Three-Dimensional Inverse Opal TiO₂ Coatings to Enable the Gliding of Viscous Oils

As a result of the increasing emphasis on accessing unconventional deposits of heavy oil and bitumen to meet global energy needs, there is an intense focus on addressing the rheological challenges involved in the transportation, handling, and processing of viscous hydrocarbons. While the design of superhydrophobic surfaces has been extensively explored, the fabrication of surfaces nonwetted by low-surface-tension and high-viscosity oils that can be scaled to meet industrial needs remains to be adequately addressed. Here, we demonstrate that colloidally templated architectures of TiO₂ particles applicable through a facile spray deposition process can form 3D inverse opal coatings adhered to low-alloy steels. Low-temperature sintering induces necking of particles, giving rise to an interconnected framework of plastrons surrounded by necked TiO₂ ligaments. Surface functionalization with 1H,1H,2H,2H-perfluorooctanephosphonic acid yields a helical surface monolayer with pendant trifluoromethyl moieties. The combination of interconnected plastrons, re-entrant curvature, and low surface energy suspends liquid droplets, of both water and heavy oil, in the Cassie–Baxter regime, yielding contact angles of 164° ± 5° and 161° ± 2°, respectively. The interconnected network of plastrons further enables the facile gliding of heavy oil (<100 s) upon immersion within a bath, whereas a comparable untreated surface remains completely fouled. The performance of this coating suggests a promising solution to mitigate the challenges of handling viscous oils in midstream applications and furthermore delineates a route to designing coatings for a broad host of rheologically challenging fluids.