MEAN-FIELD POTENTIAL FOR HETEROGENEOUS ELECTRICAL DOUBLE-LAYERS, WITHAPPLICATION TO THE SURFACE PRESSURE OF CHARGED MONOLAYERS

In this paper expressions are derived for the electrostatic mean-field potential at a nonuniformly charged interface. Within the Gouy-Chapma nn model of electrical double layers two levels of approximation are c ompared. In the first scheme, solution of the linearized Poisson-Boltz mann equation gives a generalization of the familiar Debye-Huckel form ula. In the second, semi-nonlinear approach, the leading order term wh ich describes the case of a uniform surface charge is retained at the nonlinear level of theory, while higher-order contributions associated with the charge heterogeneity are treated perturbatively, each term b eing governed by a linear differential equation having an explicit sol ution. As an application of the model, systems of charged heterogeneou s monolayers at the air/water interface are considered. An analytic fo rmula for the electrostatic contribution to the surface pressure of a heterogeneous film is given. (C) 1995 Academic Press, Inc.