Molecular dynamics study of thermal diffusion in a binary mixture of alkanes trapped in a slit pore

We have used direct non-equilibrium molecular dynamics computer simulations to study the influence of an alummosilicate slit pore on thermal diffusion in equimolar methane-n-decane. We have computed the Soret coefficient S-T as a function of the pore width. The ST values deviate from those in a pore-free situation only for pores narrower than 35 Angstrom We have then investigated the possible causes for this deviation. We have noticed that the solid behaves as a thermal short circuit for the liquid but this has no consequence on the thermal and solutal profiles in the mixture. The main influence of the confinement of the liquid lies in the 'freezing' of the layer of molecules in contact with the pore walls. Outside this layer, the thermal diffusive behaviour of the mixture does not depart from that in the bulk fluid. This finding has enabled us to compute a 'corrected' Soret coefficient where the influence of the porous medium is eliminated.