Conductance behaviour of a microporous membrane and the application of absolute reaction rate theory

The membrane conductance of a microporous membrane prepared by the hydrogen peroxide (5%) treatment of ion-exchange membranes of the ‘Neosepta’ family has been studied at different temperatures. The membranes were bathed in some common uni-univalent chloride solutions at different concentrations. In general, the membrane conductance, in the temperature range studied, shows values increasing more or less linearly with increases in concentration, but tends towards limiting values at higher concentrations. The magnitudes follow the order K⁺ > NH₄⁺ ≥ Na⁺ > Li⁺, which is the reverse order of the hydrated sizes of these ions. The temperature variations of the conductance have been utilised to calculate the activation parameters, E_a, ΔH3, ΔG3 and ΔS3, assuming the applicability of the theory of absolute reaction rate. The activation energies for conduction increase in the order K⁺ < NH₄⁺ ≤ Na⁺ < Li⁺, which is the reverse of the order of conductances but the same as the sequence of the hydrated sizes of the cations. For a particular electrolyte solution, the energy values decrease with increasing concentrations of the bathing electrolyte. The ΔS3 values are found to be mostly very small positive quantities, indicating that virtually neither any bond formation nor any loss of membrane structure takes place during the permeation process.