Contact Angles for Equilibrated Microemulsion Systems

Advanced and receded contact angles have been measured on various high- and low-energy substrates as functions of microemulsion-excess phase interfacial tensions (IFT’s). Many experimental difficulties peculiar to these low-tension systems caused large measurement errors. But with this constraint and with one exception, contact angles were hysteresis-free and independent of the substrate. For lower-phase microemulsions and high-energy substrates, it is proposed that the surfactant polar group adsorbs on the solid and then a surfactant bilayer forms. This bilayer provides the effective substrate that relates to contact angle and IFT’s through Young’s equation. An optimal salinity for contact angles is defined and related to previously introduced optimal salinities, in particular to that associated with best oil recovery. Results suggest the optimum attainable contact angles for microemulsion-based oil recovery may not be 0°.