Growth Of Nanobubbles Research Articles

Threshold current density for diffusion-controlled stability of electrolytic surface nanobubbles

Understanding the stability mechanism of surface micro/nanobubbles adhered to gas-evolving electrodes is essential for improving the efficiency of water electrolysis, which is known to be hindered by the bubble coverage on electrodes. Using molecular simulations, the diffusion-controlled evolution of single electrolytic nanobubbles on wettability-patterned nanoelectrodes is investigated. These nanoelectrodes feature hydrophobic islands as preferential nucleation sites and allow the growth of nanobubbles in the pinning mode. In these simulations, a threshold current density distinguishing stable nanobubbles from unstable nanobubbles is found. When the current density remains below the threshold value, nucleated nanobubbles grow to their equilibrium states, maintaining their nanoscopic size. However, for the current density above the threshold value, nanobubbles undergo unlimited growth and can eventually detach due to buoyancy. Increasing the pinning length of nanobubbles increases the degree of nanobubble instability. By connecting the current density with the local gas oversaturation, an extension of the stability theory for surface nanobubbles [Lohse and Zhang, Phys. Rev. E 91, 031003(R) (2015)] accurately predicts the nanobubble behavior found in molecular simulations, including equilibrium contact angles and the threshold current density. For larger systems that are not accessible to molecular simulations, continuum numerical simulations with the finite difference method combined with the immersed boundary method are performed, again demonstrating good agreement between numerics and theories.

Molecular Dynamics Simulation Combined with Near-Field Electromagnetic Analysis for Ultrashort-Pulsed Light-Induced Plasmonic Nanobubbles.

Ultrashort-pulsed light-induced nanobubbles gain great attention in research fields such as cancer therapy, optical imaging, and drug delivery. However, the mechanism governing the nucleation and growth of nanobubbles remains controversial. In this study, a molecular dynamics simulation combined with near-field electromagnetic theory is developed to investigate the influence of the localized surface plasmon resonance effect (LSPR) on nanobubble nucleation under various time-length pulsed light and to reveal the energy transfer differences during the nanobubble generation process. The results show that when silver nanoparticles (NPs) are irradiated by a 5 ps shorter-pulsed light, the temperature of the water layer adjacent to the nanoparticle surpasses that of the nanoparticle itself and reaches the spinodal temperature. This leads to nanobubbles' rapid nucleation at approximately 20 ps, which is 80 ps earlier than that irradiated by a 100 ps longer-pulsed light. Comparatively, during longer-pulsed light irradiation, a slower increase in both the temperature of the silver NPs and the water layer results in delayed nucleation of nanobubbles. Therefore, the plasmonic nanobubbles (PNBs) were observed around in 74 and 100 ps when irradiated by 50 and 100 ps longer-pulsed light, respectively. Moreover, the result indicates that the LSPR-induced enhanced electric field by shorter-pulsed light (5 ps) is 2.1 × 1010 V/m, which can accelerate the motion of water molecules surrounding silver NPs, resulting in rapid generation of nanobubbles. However, the intensities of the resonant electric field drop to 5.6 × 109 and 5.0 × 109 V/m when the duration times of pulsed light are 50 and 100 ps, respectively. These results indicate that the energy transfer mechanism of plasmonic nanobubbles (PNBs) under ultrashort-pulsed light irradiation might be very different from that of thermally mediated nanobubbles (TNBs). This work provides new insights into understanding the generation of PNBs induced by ultrashort-pulsed light.

The behavior of surface nanobubbles on different substrates in electrochemistry

In the gas evolution reaction, surface nanobubbles generally nucleate heterogeneously and grow on the electrode. It is important to understand the relationship between the evolution of nanobubbles and the structure of the electrode surface. In this work, we used molecular dynamics simulation to study the effect of different surface structures on the nucleation and growth of nanobubbles. The simulation shows that the current in the induction stage is proportional to the conversion frequency. The reaction rate in the nucleation and growth stages increases with the increase of the conversion frequency. During the stable stage, the reaction rate is higher on the plane than on the concave surface, independent of the conversion frequency. The gas influx at the contact line in the dynamic equilibrium model of nanobubbles on the electrode surface is reconsidered. The gas flux into the nanobubbles at the concave surface during the stable stage is smaller and the contact angle is smaller compared to the plane. The concave substrate restricts the flow of water molecules to the electrode surface's contact line.

Are bubbles in ice the potential space for hydrogen storage?

A major challenge in hydrogen storage is to achieve higher storage capacity, simpler storage technology, less capital cost, lower storage risk, and near zero-carbon emissions. Here, we suggested that bubbles formed in the ice provide the potential space for hydrogen storage as needs. Further, we proposed a coupled mechanism of the supercooled pre-melted quasi-liquid layer to thermoelectric force under a temperature gradient for explaining the bubble formation in ice, based on both diverse laboratory experiments from the firn specimens at different stresses and temperatures and related assumption of thermoelectric effect. As a result, the size of the bubble nucleated was estimated to be 5.8–7 nm. Nanobubbles strengthen the role of the pressure booster of bubbles for improving the hydrogen storage capacity via the hydrogen clathrate hydrate (HCH). Additionally, the post-nucleation growth of nanobubbles in ice from 5.8 to 7 nm to ∼13.8 ± 3.3 μm likely connects the molecular to geological hydrogen storages. Lastly, this work is helpful to design and develop 3-D printed programmable bubble-born cryo-materials coupled to other hydrogen storage systems, e.g. the HCH.

Oxygen-Rich Graphene/ZnO2-Ag nanoframeworks with pH-Switchable Catalase/Peroxidase activity as O2 Nanobubble-Self generator for bacterial inactivation

The oxygen-rich organic/inorganic (reduced graphene oxide (rGO)/ZnO2-Ag) nanoframeworks as suppliers of O2 nanobubbles (NBs) with dual pH-and-temperature-sensitive behavior were developed to suppress bacterial growth. It was demonstrated that not only the rate but also the final product of oxygen-rich ZnO2 decomposition (to an intermediate product of H2O2) rate was dramatically controlled by pH adjustment. Furthermore, in the presence of Ag nanoparticles, ̇OH radical generation switched to O2 NBs evolution by shifting the pH from acidic to basic/neutral conditions, demonstrating an adjustable nanozyme function-ability between catalase and peroxidase-like activity, respectively. Antibacterial properties of the in-situ generated O2 NBs substantially enhanced against bacterial models including methicillin-resistant Staphylococcus aureus in the presence of rGO. In fact, deflecting the electrons from their main respiratory chain to an oxygen-rich bypath through rGO significantly stimulated reactive oxygen species (ROS) generation, combating bacteria more efficiently. Moreover, NIR laser irradiation-induced temperature rise (due to the inherent photothermal properties of rGO) facilitated ZnO2 decomposition and accelerated growth and collapse of NBs. The simultaneous microscale thermal and mechanical destructions induced stronger antibacterial behavior. These results hold great promises for designing simple organic/inorganic nanoframeworks as solid sources of NBs with tunable enzyme-like ability in response to environmental conditions suitable for forthcoming graphene-based bio-applications.

Mechanisms of helium nanobubble growth and defect interactions in irradiated copper: A molecular dynamics study

It is well-established that mechanical behavior of the materials is significantly affected under irradiation. This is often due to the growth of nanobubbles that changes the microstructure of the irradiated materials. In this work, growth of helium nanobubbles with different sizes and helium to vacancy (He/V) ratios in copper is investigated using molecular dynamics (MD) simulations. Our simulations reveal that the nanobubble growth is accommodated by nucleation of various types of defects such as: stacking fault octahedron (SFO), dislocation network, punched-out dislocation loop, stacking fault tetrahedron (SFT) etc. around the nanobubbles. We also unveil the mechanisms of formation as well as punching-out of the dislocation loops, and further show that such defects are activated beyond a threshold of bubble size and He/V ratio. In final, we propose an equation of state (EOS) for predicting the pressure of the nanobubbles inside copper from the input bubble size, He/V ratio, and temperature.

Diffusively Controlled Growth of Nanobubbles under Contact Line Pinning: Implication of Nanoscale Flow and Heat Controls by Nanobubbles

Diffusively Controlled Growth of Nanobubbles under Contact Line Pinning: Implication of Nanoscale Flow and Heat Controls by Nanobubbles

Dynamic Processes of Nanobubbles: Growth, Collapse, and Coalescence

Abstract Nanobubbles are typically classified as gas/vapor phase cavities in an aqueous solution with a characteristic length of approximately 100 nanometers (nm). The theoretical lifetime of these nanobubbles has been estimated to be less than ∼1 μs at a diameter of 100 nm based upon the Young-Laplace pressure, but experimental observations have been reported that indicate that they may exist for many hours, or even days. These nanobubbles can be generated by a number of different methods, such as solvent exchange, pressure and/or temperature variations, chemical reactions, or through the electron beam radiolysis of water. The imaging methods utilized to observe these nanobubbles have evolved from low temporal resolution/high spatial resolution, using atomic force microscopy (AFM); or low spatial resolution/high temporal resolution, using optical microscopy (X-rays); or finally, high spatial/high temporal resolution using more recent electron microscopy techniques. A review of the various methods utilized in the nucleation of nanobubbles and the different imaging technologies utilized, along with a summary of the most recent experimental and theoretical investigations of the dynamic behavior and processes of these nanobubbles, including nanobubble growth, nanobubble collapse, and nanobubble coalescence, are presented, discussed and summarized.

Effect of CO2 nanobubbles incorporation on the viscosity reduction of fruit juice concentrate and vegetable oil

AbstractViscosity is one of key parameters to handle liquid food during processing and transport. In this work, viscosities of apple juice concentrate (APJC) and canola oil (CANO) injected with CO2 nanobubbles (NBs), having size ranged approximately from 50 to 850 nm, were investigated. A significant (P ≤ 0.05) viscosity reduction was observed by up to 18% and 10% in APJC and CANO, respectively, after the NBs injection. When being stored at ambient (23 °C) and refrigerated (4 °C) temperatures for 7 days, the reduction effect on viscosities of samples treated with NBs tended to diminish in accordance with the growth of NBs’ size and the decrease of dissolved CO2 concentration. Besides, the suspension of CO2 NBs insignificantly affected pH, total soluble solid content of APJC, as well as densities of APJC and CANO. These findings suggested that utilisation of NBs can be a feasible mean to reduce viscosity and enhance processing efficiency of food fluids.

Gas supersaturation and diffusion joint controlled CH4 nanobubble evolution during hydrate dissociation

Nanobubbles have attracted wide scientific attention due to their large number of potential applications in nanotechnology, and they are ubiquitous during natural gas hydrates (NGHs) mining which is one of the strategic energy resources. Molecular dynamic simulations were performed to investigate CH4 nanobubble characteristics during NGHs dissociation. The nucleation mechanism and evolution characteristics of nanobubbles vary with hydrate dissociation temperature. The higher the temperature, the earlier the bubble nucleation, the more small methane clusters are produced, and the more complex the evolution path of nanobubbles, the initial position of bubble nucleation is closer to the decomposition interface. The gas reservoir can provide another possibility for methane molecules to overcome solubility barriers to avoid the formation of nanobubbles at lower dissociation temperature. CH4 nanobubble evolution was found to be governed by the gas supersaturation and the diffusion of CH4 molecules. The self-diffusion coefficient of CH4 molecules near the decomposition interface area is small due to the adsorption effect of the incomplete cages, nanobubbles are more likely to form outside the adsorption zone where the CH4 diffusion coefficient is larger at a lower temperature. A direct proof of speeding up of hydrate dissociation by nanobubble growth was given. The acceleration of dissociation is later than nanobubble growth and the accumulation of nanobubbles on dissociation interface may have a negative influence. The new findings on nanobubble evolution may help design and optimize nanobubble formation techniques in nanotechnology and efficient gas hydrate production protocols.

Generation and Evolution of Nanobubbles on Heated Nanoparticles: A Molecular Dynamics Study.

Molecular dynamics simulations were conducted to investigate the generation and evolution of nanobubbles on heated gold-like nanoparticles (GNPs). The effects of surface wettability (β) and heating intensity (Q) of the GNPs are studied. We found that nanobubbles are generated faster on the superhydrophobic GNP than on the superhydrophilic GNP where nanobubble formation appears after a delay. In the case of the superhydrophilic GNP, the nanobubble is observed to grow explosively because it is initially generated at a distance from the GNP surface instead of on its surface. In the case of the superhydrophobic GNP, the faster generation of the nanobubble is promoted by the larger temperature difference between the GNP and the surrounding fluid and an ultrathin low-density layer that exists before the GNP is heated. For a given β, faster generation and growth ofnanobubbles are observed with increasing Q. Furthermore, the maximum radius of the nanobubble is found to be dependent on β and not Q. The mechanism is elaborated based on the thermal resistance analysis at the melting point of GNPs. Additionally, it was found that there exists a threshold Q for nanobubble generation and the threshold value for the case of the superhydrophobic GNP is lower than that for the case of the superhydrophilic GNP. The present results have demonstrated that the superhydrophobic GNP is favorable for fast and energy-saving nanobubble generation.Our work provides further understanding in the generation and evolution of nanobubbles and potentially offers a new insight for nanobubble manipulation.

Monitoring nanobubble nucleation at early-stage within a sub-9nm solid-state nanopore.

Nanobubble nucleation study is important for understanding the dynamic behavior of nanobubble growth, which is instructive for the nanobubble applications. Benefiting from nanopore fabrication, herein, we fabricated a sub-9nm SiNX nanopore with the comparable size to nanobubbles at early-stage. The confined nanopore interface serves as a generator for producing nanobubbles by the chemical reaction between NaBH4 and H2 O and as an ultra-sensitive sensor for monitoring the H2 nanobubble nucleation process. By carrying out the NaBH4 concentration-dependent experiments, we found the life-time of nanobubbles decreased 250 times and the frequency of nanobubble generation increased 38 times with the NaBH4 concentration increasing from 6 to 100mM. The long-time equilibrium between gas molecules inward flux and outward flux could prolong the life-time of nanobubbles to hundreds of milliseconds at low NaBH4 concentration. The raw current trace depicted that the transient accumulation and dissolution of cavity occurred during all the life-time of nanobubbles. Therefore, the sub-9nm SiNX nanopore shows a strong ability for real-time monitoring the nanobubble nucleation at early-stage with high temporal and spatial resolution. This work provides a guide to study the dynamic and stochastic characteristics of nanobubbles.

Role of a nanoparticle on ultrasonic cavitation in nanofluids

Ultrasonic cavitation in nanofluids improves material removal rate and surface quality. Ultrasonic cavitation in nanofluids was investigated using molecular dynamics simulations. The formation and growth of nanobubbles were promoted, by nanoparticles in water systems. Three distinct impact stages were observed which were caused by the impact of the shock wave, nanojet and nanoparticle. These differed in the system without a nanoparticle. The material removal rate was primarily caused by the nanoparticle hit, a result of the nanobubble collapsing during the third impact. A mechanism of material removal in ultrasonic polishing is discussed at a nanometric level.

Molecular dynamic simulation of bubble nucleation in a nanochannel with a groove

Molecular dynamics methods are used to investigate the effect of wall wettability and initial fluid density on the nucleation and growth of nanobubbles in a nanochannel with a groove. Surface wettability is controlled by adjusting the parameters of the solid-liquid potential energy and the results show that groove wettability greatly influences the bubble nucleation process. In the case of a groove with a weak solid-liquid interaction, fluid atoms in the groove are strongly affected by repulsive forces attributed to solid atoms, the density of the fluid atoms is low, and atomic collision frequency increases. The local activation energy is concentrated in the groove, resulting in bubble nucleation. In the case of a groove with a stronger solid-liquid interaction, the bubble is formed in the center of the nanochannel. In general, the bubble radius of curvature and contact angle remain unchanged during the growth process in the case of a uniform wettability nanochannel with a groove, while significant changes are observed for a nonuniform wettability nanochannel. The radius of curvature for the generated bubble increases with increasing fluid initial density, while the steady contact angle decreases. At the request of the authors this paper is being retracted. This action is taken because in the simulation cases of β=0.3 and β=0.4, the temperature control method is incorrect, resulting in flawed simulation results in Figs. 8 and 9. In addition, the number of atoms (and hence the density) in the simulation box is also not correct due to errors in the initialization phase of the simulation. Thus, the calculated phase diagram in Fig. 2 is incorrect. The authors sincerely apologize for these errors and omissions and regret any inconvenience they may have caused.

Helium plasma induced nanostructure formation in copper and nickel

Copper and nickel samples were exposed to helium plasma to investigate surface nanostructure formation and associated helium nano-bubble growth. Plasma fluences from 3.9 × 1023 He m−2 to 3.1 × 1024 He m−2 were used for this study. For copper with an unpolished surface finish 50–100 nm wide nanoscale pillars were formed, with more complex structures observed at higher plasma fluences. This is due to the uneven topography providing nucleation sites that stabilises the growth of these features. For polished copper surfaces nano-scale pillars formed on some crystal grains but not others, indicating strong crystal orientation effects on nano-structure formation. The formation of nano-scale islands and pillars was also observed in both polished and unpolished nickel samples, with nano-structure formation occurring across all crystal grains.Nanostructures that formed on nickel samples exposed to helium plasma at controlled temperatures from 200 °C to 325 °C showed significant sensitivity to the sample temperature. Dense fields of 50 nm diameter nanostructures formed at 300 °C, larger but sparse nanostructures formed at 325 °C, and little change was observed at and below 250 °C.Sub-surface helium bubbles were measured and displayed similar sizes for bubbles formed in both copper and nickel samples.

Formation and coalescence of nanobubbles under controlled gas concentration and species

Using molecular dynamics simulations, the effects of gas concentration and species on the coalescence and growth of nanobubbles were systematically investigated. With increasing gas concentration, not only surface nanobubbles but also bulk nanobubbles are formed. The bulk nanobubble in water is less explored so far. Here, its coalescence, stability, movement trajectory and velocity are discussed. A comparison of the motion and coalescence of the bulk nanobubble to the surface nanobubble, directly demonstrates that the three-phase contact line plays a crucial role for surface nanobubble stability. Compared with the bubble size, the distance between surface nanobubbles is a more important factor to decide the merging order among three nanobubbles. The study also shows that three factors including the oversaturated gas concentration, the distance between surface nanobubbles, and the stronger solid-gas interactions influence the formation of the gas-enrichment layer at the solid-liquid interface. The result has an important significance to enhancing the boundary slip due to the presence of nanobubbles.

Monitoring the dynamic photocatalytic activity of single CdS nanoparticles by lighting up H2 nanobubbles with fluorescent dyes.

The capability of semiconductor nanomaterials to convert solar energy to chemical energy has led to many promising applications, for instance, photocatalyzed H2 generation. Studying this important photocatalytic reaction at the single nanocatalyst level provides a great opportunity to understand the microscopic reaction kinetics and mechanism by overcoming the chemical and structural heterogeneity among individuals. Here we report a fluorescence (FL) labeling strategy to visualize individual H2 nanobubbles that are generated at single CdS nanoparticles during photocatalysis. In operando imaging of nanobubble growth kinetics allows for determination of the photocatalytic activity of single nanocatalysts, which was found to randomly alternate among high activity, low activity and inactive states. In addition to H2 nanobubbles, the present labeling strategy is also suitable for other types of gas nanobubbles. Since nanomaterial-catalyzed gas generation is widely involved in many important photochemical (water splitting), electrochemical (electrolysis) and chemical (nanomotors) reactions, the present work is promising for the general applicability of single nanoparticle catalysis in broad basic and industrial fields by lighting up nanobubbles under commercial and conventional FL microscopes.

Measuring temperature effects on nano-bubble growth in tungsten with grazing incidence small angle X-ray scattering

W samples were exposed to He plasma in the MAGPIE, NAGDIS-II and PISCES-A across a range of sample temperatures between 473–1123K. GISAXS was used to quantify the effect of plasma fluence and W surface temperature on He nano-bubble size distributions. In NAGDIS-II at 873K nano-bubbles are exponentially distributed with mean diameters μ=0.64±0.01nm, similar to the value of μ=0.62±0.01nmfound for the MAGPIE plasma device at the much lower temperature of 473K. Above ∼900K nano-bubbles followed an approximately exponential distribution with μ > 0.72 nm demonstrating a significant increase in nano-bubble sizes at higher temperatures.

Nanobubble nucleation studied using Fresnel fringes in liquid cell electron microscopy

Liquid cell electron microscopy is a useful technique for the observation of chemical, biological, and mechanical processes in liquids at nanometer-scale resolution. This study investigated the generation and growth of nanobubbles using the Fresnel fringe method, which enabled us to determine the location of bubble interface; the nanobubbles were induced in the 600-nm-thick water sample in the cell, by the electron beam. Nucleation occurred first at the solid–liquid interface in the upstream side of electron beam, and this was followed by second-group nucleation at the downstream-side interface; all of the stable nucleations occurred on the solid surfaces. The size of the nucleated bubbles at the moment they became visible depended on the magnification used in the electron microscope, and a higher-energy density in the electron beam induced larger bubbles. The underlying mechanism was also considered in this study.

Photoresistance Switching of Plasmonic Nanopores

Fast and reversible modulation of ion flow through nanosized apertures is important for many nanofluidic applications, including sensing and separation systems. Here, we present the first demonstration of a reversible plasmon-controlled nanofluidic valve. We show that plasmonic nanopores (solid-state nanopores integrated with metal nanocavities) can be used as a fluidic switch upon optical excitation. We systematically investigate the effects of laser illumination of single plasmonic nanopores and experimentally demonstrate photoresistance switching where fluidic transport and ion flow are switched on or off. This is manifested as a large (∼1–2 orders of magnitude) increase in the ionic nanopore resistance and an accompanying current rectification upon illumination at high laser powers (tens of milliwatts). At lower laser powers, the resistance decreases monotonically with increasing power, followed by an abrupt transition to high resistances at a certain threshold power. A similar rapid transition, although at a lower threshold power, is observed when the power is instead swept from high to low power. This hysteretic behavior is found to be dependent on the rate of the power sweep. The photoresistance switching effect is attributed to plasmon-induced formation and growth of nanobubbles that reversibly block the ionic current through the nanopore from one side of the membrane. This explanation is corroborated by finite-element simulations of a nanobubble in the nanopore that show the switching and the rectification.