High-concentration solvent exfoliation of graphene

A method is demonstrated to prepare graphene dispersions at high concentrations, up to 1.2mg mL^-1, with yields of up to 4 wt% monolayers. This process relies on low-power sonication for long times, up to 460 h. Transmission electron microscopy shows the sonication to reduce the flake size, with flake dimensions scaling as t^-1/2. However, the mean flake length remains above 1 μm for all sonication times studied. Raman spectroscopy shows defects are introduced by the sonication process. However, detailed analysis suggests that predominately edge, rather than basal-plane, defects are introduced. These dispersions are used to prepare high-quality freestanding graphene films. The dispersions can be heavily diluted by water without sedimentation or aggregation. This method facilitates graphene processing for a range of applications.