Effective one-body interactions due to the presence of a liquid–vapor interface

In this study we investigate the behavior of additive binary square-well mixtures within the framework of classical density functional theory. By leveraging on the geometrical structure of the square-well interaction, we propose a novel form of the perturbation theory contribution to the density functional in terms of weighted densities, inspired by fundamental measure theory. We apply this functional in order to study the effective one-body interaction due to the liquid–vapor interface of the solvent acting on a dilute component of dissolved nano particles. The effective one-body interaction attracts the nano particles strongly to the interface. We show that this effective interaction potential can be calculated either from the density profiles of the full mixture, at low but non-vanishing concentrations of the nano particles, or by employing the Widom insertion theorem in the dilute limit of vanishing density of nano particles. Both routes display excellent agreement.