Ionic solution near an uncharged surface with image forces

Abstract

We studied the ion density in a dilute electrolyte solution which is next to an uncharged surface at which there is a discontinuity in the dielectric constant. In particular, we treated the restricted primitive model of a 1–1 aqueous solution next to a pure phase of unit dielectric constant. This served as a primitive model of the interface between an electrolytic solution and the air. Monte Carlo data are presented: the image forces are included and treated exactly. The model was also treated using the Born–Green–Yvon (BGY) integral equation approach; a modification of BGY theory which ensures electroneutrality is in very good agreement with the Monte Carlo data. The use of a "screened self-image" approximation to the potential energy has been tested using Monte Carlo computation and is found to be inadequate for the present model. Hypernetted-chain equation results using this approximation are also reported.