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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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Dynamics of bubble formation on superhydrophobic surface under a constant gas flow rate at quasi-static regime
In this work, we experimentally studied bubble formation on the superhydrophobic surface (SHS) under a constant gas flow rate and at quasi-static regime. SHS with a radius RSHS ranging from 4.2 to 19.0 mm was used. We observed two bubbling modes A and B, depending on RSHS. In mode A for small RSHS, contact line fixed at the rim of SHS, and contact angle (θ) initially reduced, then maintained as a constant, and finally increased. In mode B for large RSHS, contact line continuously expanded, and θ slowly reduced. For both modes, during necking, contact line retracts, and θ was close to the equilibrium contact angle. Moreover, the pinch-off of bubble at the early stage was similar to the pinch-off of bubble from a nozzle and followed a power-law relation Rneck ∼ τ0.54, where Rneck is the minimum neck radius and τ is the time to detaching. Furthermore, we calculated the forces acting on the bubble and found a balance between one lifting force (pressure force) and two retaining forces (surface tension force and buoyancy force). Last, we found a waiting time for a finite volume to be detected for large RSHS. The detached volume was well predicted by Tate volume, which was derived based on balance between buoyancy and surface tension and was a function of bubble base radius.
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- PAR ID:
- 10557204
- Publisher / Repository:
- AIP Publishing
- Date Published:
- Journal Name:
- Physics of Fluids
- Volume:
- 36
- Issue:
- 8
- ISSN:
- 1070-6631
- 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/10.1063/5.0219321
