ELECTROCHEMICAL PROPERTIES OF CELLULOSIC ION-EXCHANGE MEMBRANES .1. EQUILIBRIUM AND PERMSELECTIVITY

The emf values of the cell Ag,AgCl\KCl(a')\ membrane\KC\(a'')\Ag,AgCl have been measured. Two types of cellulosic strong ion-exchange membra nes were tested, containing either cationic or anionic fixed groups. T he membranes were prepared by grafting acrylic monomers onto paper fol lowed by opening of epoxy groups. The membrane phase was analysed for its electrolyte and water contents, and intramembrane activity coeffic ients were derived as a function of external electrolyte concentration . The data were used for calculation of the emf of membrane cells usin g the TMS theory reformulated by Hills et al. The main finding of this investigation is that, for dilute external solutions, the membrane po tentials are close to the maximum theoretical value and can be calcula ted with reasonable accuracy using the fixed charge theory. With a mor e concentrated solution this is not so; the membrane potentials are pr ogressively smaller than the maximum value and the theory did not give satisfactory agreement between the observed and the calculated emf of the membrane cells. This is readily explained by the decrease in the selectivity of the membranes, the increasing concentrations of co-ions , and the diffusion of electrolyte through the membrane.