Localization of clay particles at the oil–water interface in the presence of surfactants

In this study, the interfacial localization of natural and organically modified clay in a model emulsion (single droplet) is investigated under the influence of additionally added surfactants. In order to control the surfactant adsorbing to the interface, the surfactants are supplied either before or after the generation of an oil droplet stabilized with clay. If the surfactant is present before drop generation or a drop is generated under the presence of surfactant, the interfacial tension is reduced as much as it enhances the detachment of droplet, while clay is enhanced to desorb. On the other hand, the surfactant enhances the interfacial localization of the clay if the surfactant is supplied after drop generation and clay adsorption. The surfactant tends to destroy or build up the formation of natural clay interface since the surfactant changes the balanced wetting property of the clay and enhances desorption of clay. The surfactant has a strong attraction with the clay; it rather promotes the formation of complex interfaces than desorbs the clay. Enhanced localization of clay with surfactant increases interfacial modulus due to the increased concentration of clay at the interface. Without strong chemical attraction between clay and surfactant, interfacial modulus is rather decreased due to desorption of interfacial localized clay. It suggests that the combined addition of clay and surfactant stabilizes the emulsion only with strong interaction between clay and surfactant.