Bubble Stability Research Articles

Enhancement of Bubble Stability in Cement-Based Materials by a Sustained-Release Effect of Silica Nanoparticles

Enhancement of Bubble Stability in Cement-Based Materials by a Sustained-Release Effect of Silica Nanoparticles

Efficient Bubble Transport on Bioinspired Topological Ultraslippery Surfaces.

Slippery liquid-infused porous surfaces (SLIPS) with micro-/nanostructures inspired by the Nepenthes pitcher plant exhibit excellent characteristics in terms of liquid repellency, self-healing, pressure tolerance, and so forth. In particular, stable bubble transport on SLIPS can be achieved when the surface is submerged in water. However, more precise and sophisticated bubble manipulations on SLIPS still remain challenging. In this research, a three-dimensional topological SLIPS combined with a submillimeter rice leaf-like groove array is fabricated to guide the underwater bubble motion precisely. The dynamic behavior and wetting state of bubbles on SLIPS were investigated experimentally. Furthermore, topological SLIPS with different geometric textures were designed and created for sophisticated bubble manipulations, such as fast bubble directional transport and collection. The results indicated that a lubricant with low surface tension and low viscosity could improve the adhesion force to bubbles and the transport velocity of bubbles, simultaneously. The current findings are helpful to deepen the cognition of interaction between bubbles and SLIPS and to promote their wide applications in the field of smart bubble manipulation and catalytic chemistry.

Synergistic effects of frothers, collector and salt on bubble stability

This work investigates synergistic and antagonistic effects of flotation reagents and salt on the air–liquid interface and stability of air bubbles under quasi-static conditions. Frothers of different families (aliphatic alcohol, polypropylene glycol and propylene glycol methyl ether), potassium amyl xanthate (PAX), a common collector used in the flotation of sulphide minerals, and sodium chloride (NaCl) were employed in the study. Adsorption of frother and collector molecules from individual and mixed solutions was studied through surface tension and Quartz Crystal Microbalance with Dissipation (QCM–D) measurements, while bubble stability was examined by the coalescence time of the bubble pairs in these solutions. The results show that NaCl enhanced the adsorption of frothers, while PAX's impact on the adsorption of the frother was found to be rather insignificant compared to the salt. The bubble coalescence time measurements, however, pointed to a significant synergistic effect between PAX and two frothers i.e., Methyl Iso Butyl Carbinol (MIBC) and Di Propylene Glycol (DPG) as reflected in the improvement of bubble stability. In the ternary solution systems (frother/NaCl/PAX), the concentration of salt in the MIBC mixture solution was found to have an opposite impact on the bubble lifetime in the DPG and DPM solutions. For instance, bubble lifetime increased with higher NaCl concentrations added to the DPG and DPM solutions, whereas it decreased in the MIBC solutions.

Dynamics and observational signatures of shell-like black hole mimickers

We undertake the task of studying the non-linear dynamics of quantum gravity motivated alternatives to black holes that in the classical limit appear as ultra-compact shells of matter. We develop a formalism that should be amenable to numerical solution in generic situations. For a concrete model we focus on the spherically symmetric AdS black bubble -- a shell of matter at the Buchdahl radius separating a Schwarzschild exterior from an AdS interior. We construct a numerical code to study the radial dynamics of and accretion onto AdS black bubbles, with exterior matter provided by scalar fields. In doing so we develop numerical methods that could be extended to future studies beyond spherical symmetry. Regarding AdS black bubbles in particular, we find that the original prescription for the internal matter fluxes needed to stabilize the black bubble is inadequate in dynamical settings, and we propose a two parameter generalization of the flux model to fix this. To allow for more efficient surveys of parameter space, we develop a simpler numerical model adapted to spherically symmetric bubble dynamics. We identify regions of parameter space that do allow for stable black bubbles, and moreover allow control to a desired end-state after an accretion episode. Based on these results, and evolution of scalar fields on black bubble backgrounds, we speculate on some observational consequences if what are currently presumed to be black holes in the universe were actually black bubbles.

Shock response of He bubble in single crystal tungsten: molecular dynamics simulation study

Nonequilibrium molecular dynamics simulations are performed to study the shock response of He bubble with various He-vacancy ratios in single crystal W. Simulation results show that the plastic deformation mode of He bubble is realized by emission of a [100] vacancy type of prismatic dislocation loop, which is formed by reaction of 1/2<111> type of edge dislocations. He bubble with high He-vacancy ratio is more stable than that with low He-vacancy ratio. Finally, the plastic deformation mode and stability of the He bubble are discussed in term of elasticity theory. It is found that the distribution character of resolved shear stresses on the bubble surface is the underlying cause to control the formation of the vacancy type prismatic dislocation loop; and that the resolved shear stress on the He bubble surface decreases with increase of He-vacancy ratio is the reason why He bubble can be stabilized by increase of its He-vacancy ratio.

Real-Time Single-Molecule Studies of RNA Polymerase–Promoter Open Complex Formation Reveal Substantial Heterogeneity Along the Promoter-Opening Pathway

The expression of most bacterial genes commences with the binding of RNA polymerase (RNAP)–σ70 holoenzyme to the promoter DNA. This initial RNAP–promoter closed complex undergoes a series of conformational changes, including the formation of a transcription bubble on the promoter and the loading of template DNA strand into the RNAP active site; these changes lead to the catalytically active open complex (RPO) state. Recent cryo-electron microscopy studies have provided detailed structural insight on the RPO and putative intermediates on its formation pathway. Here, we employ single-molecule fluorescence microscopy to interrogate the conformational dynamics and reaction kinetics during real-time RPO formation on a consensus lac promoter. We find that the promoter opening may proceed rapidly from the closed to open conformation in a single apparent step, or may instead involve a significant intermediate between these states. The formed RPO complexes are also different with respect to their transcription bubble stability. The RNAP cleft loops, and especially the β′ rudder, stabilise the transcription bubble. The RNAP interactions with the promoter upstream sequence (beyond −35) stimulate transcription bubble nucleation and tune the reaction path towards stable forms of the RPO.

A variable-gap model for helium bubbles in nickel

In nuclear fission reactors, the amount of helium produced in materials by transmutation reactions at the end of the lifetime may reach several thousands of atomic parts per million (appm). Such high levels of helium production can impact the evolution of microstructures, particularly by forming helium bubbles. To better understand the role of helium on the stability of bubbles, a “variable-gap model” was parametrized with molecular dynamics (MD) calculations performed in nickel. This model predicts binding energies in a good agreement with MD values, especially for large bubbles. For very small bubbles, the influence of magic number sizes and faceting is more complex than can be described with the model. For these cases, it is proposed to use MD values directly.

Comparative study of stabilization of coffee bubbles at the air-water interface through different surfactants

This investigation reveals the influence of self-assembly of surface active components of surfactants in instant coffee in rendering a stable foam, thereby providing a visual delight. Three surfactants, sucrose stearate, quillaja saponin, and Tween 80, were administered to improve the foam quality of instant coffee. The influence of the addition of these surfactants showed a reduction in surface tension of the coffee solution. Sucrose stearate showed excellent foaming properties as well as foam stability for over 1200 s. For sucrose stearate, the maximum foam height of 168.2±0.1 mm was achieved at 75.98±1.87 s that sustained for 60.27±3.59 s with a minimum coalescence rate of 0.012±0.005 μm/s, compared to other surfactants. FE-TEM results proved that closely packed patterned morphology of micelles at the air-water interface, specifically in sucrose stearate foam, could have aided in the development of the most stable foam. As deduced from the present findings, the preferred hierarchy of surfactant for a stable foam in instant coffee is sucrose stearate> quillaja saponin > Tween 80.

Ultrafast dynamics of acoustic vaporization and payload release of phase-shift emulsions

Acoustic droplet vaporization (ADV) is the phase-transitioning of perfluorocarbon emulsions via focused ultrasound. ADV has been utilized in many biomedical applications. For drug delivery and tissue regeneration, we developed composite hydrogel scaffolds, termed acoustically responsive scaffolds (ARSs), which here contained fluorescently labeled monodispersed emulsions (Ø: 12.3 ± 0.8 μm). Using ultra-high speed microscopy, we investigated the dynamics of ADV (2.5 MHz, P-: 6 MPa, pulse length: 6μs) in ARSs containing emulsions with perfluoropentane, perfluorohexane, and perfluorooctane. Vaporization and growth dynamics were studied in micro- to millisecond time scales at frame rates up to 10 Mfps. During ADV, the generated bubbles expanded 4.8-, 2.8-, and 2-fold greater than the initial diameter of the perfluoropentane, perfluorohexane, and perfluorooctane emulsions, respectively. Stable bubbles formed from ADV in perfluoropentane and perfluorohexane, though growth rates post-ADV were significantly different. Bubbles recondensed within perfluorooctane emulsions, which exhibited a 20% decrease in diameter following five repeated ADV events. Stable or transient bubble formation was further compared with classical nucleation theory predictions. Additionally, we compared the release dynamics of fluorescently labeled payloads from the emulsions. The results provide physical insight enabling the modulation of bubble dynamics with ADV and hence release kinetics, which can be used for therapeutic applications.

Foamability of surfactant solutions: Interplay between adsorption and hydrodynamic conditions

The foamability of surfactant solutions depends strongly on the adsorption properties of the surfactants, their concentrations, and the foaming test used for foam generation. The aim of the current study is to analyse the subtle interplay between the hydrodynamic conditions and the surfactant adsorption layers formed during foaming. We compare the results from three foam tests, characterized with very different hydrodynamic conditions. The Bartsch test (fast-foaming method) is characterized by a very short time, of the order of milliseconds, allowed for surfactant adsorption before the newly generated bubbles collide with each other. The other two “slow-foaming” tests, the planetary mixer and the foam rise method, are very different from this viewpoint – the characteristic time for surfactant adsorption before the bubble collisions is much longer, of the order of seconds. Surfactants of two different types, nonionic and anionic, with different chain-lengths are compared. The obtained results reveal that the long-chain nonionic surfactants with 16 carbon atoms are unable to stabilize the foams in the fast-foaming test, even at very high surfactant concentrations (50 mM), due to their relatively slow adsorption. Interestingly, the same surfactants are excellent foam stabilizers in the slow-foaming tests. On the other hand, the medium-chain anionic surfactants with 12 carbon atoms are very suitable for stabilization of the gas bubbles in the fast-foaming test, even at relatively low concentrations, due to their rapid adsorption and inherent electrostatic repulsion. In slow-foaming tests, however, the anionic surfactants show lower foamability to the nonionic ones. All results from the foam tests are explained in a unified approach which accounts explicitly for the rate of surfactant adsorption and for the characteristic time-scales of the various foaming tests.

Tailoring structure and properties of long-lived emulsion foams stabilized by a natural saponin glycyrrhizic acid: Role of oil phase

Novel supramolecular nanofibrils assembled from food-grade saponin glycyrrhizic acid (GA) are effective building blocks to make complex multiphase systems, e.g., emulsion foams. In this work, the effects of different oil phases (castor oil, sunflower oil, dodecane, and limonene) on the formation, stability and structural properties of long-lived emulsion foams prepared by GA nanofibrils (GNs) were investigated. The obtained results showed that soft-solid emulsion foams (4 wt% GNs) can be fabricated, independently of oil phase, and their structural properties, viscoelasticity, and tribological properties can be well tuned by oil phase polarity. Compared to the GNs aqueous foams, the presence of jammed emulsion droplets in the liquid channels and at the surfaces of bubbles can provide a higher bubble stability for emulsion foams. For more polar oil phase (castor oil), GNs showed a higher affinity to the oil–water interface with a lower interfacial tension, thus forming smaller oil droplets and bubbles, which leads to the higher mechanical strength, denser network microstructures, and lower friction coefficients of emulsion foams. However, the limonene foam exhibited weak storage stability and rheological properties, as well as the relatively low lubrication, which may be related to the formation of oil droplet aggregates and clusters induced by the volatility of limonene. GN-based emulsion foams are thermoresponsive, independently of oils, and the temperature-switchable process for the destabilization and regeneration of foams can be controlled and repeated. These emulsion foams based on natural saponin nanofibrils with tunable properties have potential sustainable applications in foods, pharmaceuticals, and personal care products.

Theranostic nanobubbles towards smart nanomedicines

Targeted therapy and early accurate detection of malignant lesions are essential for the effectiveness of treatment and prognosis in cancer patients. The development of gaseous system as a versatile platform for the fabricated nanobubbles, has attracted much interest in improving the efficacy of ultrasound therapeutic, diagnostic, and theranostic platforms. Nano-sized bubble, as an ultrasound contrast agent, with spherical gas-filled structures exhibited contrast enhancement capability due to their inherent EPR effect. Additionally, nanobubbles exhibited good stability with extended retention time in the blood stream. The current review summarized various nanobubbles and discussed about the crucial parameters affecting the stability of ultrafine bubbles. Furthermore, therapeutic and theranostic gaseous systems for fighting against cancer were described.

Non-linear stability of double bubbles under surface diffusion

We consider the evolution of triple junction clusters driven by the surface diffusion flow. On the triple line we use the boundary conditions derived by Garcke and Novick-Cohen as the singular limit of a Cahn-Hilliard equation with degenerated mobility. These conditions are the concurrency of the triple junction, angle conditions between the hypersurfaces, continuity of the chemical potentials and a flux-balance. For this system we show stability of its energy minimizers, i.e., standard double bubbles. The main argument relies on a Łojasiewicz-Simon gradient inequality. The proof of it differs from others works due to the fully non-linear boundary conditions and problems with the (non-local) tangential part.

Breakdown of Universal Scaling for Nanometer-Sized Bubbles in Graphene.

We report the formation of nanobubbles on graphene with a radius of the order of 1 nm, using ultralow energy implantation of noble gas ions (He, Ne, Ar) into graphene grown on a Pt(111) surface. We show that the universal scaling of the aspect ratio, which has previously been established for larger bubbles, breaks down when the bubble radius approaches 1 nm, resulting in much larger aspect ratios. Moreover, we observe that the bubble stability and aspect ratio depend on the substrate onto which the graphene is grown (bubbles are stable for Pt but not for Cu) and trapped element. We interpret these dependencies in terms of the atomic compressibility of the noble gas as well as of the adhesion energies between graphene, the substrate, and trapped atoms.

Hydroxyapatite as a scavenger of reactive radiolysis species in graphene liquid cells for in situ electron microscopy

Liquid cell electron microscopy is an imaging technique allowing for the investigation of the interaction of liquids and solids at nanoscopic length scales. Such in situ observations are increasingly in-demand in an array of fields, from biological sciences to medicine to batteries. Graphene liquid cells (GLCs), in particular, have generated a great interest as a low-scattering window material with the potential for increasing the quality of both imaging and spectroscopy. However, preserving the stability of the liquid and of the sample in the GLC remains a considerable challenge. In the present work we encapsulate water and hydroxyapatite (HAP), a pH-sensitive biological material, in GLCs to observe the interactions between the graphene, HAP, and the electron beam. HAP was chosen for several reasons. One is its ubiquity in biological specimens such as bones and teeth, and the second is the presence of phosphate ions in common buffer solutions. Finally, there is its sensitivity to changes in pH, which result from beam-induced hydrolysis in liquid cells. A dynamic process of dissolution and recrystallization of HAP was observed, which correlated with the production of H+ ions by the beam during imaging. In addition, a large increase in the stability of the GLC under irradiation was noted. Specifically, no stable hydrogen bubbles were detected under the electron fluxes routinely exceeding 170 e− Å−2 s−1. With the measured threshold dose for the bubble formation in pure water equaling 9 e− Å−2 s−1, it was concluded that the presence of HAP increases the resistance of water against radiolysis in the GLC by more than an order of magnitude. These results confirm the possibility of using biological materials, such as HAP, as stabilizers in liquid cell electron microscopy. They outline a potential route for stabilization of specimens in liquid cells through the addition of a scavenger of reactive species generated by the beam-induced hydrolysis of water. These improvements are essential for enhancing both the resolution of imaging and the available imaging time, as well as avoiding the beam-induced artifacts.

Preparation and Performance of A Novel Type of Concrete Air Entraining Agent

This article uses 1,4-dibromobutane, hexadecyl primary amine, sodium 3-chloro-2-hydroxypropionate, formaldehyde and formic acid as raw materials to synthesize a new type of concrete air entraining agent of (1,4)-bis(cetylmethyl hydroxy-propionic acid quaternary ammonium salt) butane through the reaction of ammonia alkylation and quaternization. The article characterizes the molecular architecture of the product, the surface activity of the aqueous solution, the bubble properties, the air entraining and air stabilizing properties of the fresh concrete, and the pore structure of the concrete after hardening. The research results show that the synthesized (1,4)-bis(cetylmethyl hydroxy-propionic acid quaternary ammonium salt) butane has good surface activity in aqueous solution, and its critical micelle concentration (cmc) is 5.3×10-4 mmol/L, γ cmc is 28.86 mN/m; (1,4)-bis(cetylmethyl hydroxy-propionic acid quaternary ammonium salt) butane has better air-entraining performance and bubble stability in aqueous solution and concrete than SDS and AOS air entraining agents. The average chord length and spacing coefficient of bubbles in hardened concrete are smaller than that of SDS and AOS air entraining agent, giving rise to a better overall pore structure of the concrete. Compared with SDS and AOS, the concrete mixed with (1,4)-bis(cetylmethyl hydroxy-propionic acid quaternary ammonium salt) butane air entraining agent shows better mechanical property and durability.

Effects of surface tension on the dynamics of a single micro bubble near a rigid wall in an ultrasonic field

Acoustic cavitation is a very important hydrodynamic phenomenon, and is often implicated in a myriad of industrial, medical, and daily living applications. In these applications, the effect mechanism of liquid surface tension on improving the efficiency of acoustic cavitation is a crucial concern for researchers. In this study, the effects of liquid surface tension on the dynamics of an ultrasonic driven bubble near a rigid wall, which could be the main mechanism of efficiency improvement in the applications of acoustic cavitation, were investigated at the microscale level. A synchronous high-speed microscopic imaging method was used to clearly record the temporary evolution of single acoustic cavitation bubble in the liquids with different surface tension. Meanwhile, the bubble dynamic characteristics, such as the position and time of bubble collapse, the size and stability of the bubbles, the speed of bubble boundaries and the micro-jets, were analyzed and compared. In the case of the single bubbles near a rigid wall, it was found that low surface tension reduces the stability of the bubbles in the liquid medium. Meanwhile, the bubbles collapse earlier and farther from the rigid wall in the liquids with lower surface tension. In addition, the surface tension has no significant influence on the speed of the first micro-jet, but it can substantially increase the speed of second and the third micro-jets after the first collapse of the bubble. These effects of liquid surface tension on the bubble dynamics can explain the mechanism of surfactants in numerous fields of acoustic cavitation for facilitating its optimization and application.

Bubble size distribution and stability of CO2 microbubbles for enhanced oil recovery: effect of polymer, surfactant and salt concentrations

Fluids incorporating carbon dioxide (CO2) microbubbles have been utilized to promote enhanced oil recovery from hydrocarbon reservoirs. The performance of such fluids in porous media is greatly affected by both the bubble size and stability. On this basis, the present study evaluated the effects of varying the concentrations of a xanthan gum (XG) polymer, a surfactant (sodium dodecyl sulfate: SDS) and sodium chloride (NaCl) on both the stability and bubble size distribution (BSD) of CO2 microbubbles. CO2 microbubble dispersions were prepared using a high-speed homogenizer in conjunction with the diffusion of gaseous CO2 through aqueous solutions. The stability of each dispersion was ascertained using a drainage test, while the BSD was determined by optical microscopy and fitted to either normal, log-normal or Weibull functions. The results showed that a Weibull distribution gave the most accurate fit for all experimental data. Increases in either the SDS or XG polymer concentration were found to decrease the microbubble size. However, these same changes increased the microbubble stability as a consequence of structural enhancement. The addition of NaCl up to a concentration of 10 g/L (10 g/1000g) decreased the average bubble size by approximately 2.7%. Stability was also reduced as the NaCl concentration was increased because of the gravitational effect and coalescence.

Foaming and sensory characteristics of protein-polyphenol particles in a food matrix

As food ingredients, protein-polyphenol aggregate particles provide a combination of structural and health-relevant functional benefits. Particles made by complexing whey (WPI) or rice (RPI) protein isolates and blueberry (BB) extracts were evaluated for foaming properties (foam volume, stability, and yield stress) using a high energy-input foaming operation (with an Ultra Power Mixer), and then also compared at low energy-input (foamed using a hand-held mixer). In the high energy-input foaming operation, whey protein rapidly formed foams (within 2 min). Whey protein-blueberry (WPI-BB) particles significantly improved yield stress and foam stability (2-fold) as compared to foams made with unmodified WPI. Rice protein required longer (>8 min) to produce foams, but foams were significantly more stable (longer drainage half-life) both when the protein was unmodified (RPI) or formulated as particles (RPI-BB). Protein-polyphenol particle foams (WPI-BB or RPI-BB) had a much greater proportion of smaller sized bubbles than polyphenol-free foams. WPI foams formed for descriptive analysis using the low energy-input method rapidly produced structures with fine, stable bubbles resistant to breakdown in the mouth, while those made with RPI had fewer, larger and looser bubbles which broke more easily after mixing and in the mouth. Inclusion of WPI-BB or RPI-BB particles enhanced palatability of protein isolates in a model (protein bars) food system as compared to non-complexed proteins. The complexed aggregate particles also provided sweetness, dark berry and dried fruit flavors and minimized bitterness and astringency. This work provides a context for understanding the utilization of protein-polyphenol particles as multifunctional ingredients that simultaneously deliver concentrated polyphenols associated with health benefits.

Turbulence and capillary waves on bubbles.

We present a link between the theory of deep water waves and that of bubble surface perturbations. Theory correspondence is shown analytically for small wavelengths in the linear regime and investigated numerically in the nonlinear regime. To do so, we develop the second-order spatial perturbation equations for the Rayleigh-Plesset equation and solve them numerically. Our code is publicly available. Studying capillary waves on stable bubbles, we recreate the Kolmogorov-Zakharov spectrum predicted by weak turbulence theory, putting wave turbulence theory to use for bubbles. In this investigation, it seems that curvature does not affect turbulent properties. The calculated bubble surface responds qualitatively to low gravity experiments. The link demonstrated opens new possibilities for studying several bubble phenomena, including sonoluminescence and cavitation, using the extensive tools developed in the wave turbulence framework.