Effect of ionic van der Waals forces on the diffuse potential of model colloids

In this work, the role of ionic dispersion forces in specific ion effects is evaluated through Monte Carlo simulations in the primitive model. More specifically, we assess the effect of such forces on the diffuse potential, since this property is essential to understand the electrokinetic behavior of colloids. In this way, ion specificity arises naturally since ion dispersion forces depend on ionic polarizability, which differs for ions with the same valence. This property is included in the primitive model by means of the Lifshitz theory. The results for different ions are summarized with the help of a nondimensional parameter characterizing the relative weight of ionic van der Waals interactions. Our data reveal that for small ions with high polarizability the ionic dispersion forces can considerably contribute to the specificity of the diffuse potential. In any case, the specific ion effects due to ion polarizability are strongly influenced by ion size.