Selectivity Of Polyelectrolyte Membranes

The major factors contributing to the selectivity of charged synthetic membranes are discussed. Transport through porous polyelectrolyte membranes, containing ater-filled interstices, can be predicted approximately from Donnan equilibria, representing the interaction between polyelectrolyte and counter-ions by “ion-binding”. A simple relation between permselectivity and maximal salt rejection in hyperfiltration is given for porous aqueous membranes. The role of the streaming potential, especially in the filtration of mixed electrolyte, is demonstrated. Dense polyelectrolyte membranes which sell only slightly in ater, give much higher salt rejection than predicted for their permselectivity, according to the Donnan-based relation mentioned: they comprise a separate non-aqueous phase. Porous membranes, sollen with an organic solvent sho very high permselectivity at lo charge density. Ion-specificity can be imparted to them by specific complexing agents. It is shon that the change in the dissociation between fixed ionic site and mobile counter-ion by the ligand, may be more important than the change of ion-uptake by the membrane, from the mixed aqueous solution.