Adsorption kinetics of the partially dissociated ionic surfactants: The effect of degree of dissociation

Abstract

Abstract The effect of the degree of dissociation on the adsorption kinetics of partially dissociated ionic surfactants was examined theoretically. The equilibrium and dynamic surface tension (ST) curves with different degrees of dissociation were theoretically generated for surfactants following the Langmuir adsorption isotherm. Two cases were examined. In the first case, it was examined what mistake would be obtained if a non-ionic model or an ionic model was simply used to describe the equilibrium and dynamic simulated ST data of a partially dissociated surfactant. The second case considered the mistake when a non-ionic model was used on an ionic surfactant. The results of this study show that either the ionic or nonionic model can provide a reasonably good description of the equilibrium/dynamic ST curves of a partially dissociated ionic surfactant. When a non-ionic model was applied to describe an ionic surfactant, a reasonably good fitting was also obtained for the equilibrium and dynamic ST data. However, a significant deviation of the model parameters and surfactant diffusivity was obtained. The results in this study indicate that it is difficult to detect an improper choice of the degree of dissociation from the quality of fitting of the equilibrium and dynamic ST data.