This review focuses on the current knowledge regarding (i) the mechanisms governing foamability and foam stability, and (ii) models for the foam column kinetics. Although different length scales of ...foam structure, such as air–water interface and liquid film, have been studied to elucidate the mechanisms that control the foamability and foam stability, many questions remain unanswered. It is due to the collective effects of different mechanisms involved and the complicated structures of foam sub-structures such as foam films, Plateau borders and nodes, and foam networks like soft porous materials. The current knowledge of the effects of solid particles on liquid film stability and foam drainage is also discussed to highlight gaps in our present level of understanding foam systems with solid particles. We also critically review and summarize the models that describe macroscopic foam behaviors, such as equilibrium foam height, foam growth and collapse, within the context of the mechanisms involved.
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•Mechanisms governing foamability and foam stability are reviewed.•Studies on interfacial properties and foam films are inadequate for foam properties.•Solid particles significantly affect film stability and foam drainage.•Foam growth and collapse are poorly quantified in the literature.
Surfactants are centrally important in many scientific and engineering fields and are used for many purposes such as foaming agents and detergents. However, many challenges remain in providing a ...comprehensive understanding of their behavior. Here, we provide a brief historical overview of the study of surfactant adsorption at the air–water interface, followed by a discussion of some recent advances in this area from our group. The main focus is on incorporating an accurate description of the adsorption layer thickness of surfactant at the air–water interface. Surfactants have a wide distribution at the air–water interface, which can have a significant effect on important properties such as the surface excess, surface tension, and surface potential. We have developed a modified Poisson–Boltzmann (MPB) model to describe this effect, which we outline here. We also address the remaining challenges and future research directions in this area. We believe that experimental techniques, modeling, and simulation should be combined to form a holistic picture of surfactant adsorption at the air–water interface.
Hydrogen and methane can be molecularly incorporated in ice-like water structures up to mass fractions of 4.3% and 13.3%, respectively. The resulting solid structures, called gas hydrates, offer ...great potential for the efficient storage of hydrogen and natural gas. However, slow gas encapsulation by bulk water hinders this application. Porous structures have been shown to effectively promote gas hydrate formation and are a potential enabler for the development of hydrate-based gas storage technologies. Here, we offer an insightful perspective on using porous structures as nanoreactors for achieving fast gas hydrate formation for gas storage applications. We critically discuss and elucidate the working mechanisms of nanoreactors and identify the criteria for efficient nanoreactors. Based on the concepts founded, we propose a theoretical framework for designing next-generation porous materials for delivering better promoting effects on gas hydrate formation.
An effective flotation collector determines the flotation performance and efficiency of fine coal particles. Generally, hydrocarbon oils, such as diesel and kerosene are widely applied in the ...flotation circuit in coal preparation plants. However, hydrocarbon oils are not effective enough for difficult-to-float coals, such as low rank coal and difficult to float coking coal. In this study, the mixture of candle soot and hydrocarbon oil (dodecane) was used as a novel flotation collector in the flotation of coking coal and low rank coal. X-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to indicate the surface properties of candle soot. Scanning electron microscopy with energy dispersive spectrometer (SEM/EDS) and attachment time measurer were used to show the adsorption of candle soot on coal particle surface. XPS and contact angle results showed that the candle soot was very hydrophobic. SEM/EDS results showed the candle soot consisted of plenty of carbon nanoparticles which could attach and adsorb on the coal particle surface and hence shortens the attachment time of coal particle and bubble. The flotation recovery of both coking and low rank coals using the mixture of candle soot and dodecane as a collector were higher than that using solo dodecane as collector. The adsorption of candle soot and other ultra-fine particles on coal particle surface enhanced the surface hydrophobicity and floatability of coking and low rank coal particles.
•Candle soot is super-hydrophobic and can be used to enhance coal flotation.•Mixing candle soot with hydrocarbon oil to create a novel flotation collector.•Candle soot collector particles can adsorb onto the coal surface.•Candle soot speeds up the rupture of water film between coal particle and bubble.•Flotation performance using this novel collector is much better.
Additives such as surfactants, polymers, salts, and hydrophobic particles are well-known (and used) to influence gas hydrate formation (GHF). This paper reviews and discusses the mechanisms of their ...effects. The effects of additives on GHF appear to vary greatly from one additive to another. Even a given additive can change from a promoter to an inhibitor and vice versa when the working conditions are changed. The available literature cannot explain the diverse effects of additives. We argue that the hydrophobic effect plays a critical role in gas hydrate formation. A dissolved hydrophobe organizes the surrounding water into a clathrate-like structure and thereby promotes hydrate formation. A hydrophile, however, disrupts the surrounding water structure and inhibits hydrate formation. Moreover, cooperative hydrophobic interactions create an increased gas concentration around a hydrophobe, which also favors the hydrate formation. In contrast, a hydrophile competes with the gas for water and thereby hinders hydrate formation. In particular, when the additive is an amphiphile, the observed effect is the result of the competition between the hydrophobic moiety (a promoter) and hydrophilic moiety (an inhibitor). This hypothesis provides a universal explanation for the various effects of hydrate additives.
•Cu-activated sphalerite and pyrite were characterised by XPS and zeta potential.•Covellite on sphalerite is formed by reducing exchanged Cu2+ to Cu+ and oxidising S2− to S−.•Chalcopyrite on pyrite ...is formed by reducing Cu2+ to Cu+, oxidising S2− to S− and Fe2+ to Fe3+.•Depth profiling shows Cu diffusion to sphalerite up to 10nm and 3nm Cu-product on pyrite.•The zeta potentials confirmed CuS and CuFeS2 on sphalerite and pyrite, respectively.
Adsorption of copper sulphate onto the sphalerite and pyrite surfaces during the selective flotation is not fully understood. In this paper, this phenomenon is investigated by Cryogenic X-ray Photoelectron Spectroscopy (Cryo-XPS) and zeta potential measurements. The Cryo-XPS results have showed that the copper activation occurs in two steps. For sphalerite, surface Zn2+ is substituted by Cu2+ by ion exchange reaction, and then CuS-type layer is formed by reduction of the exchanged Cu2+ to Cu+ and oxidation of surface S2− to S−. Cu2+ can also activate pyrite, first, through reduction of Cu2+ to Cu+ and oxidation of surface S2− species to S−, then surface Fe2+ is oxidised to Fe3+ by reduction of S− to S2−, leading to the formation of CuFeS2-type layer. In the reducing potential of the activation, enhancement of copper adsorption on the pyrite surface is confirmed by XPS. Depth profiling after 10min activation revealed copper diffusion into the sphalerite lattice up to 10nm, while the thickness of the activation product on pyrite surface was less than 3nm. The zeta potential studies confirmed CuS-type layer formation on copper activated sphalerite, whereas the surface product of the activated pyrite was CuFeS2-type. This study leads to a better understanding of sphalerite-pyrite Cu2+ activation during flotation for an effective separation.
Hydrophobic solid surfaces have been found to promote the formation of gas hydrates effectively and thus help to realize the immense potential applications of hydrates in many sectors such as energy ...supply, gas storage and transportation, gas separation, and CO2 sequestration. Despite the well-known effectiveness, the molecular mechanism behind the promotion effect has not been thoroughly understood. In this work, we used both simulation and experimental means to gain insights into the microscopic level of the influence of hydrophobic solid surfaces on gas hydrate formation. On one hand, our simulation results show the presence of an interfacial gas enrichment (IGE) at hydrophobic surface and a gas depletion layer at hydrophilic surface. In the meantime, the analysis of water structure near the hydrophobic solid interface based on the molecular trajectories also shows that water molecules tend to get locally structured near a hydrophobic surface while becoming depressed near a hydrophilic surface. On the other hand, the experimental results demonstrate the preferential formation of gas hydrate on a hydrophobic surface. The synergic combination of simulation and experimental results points out that the existence of an IGE at hydrophobic solid surface plays a key role in promoting gas hydrate formation. This work advances the molecular level understanding of the role of hydrophobicity in governing the gas hydrate as well as interfacial phenomena in general.
Some salts have been proven to inhibit bubble coalescence above a certain concentration called the transition concentration. The transition concentration of salts has been investigated and determined ...by using different techniques. Different mechanisms have also been proposed to explain the stabilizing effect of salts on bubble coalescence. However, as yet there is no consensus on a mechanism which can explain the stabilizing effect of all inhibiting salts. This paper critically reviews the experimental techniques and mechanisms for the coalescence of bubbles in saline solutions. The transition concentrations of NaCl, as the most popularly used salt, determined by using different techniques such as bubble swarm, bubble pairs, and thin liquid film micro-interferometry were analyzed and compared. For a consistent comparison, the concept of TC95 was defined as a salt concentration at which the “percentage coalescence” of bubbles reduces by 95% relative to the highest (100% in pure water) and lowest (in high-salt concentration) levels. The results show a linear relationship between the TC95 of NaCl and the reciprocal of the square root of the bubble radius. This relationship holds despite different experimental techniques, salt purities and bubble approach speeds, and highlights the importance of the bubble size in bubble coalescence. The available theoretical models for inhibiting effect of salts have also been reviewed. The failure of these models in predicting the salt transition concentration commands further theoretical development for a better understanding of bubble coalescence in salt solutions.
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•Review of experimental techniques and results of bubble coalescence in salt solutions•“TC95” found consistent for NaCl transition concentrations by different techniques•Linear change of TC95 of NaCl vs. reciprocal of the square root of bubble size•Review of hypotheses for bubble coalescence inhibition in salt solutions•Theoretical models for transition salt concentrations were reviewed and scrutinized.
Sexually transmitted diseases are major causes of infertility, ectopic pregnancy, and premature birth. Here, we developed a new multiplex real-time polymerase chain reaction (PCR) assay for the ...simultaneous detection of nine major sexually transmitted infections (STIs) found in Vietnamese women, including Chlamydia trachomatis, Neisseria gonorrhoeae, Gardnerella vaginalis, Trichomonas vaginalis, Candida albicans, Mycoplasma hominis, Mycoplasma genitalium, and human alphaherpesviruses 1 and 2. A panel containing three tubes × three pathogens/tube was predesigned based on double-quenched TaqMan probes to increase detection sensitivity. There was no cross-reactivity among the nine STIs and other non-targeted microorganisms. Depending on each pathogen, the agreement with commercial kits, sensitivity, specificity, repeatability and reproducibility coefficient of variation (CV), and limit of detection of the developed real-time PCR assay were 99.0%-100%, 92.9%-100%, 100%, <3%, and 8-58 copies/reaction, respectively. One assay cost only 2.34 USD. Application of the assay for the detection of the nine STIs in 535 vaginal swab samples collected from women in Vietnam yielded 532 positive cases (99.44%). Among the positive samples, 37.76% had one pathogen, with G. vaginalis (33.83%) as the most prevalent; 46.36% had two pathogens, with G. vaginalis + C. albicans as the most prevalent combination (38.13%); and 11.78%, 2.99%, and 0.56% had three, four, and five pathogens, respectively. In conclusion, the developed assay represents a sensitive and cost-effective molecular diagnostic tool for the detection of major STIs in Vietnam and is a model for the development of panel detections of common STIs in other countries.
•The principles of magnetic separation have been critically reviewed.•Both external and interparticle forces for ultrafine particles are reviewed and compared.•Suspensions stability of the particles ...factors are described and analyzed.•Various modeling of magnetic flocculation are introduced and some of the applications are illustrated.
Magnetic separation has been used in industries to concentrate or remove magnetic minerals/particles for many years. The separation of ultrafine magnetic particles is significantly influenced by aggregation between particles due to various external and interparticle forces, such as gravity, magnetic attraction, van der Waals, electrical double-layer, hydrodynamic, and Brownian diffusion forces. This review focuses on the principles of the magnetic flocculation and separation of micrometer-sized particles in solution. Potential energies between particles are linked to the particle aggregation (i.e. stability), sedimentation and dispersion in applied magnetic fields. Prediction and control of magnetic flocculation are achieved by simulating particle motions around the surface of the magnetic separators using various mathematical models, with some large-scale applications of magnetic flocculation are being demonstrated.
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