| Graphene has received considerable attention since2004because of its extraordinary electronic, mechanical, and thermal properties, which make it a great promise for potential applications in nanoscience and technology including flexible thin-film transistors, capacitors, sensors, and nanocomposites. Among the methods of graphene preparation, chemical reduction of graphene oxide (GO) has been demonstrated to be an efficient approach for large-scale production of graphene. The surface of GO sheets had to be pre-modified by surfactants or polymers before the chemical reductions to avoid the re-stacking of the reduced GO sheets (RGO) and improve the compatibility between RGO sheets and polymer matrices. To address the abovementioned issues, we developed simultaneous reduction and surface modification of GO and three dimensional graphene to prepare epoxy/graphene nanocomposites. And main work of this thesis is shown as below:(1) By refluxing GO with polyetheramine (D2000), simultaneous functionalization and reduction of GO is realized. Compared to GO, the D2000-treated GO (GO-D2000) becomes hydrophobic, thermally stable and highly conductive with an electrical conductivity of11S/m, which is almost8orders of magnitude higher than that of GO. Due to the high conductivity and improved dispersion of GO-D2000, its epoxy nanocomposites exhibit a sharp transition from electrically insulating to conducting with a low percolation threshold of0.71vol%. With3.6wt%GO-D2000, the glass transition temperature of its epoxy nanocomposite is27℃higher than that of neat epoxy.(2) Simultaneous reduction and surface functionalization of GO was achieved by refluxing with a diamine, polyetheramine (D230). The D230-treated GO (GO-D230) exhibits a high electrical conductivity of1S/m, which is almost7orders higher than that of GO (1.3×10-7S/m), due to the chemical and thermal reduction. The incorporation of GO-D230significantly improved the electrical conductivity of rubbery epoxy (epoxy-D2000), exhibiting a sharp conductivity transition with a low percolation threshold of0.78vol%. Additionally, the tensile properties of epoxy were also enhanced. With5.1wt%of GO-D230, the electrical conductivity of its epoxy nanocomposite is1.0×10-4S/m, nearly11orders of magnitude higher than that of neat epoxy; meanwhile the Young’s modulus (14MPa) is about536%larger than that of the pure epoxy (2.2MPa), and the tensile strength is increased by269%from0.65to2.4MPa. In order to compare the effect of various surface chemistries of GO, we also prepared GO-D2000/epoxy-D2000nanocomposites. It is found that GO-D230is superior to GO-D2000in stiffness enhancement However, GO-D230is inferior to GO-D2000in maintaining the continuity of the rubbery epoxy matrix.(3) A three dimensional (3D) graphene aerogel was prepared by in situ reduction-assembly method using p-phenylene diamine (PPD) as the reducing and functionalizing agent of graphene oxide in an aqueous medium with ammonia. The as-prepared3D graphene-PPD aerogel (GPA) has a highly porous structure, low density, high electrical conductivity and good mechanical properties. Its epoxy composites were prepared by a vacuum-assisted impregnation process, which exhibits a high electrical conductivity of4×10-2S/m with only0.21vol%of graphene. Furthermore, the compressive strength of the epoxy is increased by ～178%with0.95%of graphene. |
PDF Full Text Request