Coaxial cross-diffusion through carbon nantoubes

JAVIER RODRIGUEZ, M. DOLORES ELOLA AND DANIEL LARIA

BRNO

Conferencia; 8TH Liblice Conference on the Statistical Mechanics of Liquids; 2010

We present results from non-equilibrium Molecular Dynamics experiments describing the relaxationof 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. Withinthe hydrophobic nanotube cavities, the equilibrium concentrations contrast sharply to those observedat the reservoirs, with a clear enhancement of ACN, in detriment of W. From the dynamicalside, the relaxation involves three well differentiated stages: the first one corresponds to the equilibrationof individual concentrations within the nanotubes. An intermediate interval with Fickiancharacteristics follows, during which the overall transport can be cast in terms of coaxial oppositefluxes, with a central water domain segregated from an external ACN shell, in close contact withthe 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 thenanotube rims.