The double layer and ion adsorption at the interface between two non miscible solutions part I. Interfacial tension measurements for the water-nitrobenzene tetraalkylammonium bromide systems

Abstract

The classical treatment of the double layer has been extended to the interface between two immiscible solutions. The model presented is composed of an inner compact layer, characterized by a dipolar potential drop, between two diffuse type layers. The systems studied are composed of C2 to C5 quaternary ammonium bromides at partition equilibrium between water and nitrobenzene for which the inner potential difference, for a given electrolyte, is independent, at least in the lower concentration range, of the concentration. Drop weight interfacial measurements and the use of the Gouy-Chapman approach show that the tetraethyl-, tetrapropyl- and tetrabutylammonium ions are not adsorbed within the inner compact layer, and the dipolar potential drop of this layer can then be determined. Tetrapentylammonium ions on the contrary are specifically adsorbed but the amount of adsorbed ions within the compact inner layer cannot be evaluated because of the impossibility, in this case, of determining the dipolar potential drop.