Surface tension of strong electrolytes

PACS. 05.70.Np – Interface and surface thermodynamics. PACS. 68.03.Cd – Surface tension and related phenomena. PACS. 61.20.Qg – Structure of associated liquids: electrolytes, molten salts, etc. Abstract. – We present a theory which accounts for the increase in interfacial tension of water due to the presence of 1:1 electrolyte. The agreement between the theory and experi-ment is excellent, extending all the way to relatively high salt concentrations of 1 M. For low concentrations of electrolyte the theory reduces to the Onsager-Samaras limiting law. Contrary to surfactant solutions, aqueous electrolytes possess surface tensions higher than pure water. An explanation of this curious phenomenon has been advanced by Wagner 1 based on then recently introduced Debye-Hückel theory of strong electrolytes 2. This work was further extended by Onsager and Samaras (OS) 3, who were able to derive a limiting law for surface tension similar to the one obtained by Debye and Hückel for bulk properties of electrolyte solutions. The OS limiting law is universal in the sense that it does not depend on specifics of electrolyte 4–7. For low concentrations, good agreement has been found between the OS theory and the experiments 5, 6. However, at larger concentrations the OS theory