The effect of heterogeneity in ion-exchange membrane structure on Donnan Exclusion

Ion-exchange membrane (IEM) can be classified into homogeneous and heterogeneous membrane according to the heterogeneity of membrane structure. Results of various studies indicated that the degree of heterogeneity significantly affects the properties and performance of IEMs, such as conductivity, permselectivity, mechanical and chemical stability, energy consumption, and limiting current density. In the case of transport properties, it may be associated with efficacy of Donnan exclusion influenced by the presence of interstitial solution and inert phase in the membrane matrix. Therefore, understanding the effect of heterogeneity on Donnan exclusion is important to provide preliminary information about IEM transport properties. In this paper, the effect of IEC/Wu on Donnan exclusion is discussed. The effect of heterogeneity on Donnan exclusion is expressed as a correlation of IEC/Wu ratio with Donnan equilibrium constant, KD, and transport number of counter-ion, t_i.