Uniform Wetting Research Articles

3D in situ observation of the capillary infiltration of molten silicon in a SiC/SiC composite by X-ray tomography

The Liquid Silicon Infiltration (LSI) process is used to decrease residual porosity of SiC/SiC composite materials. However, it is not fully mastered since the mechanisms involved at 1500 °C under high vacuum are complex to analyze, especially without direct observation. Previous work had demonstrated the feasibility of using X-ray radiography to observe the front rise of silicon in a SiC/SiC composite material during the LSI process. 2D observations, as a first approach, could give a basic understanding of the mechanisms but raised several interrogations due to the superposition of these phenomena along the thickness preventing any quantification. The setup has been improved in order to make X-ray tomography using a fully integrated DC motor in place of the rotation stage commonly used. The sets of X-ray tomographs confirm two successive fillings. First, the molten silicon rapidly and non uniformly invades the accessible intergranular micro porosity of the powder. Then, the liquid slowly fills the remaining isolated powder areas. Once the SiC matrix is fully saturated, the liquid fills the bigger porosities such as cracks and intra yarn macro porosities. In addition, this 3D analysis enabled to give a better comprehension of the non uniform wetting front in the SiC matrix powder. During the 1st step, the accessibility of the powder was known to have a major effect on the speed of progression. Also, the cracks network plays a key role in the filling of the isolated areas in the powder matrix.

Accuracy of hygro-expansive curl predictions for paper sheets based on homogenised 2D and 3D network representations

Paper, a porous-fibrous network, is made up of hydrophilic fibres, which are notably susceptible to deformations due to variations in moisture content. The response of paper sheets to full or partial wetting, based on the water-induced fibre swelling, has mostly been predicted in the past using highly idealised two-dimensional network geometries. The purpose of the present paper is to establish how precisely the two-stage process of determining effective hygro-expansivity under uniform wetting by a two-dimensional model followed by bending analysis using a continuum model predicts the curl of a fully three-dimensional network. In the present multi-scale modelling work, the moisture-induced homogenised sheet scale curl, derived from hygro-elastic deformations using non-uniform moisture profiles, is analysed based on an idealised non-woven three-dimensional fibrous network finite element model. First, the effective paper sheet swelling properties, derived computationally for the uniform wetting condition, are compared with analytically homogenised hygro-elastic properties. Whereas the analytically predicted elastic modulus has an inaccuracy of only ∼5%, the hygro-expansivity coefficient is over-predicted by roughly a third for a network with straight fibres. The difference is smaller if waviness of the fibres and wrap-around in the fibre bonds are taken into account. Fibre alignment turns out to have little influence. Subsequently, paper sheet curl predictions made by the analytical model are compared with that computed from the three-dimensional network model. The inaccuracy of the fully analytical model, based on the two-dimensional network description, relative to the fully detailed three-dimensional computational model with straight fibres is on the order of 40%–50%. The fidelity of the simple model is primarily constrained by the inaccuracy of the effective hygro-expansion coefficient. If the expansivity extracted from the three-dimensional simulations under uniform wetting is inserted, the inaccuracy drops to less than 10%. The continuum bending description hence performs adequately, provided it is based on a reliable estimation of the uniform expansion behaviour of the material.

In-situ observation of molten brazing filler metal permeating gap

Generally, brazing is completed when the brazing filler metal permeates the gap by uniform wetting. It is believed that the joining process is completed with the formation of joint defects ‘voids’ in the process of uniform wetting. However, previous studies have shown that what occurs when brazing is performed is non-uniform wetting. It is suggested that this non-uniform wetting is the cause of void generation. Wetting and spreading of brazing filler metal is tested on a metal plate, as described in JIS Z 3191. This is used to investigate the wetting of the brazing filler metal. However, this method does not cover the wetting of the molten brazing filler metal as it moves into the gap. Therefore, it is suggested that the JIS Z 3191 experiment is insufficient to evaluate the wetting of the molten brazing filler metal that penetrates into the gap. In this experiment, we created new specimen. It is called us ‘V-groove specimen’. Specimens were created with two base metals. They are pure copper and lead-free brass in which bismuth was used as an alternative element. In order to do in situ experiments, it was not possible to observe the inside of a conventional electric furnace. Therefore, we produced a furnace with a window for in-situ observation and experimented with it. As a result of experiments with V-groove specimens, it was found that there are two types of wetting of brazing filler metal. They are called ‘primary wetting’ and ‘secondary wetting’. The shape of the specimen was measured and evaluated for two types of wetting. The results showed that the primary wetting was measurable in shape and spread evenly. However, the shape of the secondary wetting could not be measured, and it was found to be non-uniformly spread.

The effect of spent coffee ground (SCG) loading, matrix ratio and biological treatment of SCG on poly(hydroxybutyrate) (PHB)/poly(lactic acid) (PLA) polymer blend

This study investigates the effects of SCG embedded into biodegradable polymer blends and aimed to formulate and characterise biomass-reinforced biocomposites using spent coffee ground (SCG) as reinforcement in PHB/PLA polymer blend. The effect of SCG filler loading and varying PHB/PLA ratios on the tensile properties and morphological characteristics of the biocomposites were examined. The results indicated that tensile properties reduction could be due to its incompatibility with the PHB/PLA matrixSCG aggregation at 40 wt% content resulted in higher void formation compared to lower content at 10 wt%. A PHB/PLA ratio of 50/50 with SCG loading 20 wt% was chosen for biocomposites with treated SCG. Biological treatment of SCG using Phanerochaete chrysosporium CK01 and Aspergillus niger DWA8 indicated P. chrysosporium CK01 necessitated a higher moisture content for optimum growth and enzyme production, whereas the optimal conditions for enzyme production (50–55 %, w/w) differed from those promoting A. niger DWA8 growth (40 %, w/w). SEM micrographs highlighted uniform distribution and effective wetting of treated SCG, resulting in improvements of tensile strength and modulus of biocomposites, respectively. The study demonstrated the effectiveness of sustainable fungal treatment in enhancing the interfacial adhesion between treated SCG and the PHB/PLA matrix.

Solvent-Assisted Graphene Exfoliation from Graphite Using Umbrella Sampling Simulations.

We employed molecular dynamics (MD) simulations coupled with umbrella sampling to explore the thermodynamics governing the exfoliation of a single graphene layer from a graphitic substrate in five different solvents such as dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), cyclohexane (CHX), and water. The substrate was modeled as a stack of three identical graphene layers with the graphene sheet undergoing exfoliation positioned on top of this stack. The initial configurations for each umbrella simulation were generated through steered MD simulations carried out along two distinct coordinates: one parallel and the other perpendicular to the graphene layers. Our analyses revealed a uniform wetting behavior for both the nanosheet and the graphitic substrate in all of the tested solvents. Consistent with experimental observations, the steered simulations confirmed that exfoliation is more favorable along the parallel direction than along the perpendicular one. All non-water solvents exhibit comparable effectiveness in the exfoliation of graphene. The calculated free energies of these solvents in parallel exfoliation consistently fell within the range of 90-100 kJ/mol/nm2. In perpendicular exfoliation, however, the corresponding energies converge to lower values. This difference is attributed to the nonequilibrium nature of the perpendicular exfoliation, primarily caused by the great steering velocity of the graphene sheet immediately after detachment from the substrate. This rapid motion of the nanosheet along the perpendicular coordinate results in an elevated system energy and heating.

Design of Superhydrophobic Shape Memory Composites with Kirigami Structures and Uniform Wetting Property.

With the continuous increase in human demand to improve aircraft performance, intelligent aircraft technologies have become a popular research field in recent years. Among them, the deformable skin structure has become one of the key technologies to achieve excellent and reliable performance. However, during the service, deformable skin structures may encounter problems such as surface impact and adhesion of droplets in rainy weather or surface icing in low-temperature environments, which can seriously affect the flight safety of the aircraft. One way to overcome these issues is to use superhydrophobic shape memory materials in the structure. In this regard, first, shape memory composites were prepared with shape memory epoxy resin as the matrix and carbon fiber orthogonal woven fabric as the reinforcement material. Superhydrophobic shape memory composites (SSMCs) were then obtained by casting the kirigami composite with superhydrophobic carbon nanotube-polydimethylsiloxane (CNT@PDMS) mixture, and the surface was processed by laser micromachining. Shape memory performance and surface wetting performance were determined by material testing methods. The results showed that the shape memory recovery rate can reach 85.11%, the surface is superhydrophobic, the average water contact angle is 156.9 ± 4.4°, and the average rolling angle is 3 ± 0.5°. The three-point bending test of the specimens with different kirigami cell configurations showed that the shape memory composite based on the rectangular structure has the best deformability with an aspect ratio of 0.4. From the droplet impact test, it was found that the impact speed of water droplets and the curvature of the surface can greatly affect the dynamic performance of water. This work is expected to be of significant research value and importance for developing functional deformable skin materials.

Experimental Study on the Influence of Wettability Alteration on Gas–Water Two-Phase Flow and Coalbed Methane Production

The surface wettability is important in the change in the relative permeability of gas and water. Due to the heterogeneous property of coal, it has a mixed wetting state, which makes it difficult to predict the change in permeability. To investigate the influence of different wettabilities on two-phase flow, a total of three different rank coal samples were collected and were treated with different chemicals. The alteration of the coal’s wettability, characteristics of gas–water flow, and relative permeability of the coal after the chemical treatments were analyzed. The research conclusions suggest that (1) the coal samples treated with SiO2 and H2O2 increased the hydrophilicity of the coal surface, while the coal samples treated with DTAB increased the hydrophobicity of the coal surface. Compared to SiO2, both H2O2 and DTAB can form a uniform wetting surface. (2) The wettability alteration mechanism among the three different chemical reagents is different. (3) All the chemicals can change the gas–water interface. The water migrates more easily through the cleats after H2O2 treatment, while it is more difficult for the water to migrate through cleats after the DTAB treatment. (4) There are two types of flow states of gas and water on different wetting surfaces. A slug flow is formed on a hydrophilic surface, while an annular flow is formed on a hydrophobic surface. (5) The crossover point and the residual water saturation of the relative permeability curves were influenced by the surface wettability.

Residence Time Distribution Analysis of Drip-Irrigated Beds—The Effect of Material and Fluid Properties with Implications for Heap Leaching Practice

The quantitative effect of particle shape, porosity, wettability, particle size, and solution viscosity on the residence time distribution (RTD) profiles of non-reactive, steady-state, drip-irrigated ore beds characteristic of heap leaching systems is presented. Results were obtained using step-up tracer tests and allowed for the analysis of preferential flow behaviour within the systems. The key findings were as follows. Increased particle sphericity enhanced channelling in beds of smaller particles, but not for larger particle sizes. Higher particle wettability caused greater liquid dispersion during both initial wetting studies and at steady-state fluid flux. Higher porosity levels and the inclusion of fines in mixed sized beds resulted in longer average solute residence times, higher liquid hold-up, longer solution and tracer breakthrough times, and increases in drain-down moisture percentages. Increasing the irrigation fluid’s viscosity, reflective of the increase in ionic concentrations in leach solutions, reduced both the solution and tracer breakthrough times and increased dispersion with signs of more discontinuous or isolated fluid volumes at steady-state. These results highlighted the importance of the inclusion of fines in agglomerated beds to improve uniform wetting especially those with low to moderate particle porosities (<2.5 m2/g specific surface area). The viscosity results suggest that there may be changes in preferential flow extent, due to variations in viscosity owing to the increasing sulphate concentration within the liquid phase in heaps and with time.

Contol Technology for the Application of Fluid Bonding Agents

The goal of this project was to enable an automated solution for the application of bonding agents to metallic bodies in the nanoliter range. For the automated application of adhesion promoters, a new control unit based on a mainboard for controlling 3D printers was used, with Marlin serving as the firmware. Adaptations were necessary in the area of motor currents, speeds, acceleration, sensitivity, print bed size and selection of mainboard and display. For the traverse paths, G-code was generated using a program in Python. For homogeneous and uniform wetting, the individual objects to be wetted are approached and the pipetting process is controlled. It was possible to establish the complete functionality.

A Method for the Immobilization of Chitosan onto Urinary Catheters

A method for the immobilization of an antibacterial chitosan coating to polymeric urinary medical catheters is presented. The method comprises a two-step plasma-treatment procedure, followed by the deposition of chitosan from the water solution. In the first plasma step, the urinary catheter is treated with vacuum-ultraviolet radiation to break bonds in the polymer surface film and create dangling bonds, which are occupied by hydrogen atoms. In the second plasma step, polymeric catheters are treated with atomic oxygen to form oxygen-containing surface functional groups acting as binding sites for chitosan. The presence of oxygen functional groups also causes a transformation of the hydrophobic polymer surface to hydrophilic, thus enabling uniform wetting and improved adsorption of the chitosan coating. The wettability was measured by the sessile-drop method, while the surface composition and structure were measured by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Non-treated samples did not exhibit successful chitosan immobilization. The effect of plasma treatment on immobilization was explained by noncovalent interactions such as electrostatic interactions and hydrogen bonds.

Improvement from discrete to uniform wetting of organic perovskite on ferromagnetic metals through a heterointerface

Considerable effort has been expended on the combination of a ferromagnetic layer with a perovskite film for application in light-controlled spintronic devices. However, to achieve such combinations, gaining control over the interface quality and the interaction between the ferromagnetic and perovskite layers is crucial. Studies have observed discrete distributions of organic perovskite (methylammonium lead bromide, MAPbBr3) films, which self-assemble into nanodiscs, on iron–palladium alloy films. To achieve uniform wetting, we proposed the insertion of an ultrathin heterointerface of an aluminum oxide or graphene layer between perovskite and metal films. Through atomic force microscopy and scanning electron microscopy, we observed that the derived MAPbBr3 coating successfully formed a continuous and dense layer without voids, with its roughness fluctuations being within a few nanometers. Magneto-optical Kerr effect measurement for material characterization revealed that the perovskite films had a negligible capping effect on magnetism. These results provide insight into the potential technological applications of perovskite/metal heterostructures.

Improvement from Discrete to Uniform Wetting of Organic Perovskite on Ferromagnetic Metals Through a Heterointerface

Improvement from Discrete to Uniform Wetting of Organic Perovskite on Ferromagnetic Metals Through a Heterointerface

Comparative study on epitaxial growth of stanene and bismuthene on InSb(111) substrate

Two-dimensional topological insulator (2DTI) with a large bandgap is prerequisite for potentially observing quantum spin Hall and other quantum phenomena at room-temperature. At present, the synthesis of such materials possesses formidable challenge. In this work, we report our experimental results on synthesis of large-gap 2DTI stanene and bismuthene on B-faced InSb(111) substrate by using molecular beam epitaxy technology. We find that both the stanene and bismuthene can be synthesized by following the forming of a wetting layer on InSb(111) substrate, but with different prospects. On the one hand, it is found that the binding energy between Sn and the substrate is not strong enough to compete the binding force between Sn atoms during the post annealing, thus resulting in a wetting layer composed of many small domains. It significantly restricts the quality of the stanene epilayers. On the other hand, the Bi atoms on InSb(111) are found more stable than the Sn atoms on InSb(111), resulting in a uniform wetting layer which can be optimized by adjusting substrate temperature and post-annealing conditions. Large size and single crystal bismuthene domains have been observed under the STM measurement, which also indicates a bulk gap of ～0.15 eV and metallic edge states.

Localized droplet heating by hydrophobic pins: Influence of pin area and droplet size on heat transfer

Localized heating of hydrophobic droplet is considered and the effects of restricted area heating and droplet size on heat transfer are examined. Samples composing of vertical steel pins located in Perspex holders are designed and manufactured. Sample surfaces are hydrophobized via depositing treated silica nanoparticles by dip coating method. Hydrophobicity of pin and Perspex surfaces are evaluated simultaneously securing uniform wetting state over sample surface. Droplet is heated via pin while creating a localized heating effect on droplet fluid. The experiments are conducted obtaining flow structures in droplet liquid. Simulations are also performed predicting thermal state in droplet liquid during heating while adopting conditions of the experiments. It is found that hydrophobizing of samples results in uniform contact angle (150° ± 2°) over the entire surface having hysteresis of 6° ± 3°. Enlarging pin diameter and droplet size alter flow structures inside droplet; hence, center of circulating structures changes, which modify the ratio of convection over conduction currents at droplet liquid interface. Increasing pin diameter enhances the Nusselt and the Bond numbers, which becomes more apparent as droplet volume increases.

Experimental and numerical investigation of the effect of laser input energy on the mechanical behavior of stainless steel and polyamide joint in the LAMP joining method

The present study investigated the effect of laser input energy on the quality and mechanical behavior of a 304 stainless steel–polyamide 6 joint in the laser-assisted metal and polymer direct joining (LAMP) method experimentally and numerically. After the proposed heat transfer model was validated, it was determined whether there was an optimal amount of laser input energy that could produce a joint with favorable quality and mechanical behavior. Among different laser input energies used in this study, 28-J/mm energy can provide more uniform and extensive wetting of the metal surface by the polymer, while excessive polymer degradation in the joint zone was prevented. As a result, an optimal combination of strength and toughness of the joint would be achieved. Further, it was found that the crystallinity of the polymer in the joint zone had a significant effect on the joint toughness so that the maximum toughness of the joint was recorded for the laser input energy of 50 J/mm, despite the reduced effective joint area due to excessive thermal degradation of the polymer in the joint zone.

Reactive boride infusion stabilizes Ni-rich cathodes for lithium-ion batteries

Engineered polycrystalline electrodes are critical to the cycling stability and safety of lithium-ion batteries, yet it is challenging to construct high-quality coatings at both the primary- and secondary-particle levels. Here we present a room-temperature synthesis route to achieve a full surface coverage of secondary particles and facile infusion into grain boundaries, and thus offer a complete ‘coating-plus-infusion’ strategy. Cobalt boride metallic glass was successfully applied to a Ni-rich layered cathode LiNi0.8Co0.1Mn0.1O2. It dramatically improved the rate capability and cycling stability, including under high-discharge-rate and elevated-temperature conditions and in pouch full-cells. The superior performance originates from a simultaneous suppression of the microstructural degradation of the intergranular cracking and of side reactions with the electrolyte. Atomistic simulations identified the critical role of strong selective interfacial bonding, which offers not only a large chemical driving force to ensure uniform reactive wetting and facile infusion, but also lowers the surface/interface oxygen activity, which contributes to the exceptional mechanical and electrochemical stabilities of the infused electrode. Coating is commonly used to improve electrode performance in batteries, but it is challenging to achieve and maintain complete coverage of electrode particles during cycling. Here the authors present a coating-and-infusion approach on Ni-rich cathodes that effectively retards stress corrosion cracking.

Friction behavior of silicone rubber hemisphere under non-uniform wetting states: With water droplets in air or air bubbles in water

The friction behavior of rubber is sensitive to real contact formation, especially on flat floors, and it can be determined by the wetting distribution (uniform or non-uniform). Here, we investigated the friction behavior and contact condition between a rubber hemisphere and a glass plate under non-uniform wetting conditions with water droplets in air and air bubbles in water. The experimental results indicated that the friction coefficient and real contact area for non-uniform wetting conditions were higher than for uniform wetting conditions without water droplets and air bubbles. Considering non-uniform wetting, a dewetting theory was developed that explains promotion of real contact formation.

The influence of the ratio between the wire and process velocities on the wetting process during laser brazing

Laser brazing is used in automotive production for the joining of car body parts with customer-visible seams, whereby the highest optical seam quality is demanded. During the wetting process, a constriction formation can occur within the molten brazing material, which subsequently collapses; this induces a stepwise progression of the wetting front, thereby decreasing the optical seam quality. The aim of this study is to investigate the influence of the wire and process velocities on this constriction formation. For this purpose, high-speed recordings of the process zone are performed during laser brazing and then evaluated concerning the wetting process. The results show that the constriction formation depends on the relationship between the process velocity and the process direction component of the wire velocity. The constriction formation only occurs when the process velocity exceeds the parallel-oriented component of the wire velocity. This constriction formation is unstable and collapses repeatedly. In this study, increasing velocity differences stabilizes the constriction existence. This stabilization correlates with a uniform wetting process and a reduced frequency of the occurrence of blowout events, probably due to improved outgassing of zinc bubbles from the melt pool.

The electrochemical interface of the cathode in high temperature PEM fuel cells

One of the most challenging areas towards the optimization of fuel cell technology is the development of catalytic layers with active, extended and stable electrochemical interfaces giving the ability to operate under a variety of operational conditions. In this work, the effect of parameters such as the amount of H3PO4 and Pt loading was examined regarding the formation of the electrochemical interface of an operating cathodic electrode in a high temperature PEM Fuel Cell. Electrodes beased on commercial 30 wt% Pt/C and H3PO4 imbibed TPS polymer electrolyte membrane were employed. Based on the thickness and catalyst loading of the catalytic layer, there is an optimum amount of acid in relation to the partial pressure of steam (pH2O) produced at the cathode that leads to uniform wetting of the catalyst avoiding catalyst poisoning and/or blocking due to flooding of the electrode. Interestingly high pH2O causes a decrease in H2 evolution reaction rate and increase in H2 adsorption coverage, implying stronger Had bonding with the Pt surface. Moreover, this work describes the development of a reliable procedure for quantitative evaluation of the real electrochemical active surface area (ECSA) of high temperature Pt electrodes by the combined analysis of CO stripping experiments and the simultaneous CO2 recording by means of online mass spectrometry. Regardless of the H3PO4 or Pt loading in the cathodic electrode, increase of steam's partial pressure progressively causes the degradation the Pt/C|H3PO4 electrochemical interface. At pH2O > 10 kPa, the ECSA decreased in all cases, but more intensely for high amounts of Η3PΟ4 within the electrode structure. The charge of the peak in the cyclic voltammogram did not completely correspond to the CO electrooxidation reaction. This difference is attributed to side oxidation reactions taking place within the same potential window as with the COad electrooxidation and depends on conditioning time (CO adsorption time), temperature and humidity.

Improving liquid distribution in a rotating packed bed

A novel design rotating packed bed is presented, aiming at mitigation of liquid maldistribution commonly encountered in rotating packed beds. The design consists of three concentric, perforated rings placed in the packing, which act as liquid redistribution rings. The effectiveness of the redistribution rings in a rotating packed bed was experimentally demonstrated, showing that an induced maldistribution of 3 × 1/16th was mitigated by at least 90 % within the design operating window. Furthermore, an induced maldistribution of 1/4th of the reactor was mitigated by at least 70 %, irrespective of whether a random packing is present or not. The proposed repeated use of redistribution rings therefore enables a more uniform wetting of the whole packing, which potentially enables a more effective scale-up of rotating packed beds. To assist the design of redistribution rings, a design equation for the thickness of the liquid layer on the redistribution rings (which determines the operating window) was developed and shown to be accurate within 10 %.