(563a) Molecular Theory of Associated Electrolyte Solutions

Abstract: Association of ions in electrolyte solutions is a general concern for molecular-scale theory and modeling of these systems. Currently, available theories, which incorporate ion association, are complicated and have not yet permitted direct application at atomic resolution. This work describes a distinct alternative to the available theories, quasi-chemical theory, which should be simple enough to permit application fully at atomic scale. We test this theoretical approach by application to a primitive model physically suggested by recent work on tetra-ethylammonium tetra-fluoroborate (propylene carbonate) solutions of electrochemical double-layer capacitors. This is system for which ion-association is a primary interest. The primitive model permits short-distance cation-anion pairs and in this encourages ion association. We leave aside the issue of the adequacy of the primitive model but focus on a demonstration and validation of the theory in a simple context. Ion-pairing in the cases of the primitive model is tested against the historically-important Fuoss approximation.