Permeation behavior of anions through poly(vinyl alcohol) membranes containing α-cyclodextrin or supramolecules composed of α-cyclodextrin and poly(ethylene glycol) in electrodialysis

Cross-linked poly(vinyl alcohol) membranes containing α-cyclodextrin or inclusion complex of α-cyclodextrin with poly(ethylene glycol) (molecular weight (MW): 1000) were prepared by the casting method, following cross-linking reaction with formaldehyde. The membranes were evaluated by electrodialyzing mixed salt solutions composed of sodium chloride and sodium salts having various anions to observe the change in transport numbers of anions relative to chloride ions. As α-cyclodextrin and its inclusion complex provided hydrophilic atmosphere to the membranes, permeation of less hydrated anions, bromide and nitrate ions, compared to chloride ions through the membranes, decreased and that of strongly hydrated anions, sulfate and fluoride ions increased. In particular, the effect of the inclusion complex on the change in permselectivity between anions was remarkable and also the membrane showed anisotropic property in permselectivity between anions. The change in the permselectivity was due to the change in mobilities of each anion in the membrane phase, not due to specific interaction of α-cyclodextrin and its inclusion complex with particular anions.