Determination of structural, selective, electrokinetic and percolation characteristics of ion-exchange membranes from conductive data

The structural, selective and electrokinetic characteristics and percolation parameters were determined for different ion-exchange polymer membranes from their conductivity data using the two-phase model of membrane conductivity and percolation theory. The two different combinations of micro-phases in IEM, used in the two-phase conductivity model and percolation theory are presented and discussed. Based on this two-phase model and concentration dependences of membrane conductivity, the structural membrane heterogeneity was determined for 14 commercial IEMs. The diffusion coefficient, molar conductivity of counter-ions and hydration capacity of the gelphase were calculated and analyzed for cross-linked and linear ion-exchange polymers. The ion-exchange equilibrium constants for MK-40 were estimated from values of membrane conductivity at the iso-conductance point in individual electrolyte solutions and their mixtures. The percolation theory was used to describe the conductivity of different membrane compositions with various volume fraction of the conducting phase. The estimation of φcr and γ percolation parameters showed that the obtained values of critical index γ agree with the theory for investigated materials, and the value of the threshold parameter φcr depends on the preparation method and structural heterogeneity of a given composition.