STABILITY AND RECOVERABILITY OF LIQUID-GAS INTERFACES ON SUBMERGED HIERARCHICALLY STRUCTURED SURFACES

The liquid-gas interface formed by immersing the surfaces with microstructures underwater is of great importance for applications such as drag reduction and so on. The stable existence of the liquid-gas interface is a prerequisite for the function of microstructure function surfaces. Therefore, how to enhance the stability of the liquid-gas interface to resist the wetting transition process, and how to implement the de-wetting process to improve the recoverability of the liquid-gas interface after collapse, both have scientific research significance and practical application value, and have triggered extensive investigations at home and abroad. This work is dedicated to investigating the stability and recoverability of liquid-gas interfaces formed on hierarchically structured surfaces after immersion in water. Different kinds of hierarchically structured surfaces were firstly designed and fabricated in order to investigate the influence of the sublevel structures respectively on the sidewalls and the bottom on the stability and recoverability of the liquid-gas interface. Experiments using laser scanning confocal microscopy to in-situ investigate the collapse and recovery process of liquid-gas interfaces were then performed. Theoretical analysis based on minimizing the total free energy of the system was further completed with the aim to better understand the inner mechanism. The experimental results agreed well with the theoretical analysis. This work reveals the mechanism of hierarchically structured surfaces resisting wetting transition and improving liquid-gas interfaces recoverability: sublevel structures (nanoparticles, fins) on the sidewalls enhance the stability of the liquid-gas interface by increasing the apparent advancing contact angle; sublevel structures (nanoparticles and "closed'' sublevel structures) on the bottom surface are able to maintain the existence of nanoscale gas pockets, which is conducive to the diffusion of dissolved gas in the bulk water into the microstructure, and eventually helps the liquid-gas interface to recover. The research in this paper provides ideas for designing hierarchically structured surfaces to obtain liquid-gas interfaces with good stability and recoverability.