Femtosecond laser structuring of Janus foam: Water spontaneous antigravity unidirectional penetration and pumping

Abstract

In this letter, we report a Janus foam that is fabricated by the femtosecond laser structuring of copper foam. Each side of the Janus foam possesses different wettabilities: one is superhydrophilic while the other is hydrophobic. On the Janus foam, water can spontaneously antigravity transport from the lower hydrophobic side to the upper superhydrophilic side without an input of external energy, but cannot pass through in the opposite direction. The Janus foam can be considered to have “water diode” characteristics, and it enables the continuous antigravity transport of water without requiring any external forces. The Janus foam is then used to design a “water pump”. These findings will aid the design and development of fluid delivery technologies.