Dual control-volume grand canonical molecular dynamics simulations permitted the direct simulation of transport diffusion on a molecular level. Such simulations of CH4/CF4 mixtures in carbon nanotubes were carried out. An approach to get composition dependent transport diffusivities directly from dual-control-volume grand canonical molecular dynamics simulations was introduced. Composition-dependent transport diffusivities and fluxes were calculated for varying driving forces in order to investigate the influence of the very large driving force in simulations which was about four orders of magnitude larger than in real experimental systems. Whereas the flux depended upon the driving force the transport diffusivity was independent of it so that dual-control-volume grand canonical molecular dynamics simulation could be used to simulate transport under experimental conditions. Furthermore, the results of composition dependent diffusivities at four different temperatures were presented. A linear function described the composition dependence and reproduces the simulated concentration profiles very well. The analysis of the temperature dependence indicates that the transport in the investigated system was due to liquid-like molecular diffusion and not to activated diffusion.

Composition Dependent Transport Diffusion Coefficients of CH4/CF4 Mixtures in Carbon Nanotubes by Non-Equilibrium Molecular Dynamics Simulations. Düren, T., Keil, F.J., Seaton, N.A.: Chemical Engineering Science, 2002, 57[8], 1343-54