Modified Microheterogeneous Model for Describing Electrical Conductivity of Membranes in Dilute Electrolyte Solutions

Many transport properties of ion-exchange membranes can be described in terms of the microheterogeneous model using a single set of parameters. However, the model is applicable in a limited concentration range of electrolyte solutions. In this paper a new modification of this model is proposed, taking into account the contribution of the electrical double layer (EDL) at the internal boundaries of the gel phase and the intergel solution of the membrane to describe the electrical conductivity of membranes in dilute electrolyte solutions. The model suggests that the EDL thickness in the internal solution phase increases with dilution of the external solution. Since EDL is more conductive than the electroneutral part of the solution, it is possible to describe the concentration dependence of the electrical conductivity of membrane more precisely as compared with the basic version of the microheterogeneous model. Comparison of the concentration dependences of the electrical conductivity of membranes shows a good agreement between the experimental and calculated data.