Journal
LANGMUIR
Volume 27, Issue 12, Pages 7502-7509Publisher
AMER CHEMICAL SOC
DOI: 10.1021/la201587u
Keywords
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Funding
- Defense Advanced Research Projects Agency [N66001-10-1-4048]
- Oak Ridge Associated Universities
- North Carolina Space Grant New Investigators Program
- Duke University
- National Science Foundation [0754963]
- Directorate For Engineering
- Div Of Engineering Education and Centers [0754963] Funding Source: National Science Foundation
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Many natural superhydrophobic structures have hierarchical two-tier roughness which is empirically known to promote robust superhydrophobicity. We report the wetting and dewetting properties of two-tier roughness as a function of the wettability of the working fluid, where the surface tension of water/ethanol drops is tuned by the mixing ratio, and compare the results to one-tier roughness. When the ethanol concentration of deposited drops is gradually increased on one-tier control samples, the impalement of the microtier-only surface occurs at a lower ethanol concentration compared to the nanotier-only surface. The corresponding two-tier surface exhibits a two-stage wetting transition, first for the impalement of the microscale texture and then for the nanoscale one. The impaled drops are subsequently subjected to vibration-induced dewetting. Drops impaling one-tier surfaces could not be dewetted; neither could drops impaling both tiers of the two-tier roughness. However, on the two-tier surface, drops impaling only the microscale roughness exhibited a full dewetting transition upon vibration. Our work suggests that two-tier roughness is essential for preventing catastrophic, hydrophobic surfaces.
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