Boundary Effects in the One-Dimensional Coulomb Gas

We use the functional integral technique of Edwards and Lenard to solve the statistical mechanics of a one-dimensional Coulomb gas with boundary interactions leading to surface charging. The theory examined is a one-dimensional model for a soap film. Finite-size effects and the phenomenon of charge regulation are studied. We also discuss the disjoining pressure for such a film. Even in the absence of boundary potentials we find that the presence of a surface affects the physics in finite systems. In general we find that in the presence of a boundary potential the long-distance disjoining pressure is positive, but may become negative at closer interplane separations. This is in accordance with the attractive forces seen at close separations in colloidal and soap film experiments and with three dimensional calculations beyond mean field. Finally, our exact results are compared with the predictions of the corresponding Poisson–Boltzmann theory which is often used in the context of colloidal and thin liquid film systems.