Compound jetting from bubble bursting at an air-oil-water interface

Amplification of Supersonic Microjets by Resonant Inertial Cavitation-Bubble Pair

We reveal for the first time by experiments that within a narrow parameter regime, two cavitation bubbles with identical energy generated in antiphase develop a supersonic jet. High-resolution numerical simulation shows a mechanism for jet amplification based on toroidal shock wave and bubble necking interaction. The microjet reaches velocities in excess of 1000  m s^{-1}. We demonstrate that potential flow theory established for Worthington jets accurately predicts the evolution of the bubble gas-liquid interfaces unifying compressible and incompressible jet amplification.

Bubble manipulates the release of viral aerosols in aeration

Bubble bursting is a common phenomenon in many industrial and natural processes, plays an important role in mediating mass transfer across the water-air interface. But the interplay between bubbles and pathogens remains unclear and the mechanisms of virus aerosolization by the bubble properties have not been well studied. The main objective of this study was to evaluate the water-to-air transfer of viruses by bubbles of different sizes. Unlike the dominant view of smaller bubbles less bioaerosols, it was found that the smaller bubbles could generate significantly more viral aerosols regardless of the virus species (Phi6, MS2, PhiX174, and T7), when the Sauter mean bubble diameters were between 0.56 and 1.65 mm under constant aeration flow rate. The mechanism studies denied the possibilities of more aerosols or better dispersion of viruses in the aerosols generated by the smaller bubbles. However, deeper bubbling could transfer more viruses to the air for MS2, PhiX174, and T7. Their concentrations in aerosols were linearly related to the bubbling depth for these non-enveloped viruses, which demonstrates the bubble-scavenging effect as a main mechanism except for the enveloped virus Phi6. Whereas, unlike these three non-enveloped viruses, Phi6 could survive relatively better in the aerosols generated from the smaller bubbles, though the enhancement of aerosolization by the smaller bubbles was much larger than the improvement of survival. Other mechanisms still remain unknown for this enveloped virus. This study suggests that the attempt of decreasing the bubble size in aeration tank of the wastewater treatment plant might significantly increase the solubility of oxygen as well as the risk of viral aerosols.

Secondary Bubble Entrainment via Primary Bubble Bursting at a Viscoelastic Surface

Bubble bursting at liquid surfaces is ubiquitous and plays a key role for the mass transfer across interfaces, impacting global climate and human health. Here, we document an unexpected phenomenon that when a bubble bursts at a viscoelastic surface of a bovine serum albumin solution, a secondary (daughter) bubble is entrapped with no subsequent jet drop ejection, contrary to the counterpart experimentally observed at a Newtonian surface. We show that the strong surface dilatational elastic stress from the viscoelastic surface retards the cavity collapse and efficiently damps out the precursor waves, thus facilitating the dominant wave focusing above the cavity nadir. The onset of daughter bubble entrainment is well predicted by an interfacial elastocapillary number comparing the effects of surface dilatational elasticity and surface tension. Our Letter highlights the important role of surface rheology on free surface flows and may find important implications in bubble dynamics with a contaminated interface exhibiting complex surface rheology.

Liquid metal droplets bouncing higher on thicker water layer

Liquid metal (LM) has gained increasing attention for a wide range of applications, such as flexible electronics, soft robots, and chip cooling devices, owing to its low melting temperature, good flexibility, and high electrical and thermal conductivity. In ambient conditions, LM is susceptible to the coverage of a thin oxide layer, resulting in unwanted adhesion with underlying substrates that undercuts its originally high mobility. Here, we discover an unusual phenomenon characterized by the complete rebound of LM droplets from the water layer with negligible adhesion. More counterintuitively, the restitution coefficient, defined as the ratio between the droplet velocities after and before impact, increases with water layer thickness. We reveal that the complete rebound of LM droplets originates from the trapping of a thinly low-viscosity water lubrication film that prevents droplet-solid contact with low viscous dissipation, and the restitution coefficient is modulated by the negative capillary pressure in the lubrication film as a result of the spontaneous spreading of water on the LM droplet. Our findings advance the fundamental understanding of complex fluids' droplet dynamics and provide insights for fluid control.

Water-to-Air Transfer of Nano/Microsized Particulates: Enrichment Effect in Bubble Bursting Jet Drops

Bubbles dispersed in liquids are widely present in many natural and industrial processes and play a key role in mediating mass transfer during their lifetime from formation to rising to bursting. In particular, nano/microsized particulates and organisms present in the bulk water can be highly enriched in the jet drops ejected during bubble bursting, impacting global climate and public health. However, the detailed mechanism of this enrichment remains obscure with the enrichment factor being difficult to predict. Here, we experimentally investigate the enrichment of nano/microsized particles in bubble bursting jet drops and highlight the underlying hydrodynamic mechanism, combining the effects of bubble scavenge and bursting on the transport of particles. Scaling laws for the enrichment factor are subsequently proposed that describe both our and prior experimental results reasonably well. Our study may provide new insights for water-to-air transfer of bulk particulates such as microbes related to bubble bursting.

Bioinspired Anisotropic Slippery Cilia for Stiffness-Controllable Bubble Transport

Bubbles play a crucial role in multidisciplinary industrial applications, e.g., heat transfer and mass transfer. However, existing methods to manipulate bubbles still face many challenges, such as buoyancy inhibition, hydrostatic pressure, gas dissolving, easy deformability, and so on. To circumvent these constraints, here we develop a bioinspired anisotropic slippery cilia surface to achieve an elegant bubble transport by tuning its elastic modulus, which results from the different contacts of bubbles with cilia, i.e., soft cilia will be easily bent by the bubble motion, while hard cilia will pierce into the bubble, consequently leading to the asymmetric three-phase contact line and resistance force. Moreover, a real-time and arbitrarily directional bubble manipulation is also demonstrated by applying an external magnetic field, enabling the scalable operation of bubbles in a remote manner. Our work exhibits a strategy of regulating bubble behavior smartly, which will update a wide range of gas-related sciences or technologies including gas evolution reactions, heat transfer, microfluidics, and so on.