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Air bubbles at the surface of water end their life in a particular way: when bursting, they may eject drops of liquid in the surrounding environment. Many uncertainties remain regarding collective effects of bubbles at the water–air interface, despite extensive efforts to describe the bursting mechanisms, motivated by their critical importance in mass transfers between the ocean and the atmosphere in the production of sea spray aerosols. We investigate the effect of surfactant on the collective dynamics and statistics of air bubbles evolving freely at the surface of water, through an experimental set-up controlling the bulk distribution of bubbles with nearly monodisperse millimetric air bubbles. We observe that for low contamination, bubble coalescence is inevitable and leads to a broad surface size distribution. For higher surfactant concentrations, coalescence at the surface is prevented and bubble lifetime is increased, leading to the formation of rafts with a surface size distribution identical to the bulk distribution. This shows that surface contamination has a first-order influence on the transfer function from bulk size distribution to surface size distribution, an intermediate step which needs to be considered when developing sea spray source function as droplet production by bubble bursting depends on the bubble size. We measure the bursting and merging rates of bubbles as a function of contamination through a complementary freely decaying raft experiment. We propose a cellular automaton model that includes the minimal ingredients to reproduce the experimental results in the statistically stationary configuration: production, coalescence and bursting after a finite lifetime.
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Acoustically Excited Micro Mass Transport for Remotely Dose-Controlable Drug Releasing
Remotely activated drug release strategy with controllable dosage is the key factor of various targeting drug delivery methods as minimal invasive treatment. This article describes mass transport in liquid in microscale with a controllability of releasing amount, which is wirelessly excited by an external acoustic excitation. A liquid droplet (releasing agent, or drug in application) is trapped in the middle of a one-end open microtube which has a ratchet-structure on its inner wall. The droplet is trapped in the tube and neighbored by two gaseous air bubbles on both sides. In the presence of acoustic wave, the air bubbles oscillate and resonate. The air bubble near the tube opening segregates the liquid droplet into smaller ones and transport them on the ratchet-surface wall of the microtube. This mass transport occurs in both directions at similar rates: from the surrounding fluid to the trapped droplet and vice versa. As a result, the overall mass of droplet remains similar. Meanwhile, the other bubble positioned back in the tube sealing side enhances mixing between incoming mass from the surrounding and existing mass in the droplet. This mass transport is significant only when the inner wall of the tube has rachets. The exchanging mass between the surrounding and droplet is monotonically proportional to the excitation period, showing high controllability of mass transport. This mass transport phenomenon possibly provides a new mechanism of in vivo, on-demand, dose controllable drug delivery.
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- Award ID(s):
- 1637815
- PAR ID:
- 10211267
- Date Published:
- Journal Name:
- 2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS)
- Page Range / eLocation ID:
- 1052 to 1055
- 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
- Conference Paper:
- https://doi.org/10.1109/MEMS46641.2020.9056218
