title: The release of monovalent counterions by addition of divalent countemons to aqueous solutions of maleic acid copolymer.
abstract: Divalent cation binding and the release of monovalent cations accompanying the cation binding were experimentally studied by ion-selective electrode methods in aqueous solutions of copolymer of maleic acid and ethyl vinyl ether. It was found that in the process of Ca2+ addition, all the Ca2+ added was bound to polyions and the initially condensed Na+ was released in proportion to the concentration of the added Ca2+ up to the critical concentration of added Ca2+ at which the condensation of Ca2+ ceases. Values of the structural charge density parameter xi(s), were determined from the end-points of condensation of Ca2+. The process of Na+ release by adding Ca2+ was analyzed on the basis of the counterion condensation theory by using these xi(s) values. In addition, the relationship between the activity coefficient gamma-- of Ca2+ and degree of neutralization alpha in salt-free solutions was obtained from the Manning theory. Agreement between the calculated and experimental values was excellent in both cases.
authors.affiliation: Department of Physics. Hamumatsu University School of Medicine, Hamamatsu, 431-31, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Shimizu
authors.forename: A
authors.initials: A
authors.lastname: Minakata
authors.forename: N
authors.initials: N
authors.lastname: Imai