-covalent approachs were adopted to modify graphene sheets. Then, the structure, morphplogies of the modified graphene and the dispersion stability of graphene suspensions were characterized. Finally, graphene/polymer composites were prepared and the effect of graphene on the properties of composites was studied. The main contents of this dissertation are summarized below:(1) Benzene hydrazine was used as reductant to modify graphene. The reduced graphene were mixed with poly (vinylidene fluoride)(PVDF) by solution blending and graphene/PVDF composites with multi-layered structure were prepared by a solution-casting and hot-pressing method. Experimental results showed that phenyl groups were introduced to surface of graphene sheets while graphene was reduced. This reduced graphene has good diespersibility in dimethylacetamide (DMAc). The dielectric constant of the composites improved significantly at extremely low content. A large dielectric constant of more than340at100Hz could be obtained within the vicinity of percolation threshold when the volume fraction of graphene (fg) was0.00177. The dielectric constant could continue to increase with the addition of graphene and the maximum value as high as7940at100Hz was obtained when fg was0.0177. These highly flexible graphene/PVDF composites with such high dielectric performance are potential materials for high-charge storage capacitors and electromagnetic-wave absorption stuff.(2) Polystyrene (PS) encapsulated modified graphene was prepared via in situ polymerization of monomer styrene on the surface of graphene with the help of ultrasonication, which plays multiple roles as dispersion, pulverizing, activation, and initiation. The as-modified graphene were used to prepare graphene/PS composites using solution coblending method. Fourier transform infrared spectrophotometer (FTIR) and transmission electron microscope (TEM) confirmed successful preparation of PS modified graphene (PS-G) and the strong interfacial bonding between the attached PS and graphene. The modified graphene exhibited good dispersibility in THF, CHCl3, and toluene. Scanning electron microscope (SEM) showed that PS-G was homogenously dispersed in PS matrix and had good compatibility and interactions with the host PS matrix. The electrical conductivity and thermal stability were improved a lot with the incorporation of small amount of graphene.(3) Ionic liquid, Methyl acryloyl oxygen ethyl trimethyl ammonium chloride (DMC) was used to decorate graphene at the time of GO being reduced. Then DMC modified graphene (DMC-rGO) was incorporated into polyvinyl alcohol (PVA) matrix by solution blending to fabricate graphene/PVA composites. Experimental results showed that a homodispersed suspension solution of DMC-rGO/water and DMC-rGO/PVA could be obtained. With the increasing content of DMC-rGO, the thermostability and electrical conductivity of the composites was improved greatly. The fastest decomposition temperature rose significantly from253.62℃(pure PVA) to353.25℃at a loading of1.0wt.%. The electrical conductivity and tensile strength were enhanced compared with pure PVA. The electrical conductivity of graphene/PVA (2.0vol.%graphene) was increased to3.12×10-4S/m by106from9.05×10-10S/m (pure PVA). The tensile strength of graphene/PVA (0.5wt.%) was increased to32.6MPa from17.6MPa. |
PDF Full Text Request