title: Evaporation of droplets on superhydrophobic surfaces: surface roughness and small droplet size effects.
abstract: Evaporation of a sessile droplet is a complex, nonequilibrium phenomenon. Although evaporating droplets upon superhydrophobic surfaces have been known to exhibit distinctive evaporation modes such as a constant contact line (CCL), a constant contact angle (CCA), or both, our fundamental understanding of the effects of surface roughness on the wetting transition remains elusive. We show that the onset time for the CCL-CCA transition and the critical base size at the Cassie-Wenzel transition exhibit remarkable dependence on the surface roughness. Through global interfacial energy analysis we reveal that, when the size of the evaporating droplet becomes comparable to the surface roughness, the line tension at the triple line becomes important in the prediction of the critical base size. Last, we show that both the CCL evaporation mode and the Cassie-Wenzel transition can be effectively inhibited by engineering a surface with hierarchical roughness.
authors.affiliation: Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Chen
authors.forename: Ruiyuan
authors.initials: R
authors.lastname: Ma
authors.forename: Jintao
authors.initials: J
authors.lastname: Li
authors.forename: Chonglei
authors.initials: C
authors.lastname: Hao
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.forename: B L
authors.initials: BL
authors.lastname: Luk
authors.forename: Shuai Cheng
authors.initials: SC
authors.lastname: Li
authors.forename: Shuhuai
authors.initials: S
authors.lastname: Yao
authors.forename: Zuankai
authors.initials: Z
authors.lastname: Wang
mesh_terms: D057927:Hydrophobic and Hydrophilic Interactions; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D012825:Silicon / Q000737:chemistry*; D013500:Surface Tension; D013816:Thermodynamics; D014835:Volatilization; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D012825:Silicon