Potentiometric titration of polyelectrolyte gels

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Abstract
The dependence of the degree of ionization of highly swollen, crosslinked polyelectrolyte gels (immersed in salt solution) on the pH of the external equilibrium solution was investigated. A potentiometric equation was derived theoretically, comprising an ideal term, a Donnan term, and a term due to polyelectrolyte electrostatic interactions. Measurements were carried out with polymethacrylate gels in solution of LiCl, NaCl, or KCl. No difference in behavior was found with the different cations, and the observed dependence of the titration curves on ionic strength, degree of crosslinking, and degree of swelling was satisfactorily accounted for by the theory.