Marangoni Convection Research Articles

Ring-shaped colloidal patterns on saline water films

HypothesisElectrostatically stabilised colloidal particles destabilise when brought into contact with cations causing the particles to aggregate in clusters. When a drop with stabilised colloidal partices is deposited on a liquid film containing cations the delicate balance between the fluid-mechanical and physicochemical properties of the system governs the spreading dynamics and formation of colloidal particle clusters. ExperimentsHigh-speed imaging and digital holographic microscopy were used to characterise the spreading process. FindingsWe reveal that a spreading colloidal drop evolves into a ring-shaped pattern after it is deposited on a thin saline water film. Clustered colloidal particles aggregate into larger trapezoidally-shaped ‘supraclusters’. Using a simple model we show that the trapezoidal shape of the supraclusters is determined by the transition from inertial spreading dynamics to Marangoni flow. These results may be of interest to applications such as wet-on-wet inkjet printing, where particle destabilisation and hydrodynamic flow coexist.

Moving Meniscus-Assisted Template-Free Optothermofluidic Nanoparticle Patterning and Its Application in Optothermoconvective Particle Trapping.

Moving meniscus-assisted vertical lifting is a commonly employed particle assembly technique to realize large-area particle patterning for the easy fabrication of colloidal photonic crystals and sensors. Though great success has been achieved for large-area patterning, inscribing desired patterns over the target substrate with precise control over the morphology remains a challenge. The target substrates need to be functionalized (physically or chemically) to realize desired patterns, which increases the complexity and limits their applicability to specific particle-liquid combinations. We demonstrate a new approach for the precise patterning of gold nanoparticles (Au NPs, diameter ∼60 nm) over solid substrates by the synergy of light-induced Marangoni flow and vertical lifting process (moving meniscus), without the requirement of photomasks or templates. The core idea relies on the particle accumulation due to light-induced Marangoni flow near the liquid meniscus in contact with a solid surface (due to plasmonic absorption of the particles) and the controlled lifting of the substrate. We present both the simulation and experimental results of the developed patterning technique. Various patterns such as continuous lines, intermittent lines with varying lengths, patterns with continuously varying widths, cross patterns, etc. are successfully inscribed. Dynamic control over the three-dimensional morphology of the deposited patterns is achieved by varying the lifting velocity, laser irradiation time, and lifting direction during the inscription process. Finally, we show the applicability of the developed plasmonically active surface for the large-area parallel manipulation of nonabsorbing microparticles based on optothermoconvective flow. The major advantage of the developed method compared to the existing light-controlled patterning techniques is its ability to inscribe patterns over large distances (up to several centimeters). We expect that the results presented in this paper will benefit different applications requiring precise particle patterning, such as optical elements, sensors, plasmonic substrates, microfluidic master templates, and electronic circuits.

P‐239: Late‐News Poster: Modeling Particle Deposition in Evaporating Colloidal Droplets

Inkjet printing is a cost‐effective method of particle deposition applicable, for example, in the manufacture of Quantum Dot (QD) color filters. However, it is a challenge to achieve uniform deposition of particles because evaporating colloidal dispersions are prone to the coffee‐ring effect.When the particle size is small, it is difficult to gauge directly by experiment how particles migrate during the evaporation process. Consequently, it is a challenge to optimize the process conditions to improve uniformity by experiment alone. To aid in this task, we have developed a simulator for colloidal droplet evaporation. Rather than use an effective particle concentration field as in previous works, motion of each individual particle is calculated by Stokesian Dynamics, with particle interactions governed by the DLVO theory. In order to facilitate the simulation of large collections of particles, GPU computing is applied to reduce the simulation time.A phase‐field approach is taken to capture the interface physics at the solvent‐air interface. Within a colloidal droplet we find that, by controlling the temperature, it is possible to promote Marangoni flow and, in turn, improve deposition uniformity. In future, we aim to use simulation to further optimize the process conditions, such as the chamber pressure and temperature, in order maximize uniformity.

Quasi-waffle solar distiller for durable desalination of seawater.

Water purification via interfacial solar steam generation exhibits promising potential. However, salt crystallization on evaporators reduces solar absorption and obstructs water supply. To address it, a waffle-shaped solar evaporator (WSE) has been designed. WSE is fabricated via a zinc-assisted pyrolysis route, combining low-cost biomass carbon sources, recyclable zinc, and die-stamping process. This route enables cost-effective production without the need of sophisticated processing. As compared to conventional plane-shaped evaporators, WSE is featured by extra sidewalls for triggering the convection with the synergistic solute and thermal Marangoni effects. Consequently, WSE achieves spontaneous salt rejection and durable evaporation stability. It has demonstrated continuous operation for more than 60 days in brine without fouling.

On the Stability and Bifurcation of Marangoni Convection of Two Immiscible Liquids with a Nondeformable Interface

On the Stability and Bifurcation of Marangoni Convection of Two Immiscible Liquids with a Nondeformable Interface

Enhanced 3D printing and crack control in melt-grown eutectic ceramic composites with high-entropy alloy doping

As a 3D printing method, laser powder bed fusion (LPBF) technology has been extensively proven to offer significant advantages in fabricating complex structured specimens, achieving ultra-fine microstructures, and enhancing performances. In the domain of manufacturing melt-grown oxide ceramics, it encounters substantial challenges in suppressing crack defects during the rapid solidification process. The strategic integration of high entropy alloys (HEA), leveraging the significant ductility and toughness into ceramic powders represents a major innovation in overcoming the obstacles. The ingenious doping of HEA particles preserves the eutectic microstructures of the Al2O3/GdAlO3(GAP)/ZrO2 ceramic composite. The high damage tolerance of the HEA alloy under high strain rates enables the absorption of crack energy and alleviation of internal stresses during LPBF, effectively reducing crack initiation and growth. Due to increased curvature forces and intense Marangoni convection at the top of the molt pool, particle collision intensifies, leading to the tendency of HEA particles to agglomerate at the upper part of the molt pool. However, this phenomenon can be effectively alleviated in the remelting process of subsequent layer deposition. Furthermore, a portion of the HEA particles partially dissolves and sinks into the molten pool, acting as heterogeneous nucleation particles, inducing the formation of equiaxed eutectic and leading primary phase nucleation. Some HEA particles diffuse into the lamellar ternary eutectic structures, further promoting the refinement of eutectic microstructures due to increased undercooling. The innovative doping of HEA particles has effectively facilitated the fabrication of turbine-structured, conical, and cylindrical ternary eutectic ceramic composite specimens with diameters of about 70 mm, demonstrating significant developmental potential in the field of ceramic composite manufacturing.

Uniaxial-Oriented Chiral Perovskite for Flexible Full-Stokes Polarimeter.

Full-Stokes polarization detection, with high integration and portability, offers an efficient path toward next-gen multi-information optoelectronic systems. Nevertheless, current techniques relying on optical filters create rigid and bulky configurations, limiting practicality. Here, a flexible, filter-less full-Stokes polarimeter featuring a uniaxial-oriented chiral perovskite film is first reported. It is found that, the strategic manipulation of the surfactant-mediated Marangoni effect during blade coating, is crucial for guiding an equilibrious mass transport to achieve oriented crystallization. Through this approach, the obtained uniaxial-oriented chiral perovskite films inherently possess anisotropy and chirality, and thereby with desired sensitivity to both linearly polarized light and circularly polarized light vectors. The uniaxial-oriented crystalline structure also improves photodetection, achieving a specific detectivity of 5.23×1013Jones, surpassing non-oriented devices by 10×. The as-fabricated flexible polarimeters enable accurate capture of full-Stokes polarization without optical filters, exhibiting slight detection errors for the Stokes parameters: ΔS1=9.2%, ΔS2=8.6%, and ΔS3=6.5%, approaching the detection accuracy of optics-filter polarimeters. This proof of concept also demonstrates applications in matrix polarization imaging.

Combined effects of electrophoresis and thermophoresis in Darcy Forchheimer flow of trihybrid nanofluid over a Riga plate: Yamada-Ota and Xue models

The physical phenomena of Darcy-Forchheimer flow of trihybrid nanofluid over a Riga plate with the influence of electrophoresis and thermophoresis on the particle deposition and non-uniform heat generation in a porous medium is discussed in this article. In a Marangoni convective flow, this study examined the impact of electrophoresis and thermophoresis on the rate at which aerosol particles deposited across a Riga plate. One of the most basic processes for moving tiny particles across a temperature gradient is known as thermophoresis particle deposition, and it is significant to both aero-solution and electrical engineering. Trihybrid nanofluid containing Cobalt iron oxide (COFe2O4), Manganese Zinc iron oxide (MnZnFeO4) and Molybdenum disulfides (MOS2) nanoparticles, and based fluid water is used. For the case of trihybrid nanoparticles, the Xue and Yamada-Ota nanofluid models have been expanded. The objective of this envisaged model is to compare the performance of two renowned ternary hybrid nanofluid models namely Xue and Yamada–Ota. The required similarity transformations are used to translate the set of governing equations into a collection of ODEs. The homotopy analysis method (HAM) is used to analytically solve these simplified equations. For the embedded non-dimensional parameters, the graphic exploration of the velocity, concentration and thermal fields is made. The study's primary outcomes are that as the Marangoni convection parameter is increased, the velocity profile is improved and the temperature and concentration distributions are lowered. The concentration profile decreases with increasing electrophoretic parameter, however the opposite behavior is seen with increasing electrophoretic parameter.

Role of volatility and thermal properties in droplet spreading: a generalisation to Tanner's law

Droplet spreading is ubiquitous and plays a significant role in liquid-based energy systems, thermal management devices and microfluidics. While the spreading of non-volatile droplets is quantitatively understood, the spreading and flow transition in volatile droplets remains elusive due to the complexity added by interfacial phase change and non-equilibrium thermal transport. Here we show, using both mathematical modelling and experiments, that the wetting dynamics of volatile droplets can be scaled by the spatial–temporal interplay between capillary, evaporation and thermal Marangoni effects. We elucidate and quantify these complex interactions using phase diagrams based on systematic theoretical and experimental investigations. A spreading law of evaporative droplets is derived by extending Tanner's law (valid for non-volatile liquids) to a full range of liquids with saturation vapour pressure spanning from $10^1$ to $10^4$ Pa and on substrates with thermal conductivity from $10^{-1}$ to $10^3\ {\rm W}\ {\rm m}^{-1}\ {\rm K}^{-1}$ . In addition to its importance in fluid-based industries, the conclusions also enable a unifying explanation to a series of individual works including the criterion of flow reversal and the state of dynamic wetting, making it possible to control liquid transport in diverse application scenarios.

The Impact of Marangoni Convection on Carbon Nanotube Blood Base Hybrid Nanofluid with Thermal Radiation Viscous Dissipation and Couple Stress, Analytical Study

The Impact of Marangoni Convection on Carbon Nanotube Blood Base Hybrid Nanofluid with Thermal Radiation Viscous Dissipation and Couple Stress, Analytical Study

Heat transfer enhancement in a trapezoidal cavity due to the cavity orientation and marangoni convection

Understanding Marangoni convection and nanoparticles' convection holds significant potential for applications in materials science, chemical engineering, and biomedical engineering. This article delves into Marangoni convection within cavity flow and its implications for fluid dynamics and thermodynamics. Our study finds out that the various orientations of the trapezoidal cavity affect the convection phenomenon inside the cavity. Additionally, the influence of nanoparticles is explored, with concentrations (0.001≤ φ ≤ 0.01), Rayleigh numbers (104 ≤ Ra ≤106) and Marangoni convection (100 ≤ Ma ≤900). A comparison study considering the Marangoni convection shows that its presence can enhance the heat transfer rate. Considering Marangoni convection with the smaller side at top leads to a notable enhancement of the Nusselt number.

Возбуждение релаксационных колебаний на искривленной межфазной границе в условиях внутренней задачи

The oscillatory mode of solutal Marangoni convection during the absorption of a surfactant from a homogeneous external solution into a water droplet is studied numerically. This is caused by the effect of gravity, which promotes the sedimentation of surfactant molecules in an aqueous medium. This version of oscillatory convection arising under the conditions of an internal problem was recently discovered experimentally. In the present paper, we consider the case of a chemically inert system, in which there are no reactions. The effects of interfacial deformation are assumed to be insignificant and thus they are neglected. The mathematical model includes the Navier—Stokes equations written in the Hele-Shaw and Boussinesq approximations, and the equations of surfactant transport in the system. We assume that the characteristic time of surfactant adsorption is shorter than the time of its diffusion in both solutions, which makes it possible to ignore the formation of a surface phase. The boundary value problem includes the equilibrium condition of the system, which takes into account different values of the chemical potential in the phases. It is shown that a water droplet is a surfactant accumulator that diffuses from the organic phase. The problem is solved in dimensional form using the COMSOL Multiphysics package and based on a set of physical constants for acetic acid which, like many other members of the carboxylic acid family, has the properties of surfactant in water. It was found that direct numerical simulation of the system is able to reproduce the relaxation oscillations observed in the experiment only under the additional phenomenological assumption of non-Newtonian rheology of the interface, which was previously proposed for the external problem. The physical mechanism which may be responsible for the delayed onset of Marangoni instability is discussed. We demonstrate that periodic oscillations are generated inside the drop due to the competition between the Marangoni effect and the gravity-dependent convective instability of the solution. Using direct numerical simulation, we identified the structures of convective motion at the interface and in its neighborhood, determined the flow intensity as a function of time, and obtained the range of change in the oscillation period.

Mechanics manipulation in large-area organic solar modules achieving over 16.5 % efficiency

High-efficiency organic solar cells (OSCs) are typically produced through spin-coating, restricting their application to small areas. Blade-coating, however, emerging as a promising method for large-scale production, yet faces challenges in film morphology optimization, which often leads to reduced power conversion efficiency (PCE). This study delves into the influence of both liquid and solid additives on the morphology of active layer in blade-coated OSCs, comparing them with spin-coated counterparts, using the high-efficiency PM6:D18:BTP-eC9 active layer. For the first time, we discovered the distinct impacts of solid versus liquid additives on the film uniformity, phase separation and crystalline regulation in blade-coating technique. Our findings reveal that liquid additives in blade-coating trigger outward Marangoni flow, causing undesirable material aggregation and phase separation, thereby impairing device performances. Conversely, switching to solid additives, like 1,4-Diiodobenzene (DIB), prevents these detrimental changes in fluid mechanics and preserves the desired additive effects. We demonstrate that solid additives can significantly change these inferior behaviors introduced by liquid additives in blade-coating, regulate phase separation, enhance π-π accumulation and delay crystallization, and ultimately boost OSC efficiency. Using DIB solid additive, we achieved a PCE of 18.81 % in blade-coated devices. Scaling up by 252 times, the PCE of large-area OSC module (15.64 cm²) sustained at 16.70 % (certified 16.66 %), ranking among the highest efficiency for OSC modules reported so far. These modules also exhibited exceptional storage stability, retaining 98 % efficiency after 5880 h in a nitrogen atmosphere. This research also provides a comprehensive understanding from various film characterizations and the perspective of fluid mechanics normally lack in the research. This research not only establishes a new framework for high-performance and large-area OSC modules but also extends its findings to other OSC systems with different additives, demonstrating a roll-to-roll compatible technique.

Thermocapillary convection in a cuboid pool with a sidewall of different temperature sections

Thermocapillary convection in a liquid cuboid pool with a sidewall of different temperature sections is investigated using 3D numerical simulation. One half section of the sidewall is heated but the other cooled. Numerical simulation is performed for Marangoni number (Ma) from 100 to 4.0 × 106 with Prandtl number (Pr) of 28.6 and aspect ratios (Ah and Aw) of 0.43. A temperature field with a weak thermocapillary convection flow is dominated by conduction for small Ma. As Ma increases, the flow becomes stronger and reveals a complex transition route to a chaotic state with a series of bifurcations. It has been demonstrated that the symmetry of the temperature field breaks between Ma = 102 and 103. A Hopf bifurcation occurs between Ma = 8.0 × 105 and 9.0 × 105 in which the flow becomes periodic. As Ma increases further, a sequence of period-doubling bifurcations occurs between Ma = 2.78 × 106 and 2.95 × 106. Once Ma exceeds 3.0 × 106, the flow becomes chaotic. Typical thermocapillary convection flows in the pool are characterized with topological analyses, spectral analyses, attractors, Lyapunov exponents, and fractal dimensions. Furthermore, the heat and mass transfer in the cuboid pool have been investigated.

Manipulating 2D Membrane Interlayer Channels with Accelerated Mass-Transfer Behavior to Boost Solar Desalination.

The scarcity of fresh water necessitates sustainable and efficient water desalination strategies. Solar-driven steam generation (SSG), which employs solar energy for water evaporation, has emerged as a promising approach. Graphene oxide (GO)-based membranes possess advantages like capillary action and Marangoni effect, but their stacking defects and dead zones of flexible flakes hinders efficient water transportation, thus the evaporation rate lag behind unobstructed-porous 3D evaporators. Therefore, fundamental mass-transfer approach for optimizing SSG evaporators offers new horizons. Herein, a universal multi-force-fields-based method is presented to regularize membrane channels, which can mechanically eliminate inherent interlayer stackings and defects. Both characterization and simulation demonstrate the effectiveness of this approach across different scales and explain the intrinsic mechanism of mass-transfer enhancement. When combined with a structurally optimized substrate, the 4Laponite@GO-1 achieves evaporation rate of 2.782kg m-2 h-1 with 94.48% evaporation efficiency, which is comparable with most 3D evaporators. Moreover, the optimized membrane exhibits excellent cycling stability (10 days) and tolerance to extreme conditions (pH 1-14, salinity 1%-15%), verifies the robust structural stability of regularized channels. This optimization strategy provides simple but efficient way to enhance the SSG performance of GO-based membranes, facilitating their extensive application in sustainable water purification technologies.

Phase-separated droplets swim to their dissolution

Biological macromolecules can condense into liquid domains. In cells, these condensates form membraneless organelles that can organize chemical reactions. However, little is known about the physical consequences of chemical activity in and around condensates. Working with model bovine serum albumin (BSA) condensates, we show that droplets swim along chemical gradients. Active BSA droplets loaded with urease swim toward each other. Passive BSA droplets show diverse responses to externally applied gradients of the enzyme’s substrate and products. In all these cases, droplets swim toward solvent conditions that favor their dissolution. We call this behavior “dialytaxis”, and expect it to be generic, as conditions which favor dissolution typically reduce interfacial tension, whose gradients are well-known to drive droplet motion through the Marangoni effect. These results could potentially suggest alternative physical mechanisms for active transport in living cells, and may enable the design of fluid micro-robots.

Effect of horizontal magnetic field position on oxygen distribution in CZ silicon crystal growth

The horizontal magnetic field-assisted Czochralski(CZ) method is gaining significant popularity in the semiconductor industry for producing 200 mm semiconductor-grade silicon wafers. In this study, the impact of the horizontal magnetic field position on the oxygen content and radial uniformity of semiconductor-grade silicon crystals produced by the CZ method was investigated. Three-dimensional simulations were conducted using finite element software to calculate the melt convection and oxygen content before and after adjustment of the magnetic field position, respectively. The simulations results predicted a decrease in the oxygen content of the crystals following the adjustment of the magnetic field position from 0 to 75 mm below the free surface, and this was experimentally verified. The velocity distribution of the free melt surface exhibits better uniformity when lowering the magnetic field position. The influence of the magnetic field position on the temperature distribution and Marangoni flow in the melt was investigated, and the result of oxygen concentration difference identified the adjustment of the magnetic field position promoted the greater Marangoni flow below the free melt surface, which promoted the volatilization of SiO gas and thus reduced the oxygen concentration in the silicon ingot. Therefore, adjusting the position of the magnetic field is an effective way to increase the Marangoni flow and to obtain semiconductor-grade silicon crystal with lower oxygen content and better oxygen radial homogeneity.

Speleothem-Inspired Copper/Nickel Interfaces for Enhanced Liquid-Vapor Transport by Marangoni and Soret Effects.

Geological formations have superior wickability and support the absorption of water and oils into narrow spaces of Earth's crust without external assistance. In this study, we present speleothem inspired heterogeneous porous and wicked copper (Cu)/nickel (Ni) interfaces for enhanced nucleate boiling of water/ethanol mixtures for energy-efficient separation processes. The incorporation of Ni strands within the copper particle matrix significantly enhanced heat transfer. Compared to plain copper, the Cu/Ni speleothem surfaces exhibited a 61% increase in the heat transfer coefficient for water/ethanol mixtures and a 332% increase for water, with a 58% faster onset of nucleate boiling. This enhancement was attributed to Marangoni and Soret effects at the Cu/Ni interfaces, driven by surface tension and concentration gradients. Furthermore, the synergistic wicking action of the Ni strands facilitated rewetting of the surface, replenishing liquid to the porous nucleation sites and preventing surface dry-out, thereby improving the overall heat transfer performance.

Numerical simulation of chemical reactive flow of Boger fluid over a sheet with heat source and local thermal non-equilibrium conditions

In this article, the effect of nonlinear heat source on chemical reactive flow of magnetized Boger fluid over a sheet with Marangoni convection and porous medium is explored. In the modelling, local thermal non-equilibrium (LTNE) conditions and heat sources are taken into account. The unique heat transport for both liquid and solid phases is provided by the LTNE model, which is based on thermal equations. As a result, various temperature profiles are used in this work for both the solid and fluid phases. It is essential for streamlining industrial procedures, improving material processing methods, comprehending biological systems like blood flow for medicine delivery, determining the environmental impact of pollutant dispersion, and increasing the effectiveness of oil and gas transportation. This model supports crucial decision-making processes in numerous disciplines by offering insights into the intricate interplay between reactive fluids, heat transmission, and chemical reactions. The appropriate similarity variables are used to compress the model equation system, and the shooting method and the conventional bvp4c solver are then used to solve the system numerically. Optimal homotopy approach is used to achieve residual errors. There are suggested best estimates for auxiliary variables. Results show that for larger values of the solvent fraction parameter, Boger fluid exhibits an enhanced velocity profile and a declining thermal profile of the liquid phase. The concentration and thermal profiles of both the solid and liquid phases are declined and enhanced the velocity of the Boger fluid for higher values of the Marangoni convection parameter.

Research on directional solidification combined with electron beam melting and refining for recycling of FGH4096 alloy scraps

The constraints of traditional manufacturing techniques have led to the generation of a considerable amount of waste superalloy, causing substantial resource wastage. The primary concern with waste superalloys lies in the excessive presence of inclusions and impurity elements, rendering them unsuitable for further utilization. This study proposes the use of directional solidification combined with electron beam melting and refining (EBMR) to prepare FGH4096 superalloy ingots (Φ120 mm), which offers a promising approach to produce large-sized powder superalloy master alloy ingots with high-purity and high homogeneity. It is found that the secondary dendrite arm spacing and the size of the γ’ phase in the alloy are significantly reduced after EBMR treatment. The concentration of O and N can be decreased to 5.7 and 0.6 ppmw, respectively. The size of inclusion can be reduced below 8.69 μm and the inclusion numbers reduce by over 50 % compared with both conventional ingots. A droplet transfer mode and melt convection mode mechanism have been proposed, which accurately predicts the melting temperature and melt flow. A quantitative study is conducted on the influence of inclusion density, the contact angle between inclusions and melt, and the surface tension of the melt on capillary forces. The results indicate that the capillary forces between inclusions in the melt range from 1.8 × 10−19 N and 1.9 × 10−17 N. Furthermore, the collision-aggregation behavior of inclusions in the melt is discussed, and an estimate of the tendency of inclusion collision-aggregation is provided. The enrichment of inclusions in the EBMR ingot is primarily the result of turbulent collision. The Marangoni effect and the extremely high surface temperature of the melt promote the collision and agglomeration of inclusions, causing them to accumulate rapidly at the melt surface. Moreover, the thorough removal of inclusions through the decomposition and dissolution process of the electron beam offers theoretical backing for the preparation of superalloys through electron beam melting and high-purity refining.