The two-phase model of structure microheterogeneity revisited by the study of the CMS cation exchange membrane

The chronopotentiometric study of the CMS membrane in contact with 0.05M NaCl shows a chronopotentiometric response at over-limiting currents typical of homogeneous membranes. Based on the two-phase model, the fraction of the interstitial phase in presence of NaCl was determined from the conductivity of the CMS membrane conditioned in NaCl solution; the interstitial volume fraction value was 13%. In addition, we have determined the sorbed amount of NaCl in the CMS membrane in contact with NaCl solution at different concentrations by the many-stage desorption method. The NaCl sorbed molality in the overall membrane varied linearly as a function of the molality of the NaCl external solution. It is noted that the majority of NaCl sorbed remains in the interstitial phase. The equilibrium partition between the external solution and the interstitial solution was estimated to be 0.89. It is shown in this work that the consideration of an equilibrium partition of the electrolyte between the external solution and the interstitial phase strengthens the two phase model of Zabolotsky and Nikonenko.