Synergistic activation of smithsonite with copper-ammonium species for enhancing surface reactivity and xanthate adsorption

Copper ions(Cu^(2+))are usually added to activate the sulfidized surface of zinc oxide minerals to enhance xanthate attachment using sulfidization xanthate flotation technology.The adsorption of Cu^(2+)and xanthate on the sulfidized surface was investigated in various systems,and its effect on the surface hydrophobicity and flotation performance was revealed by multiple analytical methods and experiments.X-ray photoelectron spectroscopy(XPS)and time-of-flight secondary ion mass spectrometry(To F-SIMS)characterization demonstrated that the adsorption of Cu^(2+)on sulfidized smithsonite surfaces increased the active Cu—S content,regardless of treatment in any activation system.The sulfidized surface pretreated with NH_(4)^(+)-Cu^(2+)created favorable conditions for the adsorption of more Cu^(2+),significantly enhancing the smithsonite reactivity.Zeta potential determination,ultraviolet(UV)-visible spectroscopy,Fourier transform-infrared(FT-IR)measurements,and contact angle detection showed that xanthate was chemically adsorbed on the sulfidized surface,and its adsorption capacity in various systems was illustrated from qualitative and quantitative aspects.In comparison to the Na2S–Cu^(2+)and Cu^(2+)–Na2S–Cu^(2+)systems,xanthate exhibited a higher adsorption capacity on sulfidized smithsonite surfaces in NH_(4)^(+)-Cu^(2+)–Na2S–Cu^(2+)system.Hence,activation with Cu^(2+)–NH4+synergistic species prior to sulfidization significantly enhanced the mineral surface hydrophobicity,thereby increasing its flotation recovery.

Surface hydrophobic modification of MXene to promote the electrochemical conversion of N_(2) to NH_(3)

Hydrophobic treatment of the catalyst surfaces can suppress the competitive hydrogen evolution reaction(HER) during the nitrogen reduction reaction(NRR).In this work,the surface of Ti_(3)C_(2)Ti_(x) MXene is modified by cetyltrimethylammonium bromide(CTAB) and trimethoxy(3,3,4,4,5,5,6,6,7,7,8,8,8-trideca fluorooctyl) silane(FOTS) to increase the hydrophobicity of MXenes.The ammonia(NH_(3)) production rate and faradaic efficiency(FE) are improved from 37.62 to 54.01 μg h^(-1)mg_(cat)^(-1).and 5.5% to 18.1% at-0.7 V vs.RHE,respectively after surface modification.^(15)N isotopic labeling experiment confirms that nitrogen in produced ammonia originates from N_(2) in the electrolyte.The excellent NRR activity of surface hydrophobic MXenes is mainly due to surfactant molecules,which inhibit the entry of water molecules and the competitive HER,which have been verified by in situ FT-IR,DFT and molecular dynamics calculations.This strategy provides an ingenious method to design more active NRR electrocatalysts.

Improving Hydrophobicity of Glass Surface Using Dielectric Barrier Discharge Treatment in Atmospheric Air

Non-thermal plasmas under atmospheric pressure are of great interest in industrial applications, especially in material surface treatment. In this paper, the treatment of a glass surface for improving hydrophobicity using the non-thermal plasma generated by dielectric barrier discharge （DBD） at atmospheric pressure in ambient air is conducted, and the surface properties of the glass before and after the DBD treatment are studied by using contact angle measurement, surface resistance measurement and wet flashover voltage tests. The effects of the applied voltage and time duration of DBD on the surface modification are studied, and the optimal conditions for the treatment are obtained. It is found that a layer of hydrophobic coating is formed on the glass surface after spraying a thin layer of silicone oil and undergoing the DBD treatment, and the improvement of hydrophobicity depends on DBD voltage and treating time. It seems that there exists an optimum treating time for a certain applied voltage of DBD during the surface treatment, The test results of thermal aging and chemical aging show that the hydrophobic layer has quite stable characteristics. The interaction mechanism between the DBD plasma and the glass surface is discussed. It is concluded that CHa and large molecule radicals can react with the radicals in the glass surface to replace OH, and the hydrophobicity of the glass surface is improved accordingly.

<i>In Vitro</i>Characterization of Cell Surface Properties of 14 Vaginal <i>Lactobacillus</i>Strains as Potential Probiotics

Probiotics are live microorganisms which when administered in adequate amounts confer a health benefit on the host. Human-origin Lactobacillus is a preferable source of probiotic bacteria. This study screened 14 vaginal Lactobacillus strains as probiotic candidates by investigating probiotic-related cell surface characteristics including cell surface hydrophobicity (CSH), Lewis acidity/basicity, autoaggregation, and biofilm formation. Moderate to high CSH and autoaggregation, high basicity and low acidity were prevalent in the 14 tested strains. Biofilm formation varied in a large range among the 14 tested strains. CSH showed a high correlation with Lewis acidity and autoaggregation, while Lewis acidity was highly correlated with autoaggregation and biofilm formation. Four strains were selected as promising probiotic strains. This study was the first one to compare antibiotic sensitivity between biofilm-forming cells and planktonic cells of Lactobacillus species, and found that biofilm-forming cells of a L. fermentum strain had a significantly higher survival rate than planktonic cells in cefotaxime, cefmetazole and tetracycline, but were as sensitive to oxacillin and ampicillin as planktonic cells were.

Molecular dynamics simulations of the nano-droplet impact process on hydrophobic surfaces

Large-scale molecular dynamics simulations are used to study the dynamic processes of a nano-droplet impacting on hydrophobic surfaces at a microscopic level. Both the impact phenomena and the velocity distributions are recorded and analyzed. According to the simulation results, similar phenomena are obtained to those in macro-experiments. Impact velocity affects the spread process to a greater degree than at a level of contact angle when the velocity is relatively high. The velocity distribution along the X axis during spread is wave-like, either W- or M-shaped, and the velocity at each point is oscillatory; while the edges have the highest spread velocity and there are crests in the distribution curve which shift toward the edges over time. The distribution along the Y axis is 〈- or 〉-shaped, and the segments above the middle have the lowest decrease rate in the spreading process and the highest increase rate in the retraction process.

Effect of surface property on mass flux in a variable-section microchannel

For microfluidic systems, interfacial phenomena in micro-reactors are of great importance because they control the transfer and reaction characteristics. This paper dwells on how the surface property and geometry influence the mass flux in a complex microchannel. The lattice Boltzmann method(LBM) with a pseudo potential model and the Shan–Chen model for the interaction between fluid and hydrophobic surface were built up, so a boundary slip effect was added and verified. On this basis, a microchannel with variable-section geometry was simulated. The results indicate that the optimal design and the flow pattern are quite different under hydrophilic and hydrophobic conditions. A microchannel with sequential hydrophilic and hydrophobic surface was also simulated. The numerical results indicate that the hydrophobic wall can improve the mass flux, irrespective of microchannel geometry. Particularly, an empirical correlation with a linearly relationship between length of hydrophobic segment and mass flux was obtained for the straight microchannel.

Preparation of Hydrophobic Surface on Titanium by Micro-Rolling and Laser Diffusion Carbonitriding

The application of rolling for fabricating grate on titanium stripe has been explored in this paper. Then the mechanically robust Ti（C,N） diffusion layer was synthetized directly on the grates by laser carbonitriding in the mixture gas of nitrogen and methane. The results shows that the carbonitriding process is accelerated by temperature enhancement with decreasing scanning speed, The Ti（C,N） diffusion layer is kept at 2 ~nn in thickness, when the scanning speed is smaller than 4 mm/s. The contact angle increases from 20~ to 143.6~ by designing an appropriate grate size and surface roughness. Meanwhile, the relationship between hydrophobicity, hardness performance and scanning speed is also discussed. The hardness of diffusion layer increases with decreasing laser scanning speed, and is up to 11.2 GPa. The surface structure and hydrophobic state are maintained after three cycles of sandpaper abrasion, which has improved the robustness of surface grate.

Synergistic effects of dodecane-castor oil acid mixture on the flotation responses of low-rank coal:A combined simulation and experimental study

The utilization of an appropriate collector or surfactant is crucial for the beneficiation of low-rank coal.However,in previous studies,the selection of surfactants was primarily based on flotation procedures,which hinders the understanding of the interaction mechanism between surfactant groups and oxygen-containing functional groups at the surface of low-rank coal.In this study,we investigate the flotation of low-rank coal in the presence of a composite collector by using a combined theoretical and experimental approach.The maximum flotation mass recovery achieved was 82.89%using a 3:1 mixture of dodecane and castor oil acid.Fourier-transform infrared and X-ray photoelectron spectroscopic analyses showed that castor oil acid was effectively adsorbed onto the surface of low-rank coal,enhancing the hydrophobicity of the coal.In addition,the diffusion coefficient of water molecules in the water-composite collector-coal system was greater than that in the dodecane system.Moreover,due to the presence of castor oil acid in the flotation process,the adsorption distance of dodecane and low-rank coal became shorter.Molecular dynamics simulations revealed that the diffusion and interaction of surfactant molecules at the interface of low-rank coal particles and water was enhanced because the adsorption of the dodecane-castor oil acid mixture is primarily controlled by hydrogen bonds and electrostatic attraction.Based on these results,a better surfactant for flotation of low-rank coal is also proposed.

Novel Hollow Re-entrant Structures Improving Hydrophobicity of Metal Surfaces

Re-entrant structures have drawn increasing attention because of their hydrophobicity.However,it is very difficult to manufacture re-entrant structures at the micron scale on metal surfaces.In this study,we designed and manufactured novel hollow re-entrant structures employing laser ablation and electrodeposition technology.This designed hollow re-entrant structure on metal surfaces has been fabricated successfully,which has high processing efficiency and good repeatability.The morphology and size of the hollow re-entrant structures were characterized.We found that the hydrophobic performance of hollow re-entrant structures was improved after being in the atmosphere for 3 days.After electrodeposition,the static contact angle was 133°.However,after being placed in the atmosphere for 3 days,the static contact angle was 140.4°,which is 5.2%higher than that after electrochemical deposition.We explained the cause of this phenomenon.The change of element content on the surface of hollow re-entrant structures was used to indicate the formation of metal oxide.After being in the atmosphere for 3 days,oxygen content increased by 0.4%.The metal surfaces with hollow re-entrant structures have a broader application prospect.

Research progress of slippage characteristic and gas film stability enhancement methods on biomimetic hydrophobic surfaces

The biomimetic hydrophobic surface is a potentially efficient underwater drag reduction method and the drag reduction mechanism of this kind of surface comes from the interfacial slippage.For now,it is a hotspot to grasp the slippage characteristic and explore slippage enhancement strategies.This paper not only summarizes our numerical simulation and experimental results of slippage characteristic at the solid-liquid interface(SLI)of hydrophobic surfaces(HS)and the gas-liquid interface(GLI)of superhydrophobic surfaces(SHS)in recent years,but also introduces some innovative methods that can effectively improve the gas film stability and drag reduction effect of SHS.First,we used the molecular dynamics(MD)simulation method to figure out the effect of the solid-liquid interaction strength,the system temperature and the shear rate on the slippage of SLI,and expound their action mechanism from molecular scale.Then,by MD and multibody dissipative particle dynamics(MDPD)method,the slippage behavior at the GLI was studied under the influence of the microstructure size and the flow driving velocity.We proposed a new kind of hybrid slip boundary condition model to describe the slippage characteristic on GLI.In addition,we found through experiment that a three-dimensional backflow will appear on the GLI under the interfacial adsorption of surfactants,and the backflow direction will reverse with the change of GLI morphology.Finally,we put forward the wettability step structure and gas injection method to enhance the stability and drag reduction effect of the gas film on SHS.

Improving the Thermal Efficiency and Performance of Refrigeration Systems:Numerical-Experimental Analysis of Minimization of Frost Formation

The frost growth on cold surfaces in evaporators is an undesirable phenomenon which becomes a problem for the thermal efficiency of the refrigeration systems because the ice layer acts as a thermal insulation,drastically reducing the rate of heat transfer in the system.Its accumulation implies an increase in energy demand and a decrease in the performance of various components involved in the refrigeration process,reducing its efficiency and making it necessary to periodically remove the frost,resulting in expenses for the defrost process.In the present work,a numerical-experimental analysis was performed in order to understand the formation process of porous ice in flat plates with different surface treatments and parameters.This understanding is of utmost importance to minimize the formation of porous ice on cold surfaces and improve equipment efficiency and performance.In this context,a low-cost experimental apparatus was developed,enabling an experimental analysis of the phenomenon under study.The environmental conditions evaluated are the temperature of the cold surface,roomtemperature,humidity,and air velocity.The material of the surfaces under study are aluminum,copper,and brass with different surface finishes,designated as smooth,grooved(hydrophilic),and varnished(hydrophobic).The numerical-experimental analysis demonstrates measurements and simulations of the thickness,surface temperature,and growth rate of the porous ice layer as a function of the elapsed time.The numerical results were in good agreement with the experimental results,indicating that the varnished surface,with hydrophobic characteristics,presents greater difficulty in providing the phenomenon.Therefore,the results showed that application of a coating allowed a significant reduction on the frost formation process contributing to the improvement of thermal efficiency and performance of refrigeration systems.

Effect of surface roughness on the angular acceleration for a droplet on a super-hydrophobic surface

The motion of droplets on a super‐hydrophobic surface,whether by sliding or rolling,is a hot research topic.It affects the performance of super‐hydrophobic materials in many industrial applications.In this study,a super‐hydrophobic surface with a varied roughness is prepared by chemical‐etching.The adhesive force of the advancing and receding contact angles for a droplet on a super‐hydrophobic surface is characterized.The adhesive force increases with a decreased contact angle,and the minimum value is 0.0169 mN when the contact angle is 151.47°.At the same time,the motion of a droplet on the superhydrophobic surface is investigated by using a high‐speed camera and fluid software.The results show that the droplet rolls instead of sliding and the angular acceleration increases with an increased contact angle.The maximum value of the angular acceleration is 1,203.19 rad/s^(2) and this occurs when the contact angle is 151.47°.The relationship between the etching time,roughness,angular acceleration,and the adhesion force of the forward and backward contact angle are discussed.

Modeling the Wettability of Microstructured Hydrophobic Surface Using Multiple-relaxation-time Lattice Boltzmann Method

Wetting properties are significant for a hydrophobic surface and normally characterized by the equilibrium contact angle.In this manuscript,a mesoscopic method based on multiphase multiple-relaxation-time Lattice Boltzmann method has been presented and applied to simulate the contact angle at three-phase interfaces of a solid surface with micro-pillar structure.The influence of different parameters including pillar height,pillar width,inter-pillar spacing,intrinsic contact angle and the volume of the liquid drop on the equilibrium contact angle has been comprehensively investigated.The effect of geometry parameters of the micro-pillar structure on the wetting transition from Cassie–Baxter state to Wenzel state has also been studied.The results indicate that when the inter-pillar spacing is less than a certain value or the pillar height is greater than a certain value,the contact form between the droplet and the surface satisfies the Cassie–Baxter state.When the contact form satisfies the Cassie–Baxter state,the contact angle gradually increases with the increase of the inter-pillar spacing;the contact angle does not change significantly with the pillar height;the contact angle gradually decreases and approaches the intrinsic contact angle with the pillar width increases.Moreover,the contact angle increases with the increase of the intrinsic contact angle,and the contact angle is not sensitive to the change of droplet volume when the droplet volume is between 0.5 and10μl.

A designable surface via the micro-molding process

A rapid prototyping process was presented to fabricate a nylon honeycomb microstructure coated with parylene C.The surface structure was designed to obtain a hydrophobic surface using the volume of fluid(VOF)model.With the micro-molding technique,the contact angle of the polymer surface could be designed and fabricated by changing the different microstructure surface diesteel mold inserts.For the honeycomb(20μm width and 60μm depth)microcavity side wall,an average micro-molding filling percentage of 95% could be achieved by using a three-section constant-pressure molding process.The solid surface wettability is governed by both the geometrical microstructures and the surface energy.A 2μm parylene C layer was deposited on the nylon honeycomb microsurface to reduce the surface energy.To design honeycomb structures with different microcavity densities,the contact angle of these artificial surfaces could change from 91°to 130°.From a comparison of the contact angle measurements with the different models,the honeycomb-structured microsurface could be described by the Cassie–Baxter model.The errors between the VOF simulation and the measured data were<10%.The drag reduction performance of the honeycomb microplates was investigated in a water tunnel with a high Reynolds number(from 0.5×10^(6) to 4.6×10^(6)).As a result,the honeycomb microplates showed a maximum drag reduction rate of 36±0.6%in comparison with the bare plates in such turbulent flow.Benefiting from the replaceable mold insert,more designable microstructure polymer surfaces can be manufactured by this rapid prototyping technique.

INVESTIGATION OF INFLUENCE OF WETTABILITY ON POISEUILLE FLOW VIA MOLECULAR DYNAMICS SIMULATION

In this article,the influence of wettability on a liquid flow between two parallel plane walls were studied by using Non-Equilibrium Molecular Dynamics（NEMD） simulation.The wettability of the solid surfaces can be described as the contact angle.The liquid flow rate,the slip velocity and the slip length which are affected by the contact angle were investigated.The results show that the boundary condition at a microscopic level is different from a ＂no-slip＂ condition at a macroscopic level.There exits a slippage of a liquid flow for the hydrophobic boundary and an external force is needed to overcome threshold pressure for the hydrophilic boundary.And the orderly layered distributions of the liquid particles near the hydrophilic surface vary from a place near the hydrophobic surface.The study indicates that the surface wettability plays a significant role on possibilities of forming a viscous layer and the direct slip at the solid surface.The resistance of liquid flow can be decreased by changing the wettability of boundary surface.

Synthesis and Characterization of Novel UV-curable Fluorinated Polyurethane-acrylate Copolymer

A series of UV-curable fluorinated polyurethane-acrylate（PUA） has been developed by incorporating octafluoropentyl alcohol into the segment of UV-curable polyurethane-acrylate to improve the thermal property and surface property of the copolymer material. The structures of the synthesized polymers were characterized by Fourier transform infrared（FTIR） spectrometry. In order to find out the effect of incorporated fluorine on the UV-cured films, the properties of the UV-cured films were tested through contact angle, water absorption, and thermogravimetric analysis （TGA）. The fractured-surface morphologies of the UV-cured coatings were investigated by scanning electron microscopy（SEM）. With increasing the content of fluorine segments, the contact angle of the UV-cured films increased and the water absorption decreased, suggesting the fluorine segments migrated and formed a fluorine-covered surface to avoid water penetration. The observation of the fractured-surface morphology through SEM test showed that the fluori- nated UV-cured films gained rough fractured-surface compared with the pure UV-cured polyacrylate film, demonstrating the migrating of the fluorine segments. The TGA curves show that the fluorinated UV-cured films gained higher thermal degradation temperature than the virgin UV-cured polyacrylate film. And as increasing the fluorine content, the thermal degradation temperature increased. These phenomena could be reasonably explained by the enrichment of fluorinecontained segment on the surface of the film and the high thermal property due to fluorine atom.

Corrosion Resistance of Silane-Modified Hydroxide Zinc Carbonate Film on AZ31 Magnesium Alloy

The corrosion resistance of magnesium alloys can be improved using functional surface modification such as hydrophobic treatment.In this study,a hierarchical hydroxide zinc carbonate（HZC） film was fabricated on AZ31 magnesium alloy via a simple chemical-bath deposition process using urea aqueous solution.The morphologies,compositions and corrosion resistance of the hydrophobic film were analyzed using scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectrometer,and electrochemical measurements as well.The results revealed that the HZC film displayed flower-like protrusions and had a thickness of approximately 100 um.The fluoroalkylsilane（FAS）-modified HZC film exhibited a hydrophobic property with a water contact angle of 131.3°.The FAS/HZC film significantly improved the corrosion resistance of the AZ31 alloy due to hierarchical structures and hydrophobic modification.

Poly(N-isopropylacrylamide)-grafted Dual Stimuli-responsive Filter Paper for Protein Separation

Thermal and salt dual stimuli-responsive filter-paper-based membranes were prepared by UV-induced grafting of NIPAM-based polymers on paper surface. The grafting ratio could be controlled by monomer concentration during grafting polymerization. The results from pressure drop measurement of the mobile phase flowed cross the membrane demonstrate that an appropriate grafting ratio would be 8%-10%. Protein adsorption on the membrane through hydrophobic interaction could be promoted by increasing temperature and lyotropic salt concentration. The effect of grafted polymer structure on protein binding performance was studied. Filter paper grafted with NIPAM-based branched copolymer consisting of hydrophobic monomer moieties shows ten times higher protein binding capacity than that of the original filter paper. The separation of plasma proteins using the dual stimuli-responsive membrane was examined to demonstrate feasible application for hydrophobic interaction chromatographic separation of proteins.

Contact Angle Determination in Multicomponent Lattice Boltzmann Simulations

Droplets on hydrophobic surfaces are ubiquitous in microfluidic applications and there exists a number of commonly used multicomponent and multiphase lattice Boltzmann schemes to study such systems.In this paper we focus on a popular implementation of a multicomponent model as introduced by Shan and Chen.Here,interactions between different components are implemented as repulsive forces whose strength is determined by model parameters.In this paper we present simulations of a droplet on a hydrophobic surface.We investigate the dependence of the contact angle on the simulation parameters and quantitatively compare different approaches to determine it.Results show that the method is capable of modelling the whole range of contact angles.We find that the a priori determination of the contact angle is depending on the simulation parameters with an uncertainty of 10%to 20%.