Underwater Gas Bubble Research Articles

Flexible dual-Janus porous membrane for underwater gas bubbles anti-buoyancy unidirectional transportation

Flexible dual-Janus porous membrane for underwater gas bubbles anti-buoyancy unidirectional transportation

Underwater Bubble Manipulation on Surfaces with Patterned Regions with Infused Lubricants.

The flexible manipulation of underwater gas bubbles on solid substrates has attracted considerable research interest from scientists in the fields of water electrolysis, bubble microreactions, drug delivery, and heat transfer. Inspired by the oxygen-binding mechanisms of aquatic organisms, scientists have designed a series of interfacial materials for use in collecting gases, detecting and grading bubbles, and conducting microbubble reactions. Aerophilic surfaces are commonly used in underwater bubble manipulation platforms due to their excellent gas-trapping properties. However, during bubble transport, some of the bubbles are retained in the rough structure of the aerophilic surface and cause gas loss, which in the long run reduces the gas transport function. In addition, the aerophilic surface is prone to failure in high-humidity and high-pressure underwater environments. The lubricant-infused surface features an oil layer that remains stable on a rough substrate and is immiscible with water. Additionally, the bubbles are transported over the oil layer without causing losses other than those dissolved in water. These attributes make it more favorable than the aerophilic surface. Inspired by the unique properties of Nepenthes and cactus spines, we developed a patterned slippery surface [patterned lubricant-infused surface (PLIS)] through laser etching and ammonia etching that facilitates the coexistence of superaerophobic and aerophilic surfaces. The PLIS executes bubble capture utilizing a difference in wettability measuring 78°, transports bubbles through Laplace force and buoyancy, and regulates bubble release by restricting the contact area on the PLIS. The PLIS can be prepared rapidly and affordably in just about an hour, and its potential for large-scale production is high. Following tests for shear, acid and alkali resistance, and corrosion resistance, the PLIS exhibited impressive weathering resistance and appears to have potential for application in some extreme environments.

Theoretical Investigation of Capture, Collection, and Targeted Transfer of Underwater Gas Bubbles Using Janus‐Faced Carbon Cloth

Recently, a straightforward method for the preparation of a Janus carbon cloth (Janus‐CC) is reported. The method relies on polydimethylsiloxane (PDMS) coating, followed by flame exposure of one face of the PDMS‐coated CC. The nonexposed to the flame face of the Janus‐CC is superhydrophobic, while the exposed to the flame face is superhydrophilic. Underwater, the superhydrophobic face shows superaerophilicity, while the supherhydophilic face shows superaerophobicity. A tethered gas bubble onto the superhydrophobic face has a paraboloid of revolution shape due to the cohesion force between the bubble and the gaseous film. Herein, the geometrical parameters of underwater tethered gas bubbles onto the Janus‐CC are obtained, and the tendency of Janus‐CC for capturing of bubbles is interpreted based on the derived Gibbs free‐energy change equation. It is experimentally observed that a small sited bubble moves toward the bigger one through the formed gaseous film, but this observation cannot be interpreted based on the classical Young–Laplace equation because here the smaller bubble has bigger curvature radius. Herein, a modified Young–Laplace equation is derived and applied for interpretation of the movement of a small bubble toward the bigger one. Also, the buoyancy force for a sited bubble on the gaseous film is discussed.

Echo grid integration: A novel method for preprocessing multibeam water column data to quantify underwater gas bubble emissions

AbstractWater column imaging multibeam echo sounder systems (MBESs) are a promising technology for quantitative estimates of the gas bubble volume flow within large gas seepage areas. Considerable progress has been made in recent years toward applicable calibration methods for MBESs as well as developing inversion models to convert acoustically measured backscattering cross sections to gas bubble volume flow. However, MBESs are still not commonly used for quantitative gas flow assessments. A reason for this is the absence of published processing methods that demonstrate how MBES data can be processed to quantitatively represent bubble streams. Here, we present a novel method (echo grid integration) that allows for assessing the aggregated backscattering cross section of targets within horizontal water layers. This derived value enables quantifying bubble stream gas flow rates using existing acoustic inversion methods. The presented method is based on averaging geo‐referenced volume backscattering coefficients onto a high‐resolution 3D voxel‐grid. The results are multiplied with the voxel volume to represent measurements of the total backscattering cross‐section within each voxel cell. Individual gridded values cannot be trusted because the beam pattern effects cause the values of individual targets to “smear” over multiple grid‐cells. The true aggregated backscattering cross‐section is thus estimated as the integral over the grid‐cells affected by this smearing. Numerical simulation of MBES data acquisition over known targets assesses the method's validity and quantify it's uncertainty for different, realistic scenarios. The found low measurement bias (< 1%), and dispersion (< 5%) are promising for application in gas flow quantification methods.

Controllable Bubble Transport on Bioinspired Heteromorphic Magnetically Steerable Microcilia

AbstractControllable transport of underwater gas bubbles is essential in various fields such as gas energy, drug delivery, and heat transfer. Although anisotropic structures are used to transport bubbles, their motion direction can only be adjusted to a limited extent because of weak structural anisotropy and small responsive deformation. Here, anisotropic bubble transport is found on microcilia surfaces of diving beetle's elytra with regular inclination and heteromorphic structure of microcilia, which have hooked tips and crescent‐shaped roots. Inspired by these, a magnetically steerable microcilia surface with large‐range inclination adjustment is proposed for highly controllable bubble transport via a heterogeneous configuration strategy. The dynamic in situ microscopic behavior shows a novel shifting phenomenon of the maximum bubble pinning position from bubble back interface for hydrophobic cilia to front interface for hydrophilic cilia under different cilium wettabilities. This shift varies the bubble shapes from unstable stretching to stable compression, thus increasing the difference in anisotropic transport by three times for hydrophilic cilia. Moreover, bioinspired heteromorphic structures can further enhance such difference by 5.5 times. Based on the proposed theory, several smart functional microcilia are designed to achieve more complex bubble manipulation, thus improving their suitability for widespread application.

Underwater gas bubbles produced by droplet impact: Mechanism to trigger volumetric oscillations

Oscillating gas bubbles formed when droplets collide with a water surface are studied experimentally. Over a short time interval, before and after the bubble detachment, the bubble surface curvature changes drastically, causing a pulse of Laplace pressure. The leading edge of the pulse occurs before the bubble detachment, and the rear (negative) edge falls on the stage of an already closed bubble, which, like a resonator, is excited into volume oscillations on the natural frequency while simultaneously emitting an acoustic wavepacket. The amplitude and steepness of the pulse are inversely related to the size of the bubble, thereby ensuring that the dynamic parameters of the triggering pulse correspond to the natural frequency of the bubble. The release of pressure during the negative trailing edge of the pulse initiates the beginning of volumetric oscillations from the expansion phase and the acoustic packet from the positive half-wave.

Fast Capture, Collection, and Targeted Transfer of Underwater Gas Bubbles Using Janus-Faced Carbon Cloth Prepared by a Novel and Simple Strategy.

Transportation of bubbles in liquids in a controlled fashion is a challenging task and an important subject in numerous industrial processes, including elimination of corrosive gas bubbles in fluid transportation pipes, water electrolysis, reactions between gases, heat transfer, etc. Using superaerophilic surfaces represents a promising solution for bubble movement in a programmed way. Here, a novel and low-cost method is introduced for the preparation of Janus-faced carbon cloth (Janus-CC) using poly(dimethylsiloxane) (PDMS) coating and then burning one side of the carbon cloth/PDMS on an alcoholic burner. The results show that the superhydrophobic face behaves as a superaerophilic surface, while the superhydrophilic side is aerophobic underwater. Subsequently, the Janus-CC is applied for pumpless transport of underwater gas bubbles even under harsh conditions. The movement of gas bubbles on the surface of the Janus-CC is interpreted based on the formed gaseous film on the aerophilic side of the Janus-CC. Various applications of the prepared Janus-CC for underwater bubble transportation, such as underwater gas distributor, gas collector membrane, gas transport for chemical reactions, unidirectional gas membrane, and elimination of gas bubbles in transport pipe, are presented.

Stimuli-Responsive Liquid-Crystal-Infused Porous Surfaces for Manipulation of Underwater Gas Bubble Transport and Adhesion.

Biomimetic artificial surfaces that enable the manipulation of gas bubble mobility have been explored in a wide range of applications in nanomaterial synthesis, surface defouling, biomedical diagnostics, and therapeutics. Although many superhydrophobic surfaces and isotropic-lubricant-infused porous surfaces have been developed to manipulate gas bubbles, the simultaneous control over the adhesion and transport of gas bubbles underwater remains a challenge. Thermotropic liquid crystals (LCs), a class of structured fluids, provide an opportunity to tune the behavior of gas bubbles through LC mesophase transitions using a variety of external stimuli. Using this central idea, the design and synthesis of LC-infused porous surfaces (LCIPS) is reported and the effects of the LC mesophase on the transport and adhesion of gas bubbles on LCIPS immersed in water elucidated. LCIPS are demonstrated to be a promising class of surfaces with an unprecedented level of responsiveness and functionality, which enables the design of cyanobacteria-inspired object movement, smart catalysts, and bubble gating devices to sense and sort volatile organic compounds and control oxygen levels in biomimetic cell cultures.

Magnetic-Actuated Robot Enables High-Performance Underwater Bubble Maneuvering on Laser-Textured Biomimetic Slippery Surfaces.

Controllable underwater gas bubble (UGB) transport on a surface is realized by geography-/stimuli-induced wettability gradient force (Fwet-grad). Unfortunately, the high-speed maneuvering of UGBs along free routes on planar surfaces remains challenging. Herein, a regime of magnetism-actuated robot (MAR) mounting on biomimetic laser-ablated lubricant-impregnated slippery surfaces (LA-LISS) is reported. Leveraging on LA-LISS, MAR-entrained UGBs can move along arbitrary directions through the loading of a tracing magnetic trigger. The underlying hydrodynamics is that MAR-entrained UGBs would be actuated slipping upon a giant magnetic-induced towing force (FM//). Once the magnetism stimuli is discharged, FM// vanishes immediately to immobilize the UGBs on LA-LISS. Thanks to the MAR's robust bubble affinity, a typical UGB (20 μL) on the optimized LA-LISS can be accelerated at 500 mm/s2 and gain an ultrafast velocity of over 205 mm/s that far exceeds previously reported figures. Moreover, fundamental physics renders MAR antibuoyancy, steering locomotive UGBs on the inclined LA-LISS. Significantly, an MAR propelling UGBs to configure desirable patterns, realize on-demand coalescence, remedy the cutoff switch, as well as facilitate a programmable light-control-light optical shutter is successfully deployed. Compared with previous smart surfaces, the current multifunctional regime is more competent for harnessing UGBs featuring an unparalleled transport velocity independent of the feeble Fwet-grad.

Electrically Induced Underwater Superaerophilicity/Superaerophobicity Switching on Polypyrrole-Coated Mesh Films for Selective Bubble Permeation.

Recently, materials with controllable superwettability have attracted much attention. However, almost all studies focused on controlling wetting of water and oil; research on underwater gas bubble wetting control is still rare. Herein, we report a mesh film prepared by coating polypyrrole (PPy) film on Ti mesh. Briefly, the film mesh is underwater superaerophilic when PPy is doped with perfluorooctanesulfonate ions (PFOS- ), and becomes underwater superaerophobic as the PFOS- are removed. The transition of the wettability can be triggered by electrical stimuli, which is attributed to the cooperative effect between the rough structure and chemical components variation. The controllable wettability allows adjustable bubble permeation. It can be envisioned that the film will provide potential applications in the future, such as underwater bubble capture/release and microfluidic devices.

Overcoming Limitations in Surface Geometry‐Driven Bubble Transport: Bidirectional and Unrestricted Movement of an Underwater Gas Bubble Using a Magnetocontrollable Nonwetting Surface

AbstractThe movement of underwater gas bubbles significantly affects the core processes of a variety of applications in water electrolysis, heat transfer, optofluidics, and other fields. To maneuver the motion of bubbles, surface geometry‐driven transport is widely applied by employing asymmetric nonwetting surfaces, which induce Laplace pressure based on the bubble radius differences in confined states. Although this method has successfully demonstrated bubble manipulations in various geometries, it has inevitably shown some critical limitations; gas bubbles move unidirectionally from tip to root direction and cease their movements upon reaching unconfined states. This unidirectional and local bubble transport restrains the method's applicability to many fields, and overcoming this obstacle still remains an enormous challenge. Herein, a magnetocontrollable lubricant‐infused surface (MCLIS) is introduced as a key solution to this issue. MCLISs manipulate the adhesion of gas bubbles by controlling magneto‐responsive microwire alignments and rendering two reversible adhesion states, sticky (upright) and slippery (laying wires). This unique characteristic of MCLISs enables the bidirectional and geometry‐unrestricted transportation of bubbles by the wire geometry‐gradient force (Fwgg) generated at sticky–slippery interfaces. Furthermore, this novel magnetic responsive surface supports anti‐buoyancy transport and presents promising applications in microreactors and optical laser shutters in aqueous media.

In Situ Tuning Underwater Bubble Movement on Slippery Lubricant-Infused Anisotropic Microgrooved Surface by Unidirectional Mechanical Strain.

Numerous studies have focused on designing and fabricating functional interfaces that control movement behavior of underwater gas bubbles, which are ubiquitous in a variety of natural and industrial settings. Nevertheless, developing surfaces with in situ tunable bubble movement remain elusive because of current complicated tuning strategies on the specific materials. Inspired by natural pitcher plant and rice leaves, here we report a kind of slippery lubricant-infused anisotropic microgrooved surface (SLI-AMGS) fabricated by femtosecond laser direct writing technology and realize the in situ reversible switching between underwater bubble sliding and pinning by unidirectional mechanical tensile strain. Different experimental parameters including lubricant oil film thickness, bubble volumes and laser power have been researched to manifest the relationship with bubble sliding behaviors. The underlying mechanism of in situ reversible switching mainly lies on the decrease of the lubricant oil film thickness during the process of mechanical stretching in which the uniform and stable oil film layer becomes uneven. This uneven lubricant oil film results in an extraordinary increase of contact angle hysteresis and resistance. At last, we demonstrate a real-time dynamic modulation of the underwater bubble on the SLI-AMGS with a changing mechanical tensile strain for several repeatable times in different acid-based environments. Our work manifests great potential applications in widespread fields including underwater bubble microfluidics and microbubble robots.

Underwater explosive bubble interaction with an adjacent submerged structure

An experimental and computational investigation was conducted to study the interaction between bubbles generated by an underwater explosive (UNDEX) and a nearby steel plate structure. The experiments were performed for different standoff distances to investigate the interaction between the gas bubble and the rigid structure. High-speed photography was utilized to capture the underwater explosive gas bubble’s behavior, and a series of pressure transducers were used to record the emitted pressure histories. The numerical simulations were performed with the Dynamic System Mechanics Advanced Simulation software, which is a full y coupled Eulerian–Lagrangian fluid–structure interaction code. The numerical simulations were validated with the experiments in terms of the detonation pressure, structural surface pressures, and UNDEX gas bubble growth and collapse. Results show that the UNDEX standoff distance greatly influences the gas bubble’s shape, migration speed, bubble jetting behavior, and loading into its adjacent structure. Moreover, the impulse generated by the shock wave on the plate surface proved to be small in comparison to the impulse generated by the collapse of the UNDEX gas bubble. The magnitude of impulse depends on standoff distance, collapse symmetry, and relative collapse location.

Understanding of Dynamic Contacting Behaviors of Underwater Gas Bubbles on Solid Surfaces.

Understanding of dynamic behaviors of gas bubbles on solid surfaces has significant impacts on gas-involving electrochemical reactions, mineral flotation, and so on in industry. Contact angle (θ) is widely employed to characterize the wetting behaviors of bubbles on solid surfaces; however, it usually fluctuates within the bubble's advancing (θa) and receding (θr) range. Although the term of most-stable contact angle (θms) was defined previously as the closest valuable approximation for thermodynamically meaningful contact angle for a droplet on a solid surface, it has not been widely studied; and the precise θms measurement methods are inadequate to describe bubbles' wetting behaviors on solid surfaces. Herein, we proposed to take θms as the mean value of θa and θr, as a more accurate descriptor of gas bubbles' dynamic behaviors on nonideal solid surfaces, similar to the definition of droplets' θms on solid surfaces. The feasibility and accuracy of the proposed θms have been evidenced by recording the bubbles' contacting behaviors on solid surfaces with varied wettabilities. In addition, it was found that the contact angle hysteresis (δ), as the difference between θa and θr, reached its maximum value when θms approached 90°, regardless of the roughness (r) of the substrates. Finally, built on the above concept, the lateral adhesion force (f) of the gas bubble on the solid interface, which worked on the three-phase contact line (TPCL) of an individual bubble on a solid surface against its lateral motion during the bubble advancing or receding process, was described quantitatively by combining θa, θr, and the liquid-gas interfacial tension (γlg). Experimental and theoretical data jointly confirmed that f reached its maximum value at θms ∼ 90°, namely, a "super-sticky" state, which described the dynamically most sluggish movement of the bubble along the solid surface.

Ladderlike Conical Micropillars Facilitating Underwater Gas-Bubble Manipulation in an Aqueous Environment.

Underwater gas-bubble manipulation in aqueous environments is of great importance in industry and academia. Although the underwater gas bubble has been proved to be directionally transportable by various structures, transporting gas bubbles in 3D space remains a challenge. In this research, two kinds of tapered pillars, that is, ladderlike and helical ladderlike, were proposed for manipulating gas bubbles. To fabricate such unique structures, an improved alternative coating and etching method was developed. To meet the requirements of underwater gas-bubble transport, a modified gas-bubble slippery technology was also developed to enhance the aerophilic ability. The dynamics of the gas bubble was analyzed using a high-speed camera. The Laplace force that resulted from the geometry gradient was found to play a significant role in tuning the gas-bubble velocity. Through adjustments on the wettability, tilt angle, and geometry of each section of the tapered pillar, tuning the transport velocity from 113.9 ± 10.3 to 309.1 ± 5.8 mm/s becomes possible. On the basis of these findings, the helical ladderlike tapered pillar was fabricated and demonstrated to be able to transport gas bubbles in 3D space. These results may provide a new and systematic way to design and fabricate materials and structures for directional gas-bubble transport in 3D space.

Numerical simulation of underwater air bubble formation under rolling conditions

Underwater gas bubbles are universal phenomenon in various industries. These bubbles appear under ocean conditions especially rolling conditions, that affect the mass transfer and produce different acoustic signals. The bubble formation and oscillation frequency characteristics under rolling conditions were investigated in this study by using a numerical method. Results showed that the bubbles followed two basic steps under rolling conditions, namely, expansion and detachment. The bubble detachment surface area and shape exhibited periodic changes because of the periodical motion of the surrounding water. A correlation was established to predict the bubble detachment surface area under rolling conditions. Similar to the bubble detachment surface area, the bubble oscillation frequency periodically changed. The oscillation mode of the bubbles under rolling conditions was the same as those under motionless condition, that is zeroth mode. A modified Minnaert formula was established to predict the bubble oscillation frequency under rolling conditions.

Dual‐Responsive Janus Membrane by One‐Step Laser Drilling for Underwater Bubble Selective Capture and Repelling

AbstractAchieving the dynamic control of underwater gas bubbles (UGBs) on smart surfaces has aroused great attention for academic research and industrial applications. To date, developing a kind of stimuli‐responsive porous membrane with asymmetric wettability which can be reversibly switched between Janus and non‐Janus systems, unfortunately, has been rarely demonstrated. Here, a light/temperature‐responsive Janus tapered‐hole arrayed zinc foil (TAZF) is unfolded by combining one‐step laser drilling and a subsequent heating which is successfully utilized for underwater bubble unidirectional transport, that is, bubble “diode.” Moreover, this TAZF can reversibly switch between Janus architecture and double‐faced aerophobic by applying alternative heating and UV dispositions for selectively capturing or repelling bubbles. The underlying mechanism revealed by X‐ray photoelectron spectroscopy spectrums is that the reversible graft and removal of hydroxyl (OH) on the top surface of TAZF dominates the wettability conversion. The quantitative relationship among the UV and heating time and the water contact angle and the underwater bubble contact angle (UGBCA) is also studied. This work provides insight for designing smart surfaces applicable in fast bubble capture, transportation, collection, and gas/liquid separation.

Remote Photothermal Actuation of Underwater Bubble toward Arbitrary Direction on Planar Slippery Fe3O4‐Doped Surfaces

AbstractUnidirectional underwater gas bubble (UGB) transport on a surface is realized by buoyant force or wettability gradient force (Fwet‐grad) derived from a tailored geography. Unfortunately, intentional control of the UGB over transport speed, direction, and routes on horizontal planar surfaces is rarely explored. Herein reported is a light‐responsive slippery lubricant‐infused porous surface (SLIPS) composed of selective lubricants and super‐hydrophobic micropillar‐arrayed Fe3O4/polydimethylsiloxane film. Upon this SLIPS, the UGB can be horizontally actuated along arbitrary directions by remotely loading/discharging unilateral near‐infrared (NIR) stimuli. The underlying mechanism is that Fwet‐grad can be generated within 1 s in the presence of a NIR‐trigger due to the photothermal effect of Fe3O4. Once the NIR‐stimuli are discharged, Fwet‐grad vanishes to break the UGB on the SLIPS. Moreover, performed are systematic parameter studies to investigate the influence of bubble volume, lubricant rheology, and Fwet‐grad on the UGB steering performance. Fundamental physics renders the achievement of antibuoyancy manipulation of the UGBs on an inclined SLIPS. Significantly, steering UGBs by horizontal SLIPS to configurate diverse patterns, as well as facilitating light‐control‐light optical shutter, is deployed. Compared with the previous slippery surfaces, light‐responsive SLIPS is more competent for manipulating UGBs with controllable transport speed, direction, and routes independent of buoyancy or geography derivative force.

Dynamics of underwater gas bubbles impact on a ratchet with gradient inclination

An underwater gas bubble may have a unidirectional movement, after impacting with a ratchet, which consists of asymmetric teeth with gradient inclination. In this work, the corresponding movements were first experimentally investigated. Small bubbles are easily pinned on a ratchet surface. In contrast, large bubbles have directional transportation from large to small inclination areas. Since the detected motions could not be interpreted using existing propulsive mechanisms, a new propulsive mechanism was then developed. Based on the new mechanism, two approaches to manipulate bubbles have been investigated experimentally.

Laser Structuring of Underwater Bubble-Repellent Surface.

Bubbles in aqueous media are pervasive and unavoidable. However, underwater gas bubbles adhesion to the metal pipework can sometimes seriously damage the surface and reduce the useful life of devices. Herein, we report a simple way to fabricate underwater bubble-repellent surface by one-step femtosecond laser direct writing technology. The as-prepared surface exhibits superhydrophilicity in air and superaerophobicity in water, and the bubble contact angles reach 159±2.5° in water. The surface presents ultralow bubble adhesion, and the rolling angle of the bubble is small. The potential mechanism is also discussed. This method offers an easy route to prepare underwater superaerophobic surfaces with ultralow bubble adhesion, and it has potential applications in underwater bubble-repelling facilities.