Dissociation of fatty acid and counterion binding at the langmuir monolayer deposition: Theoretical considerations

The influence of electrical interactions on the composition of Langmuir fil ms is theoretically studied. The overlapping electric double layers in the region close to the three-phase contact line are described on the basis of the Poisson-Boltzmann equation, taking into account the dissociation of fat ty acids and the counterion binding to the surface film. It is concluded th at the composition of the monolayer changes insignificantly during the depo sition at the considered equilibrium constants and ionic concentrations in the solution. The results of the theory are used to discuss instability mec hanisms during the Langmuir wetting process.