Thickness Of Water Layer Research Articles

Assessing the effect of a liquid water layer on the adsorption of hydrate anti-agglomerants using molecular simulations.

We have performed molecular dynamics simulations to study the adsorption of ten hydrate anti-agglomerants onto a mixed methane-propane sII hydrate surface covered by layers of liquid water of various thickness. As a general trend, we found that the more liquid water that is present on the hydrate surface, the less favorable the adsorption becomes even though there are considerable differences between the individual molecules, indicating that the presence and thickness of this liquid water layer are crucial parameters for anti-agglomerant adsorption studies. Additionally, we found that there exists an optimal thickness of the liquid water layer favoring hydrate growth due to the presence of both liquid water and hydrate-forming guest molecules. For all other cases of liquid water layer thickness, hydrate growth is slower due to the limited availability of hydrate-forming guests close to the hydrate formation front. Finally, we investigated the connection between the thickness of the liquid water layer and the degree of subcooling and found a very good agreement between our molecular dynamics simulations and theoretical predictions.

Construction of the small intestine on molecular dynamics simulation and preliminary exploration of drug intestinal absorption prediction

In this study, molecular dynamics simulation was applied to the construction of the small intestinal epithelial cell membrane and prediction of drug absorption. First, we constructed a system of a small intestinal epithelial cell membrane that was close to the real proportion and investigated the effects of temperature, water layer thickness, and ionic strength on membrane properties to optimize environmental parameters. Next, three drugs with different absorptivity, including Ephedrine (EPH), Quercetin (QUE), and Baicalin (BAI), were selected as model drugs to study the ability of drugs through the membrane by the free diffusion and umbrella sampling simulation, and the drug permeation ability was characterized by the free diffusion coefficient D and free energy barrier (△G) in the processes. The results showed that the free diffusion coefficient D and △G orders of the three drugs were consistent with the classical experimental absorption order, indicating that these two parameters could be used to jointly characterize the membrane permeability of the drugs.

Groundwater flows deep under Antarctic ice

Ice-dynamics models must be updated now that researchers have observed a thick layer of salty water in sediments beneath the West Antarctic Ice Sheet.

Effect of Humidity on the Writing Speed and Domain Wall Dynamics of Ferroelectric Domains (Adv. Electron. Mater. 6/2022)

Ferroelectric Thin Film-Based Memories In article number 2100650, Gustau Catalan, Neus Domingo, and co-workers demonstrate that the maximum speed at which ferroelectric thin film-based memories can be written accelerates with atmospheric humidity – and, conversely, slows down in dry conditions. The domain width as a function of relative humidity follows the behavior of the water adsorption isotherm, revealing the interplay between water layer thickness and screening. Image by Damaso Torres, ICN2.

Study of the Contrast Observed on Carbon by Monte Carlo Simulation on wet-STEM Tomography

Analyzing the structure of the material in the fields of material science needs a very good device and methods. Due to its principle in projected images at various tilt angles and calculation of the three-dimensional volume reconstruction with a distinct algorithm, tomography become an excellent tool for analyzing the 3D structure. Several research has been studied to apply electron tomography in ESEM (Environmental Scanning Electron Microscopy) which gives an opportunity in observing the wet material (hydrated) in the aquatic environment. In this research, we showed the advisability of wet-Carbon compound tomography by simulating the interaction of electron materials. Monte Carlo simulation was applied in this study to calculate the optimum water layer thickness in the wet material detected.Keywords: Carbon, Electron Tomography, Simulation of Monte Carlo, STEM

Investigation of the influence of impact velocity and liquid bridge volume on the maximum liquid bridge length

Several models exist to predict the capillary forces due to liquid bridges during static particle contacts. However, for dynamic impacts, there is still a lack of knowledge to accurately describe the geometry and rupture of liquid bridges. This is essential in order to calculate correctly the energy dissipation in numerical models. Therefore, the liquid bridge volume during the rebound phase of collision, the restitution coefficient, the rupture time and the maximum liquid bridge length were analyzed for a wide range of contact velocities from 0.0001to4.0 m∙s−1. To perform experiments at different velocities three experimental setups were developed. First, free-fall experiments with spherical particles colliding on a glass pane covered with a water layer were performed at different impact velocities from 0.3 to 1.5 m∙s−1 and water layer thicknesses. Secondly, a pneumatic setup was developed for investigating the maximum liquid bridge length at constant liquid bridge volume and contact velocities from 0.3 to 4.0 m∙s−1. A third setup was used to investigate the liquid bridge behavior during low velocities from 0.0001 to 0.04 m∙s−1. Based on the experimental results, a new model is presented to account for the significant influence of impact velocity on the maximum liquid bridge length.

Bio-based castor oil and lignin sulphonate: aqueous dispersions and shape-memory films

Aqueous polyurethane dispersions based on castor oil and lignin sulphonate (LS) were successfully synthesized in homogenous solution with nanoscale PU-lignin particle sizes as small as 35 nm. The particles size was found to be LS independent, while the dispersion viscosity increases dramatically with increasing the LS content. The increase in viscosity with increasing LS content was explained based on the chemical structure of LS. The LS is a water-soluble material and chemically reacted with diisocyanate to become a part of the dispersion particle (i.e., the nanoparticles is in fact a mixture or copolymer of castor oil-based polyurethane and lignin dispersed in water). The affinity of the PU-LS nanoparticle towards water could be increased with increasing the content of LS. Therefore, the PU-LS nanoparticle can adsorb thick water layer with increasing the LS content. According to this suggestion, the free water in the dispersion would significantly decrease and consequently the dispersion viscosity increases considerably. The cross-link density was also increase with increasing the LS content of the thin films obtained from dispersion cast. The PU-LS thin films obtained from dispersion cast showed an excellent shape-memory effect and the shape recovery was found to be strongly LS dependent. Furthermore, the supper critical CO2 solution was used successfully to create three-dimensional porous structure of PU-LS with cell size depends on LS content. The temporary folded shape of PU-LS with 5 wt.% LS changed to its permanent shape (plane stripe) within just 17 s once the sample was immersed in a water bath at the programing temperature.

Treelike thermal structures on the water surface

Unusual treelike thermal structures can be formed on the free surface of the evaporating water in small containers. These structures are studied in detail for the first time, and it has been established that under certain parameters (the container diameter is about 90 mm, the water layer thickness is 6–15 mm, and the container wall temperature is 28–47 °C), they are the most probable and pronounced. The presence of both horizontal and vertical temperature gradients is fundamental for the formation of such structures. An attempt has been made to numerically model treelike structures. It is shown that the classical model of heat and mass transfer in a fluid, taking into account the mechanisms of heat transfer on the free surface, usually used for water, and the reference coefficient of the surface tension of water, does not even allow one to qualitatively predict the observed treelike structures on the water surface. A hypothesis about the need to consider the influence of impurities on heat and mass transfer near the water surface has been proposed.

Experimental, Analytical and ANSYS Computation of Novel Cascade Solar Desalination Still

This study presents a simple device using solar radiation as a source of energy to convert brackish water to freshwater. To enhance the productivity of the cascade of solar stills, a new structure of the absorber plate with sloped surfaces and baffles was proposed to present a slight water layer thickness and improve the amount of solar radiation incident. A physical model is developed taking into account various parameters which affect the distillate yield of solar sills. In the present work, the modeling of the cascade solar still uses ANSYS Fluent V18 to investigate the yield. A three-dimensional model was considered to simulate the temperature of the water, absorber plate, and freshwater productivity. A comparison was conducted based on the CFD simulation results, experimental and approximate analytical model data. It showed a reasonable agreement of the results obtained using the analytical model with the experimental and the simulation using ANSYS Fluent of different working parameters especially the productivity. The best performance was obtained on 15/07/2018, with a productivity rate of more than 1.67 kg/m2.hr.

The first report on the use of deuterium-labelled water in analysing the splash phenomenon

Splash is a widely studied phenomenon, partly forming the phenomenon of erosion. Until now, tracing the origin of splash water was a highly error-prone, or impossible, task. We propose a method for tracking splash water by means of stable isotope ratio mass spectrometry (IRMS) analysis. We tested the method on a water-water model, checking the effect of drop height, water layer thickness and the effect of water evaporation. It turns out that the drop height and the thickness of the water layer have practically no effect on the origin of the water in the splash, and all the water comes from the vessel, not from the drops. The only exception is when a thin layer of water is impacted with a drop, in which case 23% of the water also comes from the drop. The proposed method could be used to study more complex systems such as water-soil.

Experimental and DEM studies on the normal coefficient of restitution of grain-block systems in the presence of thick and thin water layers under low-velocity impacts

In the present work, an experimental study was carried out investigating the influence of water at the contacts of grain-block systems subjected to low-velocity impacts using two different configurations as (i) impacts in the presence of a thick liquid layer with water thickness similar to that of the grain diameter and (ii) impacts in the presence of thin liquid layer in the form of water droplets. A parametric study was performed to understand the major contributing mechanisms in these impact tests. Additionally, part of the experimental data, in terms of the normal coefficient of restitution, was used to calibrate a numerical model using the discrete element method (DEM). The DEM analyses provided further insights into the impact behavior of grain-block systems, and an attempt was made to back-calculate the yield velocity and contact forces, combining the numerical results with analytical expressions.

Optical and Mechanical Properties of Self-Repairing Pectin Biopolymers.

Pectin’s unique physicochemical properties have been linked to a variety of reparative and regenerative processes in nature. To investigate the effect of water on pectin repair, we used a 5 mm stainless-steel uniaxial load to fracture glass phase pectin films. The fractured gel phase films were placed on a 1.5–1.8 mm thick layer of water and incubated for 8 h at room temperature and ambient humidity. There was no immersion or agitation. The repaired pectin film was subsequently assessed for its optical and mechanical properties. Light microscopy demonstrated repair of the detectable fracture area and restoration of the films’ optical properties. The burst strength of the repaired film declined to 55% of the original film. However, its resilience was restored to 87% of the original film. Finally, a comparison of the initial and post-repair fracture patterns demonstrated no recurrent fissures in the repaired glass phase films. The water-induced repair of the pectin film was superior to the optical and mechanical properties of the repaired films composed of nanocellulose fibers, sodium hyaluronate, and oxidized cellulose. We conclude that the unique physicochemical properties of pectin facilitate the water-induced self-repair of fractured pectin films.

Experimental investigation on thermal performance of water wall systems exposed to fire

Water wall systems (WWSs) are increasingly being used as glass façades in modern green buildings owing to their enhancement in building energy efficiency. However, little is known about their performance when exposed to fire. In this study, 500 × 1000 mm2 sized water wall systems with 30 mm, 50 mm and 100 mm thick water columns were tested and compared to the thermal performance of a 500 × 1000 mm2 sized single skin glass façade system. These façade systems were heated by a 400 × 600 mm2 isopropanol pool fire. The distance from the pan centre to pane 1 of the façade was 350 mm. Time to first crack and surface temperatures were measured. The experimental results indicate that single skin glass façades are more vulnerable to cracking than water wall systems, but exposed glass pane fallout can easily occur in water wall systems compared to single skin façades. Since the overall performance is dependent on the failure of the fire unexposed glass pane, water wall systems are more fire resistant than single skin glass façades. The water layer thickness significantly affects the WWS thermal performance, where a 50 mm thick water layer would result in a longer time to first crack. The experimental findings of this study are useful for developing practical guidelines for fire-safe glass façade designs.

Slippery, Water-Infused Membrane with Grooved Nanotrichomes for Lubricating-Induced Oil Repellency.

Water, abundant and ubiquitous in nature, is an easy yet powerful resource for the creatures to survive by putting together with their topologies interfacing their living environment. Here, a slippery, water‐infusing surface (SWIS) that retains a thick and stable water layer on the membrane is presented, robustly maintaining the oil repellency against the pressure and friction of immiscible liquids. Inspired by the plant trichome structures and their function, grooved nanotrichome, formed on the fibrous membrane by the oxygen plasma etching, induces robust water lubrication on the SWIS. SWIS membrane repels and separates highly viscous and adhesive oils in air and underwater by preventing oils from adhering to the lubricating surface. Repeated tests both in air and underwater confirm the antiadhesion and self‐cleaning properties of the SWIS. The SWIS oil scooper, fixed on a frame with a handle, successfully collects spilled oil on a pilot‐scale oil spill site and a real ocean oil spill site by simply scooping and recovering the oil. In addition, SWIS membrane is expected to help protect environments with further applications such as oil‐wastewater treatment and oil separation in food.

Pit Stability Predictions of Additively Manufactured SS316 Surfaces Using Finite Element Analysis

Stainless steels are susceptible to localized forms of corrosion attack, such as pitting. The size and lifetime of a nucleated pit can vary, depending on a critical potential or current density criterion, which determines if the pit repassivates or continues growing. This work uses finite element method (FEM) modeling to compare the critical pit radii predicted by thermodynamic and kinetic repassivation criteria. Experimental electrochemical boundary conditions are used to capture the active pit kinetics. Geometric and environmental parameters, such as the pit shape and size (analogous to additively manufactured lack-of-fusion pores), solution concentration, and water layer thickness were considered to assess their impact on the pit repassivation criterion. The critical pit radius (the transition point from stable growth to repassivation) predicted for a hemispherical pit was larger when using the repassivation potential (Erp) criteria, as opposed to the current density criteria (pit stability product). Including both the pit stability product and Erp into its calculations, the analytical maximum pit model predicted a critical radius two times more conservative than the FEA approach, under the conditions studied herein. The complex pits representing lack-of-fusion pores were shown to have minimal impact on the critical radius in atmospheric conditions.

Molecular Dynamics Study of Reaction Conditions at Active Catalyst-Ionomer Interfaces in Polymer Electrolyte Fuel Cells

Understanding the local reaction conditions at the catalyst-ionomer interfaces inside of polymer electrolyte fuel cells is vital for improving cell performance and stability. Properties of the water film and distributions of protons and oxygen molecules at the catalyst-ionomer interface are affected by the state of the catalyst and support surfaces and the structure of the ionomer skin layer. In this work, the interfacial region between catalyst and support surface and ionomer skin is simulated using molecular dynamics. This water-filled nanopore model is constructed to study the impact of local charge density, density of sidechains at the ionomer layer, and water layer thickness on the water structure and electrostatic conditions in the pore as well as the transport properties of water, hydronium, and molecular oxygen at the interface. The analysis of the flooded pore model indicates that surface hydrophilicity, represented by water adsorption and the formation of an ordered water layer at the surface, is a major factor determining the interfacial proton density, ionomer sidechain mobility, and interfacial oxygen transport resistance. The results obtained can guide the design of new catalyst materials, where the hydrophilicity of the surface can be tailored to minimize the local proton transport resistance and improve electrode performance.

Thermal conductivity prediction of C/CaO packing bed with molecular dynamics corrected effective medium model

High-temperature driven solid–solid reaction at coke (C)/calcium oxide (CaO) interfaces is attractive for industrial-scale production of calcium carbide (CaC2). However, the reaction rate limited by the low thermal conductivity (k) results from a high Kapitza thermal resistance (Rk) at C/CaO interfaces. Identifying various factors including temperature and absorbed moisture on the k of C/CaO pellets is significant for heat transfer enhancement. Here, we developed a modified effective medium assumption model considering the particle-packed configuration to predict the influence of temperature and moisture on the k of C/CaO pellets, in which the Rk is evaluated by the non-equilibrium molecular dynamics. The results show that the k of C/CaO pellets increases from 0.48 to 0.55 W/(m K) when the temperature increases from 300 to 900 K, which is attributed to a 19.7% decrease in the Rk of C/CaO interfaces caused by a rising temperature activated inelastic interfacial phonon scattering. Moreover, it is found that the k of C/CaO pellets decreases from 0.48 to 0.44 W/(m K) after inserting absorption water layers with a thickness of 0.5 nm at C/CaO interfaces. A further 38.4% degeneration in k is harvested when increasing the thickness of the absorption water layers from 0.5 to 1.3 nm. This work provides an overall insight into the interfacial effect on the k of C/CaO porous pellets and guides the heat transfer optimization for particle-packed systems.

Passively <i>Q</i>-switched and mode-locked 1.9 μm Tm-doped fiber laser based on pure water as saturable absorber

All-fiber laser with short pulses possesses many advantages, such as superior stability, compact structure, and high single pulse energy. Recently, short pulse laser working in a 1.8–2.0 μm spectral region has received considerable attention due to its wide applications in laser spectroscopy, biomedicine, optical communications and sensing. The passive <i>Q</i>-switched and mode-locked operations by saturable absorber (SA) have been considered to be convenient and low-cost ways to achieve short pulses. Recently, pure water has been reported as the ideal SA because of its advantages of high damage threshold, low prices, good thermal diffusivity and stability. In this work, Tm-doped all-fiber pulse laser based on pure water as the SA is demonstrated. The pure water is fixed between two FC/PC fiber patchcord by the ceramic cannula, so we can change the loss of SA easily. The <i>Q</i>-switched and mode-locked operations can be obtained by adjusting the water layer thickness. The maximum output power at <i>Q</i>-switched state is 0.531 mW, the repetition frequency is 53.45 kHz, and the pulse width is 3.01 μs. The maximum output power at mode-locked state is 2.28 mW, the repetition rate is 17.69 MHz, and the pulse width is 1.42 ps. To our knowledge, this is the first passive mode-locked fiber laser using pure water as a saturable absorber, and provides a new scheme for thulium-doped all-fiber pulse lasers.

Investigating Stability of Si Sphere Surface Layer in Ambient–Vacuum Cyclic Measurements Using Ellipsometry

This paper reports an investigation conducted to evaluate the stability of surface layers on a Si sphere in ambient–vacuum cyclic measurements. An ellipsometer equipped with a vacuum chamber and a vapor-controlling system was developed to characterize the surface layers on the Si spheres. To investigate the stability and reproducibility of the surface layer, particularly for realizing and disseminating the kilogram, surface layer thickness measurements by ellipsometry were repeatedly conducted in air and vacuum for 1.5 months on a Si sphere with natural isotopic abundance. The surface layers of the Si sphere were relatively stable throughout the cyclic measurements, and no significant contamination was observed. We also conducted ellipsometry on the Si sphere after introducing water vapor into the vacuum chamber. The adsorbed water layer thickness in the air–vacuum and water vapor–vacuum measurements were almost identical, showing that gas components other than water vapor, such as carbonaceous materials stemming from the environment, had little effect on surface layer thickness in the air-vacuum cyclic measurements.

2021 W.R. Whitney Award: The Importance of Local Chemistry and Potential in Localized Corrosion and Stress Corrosion Cracking

The nature and rates of the chemical and electrochemical reactions that occur within the occluded regions of a given alloy are controlled by the local electrochemical potential and the local solution composition. The very small physical dimensions of these regions lead to challenges in both measurement and modeling. When performed in a coordinated and complementary way, measurements and modeling provide insights into the controlling processes of a range of localized corrosion phenomena, including crevice corrosion, pitting, intergranular corrosion, and stress corrosion cracking. Examples of attempts to overcome the measurement challenges are described for a range of corrosion scenarios, including identification of the critical ionic species in stainless steel crevice corrosion and in the corrosion of aircraft lap joints, operando measurement of chemistry and potential simultaneously within stress corrosion cracks, and monitoring of water layer thickness in salt spray testing. Examples of work addressing the challenges in modeling localized corrosion including intergranular corrosion of AA5XXX alloys, scaling laws in crevice corrosion, the extent to which the Laplace Equation can be used and applied to geometrically complex galvanic structures, and an approach to modeling localized corrosion for extraordinarily long service times. Finally, suggestions regarding future avenues of research are provided.