How To Dissolve Your Carbon Nanotubes

Although carbon nanotubes are generally regarded as insoluble in all solvents, a research team led by Jonathan N. Coleman of Trinity College Dublin and James P. Hamilton of the University of Wisconsin, Platteville, has found that carbon nanotubes actually can be dissolved in N-methylpyrrolidone (NMP) and other solvents with a surface energy that matches that of graphitic surfaces (Adv. Mater., DOI: 10.1002/adma.200702451). The investigation may eventually enable researchers to process carbon nanotubes conveniently via ink-jet printing and other procedures suitable for soluble polymers. Because of carbon nanotubes' extreme insolubility, they are typically chemically modified to enable their dispersion in various liquids, including NMP. On the basis of spectroscopy and scanning-probe measurements, the team finds that nanotube bundles in NMP spontaneously exfoliate (unpeel) upon dilution and that NMP molecules adsorb (shown on top) and desorb (bottom) reversibly to the nanotubes—a key step toward dissolution. The scientists also find that the nanotube-NMP interaction is characterized by a negative enthalpy of mixing, which indicates "solubility in the classical thermodynamic sense, like sugar in water or polystyrene in acetone," Hamilton says.