Recoverable Underwater Superhydrophobicity From a Fully Wetted State via Dynamic Air Spreading

Maintaining the superhydrophobicity underwater offers drag resistance reduction, antifouling, anti-corrosion, noise reduction and gas collection for boat hulls and submarine vehicles. However, superhydrophobicity typically do not last long underwater since the Cassie state is metastable; any significant pressure fluctuation, shear flow or temperature change will lead the non-reversible transition to the fully wetted state. Here, we report a reversible and localized recovery of the superhydrophobic surface from the fully wetted state via air bubble spreading. Comprised of sparse fluorinated chained nanoparticles, the submerged surface shows super-low energy barrier for bubble attachment. In particular, by analyzing the dynamic spreading of bubbles on a simplified, truncated nanocone model, we enumerate the general geometric criteria for bubble pinning and lateral spreading without vertical growth. Numerical simulation results via COMSOL confirms the effect of geometric structure on bubble spreading. This investigation will not only offer new insights for the design of robust recoverable superhydrophobic surfaces, but also broaden the applications of superhydrophobic coatings for underwater vehicles.