Effect of mesogenic groups on characteristics of permeation and separation for benzene/cyclohexane mixtures of side-chain liquid-crystalline polymer membranes

When benzene/cyclohexane (Bz/Chx) mixtures were permeated through nematic and smectic side-chain liquid-crystalline polymer (n- and s-LCP) membranes under various conditions in pervaporation, the n- and s-LCP membranes exhibited a benzene-permselectivity for the Bz/Chx mixtures. The benzene-permselectivity of the n-LCP membrane changed from the sorption selectivity to the diffusion selectivity by the state-transformation of the membrane with an increase in the permeation temperature but the benzene-permselectivity of the s-LCP membrane was governed by the diffusion selectivity regardless of the state of the s-LCP membrane. At the low permeation temperature, the n-LCP membrane in the liquid-crystalline state exhibited a lower permeability and a higher permselectivity than the s-LCP membrane. However, at the high permeation temperature the relationship between the permeability and permselectivity of the n-LCP and s-LCP membranes in the liquid-crystalline state was vice versa. These results were led by the difference of the chemical and physical structure of the n-LCP and s-LCP membranes. (C) 1998 Elsevier Science B.V.