A 3-COMPONENT MODEL OF THE ELECTRICAL DOUBLE-LAYER

A three-component model of the electrical double layer is studied using a free energy density functional theory, which incorporates in an appropriate way the excluded volume effects and the electrostatic correlations. The new model differs from the primitive model in that the solvent is represented as a dense fluid of neutral hard spheres instead of as merely a dielectric continuum. The interfacial structure shows much richer features in the three-component electrolyte solution than either in the primitive electrolyte or in the pure hard sphere fluid. In particular we observe the coexistence of the particle layerings and the charge inversion. The electrical double layer in the three-component model is of comparatively shorter range and has a lower electrostatic potential difference across the interface than in the primitive model. The inclusion of the solvent also has large effects on the thermodynamic properties of the electrical double layer.