At study of ion permeation across a charged membrane in multicomponent ion systems as a function of membrane charge density

Abstract

The authors have described an ion flux across a charged membrane in multicomponent systems by the theories (based on the Donnan equilibrium and the Nernst-Planck equation) in the previous paper. In the present study, the permeation coefficients of ions in various kinds of electrolyte systems are calculated as functions of membrane charge density by this theory. The theory predicts that permeability coefficients of multi-valent ions will be lower than those of univalent ions according to the low charge density, and that the permeability coefficients of multi-valent ions will become negative if the membrane has high charge density. That is, they are transported against their concentration gradient. This phenomenon in 1-1- and 2-1-type electrolyte systems was examined for negatively charged membranes, which were composed of poly (vinyl alcohol) (PVA) and poly (styrenesulfuric acid) (PSSA) mixtures, and a positively charged one, which was composed of a PVA and poly(allylamine) (PAAm) mixture. The theoretical prediction agreed well with the experimental results. The uphill transport of a multivalent ion occurred under the appropriate membrane charge density. This result shows that the direction of multivalent ion transport changes with charge density. This phenomenon is applicable in a new mechanism to control ion transport direction.