Underwater Superaerophobicity/Superaerophilicity and Unidirectional Bubble Passage Based on the Femtosecond Laser-Structured Stainless Steel Mesh

To control the behavior of underwater bubbles, stainless steel meshes are treated through femtosecond laser processing, and the bubble absorption, bubble interception, and unidirectional bubble passage are realized by using structured meshes. The surface of the mesh presents a micro–sub-micro–nano trinary-scale structure (microscale mesh wires, sub-microripples, and nanoparticles) after one-step laser ablation on both sides. The surface shows superhydrophilic in air and superaerophobic once immersed in water. After further modified with fluoroalkylsilane, the wettability of the sample surface is switched to be superaerophilic in water with bubble being absorbed by the sample. When a plenty of underwater bubbles arrive at the structured stainless steel mesh surface, they can be blocked by the underwater superaerophobic mesh but pass through the underwater superaerophilic mesh. In addition, after the mesh being treated only one side and further modified, it is to be Janus mesh and presents asymmetrical wettability of aerophilicity/superaerophilicity. The Janus mesh shows the unidirectional passage of underwater bubbles. Bubbles can only penetrate from aerophilic side to superaerophilic side, but be blocked from the other direction. The mesh is verified to be used to eliminate the stuck bubbles in the container.