Coaxial cross-diffusion through carbon nanotubes

JAVIER RODRIGUEZ, M. D. ELOLA Y D. LARIA

JOURNAL OF PHYSICAL CHEMISTRY B

American Chemical Society

Lugar: Washington DC; Año: 2009 vol. 113 p. 14844 - 14848

1089-5647

We present results from non-equilibrium Molecular Dynamics experiments describing the relaxation of local concentrations at two reservoirs, initially filled with water (W) and acetonitrile (ACN), as they get connected through a membrane composed of (16,16) carbon nanotubes.  Within the hydrophobic nanotube cavities, the equilibriumconcentrations contrast sharply to those observed at the reservoirs, with a clear enhancement of ACN, in detriment of W. From the dynamical side, the relaxation involves three well differentiated stages: the first one correspondsto the equilibration of individual concentrations within the nanotubes. An intermediate interval with Fickian characteristics follows, during which the overall transport can be cast in terms of coaxial opposite fluxes, with a central water domain segregated from an external ACN shell, in close contact with the tube walls. We also found evidence of a third, much slower, mechanism to reach equilibration, which involves structural modifications of tightly bound solvation shells, in close contact with the nanotube rims.