Difference In Surface Tension Research Articles

Highly Water‐Rich Robust Coating for Separating Immiscible Liquids Mixtures of Wide Range of Surface Tension Differences

AbstractDeveloping mechanically robust and chemically tolerant coatings that maintain a high water content remains an extremely challenging task to pursue to date. Here, an optimum reinforcement of a hollow nano‐clay i.e., halloysite in a dual crosslinked and interpenetrating polymeric network is introduced to yield a high (≈95 wt%) water content coating with an ability to improve toughness (9.9 ± 0.6 MJm−3 Vs. 0.5 ± 0.03 MJ m−3) of a deformable fibrous substrate. The association of covalent and physical crosslinking chemistries provides essential tolerance against exposures to diverse severe chemically complex conditions, including extremes of pH, seawater, river water, and organic solvents. High water content in the prepared hydrogel network endows a robust bio‐inspired underwater nonadhesive superoleophobicity with oil contact angle of 160.7 ± 0.2° and force of oil‐droplet adhesion of 8.7 ± 0.3 µN. This approach provides a liquid selective filtrating membrane with ultrahigh crude oil/water separation efficiency (99.7%), superior intrusion pressure (3.5 ± 0.4 kPa), relatively high separation flux (11,162 Lm−2 h−1), and the ability to perform even when the surface tension of aqueous phase is brought down to similar of oily phase. Moreover, a mixture of immiscible, non‐aqueous liquids having differences in surface tension below 2.5 mN m−1 is successfully separated.

Microstructure and excellent arc ablation resistance of Ni–8Al coating on copper substrate by high-speed laser cladding

In the case of electrical contact, copper alloys are often unable to withstand arc ablation and premature failure. To solve this issue, Ni-8wt.%Al (Ni–8Al) coatings were successfully prepared on copper substrates utilizing the high-speed laser cladding. In addition, the microstructure evolution, microhardness, electric conductivity and arc ablation resistance of the prepared coatings were investigated in detail. As a result, the achieved Ni–8Al coatings were structurally dense with good metallurgical bonding to the substrate, of which the microstructure showed a bottom-up evolution of fine sub-grain structure. Notably, the microhardness of the coating was 191.7 HV0.2, representing an increase of 82.57% compared to the substrate, and the electrical conductivity was 18.03 %IACS, approaching that of pure nickel. Additionally, the increase in ablation currents led to changes in the ablation behaviors and failure mechanisms of both the substrate and coating. At high currents, a huge arc ablation crater appeared in the center of the substrate due to the reaction force of the anode flame and the difference in surface tension between the liquid metal at the center and the edge of the molten pool. Nevertheless, the coatings showed better arc ablation resistance due to the improvement of molten pool stability during arc ablation by the in situ formed Al2O3 layer on the coating surface.

Analysis of convection flow of a self-propelled alcohol droplet in an exoskeleton frame

This study aims to analyze the convection flow of a self-propelled 1-pentanol droplet. The droplets move spontaneously when 1-pentanol droplets are dropped into an aqueous 1-pentanol solution. This self-propulsion is due to the interfacial tension gradient caused by the concentration differences. The shape of the droplet is closely related to its behavior because the shape of the droplet changes the interfacial tension gradient. In this study, an exoskeleton is used to fix the droplet shape. In our preliminary experiments, we observed Marangoni convection in droplets dropped in exoskeleton frames with boomerang and round holes. The results showed that a large difference in surface tension was necessary to control the self-propulsion of the 1-pentanol droplets. Herein, we prepared two exoskeletons with different holes, an elongated symmetrical elliptical shape, and an asymmetrical shape to fix the shape of the droplet. The droplets were then dropped into each exoskeleton, and the droplet behavior, Marangoni convection inside the droplet, and convection in the aqueous phase were analyzed. We found that the direction of the self-propulsion of the droplet was determined by these exoskeletons, particularly in the case of the asymmetrical exoskeleton, and the direction of self-propulsion was fixed in one direction. Marangoni convection was observed in the droplet from the direction of lower surface tension to that of higher surface tension. In the aqueous phase, two convections were generated from the aqueous phase to the droplet because of the diffusion of 1-pentanol. In particular, when an asymmetrical exoskeleton was used, two convections of different sizes and velocities were observed in the aqueous phase. Based on these experimental results, the relationship between droplet behavior and convection is discussed.

Experimental study on the upward annular two-phase flow of nitrogen and ethanol aqueous solutions with different concentrations

Vertical upward annular flow experiments of nitrogen gas and ethanol aqueous solutions with volume fractions of 30 %, 60 %, and 95 % under 0.2 MPa were conducted. The characteristics of the liquid film including base, average, and maximum film thickness and height, velocity, and frequency of disturbance waves were obtained and studied based on the constant electric current method in a 5 mm inner diameter polycarbonate tube. The flow behavior was observed using a high-speed camera simultaneously. It is found that a large number of bubbles in the liquid film is critical to these characteristics. A connection between ethanol concentration and bubbles in the liquid film is found and interpreted by considering bubble stability which arises from the dynamic rise in surface tension. Our experimental investigation suggests that the effect of bubbles in the liquid film on the flow characteristics is not negligible in such annular flows under high liquid flow rates and bubble stability should be considered for annular flows employing solutions consisting of two or more components with large differences in surface tension.

Moving contact line dynamics for capillary-driven microfluidics in wetting transition regime

The dynamics of moving contact lines (MCLs) dominate the behavior of capillary-driven microfluidics, which underlie many applications including microfluidic chips. The capillary displacement dynamics in the quasi-static regime has been extensively studied. However, the behavior of MCLs in the dynamic wetting transition regime remains largely unexplored, and previously established MCL dynamic models may be inadequate. In this study, a novel capillary displacement experiment is introduced, which is achieved by reversely introducing microfluidics with surface tension differences, where the one with low surface tension undergoes the wetting transition. In addition, a generalized Navier boundary condition (GNBC)-based model of capillary displacement dynamics is developed within the framework of diffusive interface theory to investigate the MCL dynamics in the wetting transition regime. The oscillation-relaxation process is experienced for phase interface and microscopic dynamic contact angle θd in the wetting transition regime. Spontaneous filling distance follows dfill*∼t1/2, and reaching quasi-static stage follows dfill*∼t1. The previously neglected mechanism of inertial-viscous competition dominates the early dynamics of such dynamic wetting transition processes. θd∝ucl is observed to be valid solely under conditions where viscosity dominates, but it breaks down in the presence of dominant inertial effects. An escalation in slip substantially diminishes the influence of inertia, with frictional dissipation mediated by slip emerging as the predominant factor in the capillary-driven early dynamics. The origin of uncompensated Young's stress in the GNBC and its correlation with capillary forces is unified, unveiling the underlying physical mechanism governing the dynamics at the MCL. Finally, by decoupling the analysis of viscosity and slip, a new θd-viscous-slip formulation is proposed, in agreement with the model predictions.

Hybrid-Electrolytes System Established by Dual Super-lyophobic Membrane Enabling High-Voltage Aqueous Lithium Metal Batteries.

Aqueous electrolytes and related aqueous rechargeable batteries own unique advantage on safety and environmental friendliness, but coupling high energy density Li-metal batteries with aqueous electrolyte still represent challenging and not yet reported. Here, this work makes a breakthrough in "high-voltage aqueous Li-metal batteries" (HVALMBs) by adopting a brilliant hybrid-electrolytes strategy. Concentrated ternary-salts ether-based electrolyte (CTE) acts as the anolyte to ensure the stability and reversibility of Li-metal plating/stripping. Eco-friendly water-in-salt (WiS) electrolyte acts as catholyte to support the healthy operation of high-voltage cathodes. Most importantly, the aqueous catholyte and non-aqueous anolyte are isolated in each independent chamber without any crosstalk. Aqueous catholyte permeation toward Li anode can be completely prohibited without proton-induced corrosion, which is enabled by the introduction of under-liquid dual super-lyophobic membrane-based separator, which can realize the segregation of the most effective immiscible electrolytes with a surface tension difference as small as 6 mJ m-2. As a result, the aqueous electrolyte can be successfully coupled with Li-metal anode and achieve the fabrication of HVALMBs (hybrid-electrolytes system), which presents long-term cycle stability with a capacity retention of 81.0% after 300 cycles (LiNi0.8Mn0.1Co0.1O2 || Li (limited) cell) and high energy density (682Whkg-1).

Axisymmetric Compression of a Circular Particle Raft Driven by the Diffusion of Surfactant.

Particle rafts are a new kind of soft matter formed by self-organization on the interface, which possesses mechanical properties between fluid and solid, and they have been widely used in many industrial fields. In the present study, the compression experiment of a circular particle raft is first performed, where an SDS (sodium dodecyl sulfate)-coated metal ring is placed around its periphery. When the surfactant diffuses, the particle raft shrinks, and its shrinkage ratio increases with the increase in the surfactant concentration, where the experimental results are consistent with the numerical simulation. Next, the relationship between the initial surface tension difference of SDS and the radius shrinkage of the particle raft is obtained by dimensional analysis. In what follows, the diffusion model is built to quantify the diffusion process of SDS at the liquid-gas interface, and then the analytical concentration solution of the concentration of SDS at the periphery of particle raft is given. The particle raft is viewed as an elastic circular plate under the action of the radial pressure, which originates from the surface tension difference, which has been verified by the experimental result. These explorations cast a new light on how to apply loads to measure mechanical properties of soft matter, which also provide some inspirations on the design of microsensors and microfluidics.

Continuous high viscosity biphasic liquid separation

Enhancing the efficiency of separation in high-viscosity biphasic liquid purification processes can significantly reduce energy consumption and costs. This study has developed a co-axial biphasic liquid separator that can continuously and instantaneously separate two-phase mixtures with viscosities up to 2000 mPa∙s at room temperature, to meet real industrial needs. This co-axial biphasic liquid separator uses a special helix wire structure that separates the two-phase fluids based on the difference in surface tension, unaffected by the viscosity of the liquids. In experiments with PMMA-toluene-water mixtures, the flow rate can reach up to 4000 μl/min, with PMMA recovery rates consistently above 83.6 %, and as high as 91.5 %. In experiments with undiluted heavy oil–water, a purity of up to 87.58 % was achieved for heavy oil, and for diluted heavy oil, the purity even reached as high as 92.15 %. The separator demonstrated remarkable universality and durability, maintaining stable and high-purity biphasic separation across varying flow rates, through 15 cycles of repeated use, and during prolonged operations of up to one hour, without any system failures. The co-axial biphasic liquid separator developed in this study is currently the only few microseparator in continuous processes capable of separating liquids with viscosities over 2100 mPa∙s, and it could decrease the cost of relevant process development in industrial setups, realizing the vision of green manufacturing.

Self-propelled object that generates a boundary with amphiphiles at an air/aqueous interface

A benzoic acid (BA) disk was investigated as a novel self-propelled object whose driving force was the difference in surface tension. 4-Stearoyl amidobenzoic acid (SABA) was synthesized as an amphiphile to control the nature of motion based on intermolecular interactions between BA and SABA. The BA disk exhibited characteristic motion depending on the surface density of the SABA on the aqueous phase, that is, reciprocating motion as a one-dimensional motion and restricted and unrestricted motion as a two-dimensional motion. The trajectory of the reciprocating motion was determined by the initial direction of motion, and the boundary between an aqueous surface and the BA-SABA condensed molecular layer was used as the field’s boundary. The presented results indicate that the characteristic nature of motion can be designed at the molecular level based on the intermolecular interactions between an energy-source molecule and an amphiphile.

Simulating asymmetric membranes using P21 periodic boundary conditions.

Molecular dynamics (MD) simulations of symmetric lipid bilayers are now well established, while those of asymmetric ones are considerably less developed. This disjunction arises in part because the surface tensions of leaflets in asymmetric bilayers can differ (unlike those of symmetric ones), and there is no simple way to determine them without assumptions. This chapter describes the use of P21 periodic boundary conditions (PBC), which allow lipids to switch leaflets, to generate asymmetric bilayers under the assumption of equal chemical potentials of lipids in opposing leaflets. A series of examples, ranging from bilayers with one lipid type to those with peptides and proteins, provides a guide for the use of P21 PBC. Critical properties of asymmetric membranes, such as spontaneous curvature, are highly sensitive to differences in the leaflet surface tensions (or differential stress), and equilibration with P21 PBC substantially reduces differential stress of asymmetric bilayers assembled with surface area-based methods. Limitations of the method are discussed. Technically, the nonstandard unit cell is difficult to parallelize and to incorporate restraints. Inherently, the assumption of equal chemical potentials, and therefore the method itself, is not applicable to all target systems. Despite these limitations, it is argued that P21 simulations should be considered when designing equilibration protocols for MD studies of most asymmetric membranes.

Performance Improvement of an STS304-Based Dispensing Needle via Electrochemical Etching.

In this study, we explored the formation of micro-/nanosized porous structures on the surface of a needle composed of STS304 and examined the effect of conventional needles and needles capable of liquid ejection. Aqua regia, composed of HCl and HNO3, was electrochemically etched to form appropriately sized micro-/nanoporous structures. We observed that when dispensing liquids with low surface tension, they do not immediately fall downward but instead spread over the exterior surface of the needle before falling. We found that the extent of spreading on the surface is influenced by an etched porous structure. Furthermore, to analyze the effect of surface tension differences, we dispensed liquids with varying surface tensions using etched needles. Through the analysis, it was confirmed that, despite the low surface tension, the ejected droplet volume and speed could be stably maintained on the etched needle. This indicates that the spreading phenomenon of the liquid on the needle surface just before ejection can be controlled by the micro/nanoporous structure. We anticipate that these characteristics of etched needles could be utilized in industries where precision dispensing of low-surface-tension liquids is essential.

Spontaneous Separation of Immiscible Organic Droplets on Asymmetric Wedge Channels with Hierarchical Microchannels.

Spontaneous separation of immiscible organic droplets has substantial research implications for environmental protection and resource regeneration. Compared to the widely explored separation of oil-water mixtures, there are fewer reports on separating mixed organic droplets on open surfaces due to the low surface tension differences. Efficient separation of mixed organic liquids by exploiting the rapid spontaneous transport of droplets on open surfaces remains a challenge. Here, through the fusion of inspiration from the fast droplet transport capability of Sarracenia trichome and the asymmetric wedge channel structure of shorebird beaks, this work proposes a spine with hierarchical microchannels and wedge channels (SHMW). Due to the synergistic effect of capillary force and asymmetric Laplace force, the SHMW can rapidly separate mixed organic droplets into two pure phases without requiring additional energy. In particular, the self-spreading of the oil solution on the open channel surface is utilized to amplify the surface energy difference between two droplets, and SHMW achieves the pickup of oil droplets floating on the surface of the organic solution. The maximum separation efficiency on 3-SHMW can reach 99.63%, and it can also realize the antigravity separation of mixed organic droplets with a surface tension difference as low as 0.87 mN·m-1. Furthermore, SHMW performs controllable separation, oil droplet pickup, and continuous separation and collection of mixed organic droplets. It is expected that this cooperative structure composed of hierarchical microchannels and wedge channels will be realized in resource recovery or chemical reactions in industrial production processes.

Effect of filling materials on microstructure and properties of CMT-laser beam oscillation hybrid welding behavior of dissimilar Al–Mg–Si alloys

Laser oscillation-assisted cold metal transfer hybrid welding was conducted on 2.0 mm-thick 6082 and a new 6xxx aluminum alloys. The influence of wire composition on microstructure and mechanical properties of the 6082 and new 6xxx alloy joints is studied. Our results show that, due to the difference in surface tension, the cross section of a joint filled with ER4047 wire typically presents a wider U-shape profile, while the ER5183 filled joint shows a relatively narrower V-shape profile. The average grain size of the ER5183 joint is smaller than that of the ER4047 joint. The ER4047 joint exhibits better fluidity, resulting in a higher proportion of high-angle boundaries compared to the ER5183 joint, which we attribute to the higher Si content. Equiaxed grains are also observed near the fusion boundary on the new 6xxx side, while no equiaxed grain formation is observed on the 6082 side. EDS data demonstrates severe elemental segregation in the center of weld and the partially melted zone, suggesting that multiple secondary phases form unevenly within inter-dendritic regions and grain boundaries of α-Al during the welding process. The microhardness of the weld zone and the heat-affected zone on both sides in the ER5183 joint is higher than that of the ER4047 joint. The corrosion test evidences that the ER5183 joint has a slightly better corrosion resistance than the ER4047 joint. Our findings provide a new understanding on joining of dissimilar Al–Mg–Si alloys and guide the selection of appropriate filling materials and welding processes.

Configuration Evolution of a Particle Raft with a Preprepared Crack Driven by the Diffusion of a Surfactant.

In the present study, the morphology evolution of a particle raft with a preprepared crack, which is caused by injecting the surfactant sodium dodecyl sulfate (SDS) into water, is demonstrated. Experimental results on the process of crack closure and configuration evolution are captured and are in excellent agreement with the numerical simulations. Then a surface diffusion model on SDS is proposed to quantify the detailed physical scenario. The surface diffusion factor is determined through the shooting method based on the experimental result of dynamic surface tension. As a result, the analytical solution for the SDS concentration distribution is given. The theoretical result on the dependence relationship between the profile shrinkage ratio and the time variable is consistent with the experimental result. At last, the relation between the initial surface tension difference of SDS and the profile shrinkage ratio is obtained in the light of experiments and dimensional analysis, and the two results are very close. These analyses provide a comprehensive understanding of the coupling between chemicals and mechanical behaviors of soft matter, and the modulation of defects in the particle raft provides some inspiration for engineering new devices at the microscale.

Effect of Organosilane Functionalization of Kaolinite In Structure and Thermal Properties

The composite homogeneity of polymer and inorganic content is often constrained by the high difference in surface tension of the two components. Inorganic filler surface tension is usually reduced using organosilane modification to improve miscibility. In this study, organosilane was introduced into Kaolinite clay to produce silanated kaolinite (sKal). The modification was carried out by reacting kaolinite with 3-Aminopropyltriethoxy silane (APS) in ethanol media. The products were characterized by Fourier Transform InfraRed (FTIR), X-Ray Diffraction (XRD), and thermal analysis. Successful silanated modification, sKal structure, thermal properties, and dispersion stability under water were reported. The appearance of absorptions demonstrated the success of the Kaolin Aps modification. New spectra from the N-H and CH2 group organosilanes of APS, which bind to kaolinite. The addition of organosilane concentrations can affect the structure of kaolinite, increasingly more organosilanes are added, widening the plate spacing of each layer, and resulting in the breaking of the polymer chains and the exfoliation of platelets between the layers of kaolinite. Thermal stability showed an increase in thermal degradation after modification with Organosilan-APS. Furthermore, modifying Kaolinite with APS can improve dispersion stability in aqueous. Kaolinite-APS modification can accelerate the deposition of colloidal dispersions by lowering the surface tension of kaolinite. The data showed the potential of sKal as a modifier polymer in composite preparation for any application.

Processing defect, microstructure evolution and mechanical properties of laser powder bed fusion Al-12Si alloys

The laser power and scan speed are significant processing parameters influencing the defects and microstructures due to affecting the thermal state within the melt pool during laser powder bed fusion (LPBF). To this end, these process parameter combinations under a constant laser energy density are correlated with defects (balling phenomenon and pores) and microstructures (melt pool arrangement and cell morphology). Setting the parameter combination (laser power and scan speed are 200 W and 910 mm/s, respectively) yields large balling droplets (average size of 150 μm) due to the relatively high melt viscosity resulting from the low melt pool temperature. In this case, a limited surface tension difference acting on a liquid surface cannot provide sufficient driving forces against viscous drags to promote the efficient spreading of the molten alloy. Cavity regions are formed between the large balling droplets and the previous layer, forming lack-of -fusion pores. By increasing the laser power and scan speed gradually, samples with relative densities greater than 99.5% are produced. This phenomenon can be attributed to the increases in laser power and scan speed, which improves the spreading ability of the molten alloy. With increasing laser power and scan speed, the cell size decreases (from 0.51 μm to 0.42 μm) because of the increase in the cooling rate. The sample (laser power and scan speed are 350 W and 1590 mm/s, respectively) has the highest performance (310 MPa yield strength, 470 MPa ultimate tensile strength, and 6.6% fracture strain) due to its highest relative density (greater than 99.5%) and fine microstructure (average cell size of 0.45 μm). All four samples exhibit anisotropic mechanical properties resulting from the combination of the melt pool boundary and lack-of-fusion pores.

Diversified separations of immiscible organic liquids by a modification of superwettable supramolecular framework composite on porous support

Superwetting porous materials possessing wide applicability and responsiveness are becoming highly desired for the needs of the separation of immiscible liquid mixtures with less difference in surface tension during the treatment of wastes. In targeting this purpose, we propose a strategy to regulate the wettability of a sponge by coating a supramolecular framework (SF) bearing tunable wetting states under the assistance of polycaprolactone. This SF assembly-modified porous support demonstrates the under-liquid dual lyophobicity for polar liquids under nonpolar ones and for nonpolar liquids under polar ones via a simple in-situ adjustment of intermediate fluids. Depending on the capillary force of nanopores and amphiphilic components existing in the SF assembly, the switchable surface-modified sponge connecting to a pump quickly suction lyophilic organic liquids either located on the top or bottom phase despite touching the lyophobic liquids. Moreover, in-situ modulated filtrations to the emulsions comprising polar and nonpolar liquids are achieved with high efficiency (greater than 94.8 %) and flux (up to 9261.2 L m−2 h−1). Importantly, the suction and filtration separations are also available for organic liquid pairs with a high viscosity. The reversible interconversion between nonpolar and polar liquids is achieved and can be recycled several times with undiminished performance.

The core-shell structured aqueous dispersions of the siloxane-grafted polyurethane copolymers with high transparency

We have synthesized the siloxane-grafted polyurethane copolymers aqueous dispersions by semi-continuous emulsion polymerization. The mono-methacryloxypropyl terminated polydimethylsiloxane was used to react with the acrylate-terminated waterborne polyurethane, which served as seed emulsions. It is obtained that the as-synthesized copolymer dispersions are stable and have small particle sizes ranging from 77 nm to 120 nm, and they possess core-shell structures. Moreover, the results show that the prepared films exhibit high transparency and hydrophobic surface. Moreover, the enrichment of siloxane and the heterogeneous structure on the film surface was studied. The results of Raman spectra disclose that the intensities of siloxane on the surface change over time during the film formation. These results are correlated to the pressure difference of droplets and low surface tension of siloxane segments. The as-synthesized dispersions promise to be applied in the displayer coatings.

Enhancement Mechanism of Fish-Scale Surface Texture on Flow Switching and Mixing Efficiency in Microfluidic Chips.

Surface textures have a significant influence on surface-functional properties, which provide an alternative solution to create an accurate control of microfluidics flow. This paper studies the modulation ability of fish-scale surface textures on microfluidics flowing behavior on the ground of the early research on vibration machining-induced surface wettability variation. A microfluidic directional flow function is proposed by modifying the wall of the microchannel at the T-junction with different surface textures. The retention force caused by the surface tension difference between the two outlets in the T-junction is studied. In order to investigate the influence of fish-scale textures on the performance of the directional flowing valve and micromixer, T-shaped and Y-shaped microfluidic chips were fabricated. The experimental results indicated that with the aid of the fish-scale surface textures generated by vibration-assisted micromilling, directional liquid flow can be achieved at a specific input pressure range and the mixing efficiency of microfluidics can be improved dramatically.

Conformation-emulsification property relationship of partially depolymerized water soluble yellow mustard mucilage

In the current study, water soluble yellow mustard mucilage (WSM) was used as a model to study the conformation-emulsification property relationship of polysaccharides. Native WSM molecules were exposed to pectinase to hydrolyze, and the depolymerized fractions were collected from 0 to 6 h. The molecular weight (Mw) distribution of the collected fractions ranged from 1.60 to 2.33 × 106 Da, while their conformational parameters, namely radius of gyration (Rg), hydrodynamic radius (Rh) and ρ value (Rg/Rh), varied significantly (P < 0.05). Surface tension, flow behavior, droplet size, zeta-potential, solubility, emulsion creaming stability, and freeze-thaw stability of the depolymerized fractions were compared with the native WSM. The results indicated that depolymerized fractions showed no difference in surface tension, solubility and flow behavior compared to the native WSM. The fractions obtained at 2, 3 and 4 h of pectinase hydrolysis exhibited the most rigid conformation, and their corresponding emulsions possessed the smallest droplet size with the highest zeta-potential value. The native WSM and the fractions obtained from 0.5 to 6 h of pectinase hydrolysis exhibited the most flexible conformation, and showed the best emulsion creaming stability and freeze-thaw stability after going through 3 freeze-thaw cycles. It is concluded that a flexible conformation may lead to a more stable emulsion at a similar molecular weight range. The results may provide useful insight to food industries for applications of WSM and its hydrolyzed fractions as novel ingredients.