Surface tension of electrolyte solutions: Comparing the effects of ionic dispersion forces and solvation

The influence of salt on the surface tension of water is yet to be understood. We derive approximate analytical expressions for the influence of two different ion-specific effects on the surface tension of an electrolyte: the dispersion interaction between the ions and the air-water interface, and the change in solvation energy of the ions as they approach the interface. These formulae provide a simple means of comparing the relative importance of the two effects. We carry out such a comparison for the case of 1M NaCl, and find that solvation is the dominant effect.