Specific ion effects on the surface tension and surface potential of aqueous electrolytes

The phenomena of electrolytes affecting the surface tension of aqueous solutions and producing measurable surface potentials are reviewed in the light of recent studies of them. The factual information presented includes the molar ionic surface tension increments k(i) = lim(c(i) -> 0)(d sigma/dc(i)) of many ions and the surface potential increments Delta chi = chi(E) - chi(W) of electrolytes involving the cations H+, Na+, K+, and NH4+ and various anions. Gaps in the data that invite filling and inconsistencies in reported data are pointed out. Correlations of k(I) with several properties of the ions that should be relevant to their specific effects: their sizes, quantities representing their polarizabilities, their effects on the structure of the water and the binding of water molecules by them, are presented. Correlations of the surface potential increment Delta chi with the electrolyte surface tension increments and with the differences between the cation and anion increments are shown. Models recently proposed for the rationalization of the observed phenomena and relevant theoretical developments are shown and discussed. The paradox of hydrogen ions not promoting significant charge separation at the interface but yielding large surface potentials is emphasized. (C) 2016 Elsevier Ltd. All rights reserved.