Interfacial dynamics of oil on underwater oleophobic surfaces: From fundamental wetting to functional advanced design for oil/water separation.

The efficient separation of oil/water mixtures is a critical technological challenge in environmental remediation, industrial wastewater treatment, and sustainable resource management. In recent years, underwater superhydrophilic and superoleophobic materials have emerged as powerful platforms for high-performance separation membranes. Despite rapid progress, current research largely relies on static wettability descriptors, whereas the dynamic interfacial behavior of oil droplets on hydrated surfaces remains insufficiently understood. This review establishes a unified framework that connects interfacial oil dynamics with the rational design of underwater superhydrophilic interfaces. Fundamental wetting principles governing oil-water-solid interactions are first revisited, highlighting the thermodynamic and molecular origins of hydration-layer stability and oil repellency. The analysis then elucidates how surface chemistry, hierarchical morphology, surfactant interactions, and intrinsic oil properties collectively govern droplet deformation, spreading, adhesion, and detachment under realistic operating conditions. Particular emphasis is placed on dynamic antifouling mechanisms, including hydration lubrication, shear-assisted droplet removal, and rapid rehydration that enables efficient flux recovery. Emerging material strategies, including hydration-dominant chemistries, hierarchical micro-nano architectures, and mechanically robust composite systems are further discussed as key routes toward durable separation interfaces. By reframing underwater oleophobicity as a dynamic and metastable interfacial state rather than a static wetting property, this review provides mechanistic insights and design principles for engineering adaptive materials capable of sustaining high flux, strong antifouling performance, and long-term operational stability in complex environments.