Trapped Air-Induced Reversible Transition between Underwater Superaerophilicity and Superaerophobicity on the Femtosecond Laser-Ablated Superhydrophobic PTFE Surfaces

Controlling the behavior of underwater bubbles on a solid surface and establishing the contact model between a gas bubble and a solid substrate in a water medium have great significance. Herein, a method is proposed to realize the reversible switching between underwater superaerophilicity and superaerophobicity on the femtosecond laser-induced rough polytetrafluoroethylene (PTFE) surface by controlling the trapped air layer in water. The original femtosecond laser-structured PTFE surface is superhydrophobic in air and superaerophilic in water. After vacuum-pumping treatment, the trapped air layer around the microstructures of the underwater superhydrophobic PTFE surface is removed, leading to the underwater superaerophobicity of the sample surface. The trapped air layer can be recovered and the PTFE surface can regain the underwater superaerophilicity by drying treatment and the immersion of the sample in water again. Such a round-trip transition can achieve the bubble's “locating capture” and the control of the selective passage of air bubbles through a perforated rough PTFE sheet. It is believed that the resultant underwater superaerophobic and superaerophilic surfaces will have significant applications in manufacturing submarine gas-collection devices, improving the chemical reaction between liquid reagent and gas, and avoiding the microchannel blockage caused by bubbles in microfluidics and biosensor devices.