Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes with Varied Dispersity of the Ion Exchanger

The structural and transport (conductivity, diffusion permeability) properties of cation- and anion-exchange membranes with varied dispersity of ion-exchange resin particles are studied in the work. Experimental MK-40 cation-exchange and MA-41 anion-exchange membranes with variable particle size of the ion-exchange resin of <20 to <71 μm were manufactured at LLC IE Shchekinoazot (Russia). A comparative analysis of the structural characteristics of the membranes by SEM reveals the anisotropy in the properties of the surface and section. The internal phase of the membrane is characterized by high values of the fraction and sizes of the ion exchanger and macroporosity. A comparison of the concentration dependences of the specific conductivity and diffusion permeability of the experimental membranes is performed. The analysis of the values of the model transport-structural parameters shows that an increase in the conductivity of the gel phase from 0.39 up to 0.47 S/m and from 0.15 up to 0.26 S/m for cation- and anion-exchange membranes, respectively, as well as redistribution of current transfer paths in the membrane are observed in the case of a decrease in the particle size of the ion exchanger. An increase in the contribution from transfer of the internal equilibrium solution along the channel is revealed; here, the transfer numbers of counterions slightly change. Information about the changes in the structure of the transport channels in membranes with different particle sizes of the ion exchanger obtained based on the analysis of the model parameters is consistent with the data of independent studies of the morphology of their surface and section by SEM.