Drop Shape Research Articles

Influence of bending radius on the properties of flexible AMOLED displays

AbstractChoosing a suitable bending structure is an important way to optimize flexible AMOLED. In this article, we proposed and established a drop‐shape model through nonlinear finite element analysis software, comparing it with the “U”‐shaped bending model. The mechanical stress conditions under different bending radius are analyzed and compared. Aiming to find a better module folding track, we output the influence of the bending radius on the stress and strain of the device layer, so that these data and research can provide reliable support for future material selection and structural optimization. The super‐elastic and viscoelastic behaviors of optically clear adhesive are described by polynomial reduced integral and Prony series model, respectively. Both U‐shaped various layers of film and overall flexible screen module strains increase fast with the decreasing of bending radius and smaller radius will increase the fatigue damage risk. The stress and strain of the drop shape did not change significantly with the decrease of the radius. During the bending process, the most stressed part appears in the outermost TP layer. In a small radius, it can be optimized from a curved structure, and water drop and wedge shapes can be prioritized.

Load testing and simulation of asymmetric cable-net used for flexible rockfall protection barriers

Flexible protection barriers are often located on the mountainsides in order to decrease the risk of rockfall. In the present study, different scales of experimental tests are considered, to gauge the behaviour and to estimate the bearing capacity of a new type of cable-nets used for these flexible barriers in case of quasi-static loads. A large experimental campaign addressing cables characterization, as well as the behaviour of the constitutive cells of the net, which particular shape, a water drop shape instead of the classical rings, induces asymmetric loading transfer. Finally, the net behaviour itself is characterized through appropriate tests. These tests highlighted the non-linear behaviour perceived at different scales and permitted to evaluate the bearing capacity of the various components. Numerical simulations using the finite element code Abaqus were also conducted for the different components, a group of constitutive cells with rigid or fuse clip or the whole net, to reproduce the behaviour observed experimentally.

Dynamics of Drop Release from the Edge of a Spinning Disc

The direct formation of drops at the edge of a spinning disc is of fundamental interest. We use high-speed imaging to report here on the process of release of drops from a perfectly wetted disc at low inflow rates. A drop-detachment event begins by forming an incipient bulge on the disc edge, which grows into a series of shapes─triangle, inverted U, pear, and finally a nearly spherical bulge connected to the disc with an elongated neck. Neck pinching at the base of the bulge releases a primary drop followed by several secondary drops. The drop shape versus time plots show high variability under fixed conditions, which disappears on a single curve for time scaled with individual drop cycle time. The measurements at a different disc speed show the same scaled time evolution, pointing to a universal drop release process. The rapid stretching of the liquid thread as the bulge moves away before pinch-off follows a parabolic relationship with time but with only half the relative acceleration of a free object released from the disc edge. The mean values of cycle time and necking time follow a power-law decrease with disc speed. All of the drops generated in a single event move with the speed of the disc. There is no slip, which is not the case with the ligament mode of breakup. The intervals of quiescence between the successive release of drops from the entire disc follow the Poisson process.

Numerical study of microfluidic emulsion dynamics under the influence of heterogeneous surface wettability

Surface wettability plays a vital role in various natural phenomena and technical applications, such as coating, printing, membrane technology, microfluidic devices, and porous media flow. We numerically investigate the dynamics and stability of liquid–liquid dispersion flowing in a microfluidic channel with heterogeneous surface wettability, using a conservative phase-field lattice Boltzmann method. First, we validate the implementation of the wetting boundary conditions. We then perform three-dimensional simulations of a single drop motion immersed in another immiscible liquid in a square microchannel with alternating surface wettability: hydrophilic, hydrophobic, and again hydrophilic sections. The viscosity of the dispersed liquid (oil) is ten times higher than that of the continuous one (water), while the two liquids have equal densities. Depending on the drop length and Capillary number, calculated based on the drop velocity and the dynamic viscosity of the continuous phase, four different flow patterns are observed when the drop passes through the hydrophobic section. The distinct flow patterns include passing without any changes in drop shape or dynamics, adhesion of the dispersed liquid to the walls, phase inversion (i.e., water becomes the dispersed phase), and drop breakage. These outcomes are in close agreement with the experimental data. A detailed explanation of the choice of the numerical parameters is presented. The critical aspect of capturing the observed drop behavior is introducing an intervening thin-film of the continuous phase of at least three diffuse interface thicknesses (between the drop and channel walls).

Isolation And Characterization Of Biosurfactant Producing Bacteria From Different Environmental Soil Samples

Isolation And Characterization Of Biosurfactant Producing Bacteria From Different Environmental Soil Samples

Surface Modification of Medical-Grade Ni55.6Ti44.4 alloy via enhanced machining characteristics of Zn Powder Mixed-μ-EDM

The surface modification via subtractive manufacturing intends to localize the desired properties on the produced surface during the machining. In the case of miniaturized components, the powder mixed-micro-electric discharge machining (PM-μ-EDM), a potential variant of EDM , can achieve superior microfeatures such as dimensional accuracy and surface integrity, and a noteworthy surface modification on the hard and tough materials such as titanium and nickel alloys. Besides, the increasing demands for microfabricated devices used in tissue engineering and therapeutics delivery encourage their production with improved surface characteristics and biocompatibility. The superelastic nickel‑titanium alloy (Nitinol) has recently emerged as one of the most desirable biomaterials primarily in the vascular and prosthetic applications. However, the microfabrication followed by surface modification of Nitinol by the PM-μ-EDM has been rarely recorded. Hence, this research aimed to modify the Medical-grade Ni 55.6 Ti 44.4 alloy surface with the least machining time and dimensional deviation using zinc PM-μ-EDM. A comparative study between the μ-tool electrodes (copper and brass) and Zn powder particle concentrations (PPCs: 0, 2, 4, 6, 8, and 10 g/l) revealed that the copper μ-tool electrode in association with 6 g/l PPC, could achieve the most improved machinability and modified layer on the Ni 55.6 Ti 44.4 alloy surface. A field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDS) investigated the dimensional, morphological, and compositional features of the modified Ni 55.6 Ti 44.4 alloy surface and reported significant improvements. The X-ray diffraction (XRD) analysis of the modified surface detected a remarkable impact of the thermally induced variations on the crystalline phases of Ni 55.6 Ti 44.4 alloy. Further, the lactate dehydrogenase (LDH) and CellTiter-Blue assays determined improved cytocompatibility characteristics and Drop Shape Analyzer (DSA) ascertained the hydrophobicity of the modified Ni 55.6 Ti 44.4 alloy surface. • The combination of copper μ-tool electrode and 6 g/l zinc powder particle concentration improved the performance of PM-μ-EDM significantly. • PM-μ-EDM induced a noticeable variation in martensitic phases of modified surface of Ni 55.6 Ti 44.4 alloy. • The modified Ni 55.6 Ti 44.4 alloy's surface might be suggested for cardiovascular applications.

Comparative study on the heat transfer performance of micro-grooved anodized thermosyphon with R134a, R600a and R717 for low-temperature applications

A comparative heat transfer performance of an internally grooved anodized thermosyphon with eco-friendly refrigerants is presented in this study. Thermosiphons are fabricated with 50 numbers of axial micro-grooves having a width of 500 μm and a depth of 550 μm that is formed using an electrical discharge machining process. The micro-grooved surface was then anodized and characterized using SEM as well as DSA 25 drop shape analyzer. Later, the heat transfer performance of non-anodized grooved thermosyphon is studied by varying fill ratio (20-80 %), inclination angle (0-90°), and heat inputs (5-50 W). The heat transfer coefficient of the thermosyphon is improved by anodization by 20.9 %, 17.2 %, and 18.1 %, respectively, with R717, R134a, and R600a at optimum circumstances (30 % fill ratio and 60° inclination angle). Due to the performance enhancement and zero global warming potential of R717, an anodized surface with the same is recommended for a wide range of heat transfer applications.

Bi-layered disulfiram-loaded fiber membranes with antibacterial properties for wound dressing.

In this study, the bi-layered disulfiram-loaded fiber membranes with the antibacterial activity and different surface wettabilities are prepared using electrospinning technology. In the application of wound dressing, the hydrophilic surface of fiber membranes is beneficial for cell adhesion and drug release to heal the wound. Meanwhile, the outside hydrophobic surface is able to block water penetration to reduce the probability of wound infection. The obtained bi-layered drug-loaded fiber membranes are composed of polyvinylidene fluoride (PVDF) bottom surface and disulfiram (DSF)/polylactic acid (PLA) top surface. To modify the top surface wettability, the oxygen plasma modification of bi-layered membranes was carried out. The morphology, wettability, and chemical compositions of bi-layered drug-loaded fiber membranes were analyzed using the scanning electronic microscope (SEM), drop shape analysis instrument, X-ray diffractometer (XRD), and X-ray photoelectron spectrometer (XPS). The bi-layered disulfiram-loaded membranes showed the potent antibacterial activity in vitro against both Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). It was found that the bi-layered membranes had good biocompatibility with L929 cells. Thus, the obtained bi-layered disulfiram-loaded fiber membranes are suitable for wound dressing application.

Covalently Bound S-Nitroso-N-Acetylpenicillamine to Electrospun Polyacrylonitrile Nanofibers for Multifunctional Tissue Engineering Applications.

Attachment of a nitric oxide (NO) donor to an electrospun polymer has the potential to improve its proliferative and antimicrobial capabilities. This study presents the novel, covalent attachment of S-nitroso-N-acetylpenicillamine (SNAP) to polyacrylonitrile (PAN) fibers. By attaching the NO donor to the polymer, rather than blending it, leaching is reduced to maintain a NO flux within the physiologically relevant range for a longer duration, while limiting any cytotoxic effects. The synthesized fibers were characterized using a variety of techniques such as scanning electron microscopy, 1H NMR, and drop shape analysis. Due to the antimicrobial activity of NO, the SNAP-PAN fibers demonstrated a 2-log reduction of S. aureus adhesion. Furthermore, the extended zone of inhibition of S. aureus by SNAP-PAN demonstrates the ability of NO to impact the environment surrounding the material, in addition to the environment in direct contact with it. The combination of NO release, hydrophilicity of PAN, and the fibrous network led to increased fibroblast proliferation and attachment, potentially expanding the fibers as an improved cell scaffolding platform. The results from this study demonstrate a novel preparation and design of NO-releasing fibers to provide multiple benefits for a variety of biomedical applications.

Wettability and thermal performance of Ga62.5In21.5Sn16 liquid metal alloy on W-coated Cu substrates with varying film thickness

The Ga62.5In21.5Sn16 liquid metal alloy (LMA) has been considered as a promising thermal interface material for electronics cooling. In this work, the Cu substrates were deposited with tungsten (W) films or copper (Cu) films of various thicknesses to form different morphology and composition. The surface morphology and wettability of the filmed Cu substrates were investigated by the scanning electron microscope and drop shape analyzer, respectively. Thermal performances of the Ga62.5In21.5Sn16 sandwiched between filmed Cu substrates were studied using the laser flash analyzer. It was observed that the rough Cu substrate becomes smooth after being deposited with metal film. A decrease in surface roughness leads to the decrease in the contact angle of Ga62.5In21.5Sn16 droplet on filmed Cu substrate and the thermal resistance of Ga62.5In21.5Sn16 sandwiched between filmed Cu substrates. The wettability and thermal performance are strongly dependent on the surface composition. Thermal performance of the Ga62.5In21.5Sn16 sandwiched between the W-coated Cu substrates initially varies dramatically with W film thickness, and then changes slowly beyond a critical film thickness of ∼60 nm. This trend originates from the changing of surface composition arising from the thickening of W films.

Underground Upgrading of the Heavy Crude Oil in Content-Saturated Sandstone with Aquathermolysis in the Presence of an Iron Based Catalyst

Increasing the efficiency of thermal recovery methods is an important and relevant task. This study is devoted to reducing heavy components (resins and asphaltenes) and quality improvement of heavy oil by catalytic hydrothermal treatment. The object of this study is a bituminous sandstone sample from the Ashal’cha reservoir. The catalytic (iron tallate) hydrothermal simulation was carried out under reservoir conditions (200 °C, 30 bar). The composition and physicochemical characteristics of the products were studied using elemental and SARA analysis, MALDI, GC-MS, FT-IR. Moreover, the extracted rock is analyzed in XRD and DSA (Drop Shape Analyzer). The introduction of catalyst in combination with a hydrogen donor reduces the content of resins by 22.0%wt. with an increase in the share of saturated hydrocarbons by 27%wt. The destructive hydrogenation leads to a decrease in the sulfur content of upgrading products. This is crucial for the oil reservoirs of the Tatarstan Republic, as their crude oils are characterized by high sulfur content. According to the wettability data, the hydrophilicity of the rock surface increases due to inhibition of the coke formation after the introduction of the catalytic complex. Thus, the oil recovery factor can be increased due to the alteration of the oil-wetting properties of reservoir rocks.

The effect of dynamic wetting pressure on contact angle measurements

HypothesisThe drop deposition technique can impact contact angle measurements. We hypothesized that the drop pinch-off, during the traditionally used pendant drop technique, significantly alters the static contact angle. The capillary waves and dynamic wetting pressure generated during the pendant drop deposition are the source for forced spreading, which can be circumvented by alternative liquid-needle drop deposition techniques. ExperimentsTo compare the role of drop pinch-off and resultant dynamic wetting pressure, we meticulously observed and quantified the entire drop deposition process using high speed imaging until the drop attains the static contact angle in both cases, namely pendant drop and liquid needle deposition technique. Conventionally used standard substrates are compared using both techniques and further compared using literature data. The capillary waves and corresponding drop shape variations are analysed for quantifying the dynamic wetting pressure by measuring drop base diameter, contact angle and centre of mass. FindingsWe compared three parameters - drop pinch-off, spreading behaviour and respective static contact angles along with the resultant dynamic wetting pressure for both the techniques, i.e., pendant drop and liquid-needle. For the pendant drop technique we observed a pronounced drop volume dependency of these parameters even though the corresponding Bond numbers are less than unity. In contrast, for the liquid needle there is no such dependency. With a theoretical argument corroborating experimental observations, this work highlights the importance of a well controlled drop deposition, with a minimum wetting pressure, in order to guarantee contact angle data that is independent of drop deposition effects, thereby only reflecting the substrate properties.

Effect of electrolyte on the surface dilational rheological properties of branched cationic surfactant

The studies of surface dilational rheology are important to detent the nature of adsorption film and the properties of foam. In this paper, the adsorption and dilational rheological properties of branched cationic surfactant hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC) at the air-water interface in the absence and presence of electrolyte (NaCl) were investigated by drop shape analysis. The results show that the surface adsorption layer of C16G(EO)3PC behaves elastic in nature with high value up to 90 mN/m, which indicates that the slow relaxation process plays a main role because of the re-arrangement of long branched alkyl chain. The addition of NaCl will enhance diffusion-exchange process and accelerate the formation of film and decreases dilational elasticity obviously. At low NaCl concentration, the in-film slow relaxation process dominates the nature of film, dilational viscosity decreases with an increase of oscillating frequency. By adding more NaCl, diffusion-exchange process plays the crucial role and dilational viscosity increase as a function of frequency. Moreover, viscosity at high NaCl concentration shows larger value under higher oscillating frequency, indicating the contributions of fast diffusion-exchange process. The elastic adsorption film becomes to be viscoelastic by adding electrolyte.

Air humidity effects on water-drop icing.

The canonical problem of the icing of a water drop lying on a cold substrate is revisited to take into account the effects of atmospheric conditions on the icing front kinetics and on the tip formation. Here, we demonstrate both experimentally and theoretically that the air humidity induces liquid-vapor phase change at the icing droplet interface and that the associated heat transfer has a strong influence on both the icing front kinetics and the iced drop shape. The experimental results obtained in this study, as well as results from literature, compare well to a modified Stefan model accounting for the effects of humidity, showing a good agreement with the experimental data of both the front kinetics and tip angle.

Evolution and Shape of Two-Dimensional Stokesian Drops under the Action of Surface Tension and Electric Field: Linear and Nonlinear Theory and Experiment

The creeping-flow theory describing evolution and steady-state shape of two-dimensional ionic-conductor drops under the action of surface tension and the subcritical (in terms of the electric Bond number) electric field imposed in the substrate plane is developed. On the other hand, the experimental data are acquired for drops impacted or softly deposited on dielectric surfaces of different wettability and subjected to an in-plane subcritical electric field. Even though the experimental situation involves viscous friction of drops with the substrates and wettability-driven motion of the contact line, the comparison to the theory reveals that it can accurately describe the steady-state drop shape on a non-wettable substrate. In the latter case, the drop is sufficiently raised above the substrate, which diminishes the three-dimensional effects, making the two-dimensional description (lacking the no-slip condition at the substrate and wettability-driven motion of the contact line) relevant. Accordingly, it is demonstrated how the subcritical electric field deforms the initially circular drops until an elongated steady-state configuration is reached. In particular, the surface tension tends to round off the non-circular drops stretched by the electric Maxwell stresses imposed by the electrodes. A more pronounced substrate wettability leads to more elongated steady-state configurations observed experimentally than those predicted by the two-dimensional theory. The latter cases reveal significant three-dimensional effects in the electrically driven drop stretching. In the supercritical electric fields (corresponding to the supercritical electric Bond numbers), the electrical stretching of drops predicted by the present linearized two-dimensional theory results in splitting into two separate droplets. This scenario is corroborated by the predictions of the fully nonlinear results for similar electrically stretched bubbles in the creeping-flow regime available in the literature as well as by the present experimental results on a substrate with slip.

In-situ measurement of interfacial tension: Further insights into effect of interfacial tension on the kinetics of CO2 hydrate formation

Hydrate-based CO2 capture and sequestration has been viewed as one of the most attractive technologies due to its environmental friendliness and relatively moderate temperature and pressure conditions. In current work, the kinetics of CO2 hydrate formation was investigated at pressures of 2.5–3.5 MPa and temperatures of 274.15–279.15 K and the effect of interfacial tension on CO2 hydrate formation rate was discussed. The interfacial tension between CO2 and aqueous solution during the hydrate formation was in-situ measured via an axisymmetric drop shape analysis method. Under the experimental conditions of this study, the interfacial tension decreased significantly with increasing pressure, while it did not vary obviously with temperature. As to SDS aqueous solutions, the interfacial tension at the gas-liquid interface decreased approximately 12% and 42% when the SDS concentration was 100 ppm and 500 ppm, respectively. In addition, CO2 hydrate formation rate ascended by 59% and 102% when the SDS concentration is 100 ppm and 500 ppm, respectively. Furthermore, a good linear relationship was observed between hydrate formation rate and ratio of driving force to interfacial tension (R2 = 0.9211). This work provides a new idea for rapid estimation of hydrate formation rate.

On altering the wetting behaviour and corrosion resistance of a large metallic surface area by wire electrochemical texturing

This paper presents a novel and practically applicable method for a quick fabrication of uniform surface patterns (periodic micro-pillars with rectangular and square cross-section) on a large surface area of any conducting or semi-conducting material using Wire Electrochemical Micromachining (Wire-ECMM). Micro pillars with a rectangular cross-section are generated by machining mutually perpendicular micro channels. The depth, spacing, and cross-sectional area of pillars are controlled by varying the process parameters and tool travel distance. Primary pillars (level-1 texture) are machined with a constant Direct Current (DC) voltage and secondary pillars (level-2 texture) are machined with a pulsed DC voltage using a tungsten wire of diameter 100 μm. An aqueous solution of sodium nitrate (NaNO 3 ) is selected as an electrolyte having a pH of about 7.01. A good repeatability in the geometrical parameters of a pillar profile is observed on analysing 3D profilometer micrographs of the textured surfaces. Wetting behaviour of textured surfaces with different geometrical parameters is observed using drop shape analyser. A surface with two levels of textures offers highest contact angle of 147.3° with deionized water. Corrosion current and resistance of the textured surfaces are obtained using Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS), respectively. Results suggest that corrosion resistance depends upon the area of texture and is highest for the sample with the largest textured area. Also, a sample with the smallest value of area factor (ratio of total area of the top surface of all the pillars in a region to the total projected area of a region) offers highest resistance to corrosion. • A novel approach for large area texturing on any conducting and semi-conducting surface using Wire Electrochemical Micromachining (Wire-ECMM). • A study of the influence of different process parameters on various geometrical features of a textured surface. • A detailed characterization of different textured surfaces using SEM imaging and surface topography. • In depth analysis of the wetting and corrosion behaviour of the textured surfaces using drop shape analyser and Electrochemical Impedance Spectroscopy (EIS).

Symmetry-Breaking Drop Bouncing on Superhydrophobic Surfaces with Continuously Changing Curvatures.

Controlling the residence time of drops on the solid surface is related to a wide spectrum of engineering applications, such as self-cleaning and anti-icing. The symmetry-breaking dynamics induced by the initial drop shape can promote drop bouncing. Here, we study the bouncing features of spherical and ellipsoidal drops on elliptical surfaces that continuously change curvatures inspired by natural succulent leaves. The bounce characteristics highly depend on the geometric relations between the ellipsoidal drops and curved surfaces. Numerical results show that ellipsoidal shapes of the drops amplify asymmetries of the mass and momentum in synergy with an influence of the surface curvature during the impact, which is verified by experiments. Effects of the surface anisotropy and drops’ ellipticity on the residence time are investigated under various surface morphologies and Weber numbers. The residence time is closely associated with an initial surface curvature at the apex. The underlying principle of modifying the residence time via the drops’ ellipticity and initial surface curvature is elucidated based on momentum asymmetry. The understanding of the bouncing features on curved surfaces will offer practical implications for enhanced heat transfer performances and controlled water repellency, etc.

Numerical study of drop shape effects in binary drop film interactions for different density ratios

Numerical study of drop shape effects in binary drop film interactions for different density ratios

An analytical model for the evaporation of multi-component spheroidal drops based on Stefan–Maxwell equations

An analytical evaporation model for multi-component spherical and spheroidal drops, based on the analytical solution of the Stefan–Maxwell equations is proposed to study the multi-component steady diffusion in the gas phase. A comparison with the ‘classical’ approach based on the Fick’s law is reported for three families of liquid mixtures, namely alkanes, alcohols and water solutions of alcohols under a wide range of operating conditions. The local vapour fluxes of each vaporising species on the drop surface are correlated with the local Gaussian curvature. The effects of drop shape and of the modelling of constitutive equations on the evaporation rates are discussed. Comparison of the present model with experimental measurements of different compositions of tetradecane–hexadecane drops vaporising in stagnant air shows a rather satisfactory agreement.