Non-wetting Conditions Research Articles

A bi-component model to assess the rheology of soft cellular aggregates probed using the micropipette aspiration technique

The micro-pipette aspiration technique is a classical experiment used to characterize the physical properties of inert fluids and biological soft materials such as cellular aggregates. The physical parameters of the fluid, as viscosity and interfacial tension, are obtained by studying how the fluid enters the pipette when the suction pressure is increased and how it relaxes when the suction pressure is put to zero. A mathematical model representative of the experiment is needed to extrapolate the physical parameters of the fluid-like matter; however, for biological materials as cells or cell aggregates these models are always based on strong starting hypotheses that impact the significance of the identified parameters. In this article, starting from the bi-constituent nature of the cell aggregate, we derive a general mathematical model based of a Cahn-Hilliard-Navier-Stokes set of equations. The model is applied to describe quantitatively the aspiration-retraction dynamics of a cell-aggregate into and out of a pipette. We demonstrate the predictive capability of the model and highlight the impact of the assumptions made on the identified parameters by studying two cases: one with a non-wetting condition between the cells and the wall of the pipette (classical assumption in the literature) and the second one, which is more realistic, with a partial wetting condition (contact angle θs = 150°). Furthermore, our results provide a purely physical explanation to the asymmetry between the aspiration and retraction responses which is alternative to the proposed hypothesis of an mechano-responsive alteration of the surface tension of the cell aggregate. Statement of SignificanceOur study introduces a general mathematical model, based on the Cahn-Hilliard-Navier-Stokes equations, tailored to model micro-pipette aspiration of cell aggregates. The model accounts for the multi-component structure of the cell aggregate and its intrinsic viscoelastic rheology. By challenging prevailing assumptions, particularly regarding perfect non-wetting conditions and the mechano-responsive alteration of cell surface tension, we demonstrate the reliability of the mathematical model and elucidate the mechanisms at play, offering a purely physical explanation for observed asymmetries between the aspiration and retraction stages of the experiment.

Comparison of Newtonian and glycerol-water solution-based SiO2 nanofluid droplets impacting on heated spherical surfaces

The dynamic interactions of liquid droplets with heated spherical particles, relevant across various scientific and engineering disciplines, display intriguing collision behaviors whose principles are yet to be fully deciphered. This investigation utilizes high-speed photography to explore the wetting and non-wetting responses of different Newtonian and glycerol-water solution-based SiO2 nanofluid droplets upon contact with heated particles. Findings indicate that nanofluid droplets disrupt the thermal field and modify the surface morphology of particles more extensively under wetting than non-wetting conditions. Wetting conditions lead to significant alterations in the liquid film thickness and notable velocity field disruptions for droplets of deionized water and glycerol solution. Conversely, in the non-wetting phase, droplets nearing full rebound cause less disturbance to the velocity field, a behavior consistent across all fluid types and particle temperatures. The shape changes nanofluid droplets undergo when rebounding and separating from the particle surface are similar to those seen in glycerol solution and water droplets. Droplets in the breakup-rebound phase experience shorter contact times than those merely rebounding. A phase diagram is presented, detailing wetting (receding-deposition and boiling-breakup) and non-wetting (rebound and breakup-rebound) actions. An increase in the Weber number necessitates a higher particle temperature for the transition from rebound to breakup-rebound, which corroborates with theoretical insights. Furthermore, droplets achieve their maximum spreading area during the boiling-breakup mode.

Impact of wettability on capillary phase trapping using pore-network modeling

The impact of rock wettability on phase mobility and capillary trapping is significant in the valuation of geologic carbon sequestration scenarios. Wetting conditions of CO2/brine/rock systems can vary from site to site and over time due to changes in temperature, pressure, salinity, mineral composition and surface roughness. Therefore, effective predictability of CO2 mobility and trapping in underground formations requires a thorough exploration of the relationship between wetting conditions and phase saturation over a wide range of contact angles. In this paper, we use pore-network modeling to investigate the effect of wettability on phase mobility and capillary trapping. We simulate different wetting and nonwetting conditions during secondary flooding cycles where the initial phase saturations are varied significantly. Characteristic initial-residual (IR) saturation curves and the locus of residual phase connectivity and saturation are determined for each wettability condition.Simulations show that when the receding phase is the wetting phase, there is reduced trapping of that phase owing to piston-like advance by the nonwetting phase and sustained layer flow of the wetting phase. Such flow regimes cause nonlinearity in the characteristic initial-residual (IR) saturation curve, which is not captured by traditional trapping models. A proposed extended Land-based model matches the IR trends for all wettabilities. Simulations also show that the loci of residual phase saturation and phase connectivity are a strong function of wettability. When the receding phase is strongly nonwetting, the locus remains nearly constant in phase connectivity, while at increasingly wetting conditions, the locus forms a closed-loop in the saturation-connectivity space, where the endpoint of the locus is constrained by pore topology as residual saturations approach low values.

Non-axisymmetric modes in ultrathin annular liquid films coating a cylindrical fiber

This paper presents a detailed analysis of the three-dimensional stability properties of an annular liquid film coating a cylindrical fiber in the presence of van der Waals (vdW) interactions, whose influence depends on the wettability of the solid by the liquid. Under wetting conditions, vdW interactions can stabilize a uniform annular film when its thickness is smaller than a critical value that depends only on the fiber radius, the Hamaker constant, and the surface tension coefficient [Quéré et al., Science 249(4974), 1256–1260 (1990)]. In contrast, under non-wetting conditions, both surface tension and vdW forces contribute to destabilize the interface, and non-axisymmetric modes may become dominant depending on the thickness of the film and the relative strength of the surface tension and vdW forces. We perform temporal stability analyses of both the Stokes and lubrication equations of motion, allowing us to reveal the dominant azimuthal mode, as well as the optimal axial wavenumber and the corresponding temporal growth rate, as a function of the relevant governing parameters.

Liquid flow in heap leaching using the discrete liquid flow model and graph-based void search algorithm

The liquid flow in many heap leaching processes is discontinuous in nature as it occurs either as droplets or rivulets or in combination. Therefore, it cannot be represented correctly using continuum-based models at very low liquid flow rates, such as in heap leaching, or in non-wetting conditions, where liquid flow is discrete in nature. Many researchers have modelled the liquid flow through the heap packing using continuum models. However, this directly contradicts the experimental observations made by various researchers. In the current study, liquid flow is considered discrete in nature as rivulets and droplets with their rupture and merging phenomena. A single vertical layer of particles is considered for the study. A novel void search algorithm is devised to detect the position, shape, and size of the voids in a heap. The liquid flow behaviour is studied in terms of particle size, tortuosity, liquid distribution, breakthrough time, and contact angle. The study shows that heap leaching processes can be modelled more accurately using Discrete Liquid Flow (DLF) theory by avoiding uncertain experimental parameters such as bed permeability. It is found that particle size in the heap structure has significant effect on the liquid-solid contact area, which is an important parameter to determine the efficiency of the leaching process at an industrial scale.

Modeling of CO2 absorption into 4-diethylamino-2-butanol solution in a membrane contactor under wetting or non-wetting conditions

In this work, 4-diethylamino-2-butanol (DEAB) as a new type of alkanolamine solvent is used for CO2 capture in a hollow fiber membrane contactor (HFMC). A model describing the gas and liquid reactions and transport inside the membrane contactor under the wetting or non-wetting conditions was built. The countercurrent flow of natural gas and solvent was considered in the model. To investigate the influence of solvent type on decarburization efficiency, DEAB was used and compared with other common solvents such as potassium carbonate (K2CO3), triethylamine (TEA) and diethanolamine (DEA). Under the same operating conditions, the impact of parameters such as humidity, gas flow rate, liquid concentration, membrane length on the decarburization performance was examined. The results indicate that DEAB solvent had the best overall performance especially under the wetting conditions. It was noted that increasing liquid concentration, membrane length and decreasing gas flow rate enhanced decarburization.

CO2/N2 separation by glycerol aqueous solution in a hollow fiber membrane contactor module: CFD simulation and experimental validation

In this paper, CO2 separation from CO2/N2 mixed gas was experimentally and theoretically investigated inside a gas–liquid hollow fiber membrane contactor (HFMC) module along with developing and validation of a comprehensive computational fluid dynamic (CFD) model. An aqueous solution of glycerol (10 wt%) (C3H8O3), a green and cost-effective physical solvent, was employed as the liquid absorbent, flowing in the shell side of the hollow fibers. To attain a better insight into the membrane wetting effects on separation performance, all non-wetting, partially-wetting, and completely-wetting conditions were investigated. Moreover, a correlation for CO2 Henry’s law constant was developed to estimate the CO2 solubility in aqueous solutions of glycerol via adopting the literature data. The CFD simulation results revealed that the gas to absorbent flow rate ratio (Fg/Fa) is a dominant parameter in controlling the CO2 removal efficiency. CO2 separation performance was augmented via decreasing the gas flow rate, absorption temperature and increasing the membrane porosity to tortuosity ratio as well as glycerol concentration. In contrast, by increment of the membrane wettability from non-wetting to completely-wetting condition, the CO2 removal percentage was dramatically reduced from 72.5 to 18.5%. A fair agreement between the CFD simulation results and experimental data with an absolute average relative error percentage (AARE%) of 2.7% was achieved, confirming the validity of the developed model.

Novel coatings for graphite materials in PV silicon applications: A study of the surface wettability and interface interactions

Coatings are one of the promising techniques that can be applied to modify the surface properties and tailor the surface interactions with the surrounding. The development of conformable coatings for graphite materials can expand their use in silicon PV applications with no compromise on the silicon quality. However, no studies are focused on the coatings for graphite materials in silicon crystallization applications. Here we introduce different coating techniques that promise minimal interactions with the graphite and suppress the liquid silicon penetration. Five coating methods were proposed in this study: (i) one-layer coating: a mixture of silicon nitride and colloidal silica was directly coated on graphite substrates, (ii-iv) two-layer coating: a porous coating layer of silicon nitride, silicon carbide, or a combination of both materials was deposited as a protective layer below the top layer of Si3N4 and colloidal silica, and (v) a dense SiC layer was deposited on the graphite by silicon infiltration method below the top layer. The coatings’ wettability and interactions with graphite were investigated via in-situ melting experiments. The two-layer coating approach revealed a considerable improvement in the non-wetting behavior, a decrease in the coating degradation rate, and a decrease in CO evolution during the isothermal holding. The best non-wetting conditions with minimal detrimental interaction between graphite and silicon oxides were achieved by applying a two-layer coating with a thickness of 400 ± 50 μm and an initial oxygen concentration of 8 wt.% in the top layer. These findings can be utilized for the application of reusable graphite crucibles in silicon crystallization processes.

Rigorous non-isothermal modeling approach for mass and energy transport during CO2 absorption into aqueous solution of amino acid ionic liquids in hollow fiber membrane contactors

In the current study, a rigorous modeling approach was used to develop a mathematical model for the non-isothermal absorption process of CO2 in hollow fiber membrane contactors (HFMC). Four amino acid-based ionic liquids (ILs) namely, tetramethylammonium glycinate [N1111][Gly], 1-ethyl-3-methylimidazolium glycinate [C2mim][Gly], 1-butyl-3-methylimidazolium glycinate [C4mim][Gly] and 1-hexyl-3-methylimidazolium glycinate [C₆mim][Gly] were used as absorbents. These ILs have never been implemented for the membrane contactor CO2 absorption operations both on the lab scale and industrial scale. Wide ranges of operating conditions were investigated for freshly unloaded absorbents and partial conversion of absorbents considering steady-state conditions for the model. Non-wetting conditions were adopted by keeping very low transmembrane pressure. The non-isothermal model predicted a significant temperature rise along the contactor length, ranging from 10 to 25 K, which further affected the absorption and reaction kinetics. Simulations confirmed the strong influence of absorbent concentration and mild influence of process temperature on the separation performance of ILs, CO2 boundary flux, and reaction kinetics between CO2 and ILs. Very fast absorption of CO2 near the interface justified the dominancy of the chemisorption for the current absorption. Finally, the comparison with experimental data evidenced the identical trends and hence validated the model.

Numerical simulations of bubble formation in liquid metal

The process of bubble formation from submerged orifices is encountered in various industrial applications. It is therefore essential to understand the dynamics of bubble formation under such conditions. In the present work, the process of bubble formation in a steel-argon system is studied using the Local Front Reconstruction Method (LFRM), a Front Tracking method that enables the simulation of interface merging and breakup. The numerical simulations are performed over a wide range of gas injection rates to study the bubble formation dynamics under quasi-static and dynamic regimes. The simulation results show that the detached bubbles in a steel-argon system are generally bigger compared to the bubbles detached in a water-air system due to higher surface tension and lower wettability. In liquid cross-flow, the bubble at the orifice mouth becomes asymmetric due to the drag force created by the liquid flow. Under non-wetting conditions, the bubble can slide over the orifice without forming a bubble neck when the orifice plate is sufficiently large. On the other hand, under wetting conditions, the detached bubble volume decreases when the orifice plate is gradually tilted from a horizontal to vertical orientation at lower shear rates. However, this trend reverses at higher shear rates because the drag force exerted by the flowing liquid becomes dominant.

Nitric oxide reduction by hydrogen peroxide absorption through a ceramic hollow fiber membrane contactor

Nitric oxide reduction by hydrogen peroxide absorption through a ceramic hollow fiber membrane contactor was studied experimentally. A membrane contactor with a single ceramic hollow fiber was characterized by multiple techniques, including contact angle measurement, gas permeation, water permeation and spectroscopy. The superhydrophobic ceramic was first used to achieve nonwetting conditions, and overatmospheric operating conditions were applied to enhance mass transfer. The effects of the process parameters on NO reduction were tested and discussed. It was found that NO reduction increases linearly with diffusion length. The gas flow rate and absorbent flow rate are suggested to be low to achieve high-efficiency gas absorption. NO reduction increases linearly with the enhancement factor or the square root of hydrogen peroxide concentration. Elevated pressure increases NO absorption flux and helps NO reduction within the breakthrough pressure.

The effect of preliminary heat treatment on the durability of reaction bonded silicon nitride crucibles for solar cells applications

Silicon nitride crucibles have the potential to replace silica crucibles and reduce the cost of silicon crystallization because of their reusability potential. Till date, crucibles’ heat treatment before each use is a prerequisite to achieve non-wetting conditions that is needed to facilitate the ingot release and hence enable reusability. Yet, no studies have examined the heat treatment influence on the crucibles’ durability. The present investigation focuses on the crucibles’ heat treatment and its impact on the crucibles’ lifetime. Repeated heat-treatments of silicon nitride crucibles in the air at above 1100 °C leads to crucible fracture. Therefore, this study identifies the cause and the mechanism of such failures by applying different heat treatment procedures in the air. The mass gain and the oxidation rates of the crucibles at different temperatures are measured via Thermogravimetry (TG) and Differential Thermal Analyzer (DTA). The results show that the porosity and phase distribution along the crucible wall thickness, play a key role in the crucible’s behavior during oxidation. Moreover, excessive internal oxidation in the tested crucibles results in severe thermal stresses which cause cracking during cooling.

Separation of Binary Alloys in Thin Capillaries

A direct numerical simulation of the process of binary alloy separation in a thin nonuniformly heated circular capillary is carried out. The key point of this process is the assumption of the existence of a thin gas layer between the melt and the boundary of the reservoir due to the non-wetting conditions. This effect was described using the equations of interphase hydrodynamics, which made it possible to construct a phenomenological model of the processes at the melt-solid interface for mixtures of liquid metals. The problem was solved by the finite difference method in combination with an explicit scheme on the PGNIU-Kepler supercomputer at the Research and Education Center “Parallel and Distributed Computing” of the Perm State National Research University. The velocity and temperature fields, as well as the concentration of melt components in the bulk and on the surface, were determined through numerical simulation. The dynamics of the separation process is described. It is shown that the longitudinal temperature gradient and the non-wetting conditions on the lateral surface create a downward motion of the melt along the boundary, which, together with the adsorption and desorption effects, leads to the formation of volumetric nonuniformity of the concentration of the mixture components along the capillary. The experimentally observed time dependence of the difference in the volume concentrations of the components at the ends of the capillary is reproduced. The distribution of volume concentrations of the components and the surface phase along the capillary is analyzed at various values of the adsorption and desorption coefficients and the Marangoni number. The dependence of the concentration difference for the melt components at the ends of the capillary as function of its length is studied. It is found that the separation effect intensifies with an increase in the capillary length. A qualitative and quantitative comparison of most of the characteristics demonstrates a good correlation of the calculation results with the data previously obtained for the plane problem and the available experimental data. A numerical experiment shows that the motion in the surface layer is rather intense. The heavy component is transported by the convective flow to the lower part of the capillary so that its concentration increases by almost an order of magnitude on 1/8 of the capillary surface.

Electrically induced spreading of EGaIn on Cu substrate in an alkali solution under wetting and non-wetting conditions

Electrically actuated movement of liquid metals is quite promising in mechanical engineering and applied physics. However, little work has so far been performed on the effect of current polarity on the actuation of the eutectic gallium–indium (EGaIn) alloy moving on metal substrates. In this work, the spreading of EGaIn on copper (Cu) substrate under different direct-current (DC) polarities in the 0.5 mol/L NaOH solution was investigated, and the underlying mechanisms were addressed. When the Cu substrate was connected to cathode, the wetting was essentially attributed to the reduction in the oxidized surface of the Cu substrate; whereas, under the opposite polarity, the spreading was related to the tension gradient along the EGaIn–solution interface, which induced Marangoni flow, despite the fact that the EGaIn–Cu system was non-wetting in this case.

Continuous Recirculation of Microdroplets in a Closed Loop Tailored for Screening of Bacteria Cultures.

Emerging microfluidic technology has introduced new precision controls over reaction conditions. Owing to the small amount of reagents, microfluidics significantly lowers the cost of carrying a single reaction. Moreover, in two-phase systems, each part of a dispersed fluid can be treated as an independent chemical reactor with a volume from femtoliters to microliters, increasing the throughput. In this work, we propose a microfluidic device that provides continuous recirculation of droplets in a closed loop, maintaining low consumption of oil phase, no cross-contamination, stabilized temperature, a constant condition of gas exchange, dynamic feedback control on droplet volume, and a real-time optical characterization of bacterial growth in a droplet. The channels (tubing) and junction cubes are made of Teflon fluorinated ethylene propylene (FEP) to ensure non-wetting conditions and to prevent the formation of biofilm, which is particularly crucial for biological experiments. We show the design and operation of a novel microfluidic loop with the circular motion of microdroplet reactors monitored with optical sensors and precision temperature controls. We have employed the proposed system for long term monitoring of bacterial growth during the antibiotic chloramphenicol treatment. The proposed system can find applications in a broad field of biomedical diagnostics and therapy.

Statistical analysis of the effects of graphite crucible on viscosity measurement of silicate melts

Graphite crucible is widely used in high temperature viscosity measurement due to its low cost. However, it may cause measurement errors because of contamination with fine graphite particles, non-wetting conditions, or chemical reactions between melt and graphite. In order to clarify the effect of graphite crucible on viscosity measurement, in this work, more than 800 compositions and 3300 viscosity measurements within CaO-MgO-Al2O3-SiO2 systems were collected and analyzed, using a statistical and modeling-based way. It is found the viscosity data obtained in graphite crucible show much larger scatter than those obtained in metal crucibles. Averagely, viscosity obtained in graphite crucible is 24% higher. The chemical reaction SiO2(l) + 3C(s) = SiC(s) + 2CO(g) is the primary error source for viscosity measurement in graphite crucible. It is suggested that the viscosity data obtained in graphite crucible can be used only with great caution.

Micro-bubble Formation under Non-wetting Conditions in a Full-scale Water Model of a Ladle Shroud/Tundish System

Micro-bubble Formation under Non-wetting Conditions in a Full-scale Water Model of a Ladle Shroud/Tundish System

A Physical Model to Study the Effects of Nozzle Design on Dense Two-Phase Flows in a Slab Mold Casting Ultra-Low Carbon Steels

The effects of nozzle design on dispersed, two-phase flows of the steel-argon system in a slab mold are studied using a water-air model with particle image velocimetry and ultrasound probe velocimetry techniques. Three nozzle designs were tested with the same bore size and different port geometries, including square (S), special bottom design with square ports (U), and circular (C). The meniscus velocities of the liquid increase two- or threefold in two-phase flows regarding one-phase flows using low flow rates of the gas phase. This effect is due to the dragging effects on bubbles by the liquid jets forming two-way coupled flows. Liquid velocities (primary phase) along the narrow face of the mold also are higher for two-phase flows. Flows using nozzle U are less dependent on the effects of the secondary phase (air). The smallest bubble sizes are obtained using nozzle U, which confirms that bubble breakup is dependent on the strain rates of the fluid and dissipation of kinetic energy in the nozzle bottom and port edges. Through dimensionless analysis, it was found that the bubble sizes are inversely proportional to the dissipation rate of the turbulent kinetic energy, e0.4. A simple expression involving e, surface tension, and density of metal is derived to scale up bubble sizes in water to bubble sizes in steel with different degrees of deoxidation. The validity of water-air models to study steel-argon flows is discussed. Prior works related with experiments to model argon bubbling in steel slab molds under nonwetting conditions are critically reviewed.

High-throughput drawing and testing of metallic glass nanostructures.

Thermoplastic embossing of metallic glasses promises direct imprinting of metal nanostructures using templates. However, embossing high-aspect-ratio nanostructures faces unworkable flow resistance due to friction and non-wetting conditions at the template interface. Herein, we show that these inherent challenges of embossing can be reversed by thermoplastic drawing using templates. The flow resistance not only remains independent of wetting but also decreases with increasing feature aspect-ratio. Arrays of assembled nanotips, nanowires, and nanotubes with aspect-ratios exceeding 1000 can be produced through controlled elongation and fracture of metallic glass structures. In contrast to embossing, the drawing approach generates two sets of nanostructures upon final fracture; one set remains anchored to the metallic glass substrate while the second set is assembled on the template. This method can be readily adapted for high-throughput fabrication and testing of nanoscale tensile specimens, enabling rapid screening of size-effects in mechanical behavior.

Mechanical Behaviour under Quasi-Static Loading of Open-Cell Foams of 6061-T6 Al Alloys Processed by Pressurized Salt Infiltration Technique

Here, we report the mechanical behaviour of open-cell foams of 6061-T6 Al-alloys under quasi-static loading. The foams were processed by pressurized salt infiltration technique with efficient control over pore size and distribution. Spherical salt beads of NaCl of required size distribution were used as preforms. The molten alloy was infiltrated into the preforms under an inert gas pressure of 2 bar followed by cooling and leaching of the salt pattern in a suitable aqueous medium. The pressurized infiltration process is convenient to overcome the capillary forces arising from the non-wetting conditions between salt beads and molten alloys and offers a versatile and economical route for the production of open-cell foams. The shape, size and distribution of the pores were studied with optical microscope and X-ray computed tomography (X-ray CT). The developed foam samples were cut into required dimensions following ASTM E9-09 standard and their mechanical properties were analyzed under quasi-static compressive loading.