Droplet Growth Dynamics during Atmospheric Condensation on Nanopillar Surfaces


The Gibbs free energy barrier for heterogeneous nucleation of a condensed droplet on a rough surface changes significantly with changes of humidity content in the condensing environment. The influence of environmental factors (ambient temperature and relative humidity) and substrate characteristics (topology, surface chemistry, and substrate temperature) on atmospheric condensation phenomenon is very important to elucidate the condensed droplet wetting state and condensate harvesting applications. Condensation from the humid air has been reported for plain silicon and fabricated nanopillar surfaces to facilitate condensate harvesting. Droplet growth and size distributions were recorded for 90 min. Spherical droplets condensed on the silicon surfaces and irregular-shaped droplets were observed on the nanopillar surfaces due to the pinning effect of the pillars. The effect of droplet pinning on coalescence events has been described based on the energy balance for the condensed droplets. A mathematical model reveals that certain dimensional combinations (pillar pitch, pillar diameter, and pillar height) of the nanopillar geometry are required to exhibit the pinning mechanism for condensed droplets. Regeneration of droplets was observed at void spaces generated from coalescence events. The growth of individual droplets was tracked over multiple time and length scales, starting from nucleation to get further insight into the direct growth and coalescence mechanisms.

Abbreviation: ESEM: Environmental Scanning Electron Microscope; HCP: Hexagonal Closed-Packed; MPL: Microsphere Photolithography; RH: Relative Humidity.


Mechanical and Aerospace Engineering


This material is based upon work supported by the US National Science Foundation under Grant Nos. 1509589, 1604183, and 1653792. Division of Chemical, Bioengineering, Environmental, and Transport Systems [1509589, 1604183, and 1653792].

Keywords and Phrases

Atmospheric chemistry; Coalescence; Condensation; Drops; Free energy; Gibbs free energy; Nanostructures; Nucleation; Scanning electron microscopy; Substrates; Wetting; Condensation phenomenon; Droplet dynamics; Environmental scanning electron microscopes; Heterogeneous nucleation; NanoPillar; Pinning effects; Substrate characteristics; Temperature and relative humidity; Atmospheric humidity; Atmospheric condensation; Coalescence; Pinning effect

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Article - Journal

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