Thermodynamics of a polarised interface between two immiscible electrolyte solutions

Abstract The thermodynamics of a polarised interface between two immiscible electrolyte solutions is developed using the interfacial phase model of Guggenheim. The differences between the definition of the extensive variables for polarised liquid—liquid interfaces and for a metal—solution interface are discussed. It is found that the physical meaning of the surface charge density can differ from that derived for a metal in contact with a solution. The difference is due to the possibility of interfacial mixing and ion pairing, in which case the simple clear interpretation of the charge density as a smeared out plane of charge becomes obscured. The electrocapillary curve for a solution of tetrabutylammonium tetraphenylborate in 1,2-dichloroethane has been measured using a video image profile digitiser and the results have been found to be in good agreement with integrated capacitance data obtained from galvanostatic pulse experiments.