Sharp rise in resistance of ion exchange membranes in low concentration NaCl solution

Using a modified impedance measurement technique, ohmic resistance of commercial ion exchange membranes (Selemion CMV and AMV as well as Neosepta CMX and AMX) was measured in low concentration aqueous NaCl solutions. The ohmic resistance increased by an order of magnitude as the NaCl concentration was reduced from 0.5 M to 0.017 M Resistance of cation exchange membranes increased more than the anion exchange membranes. Resistance increased monotonically with a decrease in the NaCl concentration and the variation of resistance could be explained very well using a model based on the Kohlrausch law of conductivity. The model also provided value of the tortuosity for the membranes. Tortuosity of the membranes was between 3.4 and 4.5.