Range Of Surface Tensions Research Articles

Non-Aqueous Polyhedral Liquid Marbles Stabilized with Polymer Plates Having Surface Roughness.

Hydrophobic polymer plates with smooth and rough surfaces are used as a stabilizer for cubic liquid marbles (LMs) to study the effect of surface roughness on their formation. The smooth and rough polymer plates can stabilize LMs using liquids with surface tensions of 72.8-26.6 and 72.8-22.9 mNm-1, respectively. It is clarified that the higher the surface roughness, the lower the surface tension of the liquids are stabilized to form the LMs. These results indicated that the introduction of surface roughness improves the hydrophobicity of the polymer plates and the rough polymer plates can stabilize LMs using liquids with a wider surface tension range. Electron microscopy studies and numerical analyses confirmed that the LMs can be formed, when the Cassie-Baxter wetting state, where θY>90° (θY: the contact angle on smooth surfaces) and θR>90° (θR: the contact angle on rough surfaces), and the metastable Cassie-Baxter wetting state, where θY<90° and θR>90°, are realized. Finally, the synthesis of cubic polymer particles are succeeded by free radical polymerization of the cubic LMs containing a hydrophobic vinyl monomer (dodecyl acrylate) in a solvent-free manner.

Surface modification for enhanced Anti‐Wetting properties of electrospun omniphobic membranes in membrane distillation

AbstractMembrane wetting caused by substances in the feed solution with low surface tension has posed serious issues for membrane distillation (MD). Omniphobic membranes could be helpful when dealing with this problem because they strongly repel liquids with a wide range of surface tensions. We fabricated electrospun omniphobic membranes containing PVDF‐TEOS‐PFDTMS, PVDF‐HFP‐TMOS‐PFDTMS, and PVDF‐HFP‐TEOS‐PFDTMS. All electrospun membranes have shown contact angles &gt;90°, but the electrospun membrane containing PVDF‐HFP‐TEOS‐PFDTMS has shown super repellence with a contact angle &gt;150° and maintains stable salt rejection and water flux in direct contact MD processes in the presence of sodium dodecyl sulfate surfactant (up to 0.3 mM). Furthermore, the morphology and crystallinity of the electrospun membranes were studied by scanning electron microscopy and Fourier‐transform infrared spectroscopy, and the percentage composition of elements was analyzed by x‐ray photoelectron spectroscopy. liquid entry pressure, mechanical strength, and the porosity of the electrospun omniphobic membranes were also studied.

Light and Magnetism Orchestrating Aquatic Pollutant-Degradation Robots in Programmable Trajectories.

Interfacial floating robots have promising applications in carriers, environmental monitoring, water treatment, and so on. Even though, engineering smart robots with both precisely efficient navigation and elimination of water pollutants in long term remains a challenge, as the superhydrophobicity greatly lowers resistance for aquatic motion while sacrificing chemical reactivity of the surface. Here, a pollutant-removing superhydrophobic robot integrated with well-assembled iron oxide-bismuth sulfide heterojunction composite minerals, which provide both light and magnetic propulsion, and the ability of catalytic degradation, is reported. The motion velocity of the robot reaches up to 51.9mm s-1 within only 300ms of acceleration under the orchestration of light, and brakes rapidly (≈200-300ms) once turn off the light. And magnetism extends the robot to work in broad range of surface tensions in any programmable trajectory. Besides, purification of polluted water is efficiently achieved in situ and the degradation efficiency exhibits eightfold enhancements under the effect of light-triggered photothermal behavior coupled with magnetic induction, overcoming the dilemma of efficient motion with catalytic superhydrophobicity. This strategy developed here provides guidelines for the explorations of high-performance smart devices.

Liquid as Plasma Mask for Constructing Arbitrary Area with Contrary Wettability on Hydrophobic Textiles

AbstractMaterials with contrary wettability have various functions and applications. Common methods such as chemical modification and secondary treatment with solid mask to achieve relevant wettability either have harmful additives or construct fixed shape. Herein, liquid is introduced as a plasma mask for constructing arbitrary area with contrary wettability on hydrophobic textiles. In atmospheric plasma working region, exposed area of textiles achieves hydrophilic while liquid shielding area maintains the original wettability. Water–ethanol mixtures with a broad range of surface tension are chosen as template liquid to meet most hydrophobic textiles with the property of erasable evaporation without residue. Liquid mask with fluidity can be drawn in any shape at any time, meanwhile, plasma treatment highlights the merit of no chemical additive. Higher resolution will be achieved when the operation process is further refined. This study may provide insights for constructing advanced infiltrating materials and replacing solid with liquid in more application scenarios.

Insights into the estimation of surface tensions of mixtures based on designable green materials using an ensemble learning scheme

Precise estimation of the physical properties of both ionic liquids (ILs) and their mixtures is crucial for engineers to successfully design new industrial processes. Among these properties, surface tension is especially important. It’s not only necessary to have knowledge of the properties of pure ILs, but also of their mixtures to ensure optimal utilization in a variety of applications. In this regard, this study aimed to evaluate the effectiveness of Stochastic Gradient Boosting (SGB) tree in modeling surface tensions of binary mixtures of various ionic liquids (ILs) using a comprehensive dataset. The dataset comprised 4010 experimental data points from 48 different ILs and 20 non-IL components, covering a surface tension range of 0.0157–0.0727 N m−1 across a temperature range of 278.15–348.15 K. The study found that the estimated values were in good agreement with the reported experimental data, as evidenced by a high correlation coefficient (R) and a low Mean Relative Absolute Error of greater than 0.999 and less than 0.004, respectively. In addition, the results of the used SGB model were compared to the results of SVM, GA-SVM, GA-LSSVM, CSA-LSSVM, GMDH-PNN, three based ANNs, PSO-ANN, GA-ANN, ICA-ANN, TLBO-ANN, ANFIS, ANFIS-ACO, ANFIS-DE, ANFIS-GA, ANFIS-PSO, and MGGP models. In terms of the accuracy, the SGB model is better and provides significantly lower deviations compared to the other techniques. Also, an evaluation was conducted to determine the importance of each variable in predicting surface tension, which revealed that the most influential factor was the mole fraction of IL. In the end, William’s plot was utilized to investigate the model's applicability range. As the majority of data points, i.e. 98.5% of the whole dataset, were well within the safety margin, it was concluded that the proposed model had a high applicability domain and its predictions were valid and reliable.

A bio-inspired slippery coating with mechanochemical robustness for anti-ice and anti-corrosion

Slippery coatings with outstanding liquid repellency and drag reduction are essential for energy saving and economic society. However, their long-term durability is still limited by weak slippery capacity and mechanochemical stability. Here, a manta ray skin inspired coating (MSC) via straightforward spraying method is developed. The rational design of the hemispherical structures composed of silicon-containing materials endows a transparent and robust slippery surface with hardness of 0.94 GPa and an extremely low friction coefficient of 0.076. The MSC can be applied on diverse substrates with strong adhesion and exhibits an outstanding resistance to liquid with a wide range of surface tension and viscosity up to 1,499 mPa·s. The coating maintains transparency and sustains liquid repellency after 1,000 abrasion cycles under 250 g loads or 32 days treatment at extreme high/low temperatures. In addition, the distinct anti-icing/de-icing properties and good anti-corrosion performance along with a facile spraying process provide MSC a tremendous potential for achieving industrial applications.

Binary Mixture Droplet Evaporation on Microstructured Decorated Surfaces and the Mixed Stick-Slip Modes.

The interactions between liquid droplets and solid surfaces during wetting and phase change are important to many applications and are related to the physicochemical properties of the substrate and the fluid. In this work, we investigate experimentally the evaporation of pure water, pure ethanol, and their binary mixture droplets, accessing a wide range of surface tensions, on hydrophobic micro-pillared surfaces varying the spacing between the pillars. Results show that on structured surfaces, droplets evaporate following three classical evaporative behaviors: constant contact radius/pinning, stick-slip, or mixed mode. In addition, we report two further droplet evaporation modes, which are a mixed stick-slip mode where the contact angle increases while the contact radius decreases in a stick-slip fashion and a mixed stick-slip mode where both the contact angle and the contact radius decrease in a stick-slip fashion. We name these evaporation modes not yet reported in the literature as the increasing and decreasing contact angle mixed stick-slip modes, respectively. The former ensues because the fluid surface tension increases as the most volatile fluid evaporates coupled to the presence of structures, whereas the latter is due to the presence of structures for either fluid. The duration of each evaporation mode is dissimilar and depends on the surface tension and on the spacing between structures. Pure water yields longer initial pinning times on all surfaces before stick-slip ensues, whereas for binary mixtures and pure ethanol, initial pinning ensues mainly on short spacing structures due to the different wetting regimes displayed. Meanwhile, mixed stick-slip modes ensue mainly for high ethanol concentrations and/or pure ethanol independent of the solid fraction and for low ethanol concentrations on large spacing. Contact line jumps, changes in contact angle and pinning forces are also presented and discussed. This investigation provides guidelines for tailoring the evaporation of a wide range of surface tension fluids on structured surfaces for inkjet printing, DNA patterning, or microfluidics applications.

Predictive understanding of the surface tension and velocity of sound in ionic liquids using machine learning.

Knowledge of the physical properties of ionic liquids (ILs), such as the surface tension and speed of sound, is important for both industrial and research applications. Unfortunately, technical challenges and costs limit exhaustive experimental screening efforts of ILs for these critical properties. Previous work has demonstrated that the use of quantum-mechanics-based thermochemical property prediction tools, such as the conductor-like screening model for real solvents, when combined with machine learning (ML) approaches, may provide an alternative pathway to guide the rapid screening and design of ILs for desired physiochemical properties. However, the question of which machine-learning approaches are most appropriate remains. In the present study, we examine how different ML architectures, ranging from tree-based approaches to feed-forward artificial neural networks, perform in generating nonlinear multivariate quantitative structure-property relationship models for the prediction of the temperature- and pressure-dependent surface tension of and speed of sound in ILs over a wide range of surface tensions (16.9-76.2 mN/m) and speeds of sound (1009.7-1992m/s). The ML models are further interrogated using the powerful interpretation method, shapley additive explanations. We find that several different ML models provide high accuracy, according to traditional statistical metrics. The decision tree-based approaches appear to be the most accurate and precise, with extreme gradient-boosting trees and gradient-boosting trees being the best performers. However, our results also indicate that the promise of using machine-learning to gain deep insights into the underlying physics driving structure-property relationships in ILs may still be somewhat premature.

Inertial effects in just-saturated axisymmetric column collapses

This work introduces a scaling analysis of sub-aerial axisymmetric column collapses of glass beads and Newtonian glycerol-water solutions mimicking some of the behaviours of debris flows. The beads were in a size range where their inertia partly decouples their collapse behaviour from the water column. Experiments explored a range of viscous, surface tension and particle inertia effects through systematic variation of particle size and fluid viscosity. Crucially a geotechnical centrifuge was used to access elevated effective gravitational accelerations driving the collapse, allowing field-scale viscous and surface tension effects to be replicated. Temporal pore pressure and run out front position evolution data was extracted using a pressure transducer and high speed imaging, respectively. A least-squares fitted scale analysis demonstrated that all characteristic dimensionless quantities of the acceleration phase could be described as a function of the column-scale Bond number text{ Bo }, the Capillary number text{ Ca }, the system size r^*, and the grain-fluid density ratio rho ^*. This analysis demonstrated that collapses as characterised by pore pressure evolution and front positions were controlled by the ratio of text{ Bo}/text{Ca}. This indicates that grain-scale surface tension effects are negligible in such inertial column collapses where they may dominate laboratory-scale granular-fluid flow behaviour where geometric similarity between grain and system size is preserved.Graphical abstract

Amidation reaction to derive waterborne, tolerant, and optically transparent solid slippery and superhydrophobic coatings

Separate and lubrication-free association of low surface energy with hierarchically featured and highly smooth interfaces yield two distinct and prospective bio-inspired wettability—superhydrophobicity and solid slippery properties, respectively. However, the derivation of such bio-inspired wettability with high optical transparency—following a simple, completely waterborne, non-fluorinated and scalable fabrication approach is an extremely challenging task to achieve. Here, a simple amidation reaction between thioester and amine groups is rationally extended for aqueous processing of strategically selected small molecules to attend desired outputs through formation of nanoparticles. An aqueous reaction mixture of selected non-fluorinated small molecules provided a stable (for 30 days) dispersion of nanoparticles (size ∼210 nm). While the ‘in-situ’ deposition of the reaction mixture yielded completely waterborne, optically transparent, physically and chemically durable lubrication-free solid slippery coating on a planar substrate, a highly deformable superhydrophobic coating on porous and fibrous substrates was obtained following a rapid and facile post-deposition of the prepared nanoparticles. The prepared solid slippery coating remained efficient in sliding the beaded droplets of various (e.g., polar and non-polar) liquids having a wide range (70.2 mN/m to 22.3 mN/m) of surface tension. The embedded slippery property remained unaltered even after exposure of prepared coating to extremes of temperatures and severe abrasive conditions—including continuous drop of 250 g of sand, sandpaper abrasion with a distance of 500 cm under an applied load of 25 KPa, adhesive tape peeling for 500 cycles, pencil (6H) & knife scratching, and prolonged (15 days) treatments of extremes of pH, seawater, river water, etc. The synthesized superhydrophobic coating on porous and fibrous-substrate remained efficient in sustaining repetitive and large physical deformations and other relevant abrasive exposures.

Hydrodynamics and gas-liquid mass transfer in an oscillatory flow reactor: Influence of liquid properties

Liquid properties, such as, surface tension and viscosity are important parameters as they control gas-liquid mass transfer in bioprocesses. An oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC) was considered to evaluate its potential for mass transfer performance in non-pure gas-liquid systems. The effect of surface tension and viscosity on the volumetric (kLa) and liquid-side mass transfer coefficients (kL), interfacial area, (a), gas holdup (εG) and bubbles’ dynamics were investigated under different operational conditions (oscillation amplitude (x0) and frequency (f) and superficial gas velocity (ug)). Two liquid phases, ethanol and sucrose aqueous solutions covering a range of surface tension and viscosity values were used. For the bubble size distribution (BSD) measurements an image analysis technique was used. A Design of Experiment (DoE) methodology was implemented in this work to establish the relation of x0, f, ug, surface tension and viscosity with kLa. According to the results, changes in the liquid properties and operational conditions showed marked effects on bubble’s size and mass transfer. However, surface tension and viscosity had no significant influence on εG, contrary to the reported for common contactors, where εG increased in the presence of ethanol and decreased at moderate/high viscosities. Moreover, it was found that increasing the oscillatory movement notably improved kL, and kLa (2–6-fold), either in ethanol or sucrose solutions, compared to common reactors, even with moderate power consumption (∼105 W m−3). This improvement resulted from the bubbles’ breakage, which originates bubbles with small and approximately the same size (homogeneous regime) enhancing a, instead, lower oscillations resulted in large bubbles (heterogeneous regime). The results demonstrate that the OFR-SPC can ensure outstanding mass transfer rates, with potential and feasibility for use in gas-liquid bioprocesses, where mass transfer and liquid properties are important.

Numerical Study of the Effects of Surface Tension and Initial Volume Fraction on Gas-Liquid-Foam Three-Phase Flow Separation Process

Since it is low in cost and low in toxicity and has good biodegradability, gas-liquid-foam three-phase flow has been widely used in industrial fire protection. Due to the different characteristics of gas, liquid, and foam, liquid precipitation is liable to occur under static conditions, resulting in unstable performance of the mixture. To improve fire extinguishing efficiency, it is of great significance to study the separation process of gas-liquid-foam. In the present study, the effects of the surface tension (range from 0.04 to 0.07) and initial liquid volume fraction (range from 0.2 to 0.5) on the gas-liquid-foam separation process are investigated with the numerical tool Fluent. The liquid volume fraction is mainly influenced by two inverse effects: (a) the transformation of liquid into foam, and (b) the liquid drainage and bursting of foam. In the separation process, the volume fraction of small foam decreases monotonically while the volume fraction of medium and large foam increases slightly. Since the volume fraction of small foam is much greater than medium and large foam and its bursting process is dominant, the liquid volume fraction presents a monotonic increasing trend. The volume of the separated liquid increases almost linearly with time at various surface tensions and initial volume fractions, and the increase rate is about 0.004. In the range of the surface tension examined, the separation process is insensitive to the surface tension, resulting in almost the same drainage time. On the other hand, the separation process depends on the initial liquid volume fraction non-monotonically; namely, when the initial volume fraction is small, with the increase of the initial volume fraction, the liquid is more easily separated from the mixture, and when the initial volume fraction is over a critical value (about 0.4), the separation process is decelerated.

Contact-free measurement of surface tension on single droplet using machine learning and acoustic levitation

HypothesisAcoustic levitation provides the possibility to deform levitated droplets in a controllable, and quantifiable manner, thus offering a means to measure the surface tension of a liquid droplet based on its deviation from sphericity. However, for new generation of multi-source and highly stable acoustic levitators, no model relates the acoustic pressure field to the deformation and surface tension. Utilizing a machine learning algorithm is expected to identify correlations between the experimental data without any set preconditions. ExperimentsA series of aqueous surfactant solutions with a large range of surface tensions were prepared, and evaporated under levitation, while the acoustic pressure was varied. A dataset of over 50,000 images was used for the training and evaluation of the machine learning algorithm. Prior to that, the machine learning approach was validated on in silico data that also included artificial noise. FindingsWe achieved high accuracy in predicting the surface tension of single standing droplets (±0.88 mN/m), and we surpassed certain physical conditions related to the size, and shape of the suspended samples that simpler theoretical models are subject to.

An experimental and modeling investigation of the behaviors of solution in fluoropolymers hollow fiber membranes (HFMs)

This work focuses on the mass transfer in hydrophobic polyvinylidene fluoride (PVDF) and poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP) hollow fiber membranes, using a combination of experiments and computational fluid dynamics (CFD) model. Our experimental design considered a wider range of viscosity and surface tension for the feed solution (kerosene, lubricating oil and water), a larger span of operation temperature (25–85 °C), and longer usage time (8 h). The membranes were characterized for the permeability, morphologies, pore size distribution, porosity, water contact angle (WCA), roughness, differential scanning calorimetry (DSC) and tensile property. Numerical simulations of two-phase and single-phase flow in micron membrane channels were performed for several selected groups to assist interpretations of the experiments and to examine the effects of wettability, viscosity and pore size on the mass transfer process. The simulations base on the OpenFOAM-model agree well with the experimental results. Collectively, this study provides new insights regarding mass transfer in membrane channels and reference data for the use of fluoropolymers membranes for non-aqueous solution, especially high viscosity oil.

Enhanced anti-biofilm and anti-protein adsorption properties of liquid-infused silver-polytetrafluoroethylene coatings

In this work, a slippery liquid-infused silver-polytetrafluoroethylene (AgFP) coating was fabricated via a spontaneous polycondensation of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) onto an electroless AgF sublayer. The AgFP coating demonstrated great stability and superior repellence against liquids with a wide range of surface tensions. The anti-biofouling properties were investigated by adsorption of Escherichia coli, Staphylococcus aureus, fibrinogen, and bovine serum albumin. Owing to the self-cleaning property, the AgFP demonstrated enhanced anti-adhesion activity against both bacteria and proteins relative to traditional electroless coatings, despite the fibrinogen deposition significantly promoting bacterial binding. While its ultra-low surface energy was not within the optimum surface energy region for minimum bacterial or protein adhesion, the AgFP coating still displayed excellent anti-biofilm capability in a protein-bacteria co-deposition model, reducing over 80% of BSA-supplemented biomass coverage on Ag surfaces and over 60% of Fgn-supplemented biomass coverage on AgF surfaces, respectively. To understand the anti-adhesion mechanism, the XDLVO model was used to explain the adhesion behaviour of both bacteria and proteins. Cytotoxicity assays confirmed that the AgFP coating had good biocompatibility with fibroblast cells. The results from this research provide attractive prospects for the application of the AgFP coating in biomedical devices to combat infections.

Cellulose nanofiber‐based emulsion coatings with enhanced hydrophobicity and surface adhesion for preserving anthocyanins within thermally processed blueberries packed in aqueous media

AbstractTo enhance hydrophobicity and surface adhesion of edible coatings onto blueberries, an emulsion system consisting of polysaccharides and oleic acid (OA) was developed and incorporated into layer‐by‐layer (LBL) cellulose nanofiber (CNF)‐based coating. The surface tension (ST) of CNF‐based emulsion coating with chitosan (CS), carboxymethyl cellulose (CMC) and OA was 34.28 mN/m, within the range of critical ST (28.41–37.52 dyne/cm) of blueberry surface after washing and copigmentation treatment by phenolic acid, which is essential to ensure good adhesion of coatings on fruit surface. CNF‐based emulsion coating demonstrated lower water sorption (9.47%) and water solubility (35.42%) and higher water contact angle (82.49 °) than CNF‐based coating without emulsion (control; 378.60%, 51.72%, and 67.37 °, respectively). CNF‐based emulsion coating also showed lower tensile strength (5.9 MPa) and elongation at break (2.55%) than control (28.17 MPa and 17.85%, respectively). CNF‐based emulsion coating was validated on thermally processed blueberries for preventing anthocyanin pigment leaching as the first layer in a LBL coating system with sodium alginate as the second layer. The CNF emulsion incorporated LBL coating system significantly preserved anthocyanin pigment in the processed blueberries compared with that of control due to increased surface adhesion and hydrophobicity and decreased mechanical damage. This study demonstrated the effectiveness of emulsion system in coatings for enhancing hydrophobicity and surface adhesion of coatings to preserve the nutritional and organoleptic qualities of thermally processed blueberries.Practical ApplicationDegradation of anthocyanins in processed fruit and fruit products has been a long‐term challenge for processed food industry. The hydrophobic and heat‐resistant coatings developed in this study can be used to preserve antioxidant anthocyanin pigments within fruit when subjected to thermal (simulated canning) process in aqueous solution, thus overcoming the barriers that the food industry has been facing. CNF plays a critical role to enhance thermal stability and adhesion of coatings onto fruit surface. The developed technology can be utilized for not only improving existing products, but also developing new and novel fruit products.

Magnetophoresis in Centrifugal Microfluidics at Continuous Rotation for Nucleic Acid Extraction.

Centrifugal microfluidics enables fully automated molecular diagnostics at the point-of-need. However, the integration of solid-phase nucleic acid extraction remains a challenge. Under this scope, we developed the magnetophoresis under continuous rotation for magnetic bead-based nucleic acid extraction. Four stationary permanent magnets are arranged above a cartridge, creating a magnetic field that enables the beads to be transported between the chambers of the extraction module under continuous rotation. The centrifugal force is maintained to avoid uncontrolled spreading of liquids. We concluded that below a frequency of 5 Hz, magnetic beads move radially inwards. In support of magnetophoresis, bead inertia and passive geometrical design features allow to control the azimuthal bead movement between chambers. We then demonstrated ferrimagnetic bead transfer in liquids with broad range of surface tension and density values. Furthermore, we extracted nucleic acids from lysed Anopheles gambiae mosquitoes reaching comparable results of eluate purity (LabDisk: A260/A280 = 1.6 ± 0.04; Reference: 1.8 ± 0.17), and RT-PCR of extracted RNA (LabDisk: Ct = 17.9 ± 1.6; Reference: Ct = 19.3 ± 1.7). Conclusively, magnetophoresis at continuous rotation enables easy cartridge integration and nucleic acid extraction at the point-of-need with high yield and purity.

Simulating wetting phenomenon with large density ratios based on weighted-orthogonal multiple-relaxation-time pseudopotential lattice Boltzmann model

The wetting phenomenon is widespread in nature and industry, but simulating it with large density ratios remains challenging. In this study, a modified two-dimensional weighted-orthogonal multiple-relaxation-time pseudopotential lattice Boltzmann (WMRT-PLB) model is extended to simulate the wetting phenomenon at large density ratios. A simple formula describing the contact angle and interaction force is derived, and an alternative geometrical formulation scheme based on the interaction force is proposed to model the contact angle. First, theoretical analysis shows that the continuum form of the alternative geometrical formulation scheme is mathematically equivalent to that of the geometrical formulation scheme based on the pseudopotential. In contrast, the discrete forms of the two schemes are different in implementation. Then, four classical benchmark cases (static droplet on a wall, static droplet under gravity, droplet spreading on a wall and capillary intrusion) under a large density ratio (ρl/ρg=857.7) are performed to verify and evaluate the performance of the WMRT-PLB model coupled with the alternative geometrical formulation scheme. The numerical results show that in the framework of the WMRT-PLB model, compared with the two conventional geometrical formulation schemes, the alternative geometrical formulation scheme is superior in numerical stability, especially under low surface tension, and achieves comparable numerical accuracy within a large range of surface tensions and contact angles.

In Situ Modification of CaF2-SiO2-Al2O3-MgO Flux Applied in the Aluminium-Assisted Transfer of Titanium in the Submerged Arc Welding of Carbon Steel: Process Mineralogy and Thermochemical Analysis

Flux formulations are specified to target chemical and physico-chemical parameters. Chemical parameters set flux element transfer behaviours and weld metal oxygen contents. Physico-chemical parameters such as slag viscosity, surface tension and melting range are targeted to ensure an acceptable weld bead profile and surface appearance. Slag detachability is an important physico-chemical property required to ensure high welding productivity, smooth weld bead surface and no slag entrapment. Here, bead-on-plate welding tests were made with and without metal powder additions, including aluminium powder as a de-oxidiser. Difficult slag detachability was observed in weld runs made with metal powder additions. Mineralogy of the post-weld slags, and thermochemical calculations, show that the flux was modified due to the aluminothermic reduction of MnO and SiO2 from the slag to form alumina. Increased quantities of spinel phase were identified in the post-weld slag samples, at the weld pool–slag interface. The combined effect of increased slag viscosity, from increased spinel in the slag, and lowered weld pool solidus temperature, resulted in the formation of a rough bead surface morphology, which, in turn, caused mechanical fixation of the slag to the weld bead. Flux modification to higher CaF2 content should ensure that higher quantities of spinel phase can be tolerated in the slag.

Design of stable liquid infused surfaces: Influence of oil viscosity on stability

Slippery liquid-infused porous surfaces (SLIPS) have been used as a good alternative for superhydrophobic coatings due to their increased durability against mechanical forces and their ability to repel liquids with a wide range of surface tensions. SLIPS generally consists of a superhydrophobic porous structure infiltrated with a lubricant. The self-healing ability of SLIPS helps to maintain their water repellency longer than superhydrophobic surfaces. Even though SLIPS have great functionalities for practical applications, their stability is still insufficient due to the loss of lubricant from them. The oil loss from SLIPS depends mainly on the viscosity of the lubricant infiltrated into it. Even though plenty of research has been conducted over SLIPS with viscosities ranging from 1 cSt to 20, 000 cSt, a complete understanding of the oil loss mechanism is still not available. Therefore, in this work, we investigated the influence of silicone oil (lubricant) viscosity on the stability of SLIPS to determine a suitable viscosity range to fabricate stable SLIPS. Various SLIPS were fabricated by infiltrating silicone oils with a wide viscosity range. Stability studies were conducted by obtaining the volume of oil removed from the SLIPS with respect to the number of drops. Narrow SLIPS were also fabricated to understand the effect of self-healing speed on the oil loss process. Finally, a dynamic wicking experiment is conducted to determine the self-healing speed of silicone oils. SLIPS with silicone oil viscosities of 3000 cSt and 5000 cSt demonstrated lower loss rates and higher stability. However, the oil loss was fastest for SLIPS with 100 cSt silicone oil. Rapid self-healing of the lower viscosity oil was the main reason for the quick oil loss from lower viscosity SLIPS.