Vicinity Of Surface Research Articles

Evolution, Stability, and Applicability of Surfactant Aggregates in Targeted Delivery.

Self-assembly/self-aggregation of surfactant molecules in bulk and the vicinity of a surface has been a topic of interest for decades because of its utilization in numerous modern technical applications. In this article, the results of molecular dynamics simulations are reported to investigate the self-aggregation of sodium dodecyl sulfate (SDS) at an interface of mica and water. SDS molecules starting from lower to higher surface concentrations tend to create distinct aggregated structures in the vicinity of a mica surface. The structural properties, such as density profiles, radial distribution functions, and thermodynamic properties like excess entropy and second virial coefficient, are calculated to address the bits and pieces of the self-aggregation. The change in the free energy for aggregates of varied sizes approaching the surface from the bulk aqueous solution, along with the change in their shapes during the process in terms of change in the radius of gyration and its components, is reported respectively to model a generic pathway for a surfactant-based targeted delivery system.

Novel <i>operando</i> observation technique based on combined optical coherence tomography–thermogravimetry for monitoring internal structural changes of drying ceramic slurries

In the wet forming of ceramics, it is critical to control the cracking and deformation of the ceramic slurry during the drying process. This necessitates a comprehensive understanding of the changes in the internal structure of the slurry during the drying process using a high-resolution technique that enables direct and high speed observation. In this study, a combined system of optical coherence tomography (OCT) and thermogravimetry (TG) was developed for the operando observation of the evolution of the internal structure of a drying SiO2 slurry. In the early stages of drying, the OCT signal intensity changed significantly owing to the Brownian motion of the SiO2 particles in the slurry. The slurry was found to shrink as it dried and then lose its fluidity, and the ceramic particles were found to agglomerate from the surface. In the final stages of drying, localized dry regions developed in the vicinity of the slurry surface and expanded with drying. Crack formation was also observed in a part of the localized dry regions. Therefore, crack formation was attributed to inhomogeneous drying-induced shrinkage and stress generated in the drying object during the progression of localized drying. The novel operando observation technique using combined OCT-TG is successfully demonstrated to be an effective approach for understanding the internal structural changes in opaque slurries during their drying.

Droplet evaporation on pillar structured surface: A 3D lattice Boltzmann numerical study

In this paper, a three-dimensional symmetric lattice Boltzmann (LB) model is built up to investigate evaporation of a sessile droplet on pillar structured surfaces. Parametric effects on droplet evaporation, including pillar structure size, roughness, temperature and wettability, are studied comprehensively, with emphasis on the variations of contact angle, contact radius and velocity of triple-phase contact line (TPCL) as well as heat and mass fluxes during evaporation. Pillar structures are found to induce the droplet to split into spherical cap part and liquid film part, resulting in an evaporation mode different from that on a plain surface. The extent of pinning-depinning is strongly associated with structures when TPCL retracts between pillars. Increasing surface temperature can accelerate evaporation by breaking the constant contact angle (CCA) mode, and increasing surface roughness accelerates evaporation by decreasing the duration of CCA mode. The majority of heat and mass transfer takes place around TPCL. High wettability can facilitate the evaporation of spherical cap due to the meniscus at liquid–vapor interface in the vicinity of pillar top surface. The substrate heat flux directly affected by structure size is higher in the region where pillars are distributed, and the solid–liquid interfacial heat flux varies with the specific interface location within droplet. The total mass flux primarily depends on the TPCL length determined by the droplet evaporation mode. When the droplet evaporates by partial penetration in the Cassie state, the amount of evaporation at liquid–vapor interface between pillars is greater than that above pillars. This paper provides more details and insights for a deep understanding of droplet evaporation on pillar structured surfaces.

Investigation on innovative pile head breakwater for coastal protection

Coastal erosion is a global concern that has been augmenting due to the natural evolution of beaches, human activities and sea-level rise. One of the eco-friendly shore protection methods is to dissipate the wave energy by constructing offshore breakwaters. Conical pile head breakwater (CPHB) is one of the eco-friendly innovative offshore structures consisting of closely spaced piles with an enlarged cross-sectional area (conical pile head) in the vicinity of the free surface. In the present study, perforations are incorporated over the conical pile head to achieve higher efficiency by promoting energy dissipation. The influence of the perforations on the performance characteristics, namely wave transmission (Kt), wave reflection (Kr) and energy dissipation (Kd) of the perforated CPHB is comprehensively investigated through physical model studies. The effect of perforations and their distribution around the pile head (Pa), percentage of perforation (P) and size of perforations (S/D) on the wave attenuation characteristics are evaluated to arrive at an optimum configuration. The study is carried out under monochromatic waves of varying wave height (0.06–0.16 m) and wave period (1.4–2 s) at different depths of water (0.35, 0.40 and 0.45 m). A minimum Kt of 0.58 associated with Kr of 0.26 and Kd of 0.78 is obtained with an optimum configuration of Pa = 50%, P = 19.2% and S/D = 0.25. The Kt of the proposed CPHB is about 19 to 35% lesser than that of the perforated hollow pile breakwater under matching test conditions. Overall, providing the perforations is found to be effective in enhancing the wave attenuation capability by up to 12.4%. Further, empirical equations are formulated and validated with the experimental data. The empirical equations estimate the Kt and Kr values accurately with a high coefficient of determination ( R2 ≥ 0.90).

Experimental and Simulation Study for the Dissociation Behavior of Gas Hydrates─Part II: sII Mixed Gas Hydrates

This study is an extension of our research on the dissociation behavior of sI CH4 hydrates (Part I). In this study, investigations of the dissociation of binary and multicomponent structure II hydrates were carried out. A novel approach involving in situ and ex situ Raman spectroscopic measurements together with molecular dynamics simulations were applied for a systematic assessment of the hydrate dissociation and gas release behavior due to the destabilization of hydrate cavities. The hydrate decomposition was induced by thermal stimulation to mimic the warming of oceans and atmosphere brought by climate changes. The interactions between the released gas, aqueous phase, and hydrates were described. The results demonstrated that in the vicinity of the hydrate surface, the liquid phase was oversaturated with the gas molecules and some unstable partial hydrate cavities were also formed. Consequently, the release of gas was temporarily stopped or very slow. Throughout the process, the hydrate underwent decomposition–reformation–continuing decomposition until the crystal disappeared. A faster breakdown of small cavities (512) was recorded, leading to an increase in the large-to-small cavity ratio during dissociation. Moreover, the results indicated a faster release of CH4 molecules compared to C3H8 over the dissociation process of the sII CH4–C3H8 hydrate. This could be due to the higher diffusivity of CH4 molecules from the hydrate surface to the gas phase as well as its lower potential to stabilize the cavities compared to C3H8. The release of CH4 molecules was also faster compared to CO2 and C2H6 molecules in the sII mixed hydrate, leading to changes in the hydrate composition throughout the process.

Tetrapodal ZnO-Based Composite Stents for Minimally Invasive Glaucoma Surgery.

The glaucoma burden increases continuously and is estimated to affect more than 100 million people by 2040. As there is currently no cure to restore the optic nerve damage caused by glaucoma, the only controllable parameter is the intraocular pressure (IOP). In recent years, minimally invasive glaucoma surgery (MIGS) has emerged as an alternative to traditional treatments. It uses micro-sized drainage stents that are inserted through a small incision, minimizing the trauma to the tissue and reducing surgical and postoperative recovery time. However, a major challenge for MIGS devices is foreign body reaction and fibrosis, which can lead to a complete failure of the device. In this work, the antifibrotic potential of tetrapodal ZnO (t-ZnO) microparticles used as an additive is elucidated by using rat embryonic fibroblasts as a model. A simple, direct solvent-free process for the fabrication of stents with an outer diameter of 200-400 μm is presented, in which a high amount of t-ZnO particles (45-75 wt %) is mixed into polydimethylsiloxane (PDMS) and a highly viscous polymer/particle mixture is extruded. The fabricated stents possess increased elastic modulus compared to pure PDMS while remaining flexible to adapt to the curvature of an eye. In vitro experiments showed that the fibroblast cell viability was inhibited to 43 ± 3% when stents with 75 wt % t-ZnO were used. The results indicate that cell inhibiting properties can be attributed to an increased amount of protruding t-ZnO particles on the stent surface, leading to an increase in local contacts with cells and a disruption of the cell membrane. As a secondary mechanism, the released Zn ions could also contribute to the cell-inhibiting properties in the close vicinity of the stent surface. Overall, the fabrication method and the antifibrotic and mechanical properties of developed stents make them promising for application in MIGS.

The effect of temperature on the contact angle of a water drop on graphene and graphene synthesized on copper

The influence of temperature on the graphene wettability in the range from 2 °C to 97 °C was investigated. The experimental and theoretical studies have shown that the water temperature, the roughness of the wall and the crystal orientation of the copper substrate significantly affect the wettability of graphene, as well as the structuring of water molecules and hydrogen bonds in the vicinity of the graphene surface. The lowest contact angle is obtained on graphene coating on copper with orientation (111). The lowest wettability of graphene corresponds to a copper substrate with orientation (110). Temperature noticeably distorts the structuring of water molecules near the graphene layer. Defects on the surface of the substrate in the form of a “spike” lead to the formation of graphene wrinkles, which result in local exfoliation of copper and graphene and in a change in the wettability of the graphene layer.

Development of Methods for Determining Near-Surface Plasma Parameters During Tests of Fusion Reactor First-Wall Prototypes Using the PLM Device

Plasma-surface interaction and high heat flux on plasma-facing materials in magnetic fusion devices cause surface ablation and degradation, while the influx of eroded materials into plasma can have a shielding effect. The reduction of the power load due to the plasma detachment effect over tungsten fuzz is an important phenomenon to be investigated for the ITER divertor problem. Measuring near-wall plasma parameters is a challenging task, requiring the development of improved and advanced techniques, including high-resolution spectroscopic methods. In this paper, we present study results of steady-state plasma over tungsten fuzz formed in plasma linear multicusp (PLM). The PLM device is a linear plasma trap composed of an eight-pole multicusp magnetic field with steady-state plasma discharge with parameters similar to the scrape-off layer and divertor plasma in a tokamak. We used spectroscopic measurements to estimate spatial distributions of plasma radiation in the vicinity of the sample surface exposed to the plasma column. Thus, we obtained information on the temperature and composition of the boundary layer plasma and the temperature of the sample surface. Helium plasma exhibits ionization-type nonequilibrium even at atmospheric pressure, necessitating the use of specific methods to estimate its electron temperature Te. When the helium ion spectral line He II 468.5 nm is present in the spectra, its intensity ratio to one of the atomic lines He I can be described by using coronal approximation. Spectrum analysis has shown that emitting helium ions are highly sensitive indicators of average electron energy = 3kTe/2. Therefore, utilizing intensity ratios of the strongest emitting lines in the ultraviolet-visible near-infrared range, He II 468.6 nm and several He I lines with well-known electron excitation functions were found to be a reliable Te measurement method in the case of magnetized low-pressure helium plasma. We also propose a method for determining the concentrations of the metallic admixture in the plasma on the data on relative intensities of its spectral lines.

Bloch surface wave-atom coupling in one-dimensional photonic crystal structure.

Considering efforts for hot atomic vapor-nanophotonics integration as a new paradigm in quantum optics, in this paper, we introduce 1D photonic crystal-Rb vapor cell as structure with miniaturized interaction volume. The Bloch surface wave (BSW) excited on surface of a photonic crystal as electromagnetic hosting photonic mode, and altered the optical response of Rb atoms in the vicinity of surface. Coupling of atomic states with BSW confined modes would lead to quantum interference effects and results in nonlinearities in resonant coupling of atoms with BSW. We show Bloch surface wave induced transparency is highly stable under a change of incidence angle. Our results show slight changes in transitions detuning's due to nonlinear interactions like the Casimire-Polder effect under change of localized density of optical states.

Fractal Characteristics and Acoustic Emission during the Failure Process of Argillaceous Siltstone with Different Moisture Contents

Compressive strength and tensile strength are the critical parameters to determine rock performance, which can reflect the rock’s resistance to deformation and damage. Brazilian indirect tensile and uniaxial compression tests were carried out on rocks under different water immersion conditions to study acoustic emission (AE) characteristics and crack propagation during rock fracture. The test results show that water has a deteriorating effect on the argillaceous siltstone, with significant attenuation of both compressive and tensile strengths. With the increase in moisture content, the number of AE events decreased, the cumulative AE ringing count showed a gradual rise in steps, and the proportion of AE peak frequencies in the range of 0-200 kHz gradually increased. Natural rock samples are more brittle than water-saturated rock samples. The higher frequency of AE events and the higher energy released during the destruction of natural rock samples reflect in the clustering of high-energy AE source locus near the main rupture surface. The AE source locus is 1-2 energy levels higher in the vicinity of the fracture surface than in the water-saturated rock samples. The rock samples exhibited random packing of mineral particles and contained many clay minerals by SEM analysis of fracture microstructure. Water dissolves mineral particles and cementitious materials, producing microcracks with propagation potential. Analysis of the AE time sequence based on fractal theory reveals that fractal dimension value varies with the increase of moisture content. The variation of the fractal dimension D values for the water-saturated rock samples ranges from 0.4 to 0.65. This indicates that the number of microcracks is higher and their propagation more complex when the moisture content of the specimen is higher. The failure characteristics of the rock samples in the above research can provide a reference for monitoring rock mass stability under tunnel water inflow.

Molecular dynamics simulation of energy transfer in reaction process near supported nanoparticle catalyst

Recent studies of catalysis have highlighted the importance of heat-driven reaction enhancement, suggesting the need for improved understanding of heat transfer in the vicinity of catalyst particles in the reaction process. Specifically, it is essential and necessary to understand the heat of reaction transferred to catalyst particles and surrounding gas molecules in the vicinity of the catalyst surface. In the present study, we developed a method to estimate the ratio of the heat of reaction transferred to the catalyst particle and the gas molecules in the framework of ReaxFF. A molecular dynamics (MD) simulation using the ReaxFF reactive force field is applied to the case of carbon monoxide oxidation on the surface of a platinum nanoparticle. To estimate the amount of thermal energy transferred to the catalyst particle and the gas molecules during the reaction, we propose a calculation method using the interfacial thermal conductance (ITC) between the gas molecules and the solid surface. The thermal energy transferred in the vicinity of the particle was calculated from the results of MD simulation, and the heat conduction from the gas molecules to the catalyst and the substrate was calculated using the ITC. This study found that the heat of reaction transferred to the catalyst particle was of the same order as that transferred to the gas molecules in the catalytic reaction process investigated.

An experimental study on the phenomenon of flow field around the limbs of cyclists

Reduction of aerodynamic drag is an important topic in the development of a bicycle racing, making it extremely vital to study the flow field phenomenon on the surface of a cyclist. As the wind flows over the human body, the flow separation phenomenon will appear on the surface. The purpose of this research is to study the aerodynamic characteristics of cyclists by utilizing flow visualization method in both water channel and wind tunnel. Cyclist models used in water channel and wind tunnel testing were based on a real male cyclist and printed using a 3D printer. Flow visualization technique was employed to observe the flow phenomenon around the arms, thighs and calves of the cyclist model. It is found that there are vortices meandering along the axial direction at the arms and thighs, double separation lines appear at the lower legs. Then, the surface pressure coefficient of the model was measured on a full-scale model in wind tunnel experiment to verify the flow condition in the vicinity of the model surface. These research methods help in getting a better understanding of the structure of the flow field around the cyclist, and further achieve the purpose of drag reduction.

Adsorption of a water-soluble molecular rotor fluorescent probe on hydrophobic surfaces

Environmentally sensitive molecular rotors are widely used to probe the local molecular environment in e.g. polymer solutions, polymer glasses, and biological systems. These applications make it important to understand its fluorescence properties in the vicinity of a solid surface, since fluorescence microscopy generically employs cover slides, and measurements are often done in its immediate vicinity. Here, we use a confocal microscope to investigate the fluorescence of (4-daspi) in glycerol/water solutions close to the interface using hydrophilic or hydrophobic cover slips. Despite the dye’s high solubility in water, the observed lengthening of the fluorescence lifetime close to the hydrophobic surface, implies a surprising affinity of the dye with the surface. Because the homogeneous solution and the refractive index mismatch reduces the optical sectioning power of the microscope, we quantify the affinity with the help of a simple model of the signal vs. depth of focus, exhibiting surface and bulk contributions. The model reduces artefacts due to refractive index mismatch, as supported by Monte Carlo ray tracing simulations.

Electron heating and radiation in high aspect ratio sub-micron plasma generated by an ultrafast Bessel pulse within a solid dielectric

When propagating inside dielectrics, an ultrafast Bessel beam creates a high aspect-ratio cylinder of plasma with nanometric diameter that extends over several tens of micrometers to centimeters. We analyze the interaction between the intense ultrafast laser pulse and the plasma rod using particle-in-cell simulations. We show that electrons are heated and accelerated up to keV energies via transit acceleration inside the resonance lobes in the vicinity of the critical surface and compute their radiation pattern.

Numerical Modelling of an Innovative Conical Pile Head Breakwater

When moderate wave activity at the shoreline is acceptable, pile breakwaters can serve as an alternative to conventional breakwaters. Increasing the size of the pile breakwater in the vicinity of the free surface increases the hydraulic efficiency, as most of the wave energy is concentrated around the free surface. Therefore, a conical pile head breakwater (CPHB) is proposed in the present study by gradually widening the diameter of the piles towards the free surface. Using the open-source computational fluid dynamics (CFD) model REEF3D, the transmission, reflection, and dissipation characteristics of the CPHB with monochromatic and irregular waves are examined. The investigation is carried out for both perforated and non-perforated CPHBs using monochromatic waves, and the numerical results are validated using experimental data. Further, optimally configured non-perforated and perforated CPHBs are investigated numerically by subjecting them to irregular waves using the Scott–Wiegel spectrum. The wave attenuation characteristics of the CPHBs are found to be better with irregular waves compared to monochromatic waves. With irregular waves, the minimum transmission coefficients for non-perforated and perforated CPHBs are 0.36 and 0.34, respectively. Overall, the CPHB appears to be a potential solution for coastal protection.

Preparation of poly(vinyl alcohol-co-ethylene) hollow fiber membranes for high-flux ultrafiltration applications

Poly(vinyl alcohol-co-ethylene) (EVOH) hollow fiber membranes were prepared by isothermal dry-jet wet spinning of dopes containing polyvinylpyrrolidone (PVP), dimethyl sulfoxide (DMSO), and EVOH in water bath at 22 °C. DMSO and water are, respectively, a solvent and a non-solvent for EVOH, while PVP, which is water-soluble, enhances pore formation. All membranes are highly asymmetric with macrovoids that extend from the vicinity of both hollow fiber surfaces towards the central region where only interconnected cellular pores are present. Nanopores form on the external surface only in case the dope contains PVP. The internal surface is more porous than the outer one, as the out-diffusing DMSO can quickly reduce the strength of the internal bath during spinning. Water flux measurements indicate an increase-then-decrease trend, consistent with the observed morphological features. The membranes demonstrate attractive ultrafiltration features in the case of blue dextran molecules (2000 kDa); rejection as high as 97.4% at the permeation flux of 116 LMH is observed in the case of hollow fibers prepared from dopes containing 5% PVP.

DIAGNOSTICS OF THERMAL PLASMA WITH Cu AND Ni VAPOUR ADMIXTURES

This work is devoted to diagnostics of thermal electric arc discharge plasma with copper and nickel vapour admixtures by optical emission spectroscopy and possibility of its usage for investigation of plasma regions nearelectrodes surfaces. The spectra of plasma emission from such areas were obtained by registration device with spatial and spectral resolution. The Boltzmann plot technique was used to determine the radial distribution of plasma temperature of arc discharge channel in different cross-sections. Namely, the regions of arc discharge plasma in the vicinity of cathode and anode surfaces in the two different configuration of electrodes assembly (copper as a cathode, nickel as an anode and vice versa) were investigated.

Improved Multi-layer Analysis of Pavement Response Using Neural Networks to Optimize Numerical Integration

This paper presents a new accurate method to compute the mechanical response of pavement structures using an Artificial Neural Network (ANN) model coupled with Multi-Layer Elastic Analysis (MLEA). The ANN model is used to improve the numerical integration of the response function used in the MLEA method. It requires four inputs: total pavement thickness, the diameter of the contact area, radial distance, and depth of the response point; and it was trained on one million hypothetical pavement structures. The developed method has been validated by a comparative analysis against boundary conditions, finite element analysis, and available MLEA solutions using various hypothetical pavement structures. The results demonstrate that the developed solution gives excellent response in the vicinity of the pavement surface together with a significant improvement in computational efficiency.

Numerical simulation of flow structures over dunes to develop an empirical relationship for separation zone dimensions

Rivers have non-uniform beds, which are called bedforms. Depending on the hydraulic conditions, these shapes have different types that cause resistance to the flow. Despite a great number of research works and experiments on bedforms, no accurate and comprehensive equation has been proposed to estimate separation zone dimensions formed on the lee side of the dunes. The present study is mainly focused on simulating the flow motion numerically on dunes in open channels to evaluate the effect of dune geometry on the flow separation zone. Twenty-nine simulations were conducted to study the effect of the geometry of five types of dunes with different angles and heights under different hydraulic conditions and bed roughnesses. RANS and DES turbulence models were used to simulate small and large-scale dunes, respectively. The results of the numerical model were compared with the experimental results of previous researchers to validate the work, indicating the appropriate accuracy of the numerical model. Bursting events analysis were carried out to understand dominant events phenomena, it was observed that all the events have high fluctuations near the bed and none of them is dominant. However, this could decrease and diverge by getting closer to the water surface, so that all the events would tend to converge in the vicinity of the water surface. Empirical equations were derived to estimate flow separation dimensions in terms of bed characteristics and flow conditions. The equations showed that flow separations zone dimensions are highly related to lee side angle of the dunes.

The nature of nothing: exploring the quantum vacuum in microgravity

In this paper we discuss a number of investigations of the quantum vacuum that could potentially take advantage of a microgravity environment. Ultra-cold atoms are exquisite sensors of the electro-magnetic vacuum, and microgravity aids our ability to precisely position and control them in the vicinity of surfaces and cavity modes. Measurements of Casimir–Polder force, Anderson localization and the possibilities for confining atoms with vacuum forces are amongst the intriguing possibilities discussed.