The spatial variation of the axial, radial, and tangential diffusion coefficients in carbon nanotubes of various diameters was investigated. The effect of confinement and carbon nanotube wall upon the diffusion coefficient was studied. On the basis of the spatial variation of the diffusion coefficient, the diffusion mechanisms in different regions of the nanotube were identified. The dependence of the diffusion coefficient upon the carbon-water interaction parameter was investigated. The average diffusion coefficient in the nanotube as a function of the nanotube diameter was computed, and the diffusion mechanisms, including the transition regimes, were identified. The results were analyzed via hydrogen bonds and water orientations.

Spatial Diffusion of Water in Carbon Nanotubes: from Fickian to Ballistic Motion. Farimani, A.B., Aluru, N.R.: Journal of Physical Chemistry B, 2011, 115[42], 12145-9