The Vanishing water/oil interface in the presence of antagonistic salt

Abstract

Antagonistic salts are salts that consist of hydrophilic and hydrophobic ions. In a binary mixture of water and an organic solvent, these ions preferentially dissolve into different phases. We investigate the effect of an antagonistic salt, tetraphenylphosphonium chloride PPh4+Cl-, in a mixture of water and 2,6-lutidine by means of Molecular Dynamics (MD) simulations. For increasing concentrations of the salt, the two-phase region is shrunk and the interfacial tension in reduced, in contrast to what happens when a normal salt is added to such a mixture. The MD simulations allow us to investigate in detail the mechanism behind the reduction of the surface tension. We obtain the ion and composition distributions around the interface and determine the hydrogen bonds in the system and conclude that the addition of salt alters the hydrogen bonding.