Double layers at liquid/liquid interfaces

Abstract

The electrical double layer at the interface between two immiscible electrolyte solutions (ITIES) has been studied by the fast-galvanostatic-pulse method for the system consisting of aqueous NaBr and a solution of tetrabutylammonium tetraphenylborate in nitrobenzene. The double-layer capacity has been evaluated as a function of the potential difference across the interface. The modified Verwey–Niessen model, in which a layer of oriented solvent molecules (the inner layer) separates two space-charge regions (the diffuse double layer), seems to provide a reasonable framework to interpret the experimental data, assuming (i) that the approximations to the Poisson–Boltzmann equation by Gouy and Chapman are removed and (ii) that the boundary between the space-charge region and the inner layer is considered to be diffuse rather than sharp. The use of the tetrabutylammonium cation as the reference ion in voltammetric studies of the water/nitrobenzene interface is discussed.