Three-phase Contact Research Articles

Effect of particle shape on particle-bubble interaction behavior: A computational study using discrete element method

A three-dimensional Discrete Element Method (DEM) simulation model of particle-bubble interaction behavior based on particle-bubble mechanics theory was developed, and six kinds of irregular shape particle models were designed. The interaction behavior of spherical and irregular-shaped coal particles with the particle size of 0.1 mm and densities of − 1.3, 1.4–1.5, + 1.7 g/cm3 and a fixed bubble in quiescent water was simulated. The simulation results show that the interaction between spherical and irregular shape particles with the bubble can be divided into five stages: free settling, flow around the bubble surface, sliding with a liquid film, film rupture & three-phase contact line (TPCL) formation, sliding with a TPCL. Irregular shape particles have a larger critical collision angle and capture probability than spherical particles. The critical induction time of irregular particles is smaller than that of spherical particles. Irregular particles with edges and corners can promote the thinning and rupture of the liquid film between bubble and particle，thereby reducing the induction time and increasing the capture probability.

Fibrous and Spherical Aggregates of Ovotransferrin as Stabilizers for Oleogel-Based Pickering Emulsions: Preparation, Characteristics and Curcumin Delivery.

This study aimed to explore the effects and mechanisms of differently shaped aggregates of ovotransferrin (OVT) particles on oleogel-based Pickering emulsions (OPEs). Medium-chain triglyceride oil-based oleogels were constructed using beeswax, and their gel-sol melting temperatures were investigated. Atomic force microscopy confirmed that both OVT fibrils and OVT spheres were successfully prepared, and the three-phase contact angle measurements indicated that fibrous and spherical aggregates of OVT particles possessed great potential to stabilize the OPEs. Afterward, the oil-in-water OPEs were fabricated using oleogel as the oil phase and OVT fibrils/spheres as the emulsifiers. The results revealed that OPEs stabilized with OVT fibrils (FIB-OPEs) presented a higher degree of emulsification, smaller droplet size, better physical stability and stronger apparent viscosity compared with OPEs stabilized with OVT spheres (SPH-OPEs). The freeze–thaw stability test showed that the FIB-OPEs remained stable after three freeze–thaw cycles, while the SPH-OPEs could barely withstand one freeze–thaw cycle. An in vitro digestion study suggested that OVT fibrils conferred distinctly higher lipolysis (46.0%) and bioaccessibility (62.8%) of curcumin to OPEs.

Effects of brine valency and concentration on oil displacement by spontaneous imbibition: An interplay between wettability alteration and reduction in the oil-brine interfacial tension

Brine fluids have recently been of high interest to enhanced oil recovery process in both academia and industry. Both diluted formation brines and specifically formulated brines were reported to improve crude oil displacement in porous rock, owing to either their bulk salinity or brine-type. Mechanisms for such an improvement were widely proposed, including microscopic interfacial phenomena: wettability alteration and reduction in the oil-brine interfacial tension (σ), although their synergistic or interlinked contributions were vaguely clarified. To elucidate insights into this “low-salinity” enhanced oil recovery, crude oil displacement by spontaneous imbibition was conducted in the current research with focus on the effects of brine valency and concentration. Monovalent (NaCl) and divalent (CaCl2) brines at elevated concentrations (10, 100, and 1000 mM) were examined as imbibing fluids. Changes in the three-phase contact angle and the crude oil-brine interfacial tension were also investigated. Imbibition results showed that NaCl brine at ‘suitable’ concentration (100 mM) displaced greater oil (95.8 %) than too-low (10 mM) or too-high (1000 mM) concentrations, and these monovalent brines displaced more effective than those of divalent CaCl2 due to an oil-wetting as a result of divalent ion bridging phenomenon. This echoes crucial influences of both brine valency and concentration. Since no direct individual contribution from either the contact angle or σ on the oil displacement was obtained, an interplay between these two parameters were thought to control. The imbibition results were a capillary-dominated process (capillary number < 2.1 × 10−6), re-confirmed by their correlations with the calculated capillary pressures and inverse Bond numbers. The findings revealed that in a given imbibition system a required σ is a wettability-dependent: water-wet system needs high σ to enhance a driving capillarity while oil-wet system prefers lower σ to weaken a resisting capillary force. Brine formula directly attributed to wettability and σ: NaCl brines secure water-wetting with high σ while CaCl2 brines reduced σ more effectively with an assured oil-wetting. Low-salinity enhanced oil recovery mechanism was thus found to be contributed from capillary effect, which was an interplay between the interfacial tension and wettability. Paring these two parameters by formulating imbibing brine to anticipate high oil recovery is crucial and of challenge.

Effect of Surface Heterogeneities on Interactions between Air Bubbles and Heterogeneous Surfaces.

The effects of surface heterogeneities on bubble-particle interactions have received little attention although heterogeneities are common for varieties of substance surfaces. In this work, heterogeneous surfaces consisting of discrete hydrophilic dots on a hydrophobic background were fabricated. The interactions between air bubbles and heterogeneous surfaces with different hydrophilic area fractions were investigated using a high-sensitivity microbalance coupled with a high-speed video camera. It was found that the snap-in, maximum adhesion, and pull-off forces increased as the hydrophilic area fraction decreased. These experimental results were compared with the calculated interaction forces. The comparison between experimental results and the calculated interaction forces showed that the normalized contact line length (δ) should be considered in the calculation of the snap-in force, and its value was between 1 and the δ value corresponding to the maximum pinning strength. In contrast, δ = 1 is more appropriate for the calculation of maximum adhesion force, indicating that the corrugations in the three-phase contact line could be neglected. These findings demonstrate that discrete hydrophilic defects make bubble-surface attachment difficult but have nearly no effect on bubble-surface detachment. Better understanding of the interactions between air bubbles and heterogeneous surfaces potential offers a new thought to control the bubble-particle interactions using appropriately design of particle surfaces.

Programmable Birefringent Patterns from Modulating the Localized Orientation of Cellulose Nanocrystals.

Birefringence has been attracting broad attention due to its strong potential for applications in biomedicine and optics, such as biomedical diagnosis, colorimetric sensing, retardant, and polarization encoding. However, engineering architectures with precisely controllable birefringence remains a challenge due to the lack of effective modulation of the localized orientation. Here, by taking advantage of the inherently one-dimensional (1D) anisotropic structure of cellulose nanocrystals (CNCs), we demonstrate an approach to tune the alignment of CNCs with a well-controllable orientation at localized preciseness, which is in contrast to the previously reported unidirectional/radical orientation of CNC-based birefringent structures. The localized modulation of CNC orientation is facilitated by directing the 1D nanocrystals to align along the template periphery and the migrated three-phase contact line during the evaporation. The resultant CNC films exhibit birefringent extinction patterns under polarized light, in which versatile pattern designs can be obtained by employing templates with different shapes and template arrays with varied layouts. Due to the locally modulated orientation of CNCs, the films indicate "kaleidoscope-like" dynamically transformable designs of the birefringent patterns depending on the polarized angle, which has barely been observed previously. Furthermore, an N-nary encoding system for abundant information storage is demonstrated based on the sunlight-transparent CNC films, but with visible extinction patterns under polarized light, which is promising for encryptions, anticounterfeiting, and imaging, enriching the attractive research area of bio-based photonics.

Synergistic Ru-Ni-Cu interface for stable hydrogen evolution on 1% Ru-Ni@Cu alloy grown directly on carbon paper electrode

A [email protected] alloy catalyst with a well-connected two-phase or three-phase contact interface is fabricated as an alternative to a Pt-based catalyst for the hydrogen evolution reaction (HER) in water electrolysis in this study. For optimum bonding and adhesion stability, the alloy particles are grown directly on carbon paper (CP) by the hydrothermal method. The alloy particles are composed of central Cu cores, Ni nests wrapped around Cu core, and small (2.0 nm) Ru nanoparticles embedded at the Ni nests. The Ni surface readily adsorbs water, the high conductivity of Cu increases the electron density of the electrode surface to facilitate water splitting, and the Ru surface adsorbs more H+ ions, thus promoting hydrogen production in the [email protected] alloy. Eventually, despite the use of only 1.0 wt% Ru, the 1% [email protected]/CP electrode exhibits a low overpotential of −0.15 V (η = 246 mV and 87.08 mV dec−1) at 100 mA cm−2 in a 1.0 M KOH electrolyte, similarly to the −0.1 V overpotential of the 100% Pt/CP electrode. The electrode maintains excellent catalytic activity without deterioration for 10 days with a Faraday efficiency of 96.89% (50 h) HER and 3000th LSV cycles.

Water entry dynamics of rough microstructured spheres

In this work, we proposed a facile underwater air cavity generation strategy based on rough microstructured spheres and explored its water entry dynamics and drag reduction characteristics. Under the assistance of microstructures, the three-phase contact line is pinned near the sphere equator and inhibits the wetting of the liquid film along the sphere surface, so that leading the formation of air cavity. The water entry process is mainly divided into four stages: flow formation, cavity opening and stretching, cavity closure and entrapment, and cavity collapse. With the Froude number Fr, the pinch-off depth of air cavity obviously increases, and the pinch-off time is also delayed, which contributes to the formation of a longer bottom air cavity. In addition, the spheres with a larger impact velocity would fall faster in water during the initial falling period, while the terminal velocities are nearly the same for all the spheres when they are in a stable falling period. It is worth noting that for a same sphere, the larger impact velocity could not only contribute to the formation of a longer air cavity but also makes the generated air cavity keep in a stable and streamlined shape at different underwater depth, which is vitally important for achieving continuous drag reduction. Finally, we demonstrated numerically that the stable streamlined sphere-in-cavity structure could reduce the hydrodynamic resistance levels up to 91.3% at Re ∼ 3.12 × 104, which is related to the boundary slip caused by an air layer trapped in the microstructures.

How liquid–liquid phase separation induces active spreading

The interplay between phase separation and wetting of multicomponent mixtures is ubiquitous in nature and technology and recently gained significant attention across scientific disciplines, due to the discovery of biomolecular condensates. It is well understood that sessile droplets, undergoing phase separation in a static wetting configuration, exhibit microdroplet nucleation at their contact lines, forming an oil ring during later stages. However, very little is known about the dynamic counterpart, when phase separation occurs in a nonequilibrium wetting configuration, i.e., spreading droplets. Here we show that liquid-liquid phase separation strongly couples to the spreading motion of three-phase contact lines. Thus, the classical Cox-Voinov law is not applicable anymore, because phase separation adds an active spreading force beyond the capillary driving. Intriguingly, we observe that spreading starts well before any visible nucleation of microdroplets in the main droplet. Using high-speed ellipsometry, we further demonstrate that the evaporation-induced enrichment, together with surface forces, causes an even earlier nucleation in the wetting precursor film around the droplet, initiating the observed wetting transition. We expect our findings to improve the fundamental understanding of phase separation processes that involve dynamical contact lines and/or surface forces, with implications in a wide range of applications, from oil recovery or inkjet printing to material synthesis and biomolecular condensates.

Zero-contact angle solutions to stochastic thin-film equations

We establish existence of nonnegative martingale solutions to stochastic thin-film equations with quadratic mobility for compactly supported initial data under Stratonovich noise. Based on so-called alpha -entropy estimates, we show that almost surely these solutions are classically differentiable in space almost everywhere in time and that their derivative attains the value zero at the boundary of the solution’s support. From a physics perspective, this means that they exhibit a zero-contact angle at the three-phase contact line between liquid, solid, and ambient fluid. These alpha -entropy estimates are first derived for almost surely strictly positive solutions to a family of stochastic thin-film equations augmented by second-order linear diffusion terms. Using Itô’s formula together with stopping time arguments, Jakubowski’s modification of the Skorokhod theorem, and martingale identification techniques, the passage to the limit of vanishing regularization terms gives the desired existence result.

Molecular simulation on CO2 adsorption in partially water-saturated kaolinite nanopores in relation to carbon geological sequestration

CO2 geological sequestration in depleted gas/oil reservoirs is regarded as a promising strategy to mitigate CO2 emission thanks to the well-developed nanoscale pore structures providing substantial adsorption spaces. Therefore, the fundamental understanding of CO2 adsorption in shale nanopores can provide important insights into geological CO2 sequestration. In this work, we use molecular dynamics (MD) and Grand canonical Monte Carlo (GCMC) simulations to investigate CO2 adsorption in kaolinite nanopores with two different basal surfaces and study moisture effect. In the absence of water, CO2 presents stronger adsorption in gibbsite nanopores than siloxane nanopores. In gibbsite pores, water tends to spread over the surfaces forming thin water films. While CO2 is driven to the middle of the pore, an enrichment of CO2 is observed at the water-CO2 interface. On the other hand, water bridges form in siloxane pores. In siloxane mesopores, the shape of water clusters gradually turns to be spherical ones as pressure increases suggesting a more CO2-wet surface, while the deformation of water clusters in micropores is not obvious due to stronger confinement effects. The CO2 distributions in siloxane mesopores can be divided into six zones. The highest CO2 density appears in the three-phase contact areas, while CO2 has a high tendency to accumulate in two-phase contact areas. In general, the presence of water results in the reduction of CO2 adsorption in both gibbsite and siloxane pores. Overall, water has a more detrimental influence on CO2 adsorption in gibbsite pores than siloxane pores. Our work should provide important insights into CO2 adsorption in kaolinite nanopores and reveal CO2 adsorption mechanisms in the presence of water.

Preparation of a demulsifier for oily wastewater using thorn fir bark as raw materials via a hydrothermal and solvent-free amination route.

In current work, a TB-EDA demulsifier for disposing oily wastewater was prepared using thorn fir bark (TB) as starting materials via a hydrothermal and solvent-free amination route. Field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectrometer (EDS), and Fourier transform infrared spectroscope (FT-IR) were employed to characterize the TB-EDA demulsifier. Three-phase contact angle (CA), interfacial activity, formation of interfacial film (FIF), coalescence time of droplets (CTD), dynamic interfacial tension (IFT), and Zeta potential were carried out to study the possible demulsification mechanism. Bottle test was performed to investigate the effect of the TB-EDA dosage, salinity, and pH value on the demulsification performance at room temperature. Light transmittance (DL) and oil removal rate (DR) of separated water were 94.7% and 97.2%, respectively, with 100mg/L of TB-EDA demulsifier in oily wastewater at room temperature. In addition, the TB-EDA demulsifier has an excellent salt tolerance even at the salinity of 50,000mg/L. The corresponding DL and DR could reach 99.8% and 99.9%, respectively.

Controlled-Alignment Patterns of Dipeptide Micro- and Nanofibers.

Ordered assemblies of the peptide diphenylalanine (FF) are produced and deposited on planar substrates. The FF aggregate growth is achieved through precipitation from aqueous ammonia solutions induced by solvent evaporation. The applied dip-coating technique confines the FF assembly growth to a narrow zone near the three-phase contact. The growth was observed online by optical microscopy and was investigated systematically as a function of the process parameters. Depending on the external gas flow (to influence solvent evaporation), the withdrawal speed, the initial FF, and the initial ammonia concentrations, FF forms long, straight, and rigid microfibers and/or shorter, curved nanofibers. Under certain process conditions, the FF fibers can also aggregate into stripes. These can be deposited as large arrays of uniform stripes with regular widths and spacings. Scenarios leading to the various types of fibers and the stripe formation are presented and discussed in view of the experimental findings.

A macroscopic model for immiscible two-phase flow in porous media

This work provides the derivation of a closed macroscopic model for immiscible two-phase, incompressible, Newtonian and isothermal creeping steady flow in a rigid and homogeneous porous medium without considering three-phase contact. The mass and momentum upscaled equations are obtained from the pore-scale Stokes equations, adopting a two-domain approach where the two fluid phases are separated by an interface. The average mass equations result from using the classical volume averaging method. A Green's formula and the adjoint Green's function velocity pair problems are used to obtain the pore-scale velocity solutions that are averaged to obtain the upscaled momentum balance equations. The macroscopic model is based on the assumptions of scale separation and the existence of a periodic representative elementary volume allowing a local description as usually postulated for upscaling. The macroscopic momentum equation in each phase includes the generalized Darcy-like dominant and viscous coupling terms and, importantly, an additional compensation term that accounts for surface tension effects to momentum transfer that is, otherwise, incompletely captured by the Darcy terms. This interfacial term, as well as the dominant and viscous coupling permeability tensors, can be predicted from the solutions of two associated closure problems that coincide with those reported in the literature. The relevance of the compensation term and the upscaled model validity are assessed by comparisons with direct numerical simulations in a model two-dimensional periodic structure. Upscaled model predictions are found to be in excellent agreement with direct numerical simulations.

Magnetically aligned metal-organic deposition (MOD) ink based nickel/copper heater surfaces for enhanced boiling heat transfer

We present high boiling heat transfer properties achieved by magnetically aligned nickel precursor inks on copper substrates measured atmospheric pressure. Alignment was performed in a single direction and grid orientation. Pool boiling studies were performed to obtain correlations between the heat flux, heat transfer coefficients, and wall superheat using water and ethanol. The effects of surface wettability and roughness on nucleate boiling heat transfer properties and bubble dynamics are reported. Our studies yielded a critical heat flux (CHF) of 185.9 W/cm2 and a heat transfer coefficient (HTC) of 106.9 kW/m2 °K for water on Ni grid patterned surface, representing an improvement of 49.9% in CHF and 105% in HTC compared to plain copper surface. The alignment of nickel followed by its sintering introduced nucleation characteristics that improved bubble dynamics. This is attributed to a) altered three-phase contact angle via chemically heterogeneity of Ni/Cu surface, and b) increased surface roughness due to nickel microstructures that induced wickability.

Mirau interferometry of fluid interfaces deformed by colloids under the influence of external fields

The interfacial curvature surrounding colloidal particles pinned to fluid interfaces dictates their interparticle capillary interaction and assembly; however, it is a nontrivial function of particle anisotropy, surface roughness, external field conditions, macroscopic interfacial curvature, and the chemistry of each fluid phase. The prospect of dynamically modifying the pinning properties and interfacial organization of colloidal particles adhered to fluid interfaces via these approaches necessitates the development of experimental techniques capable of measuring changes in the interfacial deformation around particles in situ. Here, we describe a modified technique based on phase-shift Mirau interferometry to determine the relative height of the fluid interface surrounding adsorbed colloids while applying external electric fields. The technique is corrected for macroscopic curvature in the interface as well as in-plane motion of the particle in order to isolate the contribution of the particle to the interfacial deformation. Resultant height maps are produced with a maximum resolution of ±1nm along the height axis. The measured topography of the interface is used to identify the contact line where the two fluids meet the particle, along with the maximal interfacial deformation (Δumax) of the undulating contact line and the three-phase contact angle, θc. The technique is calibrated using anisotropic polymer ellipsoids of varying aspect ratio before the effect of external AC electric fields on the pinned particle contact angle is demonstrated. The results show promise for this new technique to measure and quantify dynamic changes in interfacial height deformation, which dictate interparticle capillary energy and assembly of colloids at fluid interfaces.

Droplet depinning on superhydrophobic surfaces: from simple rigid wetting to complex soft wetting

Droplet depinning on superhydrophobic surfaces is pervasive in nature and critical to many applications and hence has been studied extensively over the past few decades. A consensus has been reached that the droplet depinning force mainly stems from the synergistic dynamics of the three-phase contact line and the liquid–vapor interface. Nevertheless, the aforementioned conclusions were made using simple (pure water) droplets depinning on rigid superhydrophobic surfaces, denoted as simple rigid wetting, where the main influencing factors are liquid–vapor interfacial tension, surface texture geometry and material wettability. In recent years, an increasing amount of attention has been paid to complex soft wetting, where liquid physiochemical properties (e.g. viscoelasticity) and solid surface rigidity play an important role. To encourage the investigation of complex soft wetting, in this perspective, depinning of simple droplets on soft surfaces and depinning of viscoelastic droplets on rigid surfaces are briefly introduced. Then, possible factors that affect viscoelastic droplet depinning on soft superhydrophobic surfaces are discussed. Moreover, applications that are highly relevant to complex soft wetting are introduced.

Анализ сопряженного тепломассопереноса при аэрозольной флотации золота из россыпей

Introduction. The probability of replenishing the SME of placer gold by registering the reserves of new deposits is low, and the involvement of man-made waste in the economic circulation will allow maintaining the achieved level of gold production from placers for 10-15 years. Purpose of research. The aim of the study is to develop a technology for extracting gold from old wastes of alluvial mining based on the identified patterns of conjugate heat and mass transfer during aerosol flotation of metallic gold. Methodology. For the development of technogenic wastes of alluvial gold mining, an enrichment module based on gravity and flotation methods has been developed. The module equipment has passed research tests in industrial conditions. During flotation, the increase in the gold content in the operation of the main flotation is carried out by mixing the crude concentrate isolated from ½ of the original feed with the other ½ of it. A mixture of air and hot steam was used as the gas phase during flotation. Research results and discussion. The temperature difference at the gas-liquid interface is the driving force of the vapor-liquid phase transition with the release of significant condensation heat. The time of particle sticking to the bubble is commensurate with the time of heating the interfacial surface due to the heat of vapor condensation. This allows us to consider temperature as one of the reasons for changing the result of flotation by a mixture of air and water vapor. Due to vapor condensation, the bubble size and the intensity of interfacial heat transfer decrease. When the minimum size is reached, overheating of the vapor in the bubble leads to an increase in the evaporation of the solvent and pressure in the gas phase: the heat transfer between the phases and the size of the bubble begin to increase. Transient processes in steam are non-polytropic and the limiting bubble sizes decrease with time: at the minimum size and maximum temperature, the heat transfer of steam is higher than the heat transfer of water with an increase in the size of the bubble and a drop in temperature in it. The limiting transitions of the bubble size are the cause of high-speed oscillations of the bubble walls, which decay with time. When the bubble surface is stretched in the three-phase contact zone, the gas-liquid surface tension increases due to a decrease in the density of the adsorption layer of surfactant molecules, which causes an increase in the force holding the hydrophobic extractable particle on the bubble surface. Radial tensile-compression deformations lead to shedding from the bubble surface of hydrophilic gangue minerals randomly retained by the bubble surface (for example, in the case of high occupation of the bubble surface by extracted particles). Conclusion. It is substantiated that the combined gravity-flotation technology is economically justified: the added value of marketable products provides an increase in the value of the net present value and the return on investment index, and a reduction in their payback period. It has been proven that the addition of gravity technology with flotation methods for extracting gold provides an increase in annual metal production by ~27% rel. due to the additional extraction of forms of gold that are “resistant” to gravitational methods.

A Droplet-Manipulation Method Based on the Magnetic Particle-Stabilized Emulsion and Its Direct Numerical Simulation.

Droplet manipulation has found broad applications in various engineering fields, such as microfluidic systems. This work reports a droplet-manipulation method based on particle-stabilized emulsions, where the magnetic particles adsorbed to the droplet surface serve as the actuator. The movement and the release of the droplet can be controlled by applying an external magnetic field. A lattice Boltzmann model for a three-phase system containing liquids and solid particles is adopted, which could provide a full coupling between fluids and particles. The effectiveness of the present droplet-manipulation method is validated through experiments and numerical simulations. Furthermore, the numerical simulation can provide insight into the interactions between the magnetic particles and the droplet during the droplet-driven process. To drive the droplet successfully, the magnetic particle needs to adhere to its surface and act as an "engine" to provide the driving force. As it is a surface-tension-dominant problem, the capillary effect can be considered as an "energy transfer station". The magnetic driving force on the particle is transmitted primarily to the droplet through interfacial capillary forces at the three-phase contact line, which assists the droplet in overcoming the viscous resistance and moving forward. A dimensionless number is proposed as a predictor of droplet transport and particle detachment.

Droplet impacts on cold surfaces

We study drop impact for the case where the impacted surface is cooled below the freezing temperature of the liquid droplet. The freezing is found to affect the spreading dynamics of the impacting drops and, thus, the degree of surface coverage. The cooling of the surface leads to the arrest of the three-phase contact line, impeding droplet spreading and, thus, drastically reducing the maximum spreading diameter. Besides the surface temperature, the impact speed is also an important parameter: the higher the impact speed, the more the droplet spreads before arrest. Based on experimental observations of droplet impacts using two different liquids and two different substrates, we show using a combination of experiments and a one-dimensional freezing model, that droplet arrest occurs when a solid layer of the liquid forms on the substrate: droplet arrest occurs when this solid layer reaches a well-defined critical thickness. We then devise a simple model that efficiently predicts the maximum spreading diameter of droplets impinging, at different velocities, and freezing onto surfaces maintained at different temperatures below the liquid freezing point.

Experimental study on the overall heat transfer capability of the thin liquid film at different positions in the three-phase contact line area

Experimental study on the overall heat transfer capability of the thin liquid film at different positions in the three-phase contact line area