Electrolytes at charged interfaces: Integral equation theory for 2–2 and 1–1 model electrolytes

Abstract

The structure and thermodynamics of both 2–2 and 1–1 model electrolytes at a charged interface have been determined. The solvent is modeled as a structureless dielectric continuum. The structure is calculated from the ‘‘singlet’’ version of the Ornstein–Zernike integral equation, using as input the structure of the bulk electrolyte from a recent integral equation theory. The approximation in the theory is the wall–ion bridge function, which is investigated for two levels of approximation. Surface thermodynamic quantities calculated from this structural information are compared with the classical Gouy–Chapman–Stern approximation for the interfacial region, computer simulations, and selected experimental data. Higher order structure predicted by the integral equations indicates that caution should be used when interpreting results of the classical approximation.