Effect Of Meniscus Research Articles

Effect of meniscus on the permeability of mono-layered and multi-layered packed spheres

This study aims to numerically investigate the effect of meniscus curvature on the permeability of closely-packed spheres, which have widely used for heat pipes and vapor chambers. The shape of the meniscus curvature in the hexagonally-packed spheres is estimated based on surface energy minimization algorithm. The estimated meniscus shape is then imported into a CFD study for numerically predicting the permeability of the packed spheres. Based on the numerical results, the effect of contact angle and the number of sphere layers are investigated. The results show that the permeability is nearly independent to the contact angle when the contact angle is larger than 10°. However, the permeability significantly increases with the contact angle decreases when the contact angle is lower than 10°. The permeability quasi-linearly increases as the liquid filling ratio increases when 1<l∗<2, where l∗ is liquid filling ratio. When contact angle is 5°, the permeability is shown to slightly deviate from the linear behavior with respect to the liquid filling ratio. As the number of layers increases, the permeability significantly increases and approaches that obtained from Blake-Kozeny’s equation. As the number of layers increases, the influence of meniscus curvature on the permeability decreases whereas the bottom surface plays an important role in determining the permeability. Based on extensive numerical results, correlations for predicting the packed spheres are proposed.

Liquid drops attract or repel by the inverted Cheerios effect

Solid particles floating at a liquid interface exhibit a long-ranged attraction mediated by surface tension. In the absence of bulk elasticity, this is the dominant lateral interaction of mechanical origin. Here, we show that an analogous long-range interaction occurs between adjacent droplets on solid substrates, which crucially relies on a combination of capillarity and bulk elasticity. We experimentally observe the interaction between droplets on soft gels and provide a theoretical framework that quantitatively predicts the interaction force between the droplets. Remarkably, we find that, although on thick substrates the interaction is purely attractive and leads to drop-drop coalescence, for relatively thin substrates a short-range repulsion occurs, which prevents the two drops from coming into direct contact. This versatile interaction is the liquid-on-solid analog of the "Cheerios effect." The effect will strongly influence the condensation and coarsening of drops on soft polymer films, and has potential implications for colloidal assembly and mechanobiology.

A System to Measure Volume Change of Unsaturated Soils in Undrained Cyclic Triaxial Tests

It is common to employ a traditional double cell system, of which an open-ended inner cell is installed in an ordinary triaxial apparatus, to measure the volume change of unsaturated specimens. In such a system, the total apparent volumetric strain of the specimen (ev) is deduced from the water level change in the inner cell, monitored by a differential pressure transducer (DPT) considering, meanwhile, the top cap intrusion into the inner cell recorded by a vertical displacement transducer (VDT). Severe apparent volumetric strain, caused by the compliance of the double cell system (ev,SC), was observed during the undrained cyclic loading tests in a previous study. Test results on a steel-spring dummy specimen revealed that ev,SC was induced not only by such as the meniscus effect, but unexpectedly also by the asynchronous responses between the DPT and the VDT (i.e., the response of the DPT was delayed compared with that of the VDT). By doing some treatment ev,SC could be reduced to some extent, whereas the magnitude of ev,SC was still too high to be acceptable when the tested specimen approached the liquefied state. To radically solve these technical difficulties, a modified double cell system, named the linkage double cell system, was developed in this study. In this modified system, a linkage rod moving simultaneously with the loading shaft was introduced, through which the DPT could directly measure ev without considering the top cap or loading shaft intrusion. Test results for the steel-spring dummy specimen as well as for saturated and unsaturated soil specimens demonstrated that the linkage double cell system has major advantages in measuring accurately the volume change of the specimen during undrained cyclic triaxial loading tests compared with the traditional double cell system.

Elastic Cheerios effect: Self-assembly of cylinders on a soft solid

A rigid cylinder placed on a soft gel deforms its surface. When multiple cylinders are placed on the surface, they interact with each other via the topography of the deformed gel which serves as an energy landscape; as they move, the landscape changes which in turn changes their interaction. We use a combination of experiments, simple scaling estimates and numerical simulations to study the self-assembly of cylinders in this elastic analog of the “Cheerios Effect”, which describes capillary interactions on a fluid interface. Our results show that the effective two-body interaction can be well described by an exponential attraction potential as a result of which the dynamics also show an exponential behavior with respect to the separation distance. When many cylinders are placed on the gel, the cylinders cluster together if they are not too far apart; otherwise their motion gets elastically arrested.

Cheerios Effect Controlled by Electrowetting.

The Cheerios effect is a common phenomenon in which small floating objects are either attracted or repelled by the sidewall due to capillary interaction. This attractive or repulsive behavior is highly dependent on the slope angles (angles of the interface on the wall or floating object with respect to a horizontal line) that can be mainly controlled by the wettability of the wall and floating object and the density of the object. In this paper, electrowetting on dielectric (EWOD) is implemented to the wall or floating object in order to actively control the wettability and thus capillary interaction. As such, the capillary force on buoyant and dense floating objects can be easily switched between repulsion and attraction by simply applying an electrical input. In addition, the theoretical prediction for the capillary force is verified experimentally by measuring the motion of floating particle and the critical contact angle on the wall at which the capillary force changes from attraction to repulsion. This successive verification is enabled by the merit of EWOD that allows for continuous change in the contact angle. Finally, the control method is extended to continuously move a floating object along a linear path and to continuously rotate a dumbbell-like floating object in centimeter scales using arrays of EWOD electrodes. A continuous linear motion is also accomplished in a smaller scale where the channel width (3 mm) is comparable to the capillary length.

Caustics due to complex water menisci.

Shadows of leaves and other objects that can float on the surface of still or slowly flowing water such as a pond or a gently flowing stream have shapes that frequently look nothing like their boundaries because of meniscus effects. Menisci can either refract light into the shadow region making it brighter, or away from it extending the area of darkness. Generally speaking one will find both effects in the shadows of leaves with complicated outlines. In this paper we present an approximate theoretical model for the light intensity in these shadow regions with results of laboratory experiments and computer simulations matching our calculations. The calculations indicate a minimum depth for the water of ∼10 cm for typical floating leaves at which caustic structures form in the shadows. For depths significantly less than this, the shadows will more or less match the outline of the leaf. But for depths much greater the shadows will be significantly different, often not looking anything like the leaf itself.

Microscale 3D collagen cell culture assays in conventional flat-bottom 384-well plates.

Three-dimensional (3D) culture systems such as cell-laden hydrogels are superior to standard two-dimensional (2D) monolayer cultures for many drug-screening applications. However, their adoption into high-throughput screening (HTS) has been lagging, in part because of the difficulty of incorporating these culture formats into existing robotic liquid handling and imaging infrastructures. Dispensing cell-laden prepolymer solutions into 2D well plates is a potential solution but typically requires large volumes of reagents to avoid evaporation during polymerization, which (1) increases costs, (2) makes drug penetration variable and (3) complicates imaging. Here we describe a technique to efficiently produce 3D microgels using automated liquid-handling systems and standard, nonpatterned, flat-bottomed, 384-well plates. Sub-millimeter-diameter, cell-laden collagen gels are deposited on the bottom of a ~2.5 mm diameter microwell with no concerns about evaporation or meniscus effects at the edges of wells, using aqueous two-phase system patterning. The microscale cell-laden collagen-gel constructs are readily imaged and readily penetrated by drugs. The cytotoxicity of chemotherapeutics was monitored by bioluminescence and demonstrated that 3D cultures confer chemoresistance as compared with similar 2D cultures. Hence, these data demonstrate the importance of culturing cells in 3D to obtain realistic cellular responses. Overall, this system provides a simple and inexpensive method for integrating 3D culture capability into existing HTS infrastructure.

The Cartesian diver, surface tension and the Cheerios effect

A Cartesian diver can be used to measure the surface tension of a liquid to a certain extent. The surface tension measurement is related to the two critical pressures at which the diver is about to sink and about to emerge. After sinking because of increasing pressure, the diver is repulsed to the centre of the vessel. After the pressure is reduced, the diver is attracted to the side of the vessel. This phenomenon is known as the ‘Cheerios effect’. Creation of both the repulsive and the attractive phases of the Cheerios effect is feasible by changing the external pressure of the vessel.

Analysis of a pull-out test with real specimen geometry. Part II: the effect of meniscus

This paper continues our study on the platelet model of the pull-out specimen, in which the matrix droplet shape is approximated by a set of thin parallel disks with the diameters varying along the embedded fiber. Using this model, the fiber tensile stress and the interfacial shear stress profiles were calculated for real-shaped matrix droplets, including menisci (wetting cones) on the fibers, taking into account residual thermal stresses and interfacial friction. Then, these profiles were used to numerically simulate the processes of crack initiation and propagation in the pull-out test and to obtain theoretical force-displacement curves for specimens with different embedded lengths and wetting cone angles. Our simulations showed that the interfacial crack in real-shaped droplets initiated at very small (practically zero) force applied to the fiber, in contrast to the popular ‘equivalent cylinder’ approximation. As a result, the equivalent cylinder approach underestimated the interfacial shear strength (IFSS) value determined from the pull-out test and at the same time overestimated the interfacial frictional stress; the smaller was the wetting cone angle, the greater the difference. We also investigated the effects of the embedded fiber length and interfacial frictional stress in debonded areas on the calculated IFSS. The simulated force–displacement curves for the real-shaped droplets showed better agreement with experimental curves than those plotted using the equivalent cylinder approach.

Cathodic behaviour and oxoacidity reactions of samarium (III) in two molten chlorides with different acidity properties: The eutectic LiCl–KCl and the equimolar CaCl2–NaCl melt

This work presents a study on the chemical and electrochemical properties of Sm(III) solutions in two molten chloride mixtures with different acidity properties: (i) the eutectic LiCl–KCl, in the temperature range 673–823K and (ii) the equimolar CaCl2–NaCl melt at 823K. In both media and on a W inert electrode, the electro-reduction of Sm(III) takes place via one step Sm(III)/Sm(II). The second system Sm(II)/Sm(0) has not been observed within the electrochemical windows, because of the prior reduction of Li(I) and Na(I) from the solvent, which inhibits the electro-extraction of Sm species from the salts on the inert substrate.On the W electrode, the electro-reduction of Sm(III) to Sm(II) takes place in a quasi-reversible electrochemical mode. Accurate values of the reversible half wave potential, the intrinsic rate constant of charge transfer, k0, and the charge transfer coefficient, α, have been calculated for the first time in both molten chlorides, by simulation of the cyclic voltammograms and logarithmic analysis of the convoluted curves. The diffusion coefficient of Sm(III) has been also calculated by different electrochemical techniques, avoiding the meniscus effect by modification of the immersion dept of the working electrode in stages. The values of the diffusion coefficient indicate that Sm(III) diffuses slower in the equimolar CaCl2–NaCl than in the eutectic LiCl–KCl. This behaviour can be explained by the different viscosities of both media, which significantly reduces the mobility of Sm(III) in the CaCl2–NaCl melt.The identification of the SmO compounds that are stable in the melts as well as the determination of their solubility products were carried out by potentiometric titration using an yttria stabilised zirconia membrane electrode (YSZME). The results indicated that SmOCl is a solid stable compound in the studied melts and that Sm2O3 is a strong oxobase leading to the formation of SmOCl. The best chlorination conditions have been extracted from the comparison of the E-pO2− diagram of samarium and that of some gaseous chlorinating mixtures previously reported.

Capillary trapping of buoyant particles within regions of emergent vegetation

The seeds of many aquatic plants are buoyant and thus transported at the water surface, where they are subject to surface tension that may enhance their retention within emergent vegetation. Specifically, seeds may be trapped by surface tension (i.e., by the Cheerios effect) at the surface‐piercing interface of the vegetation. In this work we develop a physical model that predicts this mechanism of seed trapping, advancing the model proposed by Defina and Peruzzo (2010) that describes the propagation of floating particles through emergent vegetation. The emergent vegetation is simulated as an array of cylinders, randomly arranged, with the mean gap between cylinders far greater than the particle size, which prevents the trapping of particles between pairs of cylinders, referred to as net trapping. Laboratory experiments are used to guide and validate the model. The model also has good agreement with experimental data available in the literature for real seeds and more complex plant morphology.

Loading capacity of a self-assembled superhydrophobic boat array fabricated via electrochemical method

The fabrication of superhydrophobic surfaces depends on surface microstructures and surface chemistry. In this Letter, an electrochemical method was developed to fabricate superhydrophobic surfaces, micro/nanometre-scale rough structures were created via electrochemical etching and the surface energy was reduced by the modification of fluoroalkylsilane. Superhydrophobic hexagonal aluminium boats were fabricated via the proposed electrochemical method. These boats formed an array through self-assembly and showed a large loading capacity. In this array, the ‘Cheerios effect’ was adopted to improve the buoyant force of the floaters. The accumulation of ‘Cheerios effect’ can be reinforced with the increase of total face width per unit area or the contact angles. These results indicate that the micro/nanometre-scale rough structures can contribute to the buoyancy of the floaters, and the accumulation of dominant forces on very small scales can have a remarkable effect on a large scale. These findings can be used to improve the loading capacity of the large-scale floaters.

The effect of meniscus on the permeability of micro-post arrays

This study aims to investigate the effect of meniscus curvature on the permeability of the micro-post arrays, which are widely used for applications of microfluidics. An analytical model that accounts for the meniscus curvature is developed. The model considers two common array types: quadratic and hexagonal arrays. The permeability of micro-post arrays is estimated using the capillary rate of rise experiment and numerical simulation. The results obtained from the analytical model match the experimental and numerical results within the error of 5% over the range of parameters commonly found in microfluidic applications (0.06 < d * < 0.6 and H * > 0.2), where d * and H * are the post-diameter and the post-height, respectively, which are normalized by the pitch. Based on the analytic results, the effects of the post-diameter, post-height and the contact angle on the permeability of post-arrays are investigated. It is shown that the previous permeability models based on the flat meniscus assumption overestimate the experimental value by 26% for the quadratic array and 24% for the hexagonal array when cos θ = 1, d * = 0.5 and H *=1. The effect of the meniscus curvature is shown to become more pronounced as the contact angle or the post-height decreases.

Effect of a capillary meniscus on the Faraday instability threshold

Threshold for Faraday instability has been experimentally measured for slightly viscous liquids. Changing the size of the container containing the fluid allows us to emphasize the role played by the capillary meniscus on the onset for instability. As the container is getting smaller, an upset of the critical acceleration is observed. Below a given container diameter, eigenmodes are observed along the stability curve. A dissipation term is proposed for considering the viscous dissipation against the walls of the container.

Averaged water potentials in soil water and groundwater, and their connection to menisci in soil pores, field-scale flow phenomena, and simple groundwater flows

Abstract. The movement of subsurface water is mostly studied at the pore scale and the Darcian scale, but the field and regional scales are of much larger societal interest. Volume-averaging has provided equations at these larger scales, but the required restrictions rendered them of little practical interest. Others hypothesized a direct connection at hydrostatic equilibrium between the average matric potential of a subsurface body of water and the average pressure drop over the menisci in the soil pores. The link between the volume-averaged potential energy of subsurface water bodies and large-scale fluxes remains largely unexplored. This paper treats the effect of menisci on the potential energy of the water behind them in some detail, and discusses some field-scale effects of pore-scale processes. Then, various published expressions for volume-averaged subsurface water potentials are compared. The intrinsic phase average is deemed the best choice. The hypothesized relationship between average matric potential and average meniscus curvature is found to be valid for unit gradient flow instead of hydrostatic equilibrium. Still, this restriction makes the relationship hold only for a specific depth range in the unsaturated zone under specific conditions, and certainly not for entire fields or catchments. In the groundwater, volume-averaged potential energy is of more use: for linearized, steady flows with flow lines that are parallel, radially diverging, and radially converging, proofs are derived for proportionality between averaged hydraulic potentials and fluxes towards open water at a fixed potential. For parallel flow, a simplified but relevant transient flow case also exhibits this proportionality.

The collective motion of nematodes in a thin liquid layer

Many organisms live in confined fluidic environments such as the thin liquid layers on the skin of host organisms or in partially-saturated soil. We investigate the collective behaviour of nematodes in a thin liquid layer, which was first described by Gray and Lissmann [J. Exp. Biol., 1964, 41, 135]. We show experimentally that nematodes confined by a thin liquid film come into contact spontaneously. By analysing the time scales of this aggregation, we suggest that the initial aggregation is driven by random collisions between nematodes but the continued collective motion is due to an attractive force between them arising from the surface tension of the layer. We show that for nearby nematodes this surface tension force is typically stronger than the force that may be exerted by the nematodes' muscles. We believe this to be the first demonstration of the “Cheerios effect” acting on a living organism. However, we find that being grouped together does not significantly alter the body stroke and kinematic performance of the nematode: there are no statistically significant changes of the Strouhal number and the ratio of amplitude to wavelength when aggregated. This result implies that nematodes gain neither a mechanical advantage nor disadvantage by being grouped together; the capillary force merely keeps them stuck together after a chance encounter.

High-Throughput Screen for Escherichia coli Heat Shock Protein 70 (Hsp70/DnaK): ATPase Assay in Low Volume by Exploiting Energy Transfer

Members of the heat shock protein 70 (Hsp70) family of molecular chaperones are emerging as potential therapeutic targets. Their ATPase activity has classically been measured using colorimetric phosphate detection reagents, such as quinaldine red (QR). Although such assays are suitable for 96-well plate formats, they typically lose sensitivity when attempted in lower volume due to path length and meniscus effects. These limitations and Hsp70's weak enzymatic activity have combined to create significant challenges in high-throughput screening. To overcome these difficulties, the authors have adopted an energy transfer strategy that was originally reported by Zuck et al. (Anal Biochem 2005;342:254-259). Briefly, white 384-well plates emit fluorescence when irradiated at 430 nm. In turn, this intrinsic fluorescence can be quenched by energy transfer with the QR-based chromophore. Using this more sensitive approach, the authors tested 55,400 compounds against DnaK, a prokaryotic member of the Hsp70 family. The assay performance was good (Z' ~0.6, coefficient of variation ~8%), and at least one promising new inhibitor was identified. In secondary assays, this compound specifically blocked stimulation of DnaK by its co-chaperone, DnaJ. Thus, this simple and inexpensive adaptation of a colorimetric method might be suitable for screening against Hsp70 family members.

How does rubber truly slide between Schallamach waves and stick–slip motion?

Abstract Schallamach waves have been investigated from a new viewpoint of their dynamic behaviour. Two new insights were introduced to elucidate the mechanism of the initiation and propagation of the wave of detachment, firstly the surface interaction force can produce a meniscus effect at the rubber surface and secondly the stick–slip motion can be seen to have a significant role during the sliding of rubber. The meniscus could perhaps be a source of the initiation of the wave of detachment at the leading edge and might have a role to play in the peeling of the rubber away from the trailing edge of the contact simultaneously. The characteristics in the propagation of the waves such as their frequency, their high progression velocity and the sliding velocity dependence all correlate with the periodic stick–slip motion. True finite sliding was observed to take place during a slip stage in the stick–slip motion whether waves of detachment appear or not on the contact area. Thus, the contribution of the waves to the frictional sliding of rubber is to decrease the contact area before true sliding and allow smoother sliding with less vibration of stick–slip motion to occur during rubber friction.

Controllable growth of (001) surface-oriented colloidal crystals by edge meniscus effect

Colloidal crystal films have been fabricated on silicon substrates using a flow-controlled vertical deposition (FCVD) method. Scanning electron microscopy shows that large areas of the colloidal crystal films can exhibit regular square arrangement or related 1×n superstructure induced by the surface relaxation of colloidal spheres. They are shown to be the (100) facing crystals of face centred cubic (FCC) structure. Their formation is related to meniscus bending at the edge of the wafer, which can be controlled by varying the width of the substrate or the wetting properties of the backing substrate. This (100) surface-oriented colloidal crystal could be used as a template to fabricate square arrangements of nanopore and nanodot arrays.

An observational study on MR images of the effect of the discoid meniscus on articular cartilage thickness

The discoid meniscus is known to affect the morphology and mechanics of the knee compartment in which it is housed. To determine whether it also is determinative of the articular cartilage thickness, measurements were made on MR images. There was no statistically significant difference in femoral or tibial articular cartilage thickness between compartments with normal meniscus and compartments with discoid meniscus. These findings suggest that mechanical disturbances wrought by the discoid shape do not have a ‘Wolff law’ effect.