Unidirectional self-transport of air bubble via a Janus membrane in aqueous environment

Inspired by natural creatures, bubble manipulation by surface microstructures in aqueous media has attracted great attention due to its promising applications in industrial production. Herein, a superhydrophobic/hydrophilic Janus aluminum membrane with tapered micropore arrays was fabricated by femtosecond laser drilling, surface fluorination, and subsequent fluorination removal. Compared with the single interception or penetration of double-faced hydrophilic or superhydrophobic membranes, the Janus membrane showed a distinctive unidirectional air bubble transport ability. In experiment, the air bubbles introduced on the lower hydrophilic surface could spontaneously move to the upper superhydrophobic surface, but they were prevented in the inverse direction. The dynamic process of unidirectional transport was in-situ monitored, and the physical mechanism was systemically investigated. In addition, the concepts of air-participating chemical/physical processes were demonstrated such as discoloration of purple litmus solution by CO2 injection, which proved the Janus membrane practicability.