Assessing the selectivity of composite ion-exchange membranes within the framework of the extended three-wire model of conduction

Abstract

The possibility of assessing the selectivity of composite perfluorated membranes MF-4SK modified with polyaniline (PANI), based on the concentration dependence of their specific conductivity in terms of the extended three-wire model of conduction of ion-exchange materials is investigated. To check the reliability of results obtained, the transport numbers of ions are calculated based on the electrodiffusion coefficients of counter ions and coions determined from concentration dependences of conductivity and diffusion permeability of ion-exchange membranes. The transport numbers of hydrogen ions found by these two methods are shown to coincide with high accuracy throughout the whole range of concentrations of HCl solutions for the original MF-4SK membrane and membranes with the fixed thickness of the modified polyaniline layer on their one side. For the MF-4SK sample the with gradient distribution of polyaniline, which exhibits asymmetrical transport characteristics, the deviation between the transport numbers of ions calculated with the use of electrodiffusion coefficients of counter ions and coions and those determined in terms of the extended three-wire model of conduction is shown to increase with the increase in solution concentration but not exceed 4%.