Multiscale dynamic wetting of a droplet on a lyophilic pillar-arrayed surface

• Published in: Journal of fluid mechanics Vol. 716; pp. 171 - 188
• Main Authors: Yuan, Quanzi, Zhao, Ya-Pu
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.02.2013
• Subjects: Applied fluid mechanics; Condensed matter: structure, mechanical and thermal properties; Density; Drop size distribution; Droplets; Dynamics; Exact sciences and technology; Flow pattern; Fluid dynamics; Fluid mechanics; Fluidics; Fundamental areas of phenomenology (including applications); Hydrophilic surfaces; Molecular dynamics; Physics; Pillars; Roughness; Simulation; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Wetting; micro-/nano-fluid dynamics; drops; contact lines; Wetting; Multiscale method; Digital simulation; Drops; Modelling; Nanofluidics; Nanostructures; Microstructure; Cylinder set; Microfluidics; Contact line
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2012.539

Dynamic wetting of a droplet on lyophilic pillars was explored using a multiscale combination method of experiments and molecular dynamics simulations. The excess lyophilic area not only provided excess driving force, but also pinned the liquid around the pillars, which kept the moving contact line in a dynamic balance state every period of the pillars. The flow pattern and the flow field of the droplet on the pillar-arrayed surface, influenced by the concerted effect of the liquid–solid interactions and the surface roughness, were revealed from the continuum to the atomic level. Then, the scaling analysis was carried out employing molecular kinetic theory. Controlled by the droplet size, the density of roughness and the pillar height, two extreme regimes were distinguished, i.e. $R\sim {t}^{1/ 3} $ for the rough surface and $R\sim {t}^{1/ 7} $ for the smooth surface. The scaling laws were validated by both the experiments and the simulations. Our results may help in understanding the dynamic wetting of a droplet on a pillar-arrayed lyophilic substrate and assisting the future design of pillar-arrayed lyophilic surfaces in practical applications.