Solvent-induced ion selective transport properties of a crosslinked poly(L-glutamic acid) membrane

Ion‐selective transport of alkali metal chlorides (LiCl, NaCl, KCl and CsCl) is reported for a crosslinked poly(L‐glutamic acid) membrane immersed in aqueous alcohols CH3OH, C2H5OH and 2‐propanol ((CH3)2CHOH). In aqueous CH3OH and C2H5OH, an appreciable ionselectivity was observed for the permeability coefficient, i.e., Li+ < Na+ < Cs+ ≤ K+, in a higher alcohol composition region. This counterion sequence results from a significant increase in the salt solubility coefficient of KCl and CsCl and a substantial decrease in the diffusion coefficient of LiCl and NaCl in the relevant alcohol composition region. Membrane conductivity measurements, which were performed concomitantly for the aq. C2H5OH system, suggest the same ion specificity for the counterion mobility as for permeability. It has been suggested that the specific counterion binding to polymer charges is an essential factor for ion specificity.