ABSTRACT
A great deal of research has recently been initiated on “graphene,” a twodimensional (2D) hexagonally arranged sp2-hybridized carbon nanostructure, for its promising applications in the „elds of sensors (Schedin et al. 2007), batteries (Geim and Novoselov 2007), supercapacitors (Wang et al. 2009), hydrogen storage (Du et al. 2010; Patchkovskii et al. 2005), nanoelectronics (Du et al. 2010; Geim and Novoselov 2007), and polymer nanocomposites (Geim and Novoselov 2007; Ramanathan et al. 2008; Stankovich et al. 2006a). Graphene sheets offer extraordinary electronic (Gómez-Navarro et al. 2007), thermal (Balandin et al. 2008), and mechanical properties (Gómez-Navarro et al. 2008), and to fully exploit these properties graphene should be incorporated into polymer matrices. High-performance polymer-graphene composites may then be fabricated by uniform „ller dispersion and „ne interfacial control, which are dif„cult due to the presence of a strong cohesive force among the layers of graphene. This dif„culty in the preparation of processable graphene sheets hinders the application of graphene in various „elds tempting an increase in research activity, which is documented in the recent literature. So far, two main methods (physical and chemical) have been developed for the dispersion of graphene sheets. In the physical method, thermal expansion of graphite oxide (produced by oxidation) followed by ultrasonication in polar organic solvents (McAllister et al. 2007) and ultrasonication of graphite oxide in the presence of a surfactant in water (Lotya et al. 2010) are the general procedures followed for the dispersion of graphene. In the chemical method, oxidation/reduction techniques (Balazs et al. 2006; Gao et al. 2009; Pradhan et al. 2009) are used to obtain dispersible graphene sheets.
