Graphene Dispersion and Exfoliation in Low Boiling Point Solvents

One of the problems with solvent exfoliation of graphene is that the best solvents tend to have high boiling points and so are difficult to remove and can present problems for flake deposition and composite formation. Here, we demonstrate the exfoliation of graphene at relatively high concentration in low boiling point solvents such as chloroform and isopropanol. It is possible to achieve concentrations of up to 0.5 mg/mL, just under half that which can be achieved with high boiling point solvents such as N-methyl-pyrrolidone. These dispersions consist of graphene flakes of similar to 1 mu m length and with a thickness of less than 10 layers (<= 5 layers for isopropanol). For both solvents, > 75% of the graphene remains dispersed indefinitely. Raman spectroscopy shows the flakes to be relatively defect-free. A significant advantage of low boiling point solvents is that they allow individual flakes to be spray cast onto substrates. Deposited densities of > 10 flakes with length > 1 mu m per 10 mu m x 10 mu m square have been controllably achieved. While some on-substrate aggregation is observed, this is much less prevalent than when spraying from high boiling point solvents.