The Effects of Counterion Size on the Equilibrium Properties of Charged Interfaces

Abstract

The adsorption of iodide ion at mercury has been studied from two systems at constant ionic strength, namely, and . The surface excess of adsorbed iodide ions was calculated from differential capacity data using a modified version of the Hurwitz‐Parsons analysis which takes into consideration variation in ionic activity coefficients with solution composition. The iodide surface excess was found to depend on the nature of the cation for a given bulk concentration and electrode charge density; comparison of the present data with those previously published shows a marked dependence of adsorbed surface excess on ionic strength. The effect of counterion nature on ionic adsorption is discussed within the framework of an electrostatic model for adsorption which takes the discrete nature of the charge at the interface into consideration. Counterion effects at charged monolayers, bilayer lipid membranes, and real membranes are compared with those observed at mercury.