The results were presented of non-equilibrium molecular dynamics experiments describing the relaxation of local concentrations at two reservoirs, initially filled with water and acetonitrile, as they became connected via a membrane composed of (16,16) carbon nanotubes. Within the hydrophobic nanotube cavities, the equilibrium concentrations contrasted sharply to those observed at the reservoirs, with a clear enhancement of acetonitrile, to the detriment of water. On the dynamic side, the relaxation involved three well-differentiated stages; the first one corresponded to the equilibration of individual concentrations within the nanotubes. An intermediate interval with Fickian characteristics followed, during which the overall transport could be cast in terms of coaxial opposite fluxes, with a central water domain segregated from an external acetonitrile shell, in close contact with the tube walls. Evidence was also found of a third, much slower, mechanism for attaining equilibration, which involved structural modifications of tightly bound solvation shells, in close contact with the nanotube rims.

Coaxial Cross-Diffusion through Carbon Nanotubes. Rodriguez, J., Elola, M.D., Laria, D.: Journal of Physical Chemistry B, 2009, 113[45], 14844-8