  Graphene is at the centre of nanotechnology research. In order to fully
exploit its outstanding properties, a mass production method is necessary. Two
main routes are possible: large-scale growth or large-scale exfoliation. Here,
we demonstrate graphene dispersions with concentrations up to ~0.01 mg/ml by
dispersion and exfoliation of graphite in organic solvents such as
N-methyl-pyrrolidone. This occurs because the energy required to exfoliate
graphene is balanced by the solvent-graphene interaction for solvents whose
surface energy matches that of graphene. We confirm the presence of individual
graphene sheets with yields of up to 12% by mass, using absorption
spectroscopy, transmission electron microscopy and electron diffraction. The
absence of defects or oxides is confirmed by X-ray photoelectron, infra-red and
Raman spectroscopies. We can produce conductive, semi-transparent films and
conductive composites. Solution processing of graphene opens up a whole range
of potential large-scale applications from device or sensor fabrication to
liquid phase chemistry.
