Surface Forces Research Articles

Numerical simulation of deformation and breakage of compound droplet in air flow

The deformation process of compound droplets moving in air flow was studied by using volume of fluid model. In this paper, the kinetic process of air-in-liquid CeO2 compound droplets in air flow is reported by numerical simulation. First, the effects of initial velocity, initial diameter, and internal and external pressure difference on droplet behavior were studied when the compound droplets finally reached the morpho-steady state. The self-compiled program is used to process and analyze the digital image of the simulated broken image. The results show that, under the action of four main forces, namely, external aerodynamic force, internal pressure, viscous force, and surface tension, the inner surface of the hollow droplets gradually begins to break and continues to expand to the outer surface to break. With the increase in the pressure difference between inside and outside of the hollow drops, the pores are severely deformed and cracked. The increase in velocity leads to the imbalance of internal and external surface forces caused by the increase in aerodynamic fluctuation on the outer surface of hollow droplets. With the decrease in the diameter of the hollow droplet, the pressure threshold of the droplet breaking decreases and it is easier to break.

SonoTransformers: Transformable acoustically activated wireless microscale machines

Shape transformation, a key mechanism for organismal survival and adaptation, has gained importance in developing synthetic shape-shifting systems with diverse applications ranging from robotics to bioengineering. However, designing and controlling microscale shape-shifting materials remains a fundamental challenge in various actuation modalities. As materials and structures are scaled down to the microscale, they often exhibit size-dependent characteristics, and the underlying physical mechanisms can be significantly affected or rendered ineffective. Additionally, surface forces such as van der Waals forces and electrostatic forces become dominant at the microscale, resulting in stiction and adhesion between small structures, making them fracture and more difficult to deform. Furthermore, despite various actuation approaches, acoustics have received limited attention despite their potential advantages. Here, we introduce "SonoTransformer," the acoustically activated micromachine that delivers shape transformability using preprogrammed soft hinges with different stiffnesses. When exposed to an acoustic field, these hinges concentrate sound energy through intensified oscillation and provide the necessary force and torque for the transformation of the entire micromachine within milliseconds. We have created machine designs to predetermine the folding state, enabling precise programming and customization of the acoustic transformation. Additionally, we have shown selective shape transformable microrobots by adjusting acoustic power, realizing high degrees of control and functional versatility. Our findings open new research avenues in acoustics, physics, and soft matter, offering new design paradigms and development opportunities in robotics, metamaterials, adaptive optics, flexible electronics, and microtechnology.

Numerical simulation of solidification of boiler molten ash impinging on vertical wall based on Smoothed Particle Hydrodynamics method

In order to study the whole process of the high temperature liquid slag fly ash produced after the combustion of high alkali coal as power coal in the boiler furnace, which moves in the furnace and impinges on the water wall, the heat exchange occurs and then the cooling phase transformation deposits and slags, and the possible factors of slagging particles are studied by changing the environmental variables. In this paper, based on Smoothed Particle Hydrodynamics (SPH), the dynamic behavior of boiler molten ash impacting vertical wall is studied, and the flow spreading and solidification model of molten slag impacting vertical wall is established. Thus, the process of phase change deposition of slag particles against wall is simulated. By observing the phase distribution of slag and the change in spreading process, the complete process of the slag particles hitting the wall, spreading, shrinking and solidifying is analyzed. Based on the cohesive and repulsive surface force method, a temperature-dependent surface tension model is established to simulate the effect of surface tension on flow characteristics when molten ash impinges on low-temperature vertical walls. The influences of slag impact velocity, initial temperature and water wall temperature on deformation and solidification heat transfer are discussed. The results show that the initial velocity and initial temperature of slag particles affect the phase change deposition velocity and the final spreading factor of slag, while the temperature of the water wall has little effect on the deposition deformation and solidification process of slag.

Studying Flotation of Gold Microdispersions with Carrier Minerals and Pulp Aeration with a Steam–Air Mixture

This work is aimed at obtaining new knowledge in the field of interactions of polydisperse hydrophobic surfaces in order to increase the extraction of mineral microdispersions via flotation. The effect of high velocity and the probability of aggregating fine particles with large ones are used to increase the extraction of finely dispersed gold in this work. Large particles act as carrier minerals, which are intentionally introduced into a pulp. The novelty of this work lies in the fact that a rougher concentrate is used as the carrier mineral. For this purpose, it is isolated from three parallel pulp streams by mixing the rougher concentrate, isolated from the first stream of raw materials, with an initial feed of the second stream; accordingly, the rougher concentrate of the second stream is mixed with the initial feed of the third stream, and the finished rougher concentrate is obtained. In this mode of extracting the rougher concentrate, the content of the extracted metal increases from stream to stream, which contributes to the growth in its content in the end product. Moreover, in order to supplement forces involved in the separation of minerals with surface forces of structural origin in the third flotation stream, the pulp is aerated for a short time (about 15%–25% of the total) with air bubbles filled with a heat carrier, i.e., hot water vapor. Within this accepted flotation method, the influence that the surface currents occurring in the wetting film have on its thinning and breakthrough kinetics is proposed to be in the form of a correction to a length of a liquid slip in the hydrophobic gap. The value of the correction is expressed as a fraction of the limiting thickness of the wetting film, determined by the condition of its thickness invariability when the streams are equal in an interphase gap: outflowing (due to an action of the downforce) and inflowing (Marangoni flows and a thermo-osmotic stream). Gold flotation experiments are performed on samples of gold-bearing ore obtained from two deposits with conditions that simulate a continuous process. Technological advantages of this developed scheme and a flotation mode of gold microdispersions are shown in comparison with the basic technology. The purpose of this work is to conduct comparative tests on the basic and developed technologies using samples of gold-bearing ore obtained from the Natalka and Olimpiada deposits. Through the use of the developed technology, an increase in gold extraction of 7.99% and in concentrate quality (from 5.09 to 100.3 g/t) is achieved when the yield of the concentrate decreases from 1.86 to 1.30%, which reduces the costs associated with its expensive metallurgical processing.

Unveiling the Role of Electrostatic Forces on Attraction between Opposing Polyelectrolyte Brushes.

Electrostatic interaction and molecular excluded-volume effects are responsible for a plethora of nonintuitive phenomena in soft-matter systems, including local charge inversion and attraction between similar charges. In the current work, we study the surface forces and swelling behavior of opposing polyelectrolyte brushes using a classical density functional theory that accounts for electrostatic and excluded-volume correlations. We observe that the detachment pressure between similarly charged brushes is sensitive to salt concentration in both the osmotic and salted regimes and can be negative in the presence of multivalent counterions. A comparison of the theoretical results with the mean-field predictions unravels the role of correlation effects in determining the surface forces and brush structure. For systems containing multivalent counterions, the detachment pressure attains negative values at an intermediate brush-brush separation, and the attractive region in the pressure vs distance plot is magnified in terms of both the depth and width of attraction with increasing counterion valency. However, the interbrush attraction vanishes when the size-induced correlations are switched off. We also investigated the role of counterion size and polymer chain length on the detachment pressure. It is found that smaller counterions are more effective in neutralizing the polymer charge than bigger counterions, leading to a reduced interbrush repulsion and, in some cases, attraction between like-charged brushes at intermediate distances. Meanwhile, varying the chain length of the grafted polymers only shifts the location of the attraction basin, with little influence on the interaction strength. The theoretical predictions show qualitative agreement with experimental observations and offer valuable insights into the interaction between similarly charged polymer brushes in the presence of multivalent ions.

Asymptotic long-wave model for a high-contrast two-layered elastic plate

The paper is concerned with the derivation of asymptotically consistent equations governing the long-wave flexural response of a two-layered rectangular plate with high-contrast elastic properties. In the general case, the plate is under dynamic and variable surface, volume, and edge forces. Performing the asymptotic integration of the three-dimensional (3D) elasticity equations in the transverse direction and satisfying boundary conditions on the faces and interface, we derived the sequence of two-dimensional (2D) differential equations with respect to required functions in the first two approximations. The eight independent restraints for the generalized displacements and stress resultants are considered to formulate the 16 independent variants of boundary conditions. One of the main results of the paper is the Timoshenko–Reissner type equation capturing the effect of the softer layer and taking into account the in-plane deformation induced by the edge forces. Comparative calculations of natural frequencies were carried out based on our and alternative models.

Formation and Nanomechanical Properties of Silver-Mediated Guanine DNA Duplexes in Aqueous Solution.

Silver cations can mediate base pairing of guanine (G) DNA oligomers, yielding linear parallel G-Ag+-G duplexes with enhanced stabilities compared to those of canonical DNA duplexes. To enable their use in programmable DNA nanotechnologies, it is critical to understand solution-state formation and the nanomechanical stiffness of G-Ag+-G duplexes. Using temperature-controlled circular dichroism (CD) spectroscopy, we find that heating mixtures of G oligomers and silver salt above 50 °C fully destabilizes G-quadruplex structures and converts oligomers to G-Ag+-G duplexes. Electrospray ionization mass spectrometry supports that G-Ag+-G duplexes form at stoichiometries of 1 Ag+ per base pair, and CD spectroscopy suggests that as the Ag+/base stoichiometry increases further, G-Ag+-G duplexes undergo additional morphological changes. Using liquid-phase atomic force microscopy, we find that this excess Ag+ enables assembly of long fiberlike structures with ∼2.5 nm heights equivalent to a single DNA duplex but with lengths that far exceed a single duplex. Finally, using the conditions established to form single G-Ag+-G duplexes, we use a surface forces apparatus (SFA) to compare the solution-phase stiffness of single G-Ag+-G duplexes with dG-dC Watson-Crick-Franklin duplexes. SFA shows that G-Ag+-G duplexes are 1.3 times stiffer than dG-dC duplexes, confirming gas-phase ion mobility spectrometry measurements and computational predictions. These findings may guide the development of structural DNA nanotechnologies that rely on silver-mediated base pairing.

Numerical simulations of Atlantic meridional overturning circulation (AMOC) from OMIP experiments and its sensitivity to surface forcing

Numerical simulations of Atlantic meridional overturning circulation (AMOC) from OMIP experiments and its sensitivity to surface forcing

Contribution of surface and lateral forcing to the Arabian Gulf warming trend

The contribution of surface and lateral forcing to the observed Arabian Gulf warming trend is studied based on the results of a high-resolution (1/100°, 60 vertical layers) MIT general circulation model (MITgcm) covering the period 1993–2021. The model validation against available observations reveals that the simulation satisfactorily reproduces the main features of the Arabian Gulf’s dynamics and their variability. We show that the heat content of the Arabian Gulf generally follows the reported variability of sea surface temperature, with significant increasing trends of 0.1 × 107 J m−3 and 0.2°C per decade. The interannual variability of the heat content is dominated by the surface heat fluxes, while the long-term warming of the basin is primarily driven by lateral fluxes. The analyses of the heat exchanges through the Strait of Hormuz indicate a pronounced upward trend in the transported heat toward the Arabian Gulf, which is associated with an increase in both the volume and temperature of the exchanged waters. Considering the inflow and outflow in the Strait separately, the temperature increase is more prominent in the inflowing waters; however, the dominant factor driving the rising trend in heat content exchanges is the increase in the volume of waters being exchanged. This implies that the observed warming of the Arabian Gulf during the investigated period is directly related to the acceleration of its overturning circulation.

Effect of typical arch structure on slipstream and wake flow of 600 km/h maglev train

PurposeThe aerodynamic differences between the head car (HC) and tail car (TC) of a high-speed maglev train are significant, resulting in control difficulties and safety challenges in operation. The arch structure has a significant effect on the improvement of the aerodynamic lift of the HC and TC of the maglev train. Therefore, this study aims to investigate the effect of a streamlined arch structure on the aerodynamic performance of a 600 km/h maglev train.Design/methodology/approachThree typical streamlined arch structures for maglev trains are selected, i.e. single-arch, double-arch and triple-arch maglev trains. The vortex structure, pressure of train surface, boundary layer, slipstream and aerodynamic forces of the maglev trains with different arch structures are compared by adopting improved delayed detached eddy simulation numerical calculation method. The effects of the arch structures on the aerodynamic performance of the maglev train are analyzed.FindingsThe dynamic topological structure of the wake flow shows that a change in arch structure can reduce the vortex size in the wake region; the vortex size with double-arch and triple-arch maglev trains is reduced by 15.9% and 23%, respectively, compared with a single-arch maglev train. The peak slipstream decreases with an increase in arch structures; double-arch and triple-arch maglev trains reduce it by 8.89% and 16.67%, respectively, compared with a single-arch maglev train. The aerodynamic force indicates that arch structures improve the lift imbalance between the HC and TC of a maglev train; double-arch and triple-arch maglev trains improve it by 22.4% and 36.8%, respectively, compared to a single-arch maglev train.Originality/valueThis study compares the effects of a streamlined arch structure on a maglev train and its surrounding flow field. The results of the study provide data support for the design and safe operation of high-speed maglev trains.

Tuning the viscoelastic properties of peptide coacervates by single amino acid mutations and salt kosmotropicity

Coacervation, or liquid-liquid phase separation (LLPS) of biomacromolecules, is increasingly recognized to play an important role both intracellularly and in the extracellular space. Central questions that remain to be addressed are the links between the material properties of coacervates (condensates) and both the primary and the secondary structures of their constitutive building blocks. Short LLPS-prone peptides, such as GY23 variants explored in this study, are ideal model systems to investigate these links because simple sequence modifications and the chemical environment strongly affect the viscoelastic properties of coacervates. Herein, a systematic investigation of the structure/property relationships of peptide coacervates was conducted using GY23 variants, combining biophysical characterization (plate rheology and surface force apparatus, SFA) with secondary structure investigations by infrared (IR) and circular dichroism (CD) spectroscopy. Mutating specific residues into either more hydrophobic or more hydrophilic residues strongly regulates the viscoelastic properties of GY23 coacervates. Furthermore, the ionic strength and kosmotropic characteristics (Hofmeister series) of the buffer in which LLPS is induced also significantly impact the properties of formed coacervates. Structural investigations by CD and IR indicate a direct correlation between variations in properties induced by endogenous (peptide sequence) or exogenous (ionic strength, kosmotropic characteristics, aging) factors and the β-sheet content within coacervates. These findings provide valuable insights to rationally design short peptide coacervates with programmable materials properties that are increasingly used in biomedical applications.

Effect of Water Adsorption on Lubricating Film Stability in Slippery Coatings.

The absorption of water by slippery coatings is a ubiquitous phenomenon that arises due to small but finite water dissolution during the contact of aqueous media with lubricants. In this study, using the concept of surface forces, we have analyzed the influence of trace amounts of water in lubricants on the stability of slippery coatings for both coatings with hydrophilic porous bases, prone to form hydrogen bonds with water, and those with hydrophobic porous bases. To perform such analysis, we have considered for the first time the electrostatic problem of the distribution of the electric potential and electric field strength in stratified films that contain two thin dielectric layers imitating the lubricant and a hydrophobic layer sandwiched between the porous substrate and air or water. Based on the developed approach, the equations for the calculation of the excess free energy and the disjoining pressure, associated with water dissolution in the lubricant film, were derived. An analysis of the excess film energy and the contribution of the image interaction to the disjoining pressure isotherm indicates that the dissolved water can both stabilize and destabilize the oil film, depending on the ratio of the static and dynamic dielectric permittivities of the lubricant and the phases confining the film. The results of calculations and simple experiments carried out here indicate much better water contact stability of silicone films impregnating a hydrophobized porous substrate than films impregnating a hydrophilic porous substrate. The obtained results indicate the preference for using the hydrophobic bases for the fabrication of long-lived slippery coatings characterized by better preservation of slippery functional properties under conditions of lubricant depletion and prolonged contact with water.

Processes Contributing to Bering Sea Temperature Variability in the Late Twentieth and Early Twenty-First Century

Abstract Over recent decades, the Bering Sea has experienced oceanic and atmospheric climate extremes, including record warm ocean temperature anomalies and marine heatwaves (MHWs), and increasingly variable air–sea heat fluxes. In this work, we assess the relative roles of surface forcing and ocean dynamical processes on mixed layer temperature (MLT) tendency by computing a closed mixed layer heat budget using the NASA/JPL Estimating the Circulation and Climate of the Ocean (ECCO) Ocean State and Sea Ice Estimate. We show that surface forcing drives the majority of the MLT tendency in the spring and fall and remains dominant to a lesser degree in winter and summer. Surface forcing anomalies are the dominant driver of monthly mixed layer temperature tendency anomalies (MLTa), driving an average of 72% of the MLTa over the ECCO record length (1992–2017). The surface turbulent heat flux (latent plus sensible) accounts for most of the surface heat flux anomalies in January–April and September–December, and the net radiative flux (net longwave plus net shortwave) dominates the surface heat flux anomalies in May–August. Our results suggest that atmospheric variability plays a significant role in Bering Sea ocean temperature anomalies through most of the year. Furthermore, they indicate a recent increase in ocean warming surface forcing anomalies, beginning in 2010. Significance Statement In recent years, the Bering Sea has experienced extremes in ocean temperature, which have had adverse impacts on ocean ecology and marine fisheries and have contributed to increasingly variable sea ice extent. Our results identify anomalous heating by air–sea heat flux anomalies as the process responsible for most of the observed ocean temperature anomalies over the period 1992–2017. We additionally show that there has been an increase in atmosphere-driven ocean warming since 2010. Our work highlights the importance of investigating how ocean–atmosphere interactions might change under future climate change and how this will impact the Bering Sea.

Chemical magnetism - surface force to move motors.

If redox reactions occur on the surface of a motor and a current loop arises, then in a non-uniform magnetic field, in addition to the usual magnetic force, such a motor will also be affected by a chemical magnetic force. The chemical magnetic force belongs to the class of surface forces. Here we analyze for the first time the properties of chemical magnets, which consist of three dissimilar metals, as well as the magnetic field generated by a chemical magnet using paramagnetic nanoparticles. The results of the study show that the chemical magnetic force depends on the concentration and type of electrolyte, the pH of the solution, the temperature, and the structure of the chemical magnet. The results obtained can contribute to the creation of devices where chemical energy is directly converted into kinetic energy of motion.

Steps toward developing a comprehensive fatigue monitoring and mitigation solution: perspectives from a cohort of United States Naval Surface Force officers.

This study analyzed fatigue and its management in US Naval Surface Force warships, focusing on understanding current practices and barriers, and examining the influence of organizational and individual factors on managing chronic fatigue. Furthermore, this study explored the impact of organizational and individual factors on fatigue management. As part of a larger study, 154 naval officers (mean ± standard deviation; 31.5 ± 7.0 years; 8.8 ± 6.8 years of service; 125 male, and 29 female) completed a fatigue survey. The survey addressed (1) self-reported fatigue, (2) fatigue observed in others, (3) fatigue monitoring strategies, (4) fatigue mitigation strategies, and (5) barriers to fatigue mitigation. Logistic and ordinal regressions were performed to examine the effect of individual (i.e. sleep quality and years in military service) and organizational (i.e. ship-class) factors on fatigue outcomes. Fatigue was frequently experienced and observed by 23% and 54% of officers, respectively. Of note, officers often monitored fatigue reactively (i.e. 65% observed others nodding off and 55% observed behavioral impairments). Still, officers did not frequently implement fatigue mitigation strategies, citing few operationally feasible mitigation strategies (62.3%), being too busy (61.7%), and not having clear thresholds for action (48.7%). Fatigue management varies across organizational factors, which must be considered when further developing fatigue management strategies. Fatigue remains a critical concern aboard surface force ships and it may be better addressed through development of objective sleep and fatigue monitoring tools that could inform leadership decision-making.

Determination of driving migration force of interparticle splice surface of powder steels

Interparticle splice process during the formation of hot-deformed powder steels is studied, the driving forces of migration are determinated. The effect of the degree and temperature of deformation on the dislocation density in powder steels is considered. The intensity of development of the splicing and the contact surface is evaluated and the need for joint deformation of the near-contact volumes of material is identified. A significant contribution is made to the theory of powder materials science and the practice of producing hot-deformed powder materials.

The effect of the track plan on the damage to rails by contact fatigue crambling

An analysis of foreign and domestic experience in improving traffic safety while extending the service life of rails and improving their interaction with the wheels of rolling stock shows that the working conditions of rails are much more difficult in curved sections of the track, especially in the outer thread, due to the intense impact of the ridges of the wheels of rolling stock on the lateral working One of the reasons for the formation of contact fatigue stains on the lateral working surface of the rail head is the presence of tangential stresses that occur in the absence of perpendicular pressure of the wheel on the rail head. In addition, the movement of the wheels on the rails is accompanied by slippage, which appears due to the taper of the wheels and the occurrence of the wheel crest on the rail head. A typical case of the wheel crest running over the rail head is the movement of the crew along curved sections of the track. In this case, the guide axle runs over one of the wheels on the rail head. As a result, there is a transverse slip of the wheel on the rolling surface and friction forces between the wheel and the rail are appropriately oriented to the axes. These processes, enhanced by an increase in dynamic action, cause more intense damage to the rail heads by defects 11 in the curves, while defects mostly appear on the outer rail thread.

Effect of material composition on the action of surface active medium in ultra-precision microcutting

Ultra-precision diamond turning (UPDT) is an extensively adopted technology in optical applications owing to the nanometric surface finish and excellent form tolerance guaranteed on metallic materials. Coolants such as kerosene, isoparaffin etc. are broadly used in UPDT to reduce the friction at tool-workpiece interface for ultimately ensuring optical quality parts. However, the greater emphasis on sustainable manufacturing nowadays demand alternate approaches for minimizing cutting forces and improving the surface finish. The application of a surface active medium (SAM) over the workpiece surface prior to UPDT can be a befitting choice as it can induce Rehbinder effect on materials thereby minimizing cutting forces. Nevertheless, the performance of SAM in UPDT process with reference to material specific properties has not been widely explored in literature. The present study investigates the role of Rehbinder effect in controlling the material surface energy during UPDT of ductile materials. The surface integrity and force analysis indicate that the SAM action is significantly different for the parent metal (Cu) and alloy (Brass) under consideration. Moreover, the chip morphology inspection highlighted that SAM facilitates easier crack initiation and fracture in Cu unlike Brass. The results were further confirmed by conducting experiments on pure Zinc. Thus, the present study establishes the varying effectiveness of SAM towards material specific elemental composition.

Origin of dielectric polarization suppression in confined water from first principles.

It has long been known that the dielectric constant of confined water should be different from that in bulk. Recent experiments have shown that it is vanishingly small, however the origin of the phenomenon remains unclear. Here we used ab initio molecular dynamics simulations (AIMD) and AIMD-trained machine-learning potentials to understand water's structure and electronic properties underpinning this effect. For the graphene and hexagonal boron-nitride substrates considered, we find that it originates in the spontaneous anti-parallel alignment of the water dipoles in the first two water layers near the solid interface. The interfacial layers exhibit net ferroelectric ordering, resulting in an overall anti-ferroelectric arrangement of confined water. Together with constrained hydrogen-bonding orientations, this leads to much reduced out-of-plane polarization. Furthermore, we directly contrast AIMD and simple classical force-field simulations, revealing important differences. This work offers insight into a property of water that is critical in modulating surface forces, the electric-double-layer formation and molecular solvation, and shows a way to compute it.

Solutocapillary transport of oxygen bubbles in a diffusion-bubbling membrane core.

Bubbles are extensively explored as gas and energy carriers. However, despite notable progress, the bubble transport mechanisms are still poorly understood. At the present time there is not sufficient understanding of whether the body or surface forces play a major role in bubble transport in liquid interfacial systems. This understanding is important to be able to drive oxygen bubble transport. Here, we show the crucial role of solutocapillary forces in oxygen bubble transport in the core of a diffusion-bubbling membrane with a high density of solid/liquid and gas/liquid interfaces that operates under the oxygen chemical potential gradient. In order to describe the transport of oxygen bubbles in the membrane core, we developed a mathematical model. Both the velocity of bubbles and oxygen flux through this membrane predicted by this model agree with experiments. An in-depth understanding of the bubble transport mechanism presented in this study could eventually lead the way to more efficient bubble membrane gas separation, bubble energy generation, and bubble-assisted therapy in the future.