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Abstract In this work, we experimentally measured the pinch‐off of a gas bubble on a biphilic surface, which consisted of an inner circular superhydrophobic region and an outer hydrophilic region. The superhydrophobic region had a radius ofRSHvarying from 2.8 to 19.0 mm, where the largeRSHmodeled an infinitely large superhydrophobic surface. We found that during the pinch‐off, the contact line had two different behaviors: for smallRSH, the contact line was fixed at the boundary of superhydrophobic and hydrophilic regions, and the contact angle gradually increased; in contrast, for largeRSH, the contact angle was fixed, and the contact line shrank toward the bubble center. Furthermore, we found that regardless of bubble size and contact line behavior, the minimum neck radius collapsed onto a single curve after proper normalizations and followed a power–law relation where the exponent was close to that for bubble pinch‐off from a nozzle. The local surface shapes near the neck were self‐similar. Our results suggest that the surface wettability has a negligible impact on the dynamics of pinch‐off, which is primarily driven by liquid inertia. Our findings improve the fundamental understanding of bubble pinch‐off on complex surfaces.
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A Dynamically Responsive Surface with Switchable Wettability for Efficient Evaporation and Self-Cleaning Abilities
Evaporation is crucial in many applications. One of the critical parameters affecting evaporation is surface wettability, which is often tailored using coatings and micro- or nanoscale features on the surface. While this approach has advanced many technologies, the ability to control wettability dynamically can add new functionalities and capabilities that were not possible before. This study demonstrates how a self-cleaning superhydrophobic surface with an equilibrium contact angle of 155° can dynamically change to a superhydrophilic surface with a contact angle near 0°, resulting in drastically different evaporation characteristics. Specifically, we find that the evaporation rate and surface temperature reduction due to the resulting cooling are 3 times higher due to the change in surface wettability. This change in wetting behavior is due to the use of an amino-silane [N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane]-functionalized surface, which is altered in the presence of dilute acetic acid. Upon complete evaporation, the surface reverts to superhydrophobic behavior. This reversible behavior is not seen in traditional nonwetting coatings like perfluorodecyltrichlorosilane and lauric acid. This strategy for dynamic control of wettability and evaporation can lead to advancements in many applications ranging from self-assembly-based fabrication processes to oil–water separation and advanced thermal management technologies.
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- Award ID(s):
- 1944323
- PAR ID:
- 10383434
- Date Published:
- Journal Name:
- ACS Applied Engineering Materials
- ISSN:
- 2771-9545
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsaenm.2c00097
