Synthesis of amphiphilic graphene nanoplatelets.

Graphene, a flat monolayer of carbon atoms tightly packed into a two-dimensional honeycomb lattice, has attracted a great deal of attention in recent years for potential applications in many technological fields, such as nanoelectronics, nanocomposites, and hydrogen supercapacitors. One possible route to harnessing these properties would be to incorporate graphene sheets into composite materials. The manufacturing of such composites requires not only that the graphene sheets are produced on a sufficient scale, but also that they are incorporated, and homogeneously distributed, into various matrices. Graphite, which consists of a stack of flat graphene sheets, is available in large quantities from natural sources. It is likely the most readily available and least expensive source for the production of bulk graphene sheets. Graphite oxide (GO) is a layered material produced by the oxidation of graphite. In contrast to pristine graphite, the graphene-derived sheets in GO are heavily oxygenated and bear hydroxyl and epoxide functional groups on their basal planes, in addition to carbonyl and carboxyl groups located at the sheet edges. Unfortunately, owing to their hydrophilic nature, graphene oxide sheets can only be dispersed in aqueous media that are incompatible with most organic solvents and polymers. In addition, GO is electrically insulating, which limits its usefulness for the synthesis of composites. However, it has been demonstrated that the electrical conductivity of GO can be significantly increased and very thin graphene-like sheets can be obtained through the chemical reduction of exfoliated GO. Just like carbon nanotubes, a key challenge in the synthesis and processing of bulk-quantity graphene sheets is aggregation. Graphene sheets, due to their high specific surface area, tend to form irreversible agglomerates or even restack to form graphite through van der Waals interactions. As with carbon nanotubes, full utilization of graphene sheets in polymer nanocomposite applications will inevitably depend on their ability to achieve complete dispersion in the polymer matrix of choice.