Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties1, 2, 3, 4. Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase5. Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as ~2 mg ml−1, which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene6 or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations (~20–30 mg ml−1). Transparent, conducting films are produced from these dispersions at 1,000Ω □−1 and ~80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.
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