水下多级微结构液气界面的稳定性和可恢复性研究

微结构表面浸没水下所形成的液气界面对减阻等应用具有重要意义.液气界面的稳定存在是结构功能表面发挥作用的前提. 因此,如何增强液气界面的稳定性以抵抗浸润转变过程, 以及在液气界面失稳之后,如何实现去浸润过程以提高液气界面的可恢复性能,均具有重要的科学研究意义和实际应用价值, 也是国内外研究关注的热点问题.本文针对具有多级微结构的固体表面,研究其在浸没水下后形成的液气界面的稳定性和可恢复性.通过激光扫描共聚焦显微镜对不同压强下液气界面的失稳过程和降压后的恢复过程进行原位观察,实验结果和基于最小自由能原理的理论分析相吻合.本文揭示了多级微结构抵抗浸润转变以及提高液气界面可恢复性能的机理:侧壁上的次级结构(纳米颗粒、多层翅片)通过增加液气界面在壁面的表观前进接触角增强了液气界面的稳定性;底面的次级结构(纳米颗粒和封闭式次级结构)可以维持纳米尺寸气核的存在,有利于水中溶解气体向微结构内扩散, 最终使液气界面恢复.本文的研究为通过设计多级微结构表面来获得具有较强稳定性和可恢复性的液气界面提供了思路. 

STABILITY AND RECOVERABILITY OF LIQUID-GAS INTERFACES ON SUBMERGED HIERARCHICALLY STRUCTURED SURFACES 1)

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.