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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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Bubble pinch-off in turbulence
Although bubble pinch-off is an archetype of a dynamical system evolving toward a singularity, it has always been described in idealized theoretical and experimental conditions. Here, we consider bubble pinch-off in a turbulent flow representative of natural conditions in the presence of strong and random perturbations, combining laboratory experiments, numerical simulations, and theoretical modeling. We show that the turbulence sets the initial conditions for pinch-off, namely the initial bubble shape and flow field, but after the pinch-off starts, the turbulent time at the neck scale becomes much slower than the pinching dynamics: The turbulence freezes. We show that the average neck size, d ¯ , can be described by d ¯ ∼ ( t − t 0 ) α , where t 0 is the pinch-off or singularity time and α ≈ 0.5 , in close agreement with the axisymmetric theory with no initial flow. While frozen, the turbulence can influence the pinch-off through the initial conditions. Neck shape oscillations described by a quasi–2-dimensional (quasi-2D) linear perturbation model are observed as are persistent eccentricities of the neck, which are related to the complex flow field induced by the deformed bubble shape. When turbulent stresses are less able to be counteracted by surface tension, a 3-dimensional (3D) kink-like structure develops in the neck, causing d ¯ to escape its self-similar decrease. We identify the geometric controlling parameter that governs the appearance of these kink-like interfacial structures, which drive the collapse out of the self-similar route, governing both the likelihood of escaping the self-similar process and the time and length scale at which it occurs.
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- Award ID(s):
- 1844932
- PAR ID:
- 10145520
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 116
- Issue:
- 51
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- 25412 to 25417
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.1909842116
