Interfacial capacitance and ionic association at electrified liquid/liquid interfaces

The capacitance of the interface of immiscible electrolytes has been measured for the Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ chlorides in 1,2-dichloroethane and nitrobenzene. Evidence for ionic specific adsorption at the interface is presented. The nature of the specifically adsorbed charge is discussed in terms of the formation of interfacial ion pairs between the aqueous and the organic ions. The contribution of specific ionic adsorption to the interfacial capacitance is calculated on the basis of an ionic associated model using the Bjerrum theory of ion-pair formation. A mixed solvent region with varying penetration of the ion pairs into it, dependent on their ionic radii, best represents the structure of these interfaces.