Suppression Of Coalescence Research Articles

Underlying principles of Ge-induced early cluster-to-layer transition for ultrathin Ag layer formation on oxides

The fabrication of continuous Ag layers with thicknesses of <10 nm are challenging. Moreover, information on the crucial factors responsible for early cluster-to-layer transition is limited. Hence, this study focuses on the effects of thin Ge interlayers in forming Ag layers on SiOx substrates. Experimental and numerical analyses demonstrate the active migration and intermixing of atomic Ge in the Ag and SiOx matrices during the early Ag layering stages. The incorporation of Ge into Ag matrices facilitates a faster cluster-to-layer transition than those with Al and Cu. Ge-mediated Ag clustering reduces the rearrangement momenta of extremely small Ag clusters densely concentrated on SiOx substrates. This is attributed to the Ge-induced reduction in the diffusion of atomic Ag in the surfaces of volatile Ag clusters and consequently, the suppression of cluster coalescence. These findings provide insights into the unconventional role of Ge in Ag clustering dynamics. Thus, this study presents a crucial framework for optimizing Ag wetting on oxide substrates with ultralow optical and electrical losses via extreme dissipation of the residual amounts of metalloid wetting-inducing elements.

Effect of surfactant frequently used in soil flushing on oxygen mass transfer in micro-nano-bubble aeration system

In-site soil flushing and aeration are the typical synergetic remediation technology for contaminated sites. The surfactant presented in flushing solutions is bound to affect the aeration efficiency. The purpose of this study is to evaluate the effect of surfactant frequently used in soil flushing on the oxygen mass transfer in micro-nano-bubble (MNB) aeration system. Firstly, bio-surfactants and chemical surfactants were used to investigate their effects on Sauter mean diameter of bubble (dBS), gas holdup (ε), volumetric mass-transfer coefficient (kLa) and liquid-side mass-transfer coefficient (kL) in the MNB aeration system. Then, based upon the experimental results, the Sardeing’s and Frössling’s models were modified to describe the effect of surfactant on kL in the MNB aeration. The results showed that, for the twenty aqueous surfactant solutions, with the increase in surfactant concentration, the value of dBS, kLa and kL decreased, while the value of ε and gas–liquid interfacial area (a) increased. These phenomena were mainly attributed to the synergistic effects of immobile bubble surface and the suppression of coalescence in the surfactant solutions. In addition, with the presence of electric charge, MNBs in anionic surfactant solutions were smaller and higher in number than in non-ionic surfactant solutions. Furthermore, the accumulation of surfactant on the gas–liquid interface was more conspicuous for small MNB, so the reduction of kL in anionic surfactant solutions was larger than that in non-ionic surfactant solutions. Besides, the modified Frössling’s model predicted the effect of surfactant on kL in MNB aeration system with reasonable accuracy.

Effects of Salinity Beyond Coalescence on Submicron Aerosol Distributions

AbstractBubbles entrained by ocean waves rise to the surface and burst, creating a shower of droplets which contribute to sea spray aerosols. Submicron‐sized droplets, of which an estimated 60%–80% come from a bursting bubble film cap, play a key role in global climate atmospheric processes. However, many aspects of predicting the number and size of submicron drops emitted from a bursting bubble remain unknown. It is well‐documented that higher salinity increases submicron droplet production, which has been attributed to the role of salt in the suppression of bubble coalescence. We experimentally show that submicron drop production increases with salinity despite using a salt that does not affect bubble coalescence, indicating that salinity plays a role in the physics of submicron aerosol formation beyond coalescence. Laboratory experiments are conducted using sodium acetate solutions of salinity S = 0.001–0.1 M with millimeter‐sized bubbles generated via a needle. Unlike previous studies, the measured droplet size distributions are converted to formation diameter, revealing that the peak aerosol formation diameter decreases with higher salinity. Applying this diameter conversion to past studies, we find the peak formation diameter exhibits a scaling of Dform ∼ S−0.32 across three orders of magnitude in salinity and for a variety of salts, bubble coalescence behaviors, and bubble generation mechanisms. This result suggests that salinity has a systematic effect on the length scale of the rupturing bubble film which generates the aerosols. Consequently, salinity likely impacts the submicron aerosol production in oceanic environments even if bubble coalescence is negligible.

Совершенствование эксплуатации насосно-эжекторных систем при изменяющихся расходах попутного нефтяного газа

Application of pump-ejector systems for the utilization of associated petroleum gas reduces the negative environmental impact of its flaring, and also allows the implementation of a promising method of water-gas stimulation of the formation, which effectively increases oil recovery. Equally feasible is the use of pump-ejector systems in the operation of oil wells with a high gas factor, low bottomhole pressures to increase production rates and increase the turnaround period.A significant change in the flow rate of associated petroleum gas over time is a serious problem for the efficient operation of pump-ejector systems for the utilization of associated petroleum gas. To ensure the rational operation of the pump-ejector system under the condition of a variable flow rate of associated petroleum gas, experimental studies of a liquid-gas ejector characteristics were carried out. The article presents the results of the research, obtained pressure-energy characteristics of the investigated jet apparatus at various values of the working stream pressure before the ejector nozzle. The possibility of adapting the operation of pump-ejector systems to changes in the flow rate of the pumped gas, regulated by the working pressure and fluid flow rate through the nozzle is revealed.To successfully change the operation of the pump-ejector system, the possibility of frequency regulation of the pump shaft's rotation at changing gas flow rates in a small range of values is considered. With a large difference in the values of the possible flow rate of associated petroleum gas, it is recommended that frequency regulation should be supplemented by periodic short-term operation. The possibility of increasing the efficiency of the pump-ejector system when using salt solutions with a concentration that contributes to the suppression of bubble coalescence is noted.

Synthesis and magnetic properties of Sm2Co17 particles using salt-assisted spray pyrolysis and a reduction-diffusion process

Sm2Co17 particles, with several hundreds of nanometers to a few micrometers in diameter, were synthesized by a combination of salt-assisted ultrasonic spray pyrolysis and a reduction-diffusion (R-D) process. It was found that NaCl plays a decisive role toward the suppression of particle coalescence during R-D process. By optimizing a reductant contents, the single-phased and non-agglomerated Sm2Co17 particles were obtained. In addition, particle size was controlled by varying calcination temperature from 800 °C to 1100 °C and size-dependent magnetic properties were observed. The optimum magnetic properties were achieved at a calcination temperature of 900 °C: coercivity of 5.3 kOe, a saturation magnetization of 99.33 emu/g, and a remanence of 56.53 emu/g.

Mechanism of formation of the honeycomb-like structures by the regime of the reversing current (RC) in the second range

Electrodeposition of copper in the hydrogen co-deposition range by the regime of reversing current (RC) in the second range has been investigated by determination of the average current efficiency for hydrogen evolution reaction and by scanning electron (SEM) and optical (OM) microscopic analysis of the obtained deposits. Keeping the cathodic current density, the cathodic and the anodic pulses constant in all experiments, the anodic current density (ja) values were varied: 40, 80, 160, 240 and 320mAcm−2. The Cu deposits produced by the RC regimes with different anodic current density values were compared with that obtained in a constant galvanostatic regime (DC) at the current density equal to the cathodic current density in the RC regimes. The honeycomb-like structures were formed in the DC regime and by the RC regimes with ja of 40 and 80mAcm−2. The hole size in them was in the 60–70μm range. Due to the decrease of quantity of evolved hydrogen with increasing anodic current density, the larger dish-like holes with dendrites at their bottom and shoulder were formed with ja values of 160, 240 and 320mAcm−2. The maximum number of holes, and hence, the largest specific surface area of the honeycomb-like electrodes was obtained with ja=80mAcm−2, that can be ascribed to a suppression of coalescence of neighboring hydrogen bubbles. Application of the RC regime also led to the increase of uniformity of structures, what is concluded by cross section analysis of the formed honeycomb-like electrodes. For the first time, mechanism of Cu electrodeposition in the hydrogen co-deposition range by the RC regime in the second range was proposed and discussed.

Suppressing droplet coalescence and aggregation in immiscible homopolymer blends by interfacially cross-linked compatibilizers

In this work, we study the effect of reactive compatibilization on morphological and rheological properties of immiscible homopolymer blends of polydimethylsiloxane (PDMS) and polyisoprene (PI). The blend systems contained a chemical reaction between amine-functionalized PDMS and maleic anhydride-functionalized PI additives at high temperatures. Interfacially cross-linked compatibilizers obtained with this procedure are investigated through dynamic rheological measurements and Fourier transform infrared spectroscopy. The results show that the interfacial cross-linking constituting strong heterogeneous network is symmetric, as it reduces the sizes of the dispersed phase with higher stability in both compatibilized PI-continuous and PDMS-continuous blends compared to their uncompatibilized counterparts. A complete suppression of droplet coalescence can be concluded due to the superposition of linear viscoelasticity of the reactively compatibilized blends after different shearing protocols. In the previous work [C. DeLeo et al., J. Rheol. 55(4), 713–731 (2011)], however, the weak network at room temperature was found to have an asymmetric effect on the suppression of drop coalescence.

A note on the critical gap of bubble coalescence during foaming process: A diffuse-interface modeling

Bubble coalescence is an important stage of foaming process. A goal of foaming is to produce numerous, uniform-size bubbles. Therefore suppression of bubble coalescence is desirable during foaming process. For stationary bubbles, if their distance be less than a critical gap they will coalesce. Actually in this case, attractive forces attract the outer surfaces to touch each other and form a growing gas bridge which merge the bubbles finally. For bigger distance, the attractive forces cannot make a bridge and coalescence will not happen. In this study the dynamics of bubble coalescence is modeled using a diffuse-interface LBM. Then critical gap of bubble coalescence is defined as the maximum distance between the stationary bubbles where the coalescence will happen. Sensibility of critical gap is obtained with respect to critical properties of material, bubble size, viscosity of gas and liquid, density ratio, surface tension, temperature and interface thickness. The results show that, interface thickness is the only factor that controls the critical gap. In the other word, in the case of stationary bubbles, by a precise estimation of interface thickness, the coalescence can be predicted. Critical gap is a useful parameter in foaming where the maximum number of bubbles is desirable.

Suppression of the coalescence of gas bubbles in aqueous electrolyte solutions: dependence on the external pressure and velocity of gas flow through a column with liquid

An experiment on laser diagnostics of gas bubbles moving in aqueous solutions of different electrolytes has revealed that efficient suppression of gas bubble coalescence (collapse) occurs at certain concentrations of cation−anion pairs. It is experimentally proven that there is an optimal ion composition at which the coalescence is suppressed in a wide range of velocities of gas particle flow through a column with liquid. It is shown that the threshold ion concentrations corresponding to the onset of coalescence suppression decrease with an increase in the external pressure in the liquid. The results obtained can be used in oil production technologies to solve the problem of burning associated oil gas in torches.

The suppression of droplet-droplet coalescence in a sheared yield stress fluid

Efforts to stabilize emulsions against coalescence in flow have often focused on modifying properties of the interface between the continuous and dispersed phases, to create a repulsive barrier against coalescence. But prior to experiencing any interaction force, the liquid film between two colliding drops has to drain, and if this drainage process is arrested, coalescence will be suppressed. In this work, scaling analyses and thin-film lubrication simulations are used to study the hydrodynamic drainage properties of thin films of a Bingham fluid (a yield stress fluid, which flows only when a critical stress is exceeded) created between two drops colliding under the action of a constant force. Our study shows that the hydrodynamic drainage process can be arrested completely when the film reaches a critical thickness, before attractive forces result in the rupture of the film, provided that the film shape is in the dimpled configuration. This critical thickness is hf=6τ02R3/γ2, where τ0 is the yield stress of the suspending medium, R is the drop radius and γ is the interfacial tension between the fluids. The yield stress can thus serve as an independent tuning parameter that sets an upper bound on the drop size beyond which coalescence is turned off in sheared emulsions.

Study on Adhesion-Resistant Materials for Improving the Restoration of Exercise-Induced Muscle Tendon Fracture

The muscle tendon is connective tissue, the fracture can occur when its stress is not reasonable. With the establishment of tendon external and endogenous coalescence theory, the suppression of external coalescence and promotion of endogenous coalescence became the crucial problem of resolve adhesion of tendon. The application of adhesion prevention materials in the part of tendon surrounding was the hotspot of recent research. At present, the research about adhesion prevention materials has made remarkable achievements. However, the materials studied in exercise-induced tendon rupture were cut both ways, therefore, as a material for adhesion prevention and functional reconstruction to treatment of tendon rupture. There are still many unsolved problems in the application of adhesion prevention materials.

Morphological hysteresis in immiscible PIB/PDMS blends filled with fumed silica nanoparticles

The morphological hysteresis behavior of immiscible polymer blend reflects the dependence of their steady-state morphology on the shear protocol applied. In this work, the influences of hydrophobic and hydrophilic fumed silica nanoparticles on the morphology hysteresis behavior of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) (10/90) blends under simple shear flow were investigated by using optical shear technique. Compared with particle-free blend, the morphology hysteresis zone of filled blends was found to be expanded by the addition of hydrophobic or hydrophilic fumed silica nanoparticles. It was found that the expansion of the morphology hysteresis zone in hydrophobic nanoparticle-filled blend stemmed from the suppression of droplet coalescence. However, the expansion in the morphological hysteresis zone for hydrophilic nanoparticle-filled blend, which was less noticeable, might originate from the more difficult breakup of PIB droplets upon the addition of nanoparticles.

Role of symmetric grafting copolymer on suppression of drop coalescence

The effect of copolymer compatibilizer on the rheology of polymer blends, as well as four-roll mill studies of the effect of compatibilizer on coalescence of a pair of drops is reported, with a focus on so-called symmetric systems with equal bulk fluid viscosities and a copolymer with equal block molecular weights. The primary experimental system consists of polybutadiene (PBd) and polydimethylsiloxane (PDMS) as the bulk polymers, with a “symmetric” PBd-COO-NH3+-PDMS copolymer with equal molecular weights on each block as compatibilizer. Motivated by earlier work of Martin and Velankar, we performed experiments with PBd as the drop phase and PDMS as the matrix phase and also experiments with the roles of these two materials reversed. The rheological properties for the inverted blends are distinct, as also shown by Martin and Velkankar, and the symmetric copolymer is also shown to have an asymmetric effect in the suppression of drop coalescence when we reverse the materials of drop phase and matrix phase. Two mechanisms can lead to the suppression of drop coalescence: immobilization of the interface due to Marangoni stress leading to slow drainage of the thin film between colliding drops, and steric hindrance of film thinning. At the same copolymer concentrations, we find that the Marangoni effect is the same independent of which fluid is the drop. However, the steric effect arises from the adsorbed copolymer forming an extended polymer brush configuration on the outside of the drop, and for our present system this contribution depends on whether PDMS or PBd is the continuous phase. In general, the conformation and thickness of a polymer brush depends not only on the copolymer concentration on the interface but also the MW of the copolymer block and the molecular weight of the corresponding bulk homopolymer. With PBd drops and PDMS as the continuous phase, the experimental evidence suggests that the brush layer formed by the PDMS block of the copolymer is too thin even at very high copolymer concentrations to produce a steric effect on coalescence. On the other hand, with PDMS drops and PBd as the continuous phase, the brush thickness external to the drop is sufficiently large at high copolymer concentrations (Γ > Γc), to totally prohibit drop coalescence in the four-roll mill. These studies suggest that it is the presence or absence of an extended brush, along with the effect on average drop size that is responsible for the differences in the rheological properties of the inverted blends.

Suppressing the coalescence in the multi-component lattice Boltzmann method

This article discusses a novel phenomenological approach for suppressing the coalescence in the Gunstensen multi-component lattice Boltzmann method (LBM). The suppression of coalescence is achieved by perturbing the terminal nodes of the ambient fluid’s thin layer trapped between the approaching droplets. This additional perturbation creates a local high pressure fluid layer which eventually leads to suppressing the coalescence of the neighboring droplets while maintaining a suitable qualitative force balance representative of the physical intermolecular forces which act between them.

Time-Resolved X-ray Diffraction Measurements of High-Density InAs Quantum Dots on Sb/GaAs Layers and the Suppression of Coalescence by Sb-Irradiated Growth Interruption

Self-assembly of high-density InAs quantum dots (QDs) on Sb-irradiated GaAs buffer layers was observed in-situ by a time-resolved X-ray diffraction (XRD) technique using a combination of XRD and molecular beam epitaxy. Evolution of dot height and lattice constant was analyzed during InAs QD growth and subsequent growth interruption (GI), and as a result, dislocated giant dots due to coalescence and coherent dots were separately evaluated. An Sb-irradiated GI (Sb-GI) method to be applied after InAs growth was attempted for the suppression of coalescence. Using this method, the XRD intensity of giant dots decreased, and the photoluminescence intensity of InAs QDs was enhanced. High-density InAs QDs without giant dots were produced by using the combination of the QD growth on the Sb-irradiated GaAs buffer layers and the Sb-GI.

Insights into the physics of spray coating of SWNT films

Spray coating is a scalable and high-throughput process for fabrication of transparent and conducting coatings (TCCs) composed of single-walled carbon nanotubes (SWNTs). Presently the fundamentals of this process are not well understood. We show that suppression of coalescence of spray droplets by sufficiently rapid heat- and mass-transfer yields homogeneous SWNT films by preventing the formation of ‘coffee stains’ of larger length scale. Such heat and mass transfer is driven by differential evaporation between the top and edges of the drops, whereas thermal and compositional effects on surface tension and buoyancy are weak. Ultrasonic spraying ensures that the droplets are deposited without significant splashing, and delayed splashing at higher Weber number is evidenced. We find that the performance of spray-coated TCCs made from HiPCO SWNTs is limited by bundle diameter rather than length of the constituent SWNTs and bundes. Vapor acid doping with concentrated sulfuric acid roughly doubles the conductivity of the TCCs.

The extended release properties of HPMC matrices in the presence of dietary sugars

The mechanisms and structure-activity by which dissolved dietary sugars influence drug release from hydroxypropyl methylcellulose (Methocel ® K4M) matrices were investigated. Drug release was retarded at lower sugar concentrations, but above a critical solute concentration ( S CRIT), there was marked acceleration of release. Studies of early gel layer formation suggested this resulted from sugar-induced suppression of HPMC particle swelling and coalescence, leading to gel structures with poorer diffusion-barrier properties and reduced resistance to physical erosion. Sucrose, lactose, D-glucose, D-galactose and D-fructose all exhibited this pattern but S CRIT values varied widely between sugars (0.5 M lactose, 1.15 M D-fructose). A polynomial relationship ( r 2 = 0.994) existed between S CRIT and the ability of the sugar to depress the polymer sol–gel transition temperature (ΔCPT). Structure activity relationships across a wide range of sugars suggested ΔCPT was related to molar hydroxyl number, the orientation of the C 4 hydroxyl and the β 1→4 linkage, all factors which influence sugar compatibility with water structure. The study demonstrates how sugars in high concentration can directly influence the performance of the gel diffusion barrier and matrix drug release characteristics. There is therefore potential for influencing drug release kinetics when high concentrations of sugars are co-administered in the fed state or when they are present in HPMC ER formulations.

Improvement of Luminescent Uniformity via Synthesizing the Carbon Nanotubes on a Fe–Ti Co-deposited Catalytic Layer

Uniformity has been considered to be one of the most important criteria for carbon nanotubes (CNTs) to be utilized as the emitters in field-emission displays (FEDs) or backlight units (BLUs). Using co-deposited Fe and Ti film as a catalyst, a uniform distribution of catalytic nanoparticles was obtained after hydrogen pretreatment as compared with nanoparticles obtained only using a pure Fe film. It might be attributed to the suppression of coalescence of the Fe nanoparticles in the co-deposited Fe–Ti film during the CNTs growth. In addition, the length variation of the CNTs synthesized by thermal-chemical vapor deposition (thermal-CVD) was also remarkably suppressed. This resulted in a significant improvement of the luminescent uniformity, and homogeneous light emission was obtained from the CNTs at 700 V.

Effect of antimony on the density of InAs/Sb:GaAs(1 0 0) quantum dots grown by metalorganic chemical-vapor deposition

We report the fabrication of high-density InAs quantum dots (QDs) grown on GaAs(1 0 0) substrate by metalorganic chemical-vapor deposition (MOCVD), obtained by antimony surfactant-mediated growth. We achieved InAs/Sb:GaAs QDs with dot density ranging from 2×10 10 cm to 2–11×10 11 cm −2, with complete suppression of coalescence. We studied the dependence of the total dot density and the density of coalesced dots on the growth conditions, such as antimony irradiation time, growth temperature and growth rate. Strongly enhanced PL intensity at room temperature (RT) was obtained from InAs/Sb:GaAs QDs with density above 4×10 10 cm −2, compared to reference InAs/GaAs QDs.

High density InAs∕GaAs quantum dots with enhanced photoluminescence intensity using antimony surfactant-mediated metal organic chemical vapor deposition

The antimony surfactant-mediated growth of InAs∕GaAs quantum dots (QDs) by metal organic chemical vapor deposition was investigated. The authors show that the growth of InAs QDs on Sb:GaAs(100) can result in both a strong increase of the dot density, up to 1011cm−2, and the suppression of coalescence. They achieved InAs∕Sb:GaAs QDs with density above 4×1010cm−2, ground-state emission above 1.30μm, and enhanced photoluminescence intensity at room temperature compared to that of InAs∕GaAs QDs. Remarkably, InAs∕Sb:GaAs QDs do not exhibit an emission blueshift under annealing at temperatures as high as 630°C, contrary to InAs∕GaAs QDs.