Limited agreement between the interfacial tension and differential capacity data for the polarised water|1,2-dichloroethane interface

Quasi-elastic laser light scattering and impedance measurements at the water|1,2-dichloroethane interface are used to evaluate the interfacial tension and the differential capacity, respectively, as a function of the interfacial potential difference. Over the range of the potential differences around the zero-charge potential difference, the surface charge density obtained by integration of the capacity agrees well with that obtained by derivation of the interfacial tension. However, the ratio of these two charges starts to deviate significantly from unity close to the potential window limits, where the faradaic current associated with the transfer of the supporting electrolyte ions becomes more pronounced, and where the capacity shows a remarkable enhancement. These results corroborate our previous experimental observations and conclusions, which threw doubts on the previous interpretation of the effect of electrolytes on the differential capacity in terms of the ion association, ion interpenetration, or specific ion adsorption. In the potential range where the capacity data can be reliably obtained, an effect of the nature of the organic electrolyte on both the interfacial tension and the differential capacity is observed, which can be ascribed to the change in the thickness of the inner (compact) layer due to a difference in the radius of the ions present.