Effect of surfactant dispersed in oil on interaction force between an oil film and a steel substrate in water

The oil phase, in an oil-in-water emulsion on a steel substrate, is strongly repelled by the substrate. The oil in this situation does not wet the steel and steel/steel friction is high. In this work we disperse anionic surfactants in an oil film and study the effect of this dispersion on the force of interaction between a silica colloid probe (AFM) carrying the oil film and a steel substrate in water. It is observed that when the surfactant is oil insoluble and the interaction time is short the strong entropic repulsion (without the surfactant) is replaced by a strong attraction. The steel on steel sliding friction in this case is low compared to that what is achieved when the surfactant is soluble in oil. The rationale underlying these interactions is explored here.

. Repulsive interaction force between oil droplet and the substrate can be modulated to an attractive one. Nature of interaction is controlled by diffusion of surfactant from oil-to-water-to-substrate and capillary formation.Figure optionsDownload as PowerPoint slideResearch highlights
► Forces between oil droplet and steel surface in water medium are identified.
► The identified forces are modulated by selection and dispersion of surfactant.
► Capillary force activates when surface is wettable by oil.
► Disjoining of water film by oil droplet controls the lubricity of o/w emulation.
► Conclusions are of relevance to the field of lubrication by two phase liquids.