Meniscus Formation Research Articles

Adsorptive-rheological properties of synovial fluid in patients with gonarthrosis

In patients with gonarthrosis, indices of their bulk viscosity, module of viscoelasticity, equilibrium surface tension and relaxation time of synovial fluid increase versus indices of their blood serum. In such conditions the integral adsorptive-rheological properties of blood serum depend on the patients’ sex and age, radiological stage of the pathological process, presence of tendovaginitis, epiphyseal osteoporosis and ligamentosis. The revealed changes are associated with the severity and progression rates of articular pathology. Disorders in the adsorptive-rheological state of synovial fluid takes a significant part in the pathogenesis of tendovaginitis, bone erosions, changes of meniscus horns, intra-articular osteocalcification and formation of chondromatous bodies.

Effect of basic physical parameters to control plasma meniscus and beam halo formation in negative ion sources

Our previous study shows that the curvature of the plasma meniscus causes the beam halo in the negative ion sources: the negative ions extracted from the periphery of the meniscus are over-focused in the extractor due to the electrostatic lens effect, and consequently become the beam halo. In this article, the detail physics of the plasma meniscus and beam halo formation is investigated with two-dimensional particle-in-cell simulation. It is shown that the basic physical parameters such as the H− extraction voltage and the effective electron confinement time significantly affect the formation of the plasma meniscus and the resultant beam halo since the penetration of electric field for negative ion extraction depends on these physical parameters. Especially, the electron confinement time depends on the characteristic time of electron escape along the magnetic field as well as the characteristic time of electron diffusion across the magnetic field. The plasma meniscus penetrates deeply into the source plasma region when the effective electron confinement time is short. In this case, the curvature of the plasma meniscus becomes large, and consequently the fraction of the beam halo increases.

Effect of electrodynamic phenomena in arc furnaces on the meniscus formation in a liquid metal

The main laws of the electrodynamic action of an electric arc on the surface of the liquid metal bath in electric arc furnaces of various types are considered.

Identification of water content in nanocavities

A tapered dielectric waveguide that scans, at constant height, a sample containing a viral capsid is studied by combining a lattice gas model to simulate water meniscus formation and a finite difference time domain algorithm for light propagation through the media involved. Our results show different contrasts related to different water contents and different meniscus orientations. We propose this method as a way to study water content and evaporation process in nanocavities being either biological, like viral capsides, or nonbiological, like photonic crystals.

Quantitative particle microscopy in self‐metered fluids

We describe a simple device that volumetrically samples poured liquids and draws buoyant materials into a single field of view for quantitative particle microscopy. Our approach relies on the formation of axisymmetric menisci and computational models of the static fluid developed using surface evolver showed close agreement with experiment. The apparatus was evaluated by counting pollen and demonstrated utility for the field analysis of microparticles.

Study of beam optics and beam halo by integrated modeling of negative ion beams from plasma meniscus formation to beam acceleration

To understand the physical mechanism of the beam halo formation in negative ion beams, a two-dimensional particle-in-cell code for simulating the trajectories of negative ions created via surface production has been developed. The simulation code reproduces a beam halo observed in an actual negative ion beam. The negative ions extracted from the periphery of the plasma meniscus (an electro-static lens in a source plasma) are over-focused in the extractor due to large curvature of the meniscus.

Meniscus and beam halo formation in a tandem-type negative ion source with surface production

A meniscus of plasma-beam boundary in H− ion sources largely affects the extracted H− ion beam optics. Although it is hypothesized that the shape of the meniscus is one of the main reasons for the beam halo observed in experiments, a physical mechanism of the beam halo formation is not yet fully understood. In this letter, it is first shown by the 2D particle in cell simulation that the H− ions extracted from the periphery of the meniscus cause a beam halo since the surface produced H− ions penetrate into the bulk plasma, and, thus, the resultant meniscus has a relatively large curvature.

Top-Seeded Solution Growth of 4H-SiC Bulk Crystal Using Si-Cr Based Melt

We have grown high-quality long cylindrical (12 mm thick) 4H-SiC bulk crystals by the meniscus formation technique, which was first applied for the solution growth of bulk SiC. It enabled long-term growth by suppressing parasitic reactions such as polycrystal precipitation around the seed crystal. In addition, we could control the growth angle from −22° to 61° by adjusting the meniscus height. The thickness of the grown cylindrical crystals was 12 mm, which is the largest reported until now, and corresponded to a growth rate of 0.6 mm/h. Smooth morphology growth was maintained on the (000-1) C-face. In cross-sectional transmission optical microscopy images, few solvent inclusions and voids were observed. XRD measurements revealed that the FWHM values of the grown crystals were almost the same as those of the seed crystal.

Improving the quality factor of cantilevers in viscous fluids by the adaptation of their interface

The adaptation of the fluid-microresonator interface enables the operation of cantilevers with high quality factor in viscous fluids. Partial wetting was proposed to implement the adapted interface by meniscus formation. An excellent quality factor of 79 was achieved in water applying the concept of partial wetting to thin film silicon nitride cantilevers. Compared to the quality factor calculated from Sader’s theory of the hydrodynamic damping of fully immersed cantilevers, this is an improvement by more than one decade. As a first application the partially wetted cantilevers were employed as mass sensors in water revealing a sensitivity of 2.77 fg/Hz.

Transport Mechanisms in Capillary Condensation of Water at a Single-Asperity Nanoscopic Contact

Transport mechanisms involved in capillary condensation of water menisci in nanoscopic gaps between hydrophilic surfaces are investigated theoretically and experimentally by atomic force microscopy (AFM) measurements of capillary force. The measurements showed an instantaneous formation of a water meniscus by coalescence of the water layers adsorbed on the AFM tip and sample surfaces, followed by a time evolution of meniscus toward a stationary state corresponding to thermodynamic equilibrium. This dynamics of the water meniscus is indicated by time evolution of the meniscus force, which increases with the contact time toward its equilibrium value. Two water transport mechanisms competing in this meniscus dynamics are considered: (1) Knudsen diffusion and condensation of water molecules in the nanoscopic gap and (2) adsorption of water molecules on the surface region around the contact and flow of the surface water toward the meniscus. For the case of very hydrophilic surfaces, the dominant role of surface water transportation on the meniscus dynamics is supported by the results of the AFM measurements of capillary force of water menisci formed at sliding tip-sample contacts. These measurements revealed that fast movement of the contact impedes on the formation of menisci at thermodynamic equilibrium because the flow of the surface water is too slow to reach the moving meniscus.

Surface Finish Issues after Direct Metal Deposition

Derived from laser cladding, the Direct Metal Deposition (DMD) laser process, is based upon a laser beam – projected powder interaction, and allows manufacturing complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DMD parts usually necessitate post-machining steps. In this context, the focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish. Our experimental approach is based upon: (1) adequate modifications of the DMD conditions (gas shielding, laser conditions, coaxial or off-axis nozzles), (2) a characterization of laser-powder-melt-pool interactions using fast camera analysis, (3) a precise check of surface aspects using 3D profilometry, SEM, (4) preliminary thermo-convective simulations to understand melt-pool hydrodynamics. Most of the experimental tests were carried out on a Ti6Al4V titanium alloy, widely investigated already. Results confirm that surface degradation depends on two aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters.

Tuning the hydrophobicity of mesoporous silica materials for the adsorption of organic pollutant in aqueous solution

The ability of various as-prepared and organically modified MCM-41 and HMS mesoporous silica materials to behave as efficient adsorbents for organic pollutants in aqueous solution was investigated by using different surface functionalization procedures, so as to adjust their hydrophilic/hydrophobic balance. The hydrophilic and organophilic properties of the parent silica materials and their corresponding surface functionalized counterparts were studied by using water and toluene adsorption isotherms. Their quantification was determined by the hydrophobic static index value (HI static), as well as by the silanol and organic group densities after the functionalization step. A clear correlation could be found between the HI static values and either the superficial silanol density, or the amount of organic moieties grafted or incorporated to the silica materials. For the highly organically functionalized samples, the residual superficial silanol groups (<50%) are sufficiently isolated from each other so as to prevent the water capillary condensation within the pores, thereby leading to an increased hydrophobic character of the resulting mesoporous silica. Those hydrophobic samples, for which the water liquid meniscus formation within the mesopores was minimized or avoided, exhibited a storage capacity for an organic pollutant (N,N-diethyl-m-toluamide, DEET) in aqueous solution more than 20 times higher than that of the corresponding unmodified sample, independently of the silica nature (MCM-41 or HMS). For all calcined and silylated samples, the DEET maximum adsorption capacities determined by the Langmuir model could be correlated with the silica surface coverage by trimethylsilyl groups and thus with the remaining silanol amount.

Ultrafine Fiber Tip Etched in Hydrophobic Polymer Coated Tube for Near-Field Scanning Plasmonic Probe

We propose a novel one-step etching technique for the preparation of an optical fiber tip using a hydrophobic polymer coated tube (HP) containing 48% hydrofluoric acid (HF) to etch photosensitive single-mode fiber (PSMF). Dipping of PSMF in an HP tube suppresses the convex meniscus (CM) of the HF solution in the tube due to formation of a concave surface tension meniscus (SM) around the PSMF. The continuous etching reduces the diameter of PSMF and shortens the SM along PSMF resulting in elevation of CM around PSMF. The elevation of the CM and faster etching rate of the PSMF core digs a capillary ring along the fiber core-cladding boundary. Capillary action fills the ring with HF, which finally recedes and creates a tip at the apex of the fiber. We have fabricated a typical tip with typical features of tip height ~ 4 μm, base diameter ~ 3 μm , cone angle ~ 25°, and aperture ~ 30 nm. For the theoretical analysis, a tip similar to the fabricated one is modeled to estimate surface plasmon (SP) enhancement, ~ 200, at the end of the tip with a silver coating.

Real-Time Visualization of a Shearing Nanometer-Thick Lubricant Film by Two-Stage Imaging Ellipsometric Microscopy

A two-stage imaging ellipsometric microscopy with high lateral resolution and a wide field of view has been developed that will enable real-time visualization of the dynamic behavior of the nanometer-thick lubricant film used in head-disk interfaces incorporating contact or intermittent contact recording technology when it is sheared by the head. The first stage forms an object image at a low magnification ratio, which reduces the angle between the object image and the image sensor. This enables the first object image to be positioned perpendicular to the optical axis of the second stage. The second stage forms a final image on the image sensor at a high magnification ratio. As a result, both submicrometer lateral resolution and a wide field of view (115 μm × 85 μm) were achieved. A lubricant film sheared by an optical fiber probe with a micro ball at its end was visualized, and a bump due to meniscus formation during the intermittent contact was observed. This ellipsometric microscopy can thus visualize nanometer-thick sheared lubricant film in real time, which will be useful in the development of hard disk drives with higher recording density.

On the reliability of electrostatic NEMS/MEMS devices: Review of present knowledge on the dielectric charging and stiction failure mechanisms and novel characterization methodologies

This paper reviews the state of the art knowledge related to critical failure mechanisms in electrostatic micro- and nano-electromechanical systems (MEMS and NEMS) which are the dielectric charging and stiction. It describes also the recent employed nanoscale characterization techniques for these phenomena based on Kelvin probe force microscopy (KPFM) and force–distance curve measurements. The influence of relative humidity and dielectric deposition conditions on the charging/discharging processes is discussed. Moreover, different stiction mechanisms induced by electrostatic force and/or meniscus formation are analyzed. Finally, novel characterization methods are presented and used to correlate between the results from MEMS devices and metal–insulator–metal (MIM) capacitors. These methods are employed in view of application in electrostatic capacitive MEMS switches and could be easily extended to explore other NEMS/MEMS devices. The study provides an accurate understanding of the charging and stiction related failure mechanisms, presents guidelines for a proper packaging environment, and reveals precise explanations for the literature reported device level measurements of electrostatic MEMS devices.

Molecular Dynamics Simulation of Lubricant Redistribution and Transfer at Near-Contact Head-Disk Interface

When the spacing between the slider and lubricant in a hard disk drive decreases to less than 5 nm, the effect of the intermolecular force between these two surfaces can no longer be ignored. This effect on the lubricant distribution at the near-contact head disk interface is investigated via molecular dynamics method. In this study, the lubricant is confined between a smooth disk surface and a rough slider surface represented as a partially cosinusoidal wave. The simulation results reveal that the intermolecular force-induced meniscus formation at the near-contact head disk interface is strongly sensitive to the slider-to-disk separation, lubricant film thickness and the asperity shape (or roughness) of the slider. The attractive van der Waals forces between the slider and lubricant become weaker with increasing slider-to-disk separation and asperity mid-height, but decreasing lubricant film thickness and asperity mid-width. The Hamaker theory application to van der Waals interactions is also introduced to verify the molecular dynamics simulation. It is found that the critical separation, below which the lubricant will lose its stability to form a meniscus, increases approximately linearly with the lubricant film thickness, for slider surfaces with or without roughness both in the molecular dynamics simulation and Hamaker theory application to van der Waals interactions. Moreover, it is observed that the critical separation between a smooth disk and rough slider surface will slightly decrease when the asperity mid-height increases. The same phenomenon is observed when the asperity mid-width reduces.

Nanoscale characterization of different stiction mechanisms in electrostatically driven MEMS devices based on adhesion and friction measurements

In this work, for the first time different stiction mechanisms in electrostatic micro-electromechanical systems (MEMS) switches were studied. In these devices stiction can be caused by two main mechanisms: dielectric charging and meniscus formation resulting from the adsorbed water film between the switch bridge and the dielectric layer. The effect of each mechanism and their interaction were investigated by measuring the adhesive and friction forces under different electrical stress conditions and relative humidity levels. An atomic force microscope (AFM) was used to perform force–distance and friction measurements on the nanoscale. A novel technique was proposed to measure the induced surface potential over the dielectric surface and was used to explain the obtained adhesive and friction results. The evolution of adhesive force with time was monitored in order to study the charging/discharging processes in the dielectric film. The assessment methodology is employed for application in RF-MEMS switches and could be extended to other electrostatic MEMS devices. The study provides an in-depth understanding of different stiction mechanisms, and explanation for the literature reported device level measurements for electrostatic capacitive MEMS switches.

Progress and application of flow focusing

Flow focusing (FF) is one of capillary flows, which is first proposed in 1998, characterized by the formation of a steady meniscus in the core of an extensional high-speed fluid focused by a small hole when a fluid is injected through a capillary needle. A very thin jet is issued from the vertex of the meniscus, passes through the hole and breaks up into monodisperse droplets at a certain distance outside the hole. The FF technique is steady, controllable and does not require rigorous conditions in producing microparticles, such as droplets, bubbles, particles and capsules down to the micrometer dimension and below. It has important applications in fields of science, technology and engineering. This paper reviews the progress of flow focusing involving experiments, theories and numerical simulations. The applications are also briefly reviewed. Finally, some future issues are presented.

Correlation effects during liquid infiltration into hydrophobic nanoporous media

Correlation effects arising during liquid infiltration into hydrophobic porous medium are considered. On the basis of these effects a mechanism of energy absorption at filling porous medium by nonwetting liquid is suggested. In accordance with this mechanism, the absorption of mechanical energy is a result expenditure of energy for the formation of menisci in the pores on the shell of the infinite cluster and expenditure of energy for the formation of liquid-porous medium interface in the pores belonging to the infinite cluster of filled pores. It was found that in dependences on the porosity and, consequently, in dependences on the number of filled pores neighbors, the thermal effect of filling can be either positive or negative and the cycle of infiltration-defiltration can be closed with full outflow of liquid. It can occur under certain relation between percolation properties of porous medium and the energy characteristics of the liquid-porous medium interface and the liquid-gas interface. It is shown that a consecutive account of these correlation effects and percolation properties of the pores space during infiltration allow to describe all experimental data under discussion.

Adhesive-free colloidal probes for nanoscale force measurements: Production and characterization

We describe novel approaches for the production and characterization of epoxy- and adhesive-free colloidal probes for atomic force microscopy (AFM). Borosilicate glass microspheres are strongly attached to commercial AFM cantilevers exploiting the capillary adhesion force due to the formation of a water meniscus, and then a thermal annealing of the sphere-cantilever system at a temperature slightly below the softening point of borosilicate glass. Controlling the wettability of the surfaces involved turned out to be a crucial element for the control of surface adhesion and for the implementation of a completely adhesive-free production method of colloidal probes. Moreover, we present a statistical characterization protocol of the probe dimensions and roughness based on the AFM inverse imaging of colloidal probes on spiked gratings. We have assessed the influence of defects of the grating on the characterization of the probe, and discussed the accuracy of our characterization technique in comparison to the methods based on scanning electron or optical microscopy, or on the manual analysis of AFM inverse images.