Molecular dynamics simulations of the transport of water-ethanol mixtures through polydimethylsiloxane membranes

Molecular dynamics (MD) computer simulation studies are conducted to examine important aspects of the pervaporation process. As a model system the separation of water-ethanol feed mixtures through a PDMS membrane is taken. Since it is yet not possible to model the whole membrane fully atomistically, two regions-the bulk and the interfacial region-were simulated. In the bulk region the movement of the penetrants has the character of a jump diffusion. The experimental diffusion coefficients are well reproduced. The water molecules are faster than the ethanol molecules. In spite of this, PDMS is a preferentially ethanol permeable membrane because of the great difference in the sorption behaviour. The simulations in the interfacial region reflect the preferential ethanol sorption. The ethanol molecules accumulate at the polymer-feed interface and take a favourite orientation to the hydrophobic PDMS surface. The polymer surface shows a swelling, which is dependent on the ethanol concentration of the feed. It can be shown that the behaviour at the interface polymer-feed is dominated by hydrogen bond forces. (C) 1997 Elsevier Science Ltd.