Digital simulation of associated and nonassociated liquid membrane electrochemical properties

The method and results of a digital simulation of electrochemical properties for associated and nonassociated liquid ion-exchange membranes are presented. It is assumed that the membranes is ideally permselective, sites are completely trapped, electroneutrality holds everywhere in the membrane, and the bathing solutions contain no more than two counterions, of which one is completely dissociated in the membrane. Electrochemical properties are simulated for the single counterion case and in the interference region. Concentration profiles, potentiometric responses, transient potential responses to activity steps, and current-voltage curves are given and the effects of ion-pairing and species mobilities are studied. It is found that ion-pairing increases the potentiometric selectivity toward the complexing ion over the noncomplexing ion. Transient responses to an ion activity step are shown to depend in a complex way on the ion-pair formation constant and the various mobilities. Current-voltage curves are simulated for varying degrees of ion-pairing and qualitative agreement is found with previous theoretical treatments, as well as quantitative agreement in those cases where closed-form expressions are known.