Mass Transfer through Vapour–liquid Interfaces: a Molecular Dynamics Simulation Study

Abstract

A quasi-stationary molecular dynamics simulation method for studying mass transfer through vapour–liquid interfaces of mixtures driven by gradients of the chemical potential based on the dual control volume (DCV) method is described and tested. The rectangular simulation volume contains three bulk domains: a liquid domain in the middle with vapour on each side such that there are two vapour–liquid interfaces. The mass flux is generated by prescribing the chemical potential in control volumes in the vapour domains close to the outer boundary of the simulation volume. The simulation method was applied for studies of two binary Lennard-Jones mixtures: one in which a strong enrichment of the low-boiling component at the vapour–liquid interface is observed and another in which there is practically no enrichment. The two mixtures differ only in the dispersive interactions; their bulk diffusion coefficients are similar. Furthermore, the prescribed chemical potential difference was the same in all simulations. Nevertheless, important differences in the mass flux of the low-boiling component were observed for the two mixtures at all studied temperatures which might be related to the enrichment at the interfaces.