Crude oil/water nanoemulsions stabilized by rhamnolipid biosurfactant: Effects of acidity/basicity and salinity on emulsion characteristics, stability, and demulsification

The superiority of nanoemulsions over the traditional emulsions makes the former more attractive for various industrial applications. In this study, crude oil-in-water (O/W) nanoemulsions have been formulated and stabilized using rhamnolipid biosurfactant under various pH and salinity levels. The results revealed that rhamnolipid-stabilized O/W nanoemulsions possess very attractive characteristics with as low as 38 nm average droplet size under highly alkaline condition (i.e., pH 12). The nanoemulsions also displayed low interfacial tension, high negative zeta potential, and long-term kinetic stability (0% oil separation). Additionally, although the viscosity of the formulated crude O/W nanoemulsions increased with increasing the pH and salinity level, it remained low (below 4.2 mPa.s) relative to the crude oil viscosity. Increasing the nanoemulsion temperature caused a significant viscosity reduction. Additional important observation is the ability to fully breakdown the nanoemulsions within a period of ≤ 1 h using a simple and cheap approach, despite their extreme stability.