title: Symmetric and asymmetric meniscus collapse in wetting transition on submerged structured surfaces.
abstract: The wetting transition from the Cassie-Baxter to the Wenzel state is a phenomenon critically pertinent to the functionality of microstructured superhydrophobic surfaces. This work focuses on the last stage of the transition, when the liquid-gas interface touches the bottom of the microstructure, which is also known as the "collapse" phenomenon. The process was examined in situ on a submerged surface patterned with cylindrical micropores using confocal microscopy. Both symmetric and asymmetric collapses were observed. The latter significantly shortens the progression of the metastable state prior to the collapse when compared with the former and hence may affect the lifespan of superhydrophobicity. Further experiments identified that asymmetric collapse were induced by impurities due to prior use of the structure. The problem is thus of broad relevance, since endurance through cycles is a practical requirement for these functional surfaces. Finally, the use of hierarchical structures is proposed as a remedy. The embedded self-cleaning mechanism serves to effectively remove the impurities, so as to avoid the triggering mechanism for asymmetric collapses.
authors.affiliation: State Key Laboratory for Turbulence and Complex System, Department of Mechanics and Engineering Science, CAPT, IFSA Collaborative Innovation Center of MoE, College of Engineering and ‡Department of Biomedical Engineering, College of Engineering, Peking University , Beijing 100871, China.
authors.forename: Pengyu
authors.initials: P
authors.lastname: Lv
authors.forename: Yahui
authors.initials: Y
authors.lastname: Xue
authors.forename: Hao
authors.initials: H
authors.lastname: Liu
authors.forename: Yipeng
authors.initials: Y
authors.lastname: Shi
authors.forename: Peng
authors.initials: P
authors.lastname: Xi
authors.forename: Hao
authors.initials: H
authors.lastname: Lin
authors.forename: Huiling
authors.initials: H
authors.lastname: Duan
mesh_terms: D057927:Hydrophobic and Hydrophilic Interactions; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D013499:Surface Properties; D017155:Wettability