Femtosecond laser induced underwater superaerophilic and superaerophobic PDMS sheets with through microholes for selective passage of air bubbles and further collection of underwater gas

Controlling underwater bubble behavior on a solid surface is of great research significance, particularly in extreme cases. However, the realization of artificial underwater superaerophobic or superaerophilic surfaces is still a challenge. Herein, a micro/nanoscale hierarchical rough structure was formed on polydimethylsiloxane (PDMS) surface by one-step femtosecond laser ablation. The as-prepared surface showed superhydrophobicity in air and superaerophilicity in water. Interestingly, the wettability of such a PDMS surface could be easily switched to in-air superhydrophilicity and underwater superaerophobicity once it was further irradiated by oxygen plasma because the surface chemistry changed. The original femtosecond laser-structured underwater superaerophilic PDMS surface could absorb/capture bubbles, while the plasma-treated underwater superaerophobic surface had excellent anti-bubble ability in water. A rough through-microhole-array PDMS sheet was prepared by a mechanical drilling process and subsequent femtosecond laser ablation. The sheet could selectively allow bubbles to pass, that is, the porous underwater superaerophilic sheet allowed bubbles to pass through, while the porous underwater superaerophobic sheet was able to intercept bubbles in a water medium. Using the porous underwater superaerophilic PDMS sheet as the core component, a device that has great ability of collecting underwater bubbles/gas was also designed.