Is superhydrophobicity equal to underwater superoleophilicity? Hydrophilic wetting defects on a superhydrophobic matrix with switchable superdewetting in both air and water

Notoriously, a superhydrophobic surface always shows underwater superoleophilic behaviour in aqueous environments. However, a question remains unanswered: is superhydrophobicity equal to underwater superoleophilicity? Gaps of understanding still exist between such two extreme wetting states. Herein, beyond the thermodynamic contradiction, a well-defined porous coating integrating a simultaneous in-air superhydrophobic and underwater superoleophobic state can be realized via the rational incorporation of hydrophilic microscale defects on a superhydrophobic matrix. In contrast, a predictable underwater superoleophilic state is observed on the pristine superhydrophobic surface with completely hydrophobic surface chemistry. We underline how the hydrophilic defects regulate the underwater oil wetting and in-air water repellence simultaneously, and the superhydrophobic surface is not simply equal to the underwater superoleophilic surface. On the basis of understanding the underlying mechanism, the separation of light oil-water mixtures and surfactant-stabilized oil-in-water emulsions can be achieved using the defective superhydrophobic surface. Such findings could shed light on understanding repellence/penetration behaviours at a three phase contact line and accelerating the realization of opposite wetting states without any external stimulus.