Thermal diffusion in micropores by molecular dynamics computer simulations

This work focuses on the identification of the main microscopic processes that influence thermal diffusion (the Soret effect) in a fluid mixture confined in an uncorrugated slit pore. To achieve this purpose, a boundary driven nonequilibrium molecular dynamics scheme is applied on binary mixtures of super-critical Lennard-Jones (LJ) spheres representing methane and n-decane. Following previous work, we perform a systematic study of the influence of the parameters used to describe a model slit pore on an effective thermal diffusion factor. Among these parameters are: The nature of the reflection of the diffusing particles on the walls (specular or diffusive), the pore width with respect to the particle size and the fluid-wall potential strength. Simulations were run both on equimolar and non-equimolar mixtures. The results indicate that thermal diffusion is effectively lowered only for strong fluid-wall interactions. It is shown that the general trends, which are different under sub- and super-critical conditions, can be explained by a careful analysis of the relative sorption energies of the two compounds. (c) 2005 Elsevier B.V. All rights reserved.