Propensity of formate, acetate, benzoate, and phenolate for the aqueous solution/vapor interface: Surface tension measurements and molecular dynamics simulations

The properties of a series of aliphatic and aromatic carboxylates and phenolate-mimicking functional groups of humic acid are discussed with regard to their behavior in aqueous solutions close to the surface. Both surface tension measurements and MD simulations confirm that sodium formate behaves in accord with the classical theory of surfaces of electrolytes, whereas sodium acetate and, much more pronounced, sodium benzoate and sodium phenolate show a more hydrotropic behavior with surface active anions. Further to the surface tension data, the MD results suggest that these hydrotropes are highly oriented at the solution-vapor interface.