Graphene Oxide "Surfactant"-Directed Tunable Concentration of Graphene Dispersion

Homogeneous graphene dispersions with tunable concentrations are fundamental prerequisites for the preparation of graphene-based materials. Here, a strategy for effectively dispersing graphene using graphene oxide (GO) to produce homogeneous, tunable, and ultrahigh concentration graphene dispersions (>150 mg mL^-1 ) is proposed. The structure of GO with abundant edge-bound hydrophilic carboxyl groups and in-plane hydrophobic π-conjugated domains allows it to function as a special "surfactant" that enables graphene dispersion. In acidic solutions, GO sheets tend to form edge-to-edge hydrogen bonds and expose the π-conjugated regions which interact with graphene, thereby promoting graphene dispersion. While in alkaline solutions, GO sheets tend to stack in a surface-to-surface manner, thereby blocking the π-conjugated regions and impeding graphene dispersion. As the concentration of GO-dispersed graphene dispersion (GO/G) increases, a continuous transition between four states is obtained, including a dilute dispersion, a thick paste, a free-standing gel, and a kneadable, playdough-like material. Furthermore, GO/G can be applied to create desirable structures including highly conductive graphene films with excellent flexibility, thereby demonstrating an immense potential in flexible composite materials.