Real‐Time Monitoring and Quantification of Underwater Superhydrophobicity

Abstract Long‐lasting underwater superhydrophobicity involves stable‐in‐time air layer trapped and retained between a submersed surface and the overlying liquid. Due to its underwater nature, it is rather difficult to accurately observe this air layer in submerged systems, let alone to measure it. Here, white light reflectance spectroscopy is used for real‐time monitoring (acquisition speed 50–200 ms) of underwater superhydrophobicity as well as for the calculation of the entrapped air layer thickness on “everlasting” underwater polymeric superhydrophobic surfaces fabricated by plasma micro‐nanotexturing. The proposed method enables real‐time monitoring and accurate calculation of air layers with thicknesses ranging from a few nanometers to several tens of micrometers involving small underwater bubbles. In addition, different scale topographies of superhydrophobic plasma micro‐nanotextured surfaces are tested and found to retain underwater superhydrophobicity for at least 60 days. As a demonstration, the air layer thickness is also monitored in real time when titrating water with low surface tension liquids. Among several topographies tested, a superhydrophobic surface exhibiting hierarchical topography and a high roughness ratio is able to retain a stable air layer when submersed in liquids with surface tension down to 44 mN m −1 .