A lattice–gas model for ion pairing at liquid ∣ liquid interfaces

The interface between two immiscible solutions is modeled as a phase boundary within a three-dimensional lattice gas. Pairing between ions on opposite sides of the interface is introduced through an attractive interaction potential. The profiles of the particle densities and of the electrostatic potential are obtained by Monte-Carlo simulations. In agreement with experimental findings, ion pairing is shown to enhance the interfacial capacity significantly. There is no overshoot of the electrostatic potential at the interface; this indicates a fundamental difference between ion pairing and specific adsorption.