Substrate-independent, switchable bubble wettability surfaces induced by ultrasonic treatment.

Surfaces with switchable bubble wettability have attracted increasing interest due to their wide applications in the field of underwater drag reduction, gas collection and site water treatment. In this paper, a fast, simple and substrate-independent method that achieved reversible switching between underwater superaerophilicity and superaerophobicity on femtosecond laser induced superhydrophobic surfaces by alternative ultrasonic treatment in water and drying in air was reported. After laser processing, the as-prepared superhydrophobic surface showed underwater superaerophilicity due to the trapped air layer. In contrast, after ultrasonic treatment, the trapped air layer was removed and after being dipped into water again, the surfaces showed underwater superaerophobicity. The underwater superaerophobic surface easily recovered its superaerophilicity by drying the sample in air. Therefore, the as-prepared superhydrophobic surfaces could capture or repel air bubbles in water by selectively switching between underwater superaerophilicity and superaerophobicity. Furthermore, by combining hole processing and double side treatment, the sample allowed bubbles to pass through when the surface had underwater superaerophilicity and the sample intercepted the bubbles when the surface had underwater superaerophobicity. This switchable bubble wettability may provide an efficient route for gas bubble and water separation.