Equilibrium thickness of foam films and adsorption of ions at surfaces: Water and aqueous solutions of sodium chloride, hydrochloric acid, and sodium hydroxide.

Application of a modified Poisson-Boltzmann equation to the equilibrium film thickness gave the diffuse layer potential and the surface density of ions in the Stern layer. From the concentration dependence of the surface density, it was concluded that not only OH ions but also Cl ions and HCO and/or CO ions adsorb specifically at the water/air interface.