Preparation and characterization of graphite nanoplatelet, graphene and graphene-polymer nanocomposites.

摘要

Graphene is defined as a flat monolayer of carbon atoms tightly packed into a honeycomb lattice. This strictly two-dimensional (2D) material exhibits a range of unusual properties, such as excellent electrical and thermal conductivities and extremely high strength, which hold great promise in many applications. The main objectives of this study are to explore methods to produce graphene sheets and ultra-thin graphite nanoplatelets (GNPs), as well as utilizing them as conducting nanofillers to fabricate polymer nanocomposites.;To realize the formation of graphene, an electrochemical technique is employed to produce graphite intercalation compound (GIC); and three important factors, including stage structure and intercalant species of GIC, and the expansion technique, are specifically studied to understand their effects on the expansion and exfoliation behaviors of graphite.;Two kinds of chemical functionalization are applied on GNPs to improve the interfacial adhesion with matrix, which are UV/ozone treatment and amino functionalization. The electrical and thermal conductivities of GNPs show opposite trends with respect to the UV/ozone treatment duration. The amino-functionalized GNPs, particularly those treated with triethylenetetramine (TETA), improved the dispersion stability in solvents.;A novel and simple route to produce GNPs is proposed. The natural graphite is directly exfoliated by ultrasonication in formic acid. A stable graphene aqueous dispersion is obtained through chemical oxidation and subsequent chemical reduction of GNPs. A major advantage of this new process is to carry out the oxidation and exfoliation steps simultaneously.;The defect-free and unoxidized graphene sheets are produced from exfoliation of natural graphite in a solvent, N-methyl-pyrrolidone (NMP). A new approach is devised to transfer graphene from NMP to acetone so that the graphene sheets can be incorporated into a common matrix material, epoxy matrix. The resulting graphene/acetone dispersion is stable without any aggregates. The graphene/epoxy nanocomposite produced thereby shows significant improvements in electrical and thermal properties compared to the corresponding GNP/epoxy nanocomposites.;An alternative approach to fabricate graphene-based nanocomposites is proposed, involving the use of functionalized graphene sheets (FGS). The FGS are obtained from ultrasonication of thermally expanded graphene oxide (GO). Although the inherent electrical conductivity of FGS is deteriorated due to the existence of oxygen functional groups, the FGS/epoxy nanocomposites exhibit a much higher electrical conductivity than the corresponding GNP/epoxy nanocomposites.;Major contributions of this thesis include: (i) the development of a simple and novel route to produce GNPs and synthesis of graphene from these GNPs; and (ii) the successful fabrication of graphene/epoxy nanocomposites using two different sources of filler, namely defect-free graphene and FGS. The graphene synthesis technique proposed in this work has several advantages over other techniques, including the use of a non-toxic, environmental-friendly intercalant and the capability for mass production of graphene for industrial applications, as well as reduction of processing time required to produce GNPs. This thesis is known to be the first attempt to produce graphene nanocomposites using a thermoset resin matrix. All previous studies are based on thermoplastic matrices, which are much easier to produce. It is demonstrated that the graphene/epoxy nanocomposites fabricated here have excellent physical and mechanical properties, including the electrical conductivity being two orders of magnitude higher than the corresponding GNP/epoxy nanocomposites for the same filler content.