ELECTROKINETIC TRANSPORT-COEFFICIENTS FOR CONFINED ELECTROLYTES - IONIC CONCENTRATION EFFECT

The electrolyte concentration dependence of the electrokinetic Onsager coefficients, L(mn), that determine the transport properties of an ionic solution inside a very narrow charged slit is studied. The coefficients' dependence on the slit's width and zeta potential is also studied. Calculations were made for 2:2 and 1:1 electrolytes. The Onsager coefficients obtained for the restricted primitive model (RPM), calculated through the TPE-HNC/MSA integral equation theory, are compared to those calculated through the slit version of the classical modified Gouy-Chapman (MGC) theory for point ions. It is found that for 1:1 electrolytes, with large micropores and very low potentials, the MGC is adequate; for ultranarrow slits and/or walls's high potentials the classical theory fails to describe the nonlinear behavior predicted by the TPE-HNC/MSA theory, particularly at high salt concentrations. The presence of doubly charged ions enhances the differences and make the MGC theory inappropriate both qualitatively and quantitatively.