The thermodynamic and transport properties of water confined within long narrow carbon nanotubes were considered. Previous theoretical work had considered either short carbon nanotubes or short periods of time. By conducting molecular dynamics simulations in the microcanonical ensemble for water confined in infinitely-long carbon nanotubes with a diameter of 1.08nm, it was shown here that confined water molecules diffused via a rapid ballistic mechanism for up to 500ps at room temperature. By comparing the results obtained for the diffusion of water, to those obtained for the diffusion of a reference Lennard-Jones fluid, it was proved here that long-lasting hydrogen bonds were responsible for the ballistic diffusion of water clusters in narrow carbon nanotubes, rather than spatial mismatches between pore-fluid and fluid-fluid attractive interactions which, as shown previously by others, were responsible for the concerted motion of simple fluids in molecular sieves. It was also proved here for the first time that, in spite of the narrow diameter of the carbon nanotubes, which might suggest the operation of single-file diffusion, when the trajectories of confined water were studied at time-scales longer than 500ps, Fickian-type diffusion prevailed.

The Mechanism of Water Diffusion in Narrow Carbon Nanotubes. A.Striolo: Nano Letters, 2006, 6[4], 633-9