Molecular simulation of adsorption and transport diffusion of model fluids in carbon nanotubes

Grand canonical Monte Carlo (GCMC) and dual-control-volume grand canonical molecular dynamics (DCV-GCMD) simulations were carried out with Lennard-Jones model fluids in carbon nanotubes, with the objective of investigating the effect of varying molecular properties on adsorption and diffusion. The influence of the molecular weight, and the Lennard Jones parameters σ (a measure of the molecule size) and ε (a measure of the interaction strength) on adsorption isotherms, fluxes, and transport diffusivities was studied. For these simulations, the properties of component 1 in the mixture were held constant and one of the properties of component 2 was changed systematically. Furthermore, the validity of Graham's law, which relates the fluxes of two counter diffusing species to their molecular weight, was investigated on a molecular level. Graham's law is fulfilled for the whole range of molecular weights and Lennard-Jones parameters σ investigated. However, large deviations were observed for large values of ε₂. Here, the interaction of the two components in the mixture becomes so strong that component 1 is dragged along by component 2.