Abstract
It was recently discovered that condensation growing on a nanostructured superhydrophobic surface can spontaneously jump off the surface, triggered by naturally occurring coalescence events. Many reports have observed that droplets must grow to a size of order 10 μm before jumping is enabled upon coalescence; however, it remains unknown how the critical jumping size relates to the topography of the underlying nanostructure. Here, we characterize the dynamic behavior of condensation growing on six different superhydrophobic nanostructures, where the topography of the nanopillars was systematically varied. The critical jumping diameter was observed to be highly dependent upon the height, diameter, and pitch of the nanopillars: tall and slender nanopillars promoted 2 μm jumping droplets, whereas short and stout nanopillars increased the critical size to over 20 μm. The topology of each surface is successfully correlated to the critical jumping diameter by constructing an energetic model that predicts how large a nucleating embryo needs to grow before it can inflate into the air with an apparent contact angle large enough for jumping. By extending our model to consider any possible surface, it is revealed that properly designed nanostructures should enable nanometric jumping droplets, which would further enhance jumping-droplet condensers for heat transfer, antifogging, and antifrosting applications.
Original language | English |
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Pages (from-to) | 8499-8510 |
Number of pages | 12 |
Journal | ACS Nano |
Volume | 11 |
Issue number | 8 |
DOIs | |
State | Published - Aug 22 2017 |
Funding
A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. We thank Ryan Enright and Saurabh Nath for fruitful discussions, and Josh Vieitez for technical assistance. We also acknowledge startup funds from the Department of Biomedical Engineering and Mechanics at Virginia Tech.
Keywords
- coalescence
- condensation
- critical jumping size
- jumping droplets
- optimizing nanostructure design
- superhydrophobic