By performing molecular dynamics simulations of the micro-canonical ensemble for water confined in infinitely long C nanotubes with a diameter of 1.08nm, it was shown here that confined water molecules diffused via a fast ballistic motion mechanism for up to 500ps at room temperature. By comparing the results obtained for the diffusion of water, with those obtained for the diffusion of a reference Lennard-Jones fluid, it was proved here that long-lasting H bonds were responsible for the ballistic diffusion of water clusters in narrow C nanotubes, instead of spatial mismatches between pore-fluid and fluid-fluid attractive interactions. It had been shown previously that these 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 small diameter of the C nanotubes - which might have suggested the occurrence of single-file diffusion - a Fickian-type diffusion mechanism operated when the trajectories of the confined water molecules were studied at time-scales in excess of 500ps.

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