Adsorption equilibria in two-dimensional systems

Abstract

This paper describes first equilibrium studies of partitioning an insoluble surfactant (octadecanoic acid) between the gas—solution and solid—solution interfaces. A novel experimental approach is described in which a Wilhelmy plate is used to measure the film pressure of the insoluble organic monolayer spread at the gas—solution interface while simultaneously the film pressure of surfactants that spread from the gas—solution interface to the metal—solution interface of the electrode is monitored in situ by electrochemical means. Using as an example gold single-crystal electrodes, it is demonstrated that the equilibrium between the two-dimensional phases is strongly dependent not only on the electrode potential but also on the morphology of the solid electrode surface. The significance of these experiments for the choice of optimum conditions for transfer of insoluble monolayers from the gas solution onto the solid surface using the Langmuir—Blodgett technique is discussed.