Influence of Trace Electrolytes on Interfacial Tensions at the Oil/Detergent Solution Interface

Abstract

RECENTLY, there has been some discussion between Brady, Pethica, Cockbain and others regarding the form in which the Gibbs adsorption isotherm should be applied to surface-active electrolytes in the absence of any added electrolyte. Under such conditions, and assuming complete dissociation of the surf ace-active electrolytes, it has been shown, for example¹, that the Gibbs equation (neglecting the correction for activities) may be written in the form where γ is the interfacial tension; c the concentration of surf ace-active electrolyte; A the area occupied per film ion at the interface; k the Boltzmann constant, and T the absolute temperature. This has been verified by Cockbain² for sodium dodecyl sulphate at the oil-water interface. Other investigators, however, have found^3,4 that the form theoretically applicable in the case of excess added electrolyte, namely, appears also to apply in practice to the case of no added electrolyte.