Search

This paper investigates the flotation of cassiterite (SnO2) from ore using ricinoleic acid (RA) as a collector which is cheap and environmentally friendly. It is shown that the flotation is significantly enhanced by the activation of lead cations at pH 8. The flotation results are explained and supported by further studies to determine the changes in surface properties (hydrophobicity and surface potentials) and adsorption of RA and lead cations using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and FTIR. The results of surface (zeta) potential measurements and TOF-SIMS indicate that the amount of RA anions on the Pb-activated SnO2surface was higher than that on the natural SnO2surface. The XPS results revealed that RA anions were bound to the Sn atoms on the natural SnO2surface. In contrast, RA anions reacted with the Pb atoms instead of Sn atoms on the activated SnO2surface, improving the floatability of Pb-activated SnO2. Pb(RA)2precipitation occurred on the Pb-activated surface, and H bonds were formed between two RA anions in Pb(RA)2, which lead to a tighter assembly of collector species on the SnO2surface. The outcomes of this research shed light on the application of the cost-effective and environmentally friendly RA collector in cassiterite flotation.

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.

Objective/Background:Zingiber monophyllumGagnep., a member of the Zingiberaceae family, is known for its significant biological activities. The current study aimed to determine the volatile components of the ethyl acetate (EtOAc) fractionated extract found in the rhizomes of this species. This is the first report on the chemical composition and bioactivities of Z. monophyllumrhizomes fractionated extract. Methods:The chemical constituents were analyzed and determined using gas chromatography-mass spectrometry (GC-MS). Antioxidant activities were evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays using ascorbic acid as a positive control. Antibacterial and antifungal properties of the EtOAc fractionated extract of Z. monophyllumrhizomes were assessed against Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus, and Candida albicans. Density functional theory (DFT) and molecular docking were also employed to illustrate antioxidant and antimicrobial activities. Results:Nine components were identified by GC-MS analysis from the EtOAc fractionated extract of Z. monophyllumrhizomes. (E)-labda-8(17),12-diene-15,16-dial (9), spathulenol (2), and neointermedeol (5) were the major components (21.8%, 16.8%, and 11.9%, respectively). Moderate antioxidant activities of the EtOAc fractionated extract were observed viaboth the DPPH assay and the FRAP assay using ascorbic acid as the standard compound. The extract demonstrated remarkable antimicrobial activity against all examined microbial strains, except for P. aeruginosa. The DFT study analyzed the antioxidant potential of each component in the fractionated extract. Molecular docking study chose E. faecalisDNA gyrase B, E. coliDNA gyrase B, S. aureusbiotin protein ligase, E. faecalisAlanine racemase, and C. albicansN-myristoyltransferase as potential target proteins for antimicrobial activity. Conclusion:In this study, the chemical composition of the EtOAc fractionated extract of Z monophyllumrhizomes was demonstrated through GC-MS analysis for the first time. Nine components, including alloaromadendrene, spathulenol, globulol, τ-cadinol, neointermedeol, aromadendrene oxide-(2), ambrial, (E)-15,16-dinorlabda-8(17),11-dien-13-one, and (E)-lambda-8 (17),12-diene-15,16-dial along with relative content were identified in this fractionated extract. The bioassays revealed that the fractionated extract showed moderate antioxidant activities and significant antimicrobial activities. The antioxidant and antimicrobial potential of each component was also theoretically examined by the DFT study and molecular docking study, respectively.

Surfactant adsorption at the air–water interface is critical to many industrial processes but its dependence on salt ions is still poorly understood. Here, we investigate the adsorption of sodium dodecanoate onto the air–water interface using model saline waters of Li+or Cs+at pH values 8 and 11. Both cations enhance the surfactant adsorption, as expected, but their largest effects on the adsorption also depend on pH. Specifically, surface tension measurements, sum-frequency generation spectroscopy, and microelectrophoresis show that small (hard) Li+enhances the surfactant adsorption more than large (soft) Cs+at pH 11. This effect is fully reversed at pH 8. We argue that this salting-up (increasing adsorption) reversal is attributable to the conversion of the neutralized carboxylic (−COOH) headgroup at pH 8 into the charged carboxylate (−COO–) headgroup at pH 11, which, respectively, interact with Cs+and Li+favorably. Molecular dynamics simulation shows that the affinity of Cs+to the interface is decreased and eventually overtaken by Li+as the carboxylic groups are deprotonated. This study highlights the importance of the charge and size of salt ions in selecting surfactants and electrolytes for industrial applications.

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.

The attachment of air bubbles to solid surfaces in water is encountered in many natural processes and industrial applications. It has been established that the attachment can occur between hydrophobic surfaces and air bubbles. In this paper, we present novel experimental results to quantify the attachment in terms of the attachment time. We show that the attachment time can be determined from either the transient force curve or the transient film thickness. These techniques for determining the attachment time are based on the fact that the rupture of a thin liquid film produces a large attachment force and a rapid expansion of the three-phase contact radius in comparison with the expansion of the film radius. The experimental results are quantitatively analyzed using thin-film drainage theory and intermolecular forces, which include the advanced multilayer van der Waals force and the electrical double-layer force. The advanced van der Waals force theory allows us to incorporate the effect of interfacial gas enrichment (IGE) of dissolved gas in water at hydrophobic surfaces on the bubble-surface attachment. Critically, if the presence of IGE is ignored, the experimental results do not agree with the theory. Finally, IGE is shown to be a significant factor in controlling hydrophobic attraction between an air bubble and a hydrophobic surface and their attachment.

Ionic surfactants behave differently in the presence of various counterions, which plays an important role in many scientific and engineering processes. Previous work has shown that the counterion-specific surface tension can be reproduced with classical adsorption models, but the underlying origin of this effect has not been explained. In this paper, we extend our previously developed adsorption model to account for the specific counterion adsorption. This model can accurately predict the surface tension of surfactant solutions like sodium dodecyl sulfate (SDS) in the presence of the monovalent salts LiCl, NaCl, KCl, and CsCl. The predicted surface excess and surface potential are validated by corresponding sum-frequency generation (SFG) spectroscopy experiments. We also used molecular dynamic (MD) simulation to explain the origin of the counterion-specific effect for surfactant behavior. Our study shows that for SDS, binding of the counterion to both the headgroup and a few CH2fragments close to the surfactant head contributes to the counterion-specific effect. In general, SDS behaves like a large ion, and it prefers to bind with large counterions such as Cs+, which is consistent with Collins’s law of matching water affinity. Therefore, large counterions enhance the surface adsorption and lower the surface tension the most.

The short-range attractive forces between hydrophobic surfaces are key factors in a wide range of areas such as protein folding, lipid self-assembly, and particle–bubble interaction such as in industrial flotation. Little is certain about the effect of dissolved (well-controlled) gases on the interaction forces, in particular in those systems where the formation of surface nanobubble bridges is suppressed. Here, we probe the short-range attractive force between hydrophobized silica surfaces in aqueous solutions with varying but well-controlled isotherms of gas solubility. The first contact approach force measurement method using AFM shows that decreasing gas solubility results in a decrease of the force magnitude as well as shortening of its range. The behavior was found to be consistent across all four aqueous systems and gas solubilities tested. Using numerical computations, we corroborate that attractive force can be adequately explained by a multilayer dispersion force model, which accounts for an interfacial gas enrichment (IGE), that results in the formation of a dense gas layer (DGL) adjacent to the hydrophobic surface. We found that the DGL on the hydrophobic surface is affected only by the concentration of dissolved gases and is independent of the salt type, used to control the gas solubility, which excludes the effect of electrical double-layer interactions on the hydrophobic force.

Surfactants and/or salts at low concentrations are inherently relevant to gas hydrate formation in nature and industry. However, the combined effects of surfactants and salts at low concentrations on gas hydrate formation are poorly understood. Here, we aim to fill this gap of knowledge by examining the effects of sodium dodecyl sulfate (SDS) and sodium iodide (NaI) at millimolar concentrations on methane hydrate formation. We show that adding NaI to dilute SDS solutions reduces the induction time significantly, promoting gas hydrate nucleation. Meanwhile, adding NaI adversely reduces the growth of methane hydrate. Fundamental studies based on sum frequency generation spectroscopy indicate an electrostatically aligned water layer at the gas–SDS solution interface caused by the charged interface as a result of surface adsorption of dodecyl sulfate anions. This aligned interfacial water layer hinders the nucleation of gas hydrate at the gas–SDS solution interface. Added NaI diminishes the alignment of interfacial water, thereby favoring the nucleation of the gas hydrate. Even though, the adverse (inhibiting) effect of added NaI on the methane hydrate growth remains a puzzling observation that requires further investigations. This study sheds more light on gas hydrate formation in surfactant- and salt-containing systems that are important to many phenomena in nature and applications in the industry.

Foam films formed at the air–water interface do not have fixed adsorption sites where adsorbed surfactants can arrange themselves, resulting in the formation of thick adsorption layers. Current theories of equilibrium foam films fail to account for this feature and significantly underestimate the adsorption layer thickness. Here we show that this thickness has a significant effect on the disjoining pressure in foam films. If ignored, the theory predicts unphysical electrostatic potential profiles, which underestimate the disjoining pressure. We apply a previously developed adsorption model that incorporates a realistic thickness for the adsorption layer. This new model reproduces experimental measurements of the disjoining pressure of foam films very well over a wide surfactant concentration range without fitting parameters. Our work shows that a thick adsorption layer is less effectively screened by counterions, resulting in a higher electrostatic potential inside the film and therefore a higher disjoining pressure.

Gas hydrates are crystalline solids composed of water and gases. They occur abundantly in nature and are potentially significant to industry. Solid surfaces and confined spaces strongly affect the formation of gas hydrates. Research into this particular topic is active, particularly aiming to understand the effects of solid surfaces and confinements on gas hydrate formation and using functional solids for controlling the formation kinetics. Experimental observations appear to vary from one solid to another. The observations demand a knowledge of (1) why the effects vary among the solids and (2) what factors are determining. Here, we critically review experimental observations, discuss the underlying mechanisms, and generalize the literature findings for a better understanding of the mechanism. It is inferred that open hydrophobic solids can promote gas hydrate formation via a tetrahedral ordering of water and an increased density of gases at the solid–water interfaces. Open hydrophilic solids hinder gas hydrate formation via a distorted water structure and a depleted density of gases at the solid–water interfaces. Confining solids have rather complex effects due to the complexity of wetting in confined spaces. Therefore, confined media with moderate wettability and partial water saturation might provide optimum conditions for gas hydrate formation.

Soluble surfactants form thick adsorption layers at the air–liquid interface, but classical adsorption models fail to account for it as they treat the adsorption layer as a mathematical plane (of zero thickness). This simplification has produced several inconsistencies between theoretical predictions and experimental results, especially for the surface potential. Here, we develop a new adsorption model for ionic surfactants at the air–water interface that incorporates the effect of the adsorption layer thickness using a modified Poisson–Boltzmann equation that integrates information from molecular dynamics simulation. We show that the surface potential depends sensitively on both the thickness of the adsorption layer and the interfacial depth at which the surface potential is probed. This model, therefore, provides a much more accurate picture of the surface potential than classical models.

Details about the molecular structures of surfactant mixtures adsorbed at the air–water interface have been controversial. Using sum frequency generation vibrational spectroscopy (SFG) and isotope labeling, we show here for the first time that mixtures of dodecanol (DOH) and sodium dodecyl sulfate (SDS) adsorb at the air–water interface with the formation of a head-to-tail complex. We observed this complex formation to occur first in the aqueous subphase, followed by complex adsorption onto the interface. This new piece of evidence for the head-to-tail complex conformation contradicts the conjectured tail-to-tail adsorption of the surfactant mixtures. The SFG data also show the dominating adsorption of the SDS–DOH complex over the single molecules of SDS and DOH at the air–water interface. The interfacial DOH-to-SDS molecular ratio of approximately 2.2:1 at a DOH-to-SDS bulk concentration ratio of 10 μM/2 mM was determined by isotope labeling of the surfactants. In addition to a smaller number of gauche defects, the DOH–SDS complex was found to adopt a higher level of orderliness than the adsorbed single surfactants. These findings provide important insights into the descriptions and interpretation of DOH–SDS adsorption at the air–water interface and its properties.

Interfacial gas enrichment (IGE) of dissolved gases in water is shown to govern the strong attraction between solid hydrophobic surfaces of an atomic force microscopy (AFM) colloidal probe and solid substrate. However, the role of IGE in controlling the attraction between fluid–fluid interfaces of foam films and emulsion films is difficult to establish by AFM techniques because of the extremely fast coalescence. Here, we applied droplet-based microfluidics to capture the fast coalescence event under the creeping flow condition and quantify the effect of IGE on the drainage and stability of water films between coalescing oil droplets. The amount of dissolved gases is controlled by partially degassing the oil phase. When the amount of dissolved gases (oxygen) in oil decreases (from 7.89 to 4.59 mg/L), the average drainage time of coalescence significantly increases (from 19 to 50 ms). Our theoretical quantification of the coalescence by incorporating IGE into the multilayer van der Waals attraction theory confirms the acceleration of film drainage dynamics by the van der Waals attractive force generated by IGE. The thickness of the IGE layer decreases from 5.5 to 4.9 nm when the amount of dissolved gas decreases from 7.89 to 4.59 mg/L. All these results establish the universal role of dissolved gases in governing the strong attraction between particulate hydrophobic interfaces.

Capillary force is critical to the floatability of particles at the air–water interface. Quantification of the capillary force requires solving the Young–Laplace equation using suitable boundary conditions (BCs) at the triple contact line. For axisymmetric (two-dimensional, 2D) systems, such as single spheres floating at an initially flat air–water surface, both the Dirichlet (constant contact depth) and Neumann (constant contact angle) BCs can be applied. For three-dimensional (3D) systems, Neumann BCs (NBCs) have been successfully used. In this paper, we have challenged the use of NBCs for the 3D deformation of the air–water surface induced by floating particles, which always exhibit intrinsic contact angle (CA) hysteresis that is significantly amplified in 3D systems. Specifically, we designed and conducted the experiments using single prismatic particles, which allowed for the determination of two characteristic CAs at the two diagonal axes with a high degree of certainty. We calibrated the numerical solution to the 3D Young–Laplace equation using the deformed air–water interface profiles at the two diagonal axes and then validated the numerical solution for the capillary force on the floating particles with the measured force. We obtained reliable data for the CA along the three-phase contact line (TPCL), which displayed a significant distribution. We also discussed the findings that were significant to floating spheres in asymmetric systems, such as pairs of floating spheres. This paper provides experimental and theoretical evidence that the CA is not constant along the contact line in a 3D geometry, which invalidates the use of NBCs for 3D systems of floating particles. This study highlights the significance of the CA variation known as CA hysteresis, which should be considered when predicting the floatability of particles at the air–water interface.

The surface saturation of solutions of three low molecular weight surface-active alcohols was identified independently of bulk solution using sum frequency generation spectroscopy. Tensiometry showed that the solution surface tension kept decreasing uniformly and considerably, even after full saturation of the adsorption monolayer. We employed Guggenheim’s model of the extended interface to attribute this observation to the ongoing adsorption of alcohol molecules beneath the saturated topmost adsorption layer. Our investigation of the dynamic behavior of thin liquid films of the alcohol solutions revealed the tremendous effect of under-monolayer adsorption on the rheological characteristics of the surface. The under-monolayer region was found to function as a supplementary source of alcohol molecules. The fast diffusion of surfactants from the under-monolayer region to the topmost adsorption layer imposed a buffering effect on the dynamic response of the surface through diminishing the surface tension gradient created by the surface expansion. This resulted in a sudden drop of the surface elasticity and consequently a faster-decaying foam. While equilibrium surface tension does not distinguish between the monolayer and the under-monolayer, the dynamic properties of a fluid surface seem to be sensitive to the adsorption geometry.

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 CO2sequestration. 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.

AbstractWe consider the evolution of cooperation in finite populations and we model a scenario where two individuals can interact only if both intend to do so with their counterpart. This feature allows a possibility for individuals to remain alone for a given round and not interact with anybody. Such an individual receives a baseline payoff rather than one based upon a matrix game. We provide sufficient conditions on the payoff matrix that will guarantee fixation probabilities to be monotone relative to the baseline payoff. We then apply the findings to the Prisoner’s Dilemma and Hawk-Dove games. In both cases, the possibility that an individual might remain alone increases the chances that cooperation or non-aggression fixes within the population. Moreover, weak selection models overlap with our model, and we consider how one can generalize our model even further.

Interfacial water in close proximity to an adsorbed surfactant layer plays an important role in many areas. Here, we systematically investigate the interfacial water structure at the adsorption layer of cetyltrimethylammonium bromide (CTAB) from low concentrations to its critical micelle concentration. Our sum frequency generation (SFG) spectroscopy results show that, with increasing CTAB concentration, the water SFG signals first increase, reaching maximum intensities at 0.1 mM, and then drop, whereas the ppp SFG signals of the terminal-methyl asymmetric stretch reach maximum intensities and saturate at 1 mM, which is the critical micelle concentration of CTAB. Our analysis reveals that the interfacial water layer adopts the most orderly arrangement when the interfacial potential of the adsorption layer reaches saturation and not at the surfactant concentration of adsorption saturation. Most importantly, our SFG data provide direct evidence for the antagonistic effects of the interfacial potential and thickness compression of the electrostatic field of the surfactant adsorption layer, leading to the strongest water SFG signals at 0.1 mM. Below 0.1 mM, the increased interfacial potential can have a pronounced effect on the increase of the overall dipole moment of the interfacial water layers. Above 0.1 mM, the decreased Debye screening length significantly reduces the water dipole moment. Finally, the newly proposed adsorption model cannot explain our SFG results.

The adsorption of heavy metal ions onto negatively charged oxide (quartz) surface in environmental settings produces three surface charge reversals (CRs) described as CR1 at low pH, CR2 at middle pH, and CR3 at high pH. The available physical quantitative approaches cannot predict all these CRs and are not applicable for low salt concentrations (< 1 mM). In this study, a new model was presented to describe the CRs of the Pb(II)-quartz system by combining the ion distribution as the inner- and outer-sphere complexes within the compact (Stern) layer of the electrical double layer theory and the adsorption of Pb(II) hydroxocomplexes by the surface complexation and precipitation. The results indicated that the model agreed with the measured surface (zeta) potential values and the observed CRs for quartz particles in Pb(II) solutions over a wide range of Pb(II) concentrations, pH, and solution ionic strength. The model showed the pivotal role of Pb(II) polynuclear hydroxocomplexes (PNHCs) such as Pb3OH42+in the appearance of the CR2. The predicted surface binding constants for PNHCs were lower than their corresponding hydrolysis constants which implied an earlier formation of those species at the interface than in the bulk solution. Increasing the solution ionic strength reduced the magnitude of surface potential and shifted the CR2 to higher pH values. The model was also validated with the literature data. With better understanding the role of PNHCs sorption and CR mechanisms, this model may also be adapted to other systems containing multivalent ions that are relevant to environmental applications.

Bubble coalescence in some salt solutions can be inhibited if the salt concentration reaches a critical concentration Ccr. There are three models available for Ccrin the literature, but they fail to predict Ccrcorrectly. The first two models employ the van der Waals attraction power laws to establish Ccrfrom the discriminant of quadratic or cubic polynomials. To improve the two models, the third model uses the same momentum balance equation of the previous models but different intermolecular force generated by water hydration with exponential decaying. The third prediction for Ccrrequires the experimental input for film rupture thickness and is incomplete. We show further in this paper that the third model is incorrect. We propose a novel methodology for determining Ccrwhich resolves the mathematical uncertainties in modeling Ccrand can explicitly predict it from any relevant intermolecular forces. The methodology is based on the discovery that Ccroccurs at the local maximum of the balance equation for the capillary pressure, disjoining pressure, and pressure of the Gibbs–Marangoni stress. The novel generic approach is successfully validated using nonlinear equations for complicated disjoining pressure.

Responsive silica surfaces empower their smart applications for catalysis, mass transfer, and self-cleaning. Here, we reveal the molecular signature of an unexpected hydrophobization of silica surfaces as their pH response in a lead nitrate solution. Strikingly, the pH-dependent sum frequency generation (SFG) spectra of silica surfaces show two profound minima of the intensity at pH = 7.2 and 10.2, respectively. Our in-depth analysis of SFG spectra using the maximum entropy method show emerging vibrational bands at >3600 cm–1for the surface-bound water at this pH range, which are similar to the stretching modes of the dangling OH at the air–water surface. The observed minima in SFG intensity and the occurrence of the “hydrophobic-like” stretching modes of interfacial water provide a molecular fingerprint of the hydrophobicity of the silica surfaces, which is confirmed by contact angle measurements. These step-change findings help better deal with silica-related processes in nature and technologies.

The solid surfaces used in evaporation studies of nanoparticle sessile droplets usually exhibit significant surface roughness, causing significant pinning of the three-phase contact lines and producing different types of nanoparticle deposits, from single and multiple coffee rings (formed at the initial pining of triple contact lines) to central bumps. Here we used nanometer-scale smooth hydrophobic surfaces to investigate the evaporation of sessile water droplets containing silica nanoparticles and organic pigment nanoparticles. We observed a new type of coffee ring deposits which were not formed at the initial pinning but at the later pinning. We referred them to as the inner coffee ring deposits (ICRDs). The radius of ICRDs was smaller than the radius of the initially pinned contact area and increased with increasing concentration of added salts and nanoparticles and with increasing contact angle hysteresis of hydrophobic surfaces. We also observed different dendrite deposit patterns inside ICRDs. We argue that all the deposit patterns are due to the second pinning of the three-phase contact lines, which occur when the forces on particles are balanced. The hypothesis is further supported by the transient changes of the dynamic contact angles and contact base area radius. The contact angle hysteresis, the particle concentration, and the colloidal interaction forces such as the electrical double-layer forces play a vital role in determining the size and patterns of ICRDs and the evaporation kinetics of nanoparticle sessile droplets.

This paper describes the measured forces between a spherical silica particle and a planar oxidized silicon wafer in NaCl, KCl, and CsCl aqueous solutions using an atomic force microscope (AFM). The magnitudes of measured forces are sensitive to electrolyte type and concentration over a broad range of 0.01–4 M under study. Increasing NaCl and KCl concentrations finds the suppression of repulsion at low concentrations, the appearance of attraction at an intermediate concentration, and the suppression of the attraction at high concentrations. In contrast, no attractions were detected for CsCl solutions except at 0.5 M, and increasing the concentration would lead to suppression of repulsion at the low concentration range and enhancement of repulsion at the high concentration range. The deviation between the measured total force and the calculated double-layer repulsion can be represented in the form of a power law incorporating an effective Hamaker constant (Aeff) and an offset separation distance.

We have investigated the control preparation and aqueous stability of a potential suspension fertilizer: zinc hydroxide nitrate. We have observed that this compound can be synthesized by quick precipitation of zinc nitrate in sodium hydroxide solution under various conditions, whereas it can also be readily transformed to more stable Zn(OH)2or ZnO at pH >6.5 and aged at 50 °C. The transformation from zinc hydroxide nitrate to Zn(OH)2and ZnO has been examined with XRD/FTIR/SEM techniques and discussed in detail, presumably involving the formation and dissociation of the intermediate solution species [Zn(OH)4]2–/[Zn(OH)3]−. We have also found that as-prepared zinc hydroxide nitrate crystals are very stable when they are isolated and then dispersed in aqueous solution with pH 5–9 while slightly dissolved to give zinc ion concentration of 30–50 mg/L. Such aqueous stability and solubility have thus suggested that this compound can be used as a long-term zinc foliar fertilizer of various crops.

The mechanochemical solid-state synthesis of ZnxCd1-xS nanoparticles from zinc acetate, cadmium acetate and sodium sulphide in a planetary laboratory mill is described. Through changing the molar ratio of the Zn and Cd precursors, ZnxCd1-xS nanoparticles of different composition were prepared. Structural, surface and morphological properties were investigated by XRD, XPS, SEM and UV-VIS. Diffusion structural diagnostics was characterised by the emanation thermal analysis (ETA) results measured on heating of the samples. The cubic phase was found to be stable under mechanochemical treatment, as determined by XRD. The mixed phases were found to have ideal solution behaviours. In addition, microstructural characterisation indicated that mechanochemical treatment resulted in a structural refinement with a surface weighted crystallite size about 2 nm. The additional information of microstructure development and transport properties of the samples on heating was obtained by ETA. The calculated lattice parameters of mixed crystals linearly depend on the composition of ZnxCd1-xS nanoparticles. The S(2p), Zn(2p) and Cd(3d) core levels of the ZnxCd1-xS nanocrystallites reveal two different types of sulphur, zinc and cadmium unlike bulk CdS and ZnS. The calculated results indicate that the quantum-size effect in the nanoparticles is not negligible. The differences in the absorption edge and the emission peak position of the nanoparticles depend not only composition. Applied high-energy milling is a facile, efficient, and scalable process that does not require a solvent and can be performed under ambient conditions. Therefore, it is a promising candidate for the production of nanocrystalline materials.

The article examines the parameters influencing the corrosion of metallic coatings on wire exposed to marine environments. Marine aerosol carried inland from the ocean is main source of corrosion. It is made up of discrete particles of a given distribution in size. The aerosol capture efficiency was found to be markedly higher for 1 mm diameter cylinders. Its mode of capture is dependent on particle size with small particle size being affected by turbulent diffusion.

Bubble–particle dewetting kinetics relevant to froth flotation was experimentally studied on a modelled system using a CCD high-speed video microscopy. The experimental system included a gas–liquid interface formed at the bottom of a glass capillary filled with either deionized Milli-Q water or a solution of dodecylamine chloride DAC and hydrophobic glass beads dropping onto the interface in the solution inside the capillary under gravity. The dewetting process was observed underside the gas–liquid interface with a metallographic inverted microscope and a CCD high-speed video system operating at about 1000 frames s−1for imaging the dewetting process. The velocities of the dewetting process showed a maximum in the pH-domain where the flotation recovery also showed a maximum. This good correlation between the dewetting kinetics and flotation recovery indicates that the dewetting kinetics is equally necessary as the thinning and rupture of the intervening liquid film between bubbles and particles for success of the flotation process. The discussion highlighted the need of developing a better understanding of the particle–bubble contact interaction, in particular, the difference in contact angles on micron-sized particles and flat surfaces.

In this study the bubble size distribution and energy dissipation rate are measured in a plunging liquid jet bubble column. The maximum stable bubble diameter in the mixing zone was successfully predicted based on Weber number analysis. A Pareto analysis indicated that the coalescence of bubbles principally occurred as a binary process. The bubble number flux was modeled based on the bubble number concentration, collision frequency of two bubbles of the same diameter, and the probability of coalescence taking place. In general, the predictions were in good agreement with the measurements for both the mixing and pipe flow zones.

Simple yet accurate expressions for the electrical double-layer interaction force and energy between the particles that hold for a wide range of surface potential is required in the modeling, simulation, and optimization of many processes employed in industry. In this paper, simple approximate expressions for the interaction are obtained based on the asymptotic results and the numerical solution to the Poisson–Boltzmann equation for identical parallel plates with constant surface potential up to 180/zimV at 25°C, and the Derjaguin approximation. Within the moderate surface potential range, the semianalytical expressions agree well with the exact numerical results and are convenient to use for the purpose of process modeling and simulation.

Due to the highly polar nature with a multipeak absorption spectrum of water, the contribution of the relaxation in the microwave and infrared regions to the water dielectric spectrum is significant. The old data obtained by the Cauchy plot analysis of the parameters of the single-relaxation representation of water dielectric spectrum produce the discrepancy in the Hamaker constants computed by the complete continuum theory. New data are obtained by the direct fitting of the single-relaxation model to the complete water dielectric spectrum. The Hamaker constants computed using the improved approximate and the complete spectra for water permittivity are in good agreement. The Hamaker function of quartz–water–quartz and quartz–water–air systems computed using the improved approximation for water and the Cauchy plot approximation for quartz also agrees with that computed using the complete spectrum for both liquid water and crystalline quartz. The new data are to be used, instead of the old Cauchy plot analysis data, in the calculation of the van der Waals interaction across water films based on the available simplified expressions.

No Abstract.