A Novel Approach to Designing a Biomimetic Wettable Patterned Surface for Highly Efficient and Continuous Surfactant-Free Oil Emulsion Separation

Abstract Emulsion separation has global environmental implications owing to the increasing generation of oily industrial wastewater and oil spill incidents. For most existing emulsion separation techniques, secondary treatments are required, such as using additional chemicals or high voltages for emulsion decomposition. Furthermore, the minimum diameter of separable oil droplets is limited, or the separation flux is low. Conventional methods are difficult to apply in practice owing to their low continuity, lack of separation ability, or limited throughput capacity. In this study, a wettability-patterned surface is designed to realize micron-sized oil droplet separation and high-purity oil collection (99.9%). The surface comprises a subaqueous superoleophobic region (interior space) and a subaqueous superoleophilic region (exterior rectangle), with a subaqueous superoleophilic drainage path. The surface outlet geometry was optimized according to Stokes’ law to enable quick delivery of the condensed oil film to the collector, thereby improving the practical oil collection efficiency. An underwater system with this patterned surface can be used to continuously separate oil–water emulsions. The proposed method is considered to be the world’s first surfactant-free emulsion-separation technique, and serves as a promising tool for isolating and collecting micron-sized oil droplets in real aquatic environments for reuse.