BEHAVIOR OF WATER ETHANOL MIXTURES IN THE INTERFACIAL REGION OF DIFFERENT POLYSILOXANE MEMBRANES - A MOLECULAR-DYNAMICS SIMULATION STUDY/

Results from molecular dynamics (MD) simulations in the interfacial re gion of three polysiloxanes, polydimethylsiloxane (PDMS), polyoctylmet hylsiloxane (POMS) and polymethylphenylsiloxane (PMPhS), and ethanol/w ater mixtures are reported. The behaviour of all polysiloxanes in cont act with the same solvent composition is very similar. The ethanol mol ecules accumulate at the surface of the polysiloxanes and the polymers begin to swell. The diffusive movement of these partly sorbed ethanol molecules is strongly hindered in the direction of the water phase. P arallel to the polymer surface the diffusion of the ethanol is faster but still slower than in the free diffusion case. The ethanol molecule s in the interfacial layer show a favourite orientation wherein the hy drophobic parts point in the direction of the polymer and the hydrophi lic parts point in the direction of the water molecules. The ethanol c oncentration of the feed has a strong influence on the interfacial beh aviour. (C) 1998 Elsevier Science Ltd. All rights reserved.