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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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This content will become publicly available on June 1, 2026
Effect of Surfactant on Bubble Formation on Superhydrophobic Surface in Quasi-Static Regime
We experimentally studied the effect of a surfactant on bubble formation on a superhydrophobic surface (SHS). The bubble was created by injecting gas through an orifice on the SHS at a constant flow rate in the quasi-static regime. The surfactant, 1-pentanol, was mixed with water at concentration C ranging from 0 to 0.08 mol/L, corresponding to surface tension σ ranging from 72 to 43 mN/m. We found that as C increased, the bubble detachment volume (Vd) and maximum bubble base radius (Rdmax) decreased. For a low surfactant concentration, the static contact angle θ0 remained nearly constant, and Vd and Rdmax decreased due to lower surface tensions, following the scaling laws Rdmax~σ1/2 and Vd~σ3/2. The bubble shapes at different concentrations were self-similar. The bubble height, bubble base radius, radius at the bubble apex, and neck radius all scaled with the capillary length. For high surfactant concentrations, however, θ0 was greatly reduced, and Vd and Rdmax decreased due to the combined effects of reduced θ0 and smaller σ. Lastly, we found that the surfactant had a negligible impact on the forces acting on the bubble, except for reducing their magnitudes, and had little effect on the dynamics of bubble pinch-off, except for reducing the time and length scales. Overall, our results provide a better understanding of bubble formation on complex surfaces in complex liquids.
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- PAR ID:
- 10648917
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Biomimetics
- Volume:
- 10
- Issue:
- 6
- ISSN:
- 2313-7673
- Page Range / eLocation ID:
- 382
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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