Ionic distribution of MgCl2 near the alcohol/water interface

Abstract An equation is developed to describe the surface potential at the diffuse plane for MgCl2 solutions. The equation, in combination with surface tension and surface potential data, was used to predict the Mg2+/Cl- distribution near the air/water surface of MIBC solution. It was found that net ionic adsorption has a negative charge, that it is more anionic than cationic. The result was contrasting to MIBC/NaCl system. The negative charge was confirmed by molecular simulations. Despite its small size, the divalent nature prevents Mg2+ from penetrating the anionic layer. The study provides important insights into the adsorption of electrolytes with unequal charges between anion and cation. One of the main applications of the study is predicting the bubble surface charge of foaming systems in the “hard” water.