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Spontaneous high-concentration dispersions and liquid crystals of graphene

Abstract

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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Figure 1: Solubility and solvent quality of graphite dispersions.
Figure 2: G′ band Raman spectra performed using an excitation laser wavelength of 514 nm.
Figure 3: Evidence for single-layer dissolution.
Figure 4: Graphene as a rigid platelet.
Figure 5: Evidence for the graphene liquid-crystalline phase.

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Acknowledgements

The authors acknowledge the helpful input of Y. Kauffmann, H. Schmidt, C. Young, M. Majumder, A. Mela, W. Adams and B. Chen. Funding was provided by Air Force Office of Scientific Research (AFOSR) grants FA9550-06-1-0207 and FA9550-09-1-0590, Department of Energy (DOE) (DE-FC-36-05GO15073), Air Force Research Laboratories (AFRL) agreements FA8650-07-2-5061 and 07-S568-0042-01-C1, the Robert A. Welch Foundation (C-1668), US Army Corps of Engineers Environmental Quality and Installation Program under grant W912HZ-08-C-0054, the USA–Israel Binational Science Foundation and the Evans–Attwell Welch Postdoctoral Fellowship. Mitsui & Co. generously donated the MWCNTs used for preparing the nanoribbons. Cryo-TEM was performed at the Electron Microscopy of Soft Matter Laboratory, supported by the Technion Russell Berrie Nanotechnology Institute (RBNI). The HRTEM work was carried out at the Electron Microscopy Center at the Department of Materials Engineering, the Technion.

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J.L. and N.B. conceived, designed and performed the experiments including dispersion and film fabrication. J.L. and A.S. performed AFM. N.B. and D.T. performed and interpreted the Raman measurements. N.B. characterized the liquid crystallinity. N.B. and A.N.G.P.V. designed the HRTEM experiments. A.S. fabricated the electronic devices. N.B., J.L. and A.S. performed electrical measurements. N.B. and A.S. performed SEM. N.B. performed STEM and electron diffraction. N.B. and A.L.H. prepared HRTEM samples, performed HRTEM experiments and interpreted the images. D.K. provided nanoribbons and graphite oxides. Y.T., Y.C., J.S., M.J.G. and E.K. performed HRTEM and cryo-TEM experiments and interpreted the images. N.B., M.J.G., A.L.H., A.S., J.L., Y.T., J.M.T. and M.P. co-wrote the paper. M.P., Y.T., Y.C. and J.M.T. supervised the project.

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Correspondence to James M. Tour or Matteo Pasquali.

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The authors declare no competing financial interests.

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Behabtu, N., Lomeda, J., Green, M. et al. Spontaneous high-concentration dispersions and liquid crystals of graphene. Nature Nanotech 5, 406–411 (2010). https://doi.org/10.1038/nnano.2010.86

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