Temperature effect on the permeation through poly(2-hydroxyethyl methacrylate) membrane

The temperature dependence of permeability through highly syndiotactic poly(2-hydroxyethyl methacrylate) P(HEMA)] membrane is reported for highly polar organic solutes such as ureas, methyl substituted ureas and amides, and for NaCl and Na₂SO₄. The membranes used were equilibrated in distilled water at each temperature before measurements. From the linear correlationship between the excess heat capacities, ?C_p^o(excess) in aqueous solution at infinite dilution and the permeability parameter PM^1/3, it is found that the water structure perturbing capability of the polar organic solutes is a controlling factor in the permeation mechanism at relatively low temperature, where P(HEMA) membrane has higher water content and more structured water. In addition, it is found that the poor separation for urea of cellulose acetate membrane in the reverse osmosis practice is due to the higher water structure-breaking capability of urea.