The interaction of liquid water with grapheme carbon surfaces is important for nanotube dispersion and processing 1, nanotube fluidics 2,3, aqueous phase sorbent applications 4, protein adsorption and cell behaviour on carbon implant surfaces 5, and the rates of cell uptake and biological membrane translocation that influence nanomaterial toxicity 6. In many carbon applications one wishes to decrease contact angle to improve aqueous dispersion 1 or increase biocompatibility 5, but there is also interest in systematically increasing contact angle, in particular into the so-called superhydrophobic range beyond 150 deg to create water-repelling, surface-cleaning surfaces 7. The technique used most often to increase hydro-philicity (decrease water contact angle) is surface oxidation, where there are a range of competing oxidants and treatment protocols, but very few studies comparing quantitative water contact angles. Recently Mattia et al. 2,8 report enhanced hydrophilicity upon NaOH treatment using CVD films as models for nanotubes and nanopipes. Several recent studies in the nanotube literature use aryl-sulfonation through diazonium salt chemistry to improve nanotube dispersion 1. This treatment may extend the range of carbon hydrophilicity, but quantitative comparisons of this and other treatments based on contact angle have not been made to our knowledge.
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