Colligative properties of polyelectrolyte solutions. VI. Donnan membrane equilibrium

Abstract

AbstractThe Donnan membrane equilibrium of a linear polyelectrolyte solution was studied, using sodium polyvinyl alcohol sulfate as the sample and sodium chloride as the diffusible salt. Simultaneous measurements of membrane potential, sodium and chloride ion activities, sodium chloride distribution, osmotic pressure, and viscosity were carried out. The measurements of membrane potential and ionic activities gave consistent results which could be accounted for by the Donnan theory. The second virial coefficient, which was found to be much lower than the ideal Donnan term, was examined according to Scatchard's theory. It was found that while the theory gave a good qualitative explanation to the experimental results, it could not be used for quantitative discussion. For quantitative examination of the experimental second virial coefficient, the value of second virial coefficient was calculated from the assumption that osmotic pressure is proportional to the difference of the sum of solute activities on both sides of membrane, and was found to be nearly equal to the observed value.