Water conduction through the hydrophobic channel of a carbon nanotube

Confinement of matter on the nanometre scale can induce phase transitions n ot seen in bulk systems(1). In the case of water, so-called drying transiti ons occur on this scale(2-5) as a result of strong hydrogen-bonding between water molecules, which can cause the liquid to recede from nonpolar surfac es to form a vapour layer separating the bulk phase from the surface(6). He re we report molecular dynamics simulations showing spontaneous and continu ous filling of a nonpolar carbon nanotube with a one-dimensionally ordered chain of water molecules. Although the molecules forming the chain are in c hemical and thermal equilibrium with the surrounding bath, we observe pulse -like transmission of water through the nanotube. These transmission bursts result from the tight hydrogen-bonding network inside the tube, which ensu res that density fluctuations in the surrounding bath lead to concerted and rapid motion along the tube axis(7-9). We also rnd that a minute reduction in the attraction between the tube wall and water dramatically affects por e hydration, leading to sharp, two-state transitions between empty and fill ed states on a nanosecond timescale. These observations suggest that carbon nanotubes, with their rigid nonpolar structures(10,11), might be exploited as unique molecular channels for water and protons, with the channel occup ancy and conductivity tunable by changes in the local channel polarity and solvent conditions.