Drop Shape Research Articles

In situ generated silver nanoparticles embedded in polyethersulfone nanostructured membranes (Ag/PES) for antimicrobial decontamination of water

AbstractBACKGROUNDThe general performance of polymeric membranes is hindered by the build‐up of microbial foulants both on the surface and inside the pores. This justifies the inclusion of antimicrobial agents within the membranes in order to circumvent the biofouling process. A nonsolvent‐induced phase separation process was used to fabricate the membranes following the in situ reduction of silver (Ag) in the polymer dope solution. Fourier transform infrared, atomic force microscopy (AFM), scanning and transmission electron microscopy, and drop shape analyzer were used to study different properties of the membranes.RESULTSBased on the results of AFM and contact angle measurements, the inclusion of Ag nanoparticles (NPs) improved the membrane hydrophilicity. The disk diffusion method was applied to study the antimicrobial properties of the membranes. The fabricated Ag/ polyethersulfone (PES) membranes showed antimicrobial activity against representatives of both Gram‐positive and ‐negative bacteria, and this was confirmed by the zones of inhibition (11 mm for Escherichia coli; 13 mm for Bacillus cereus). From this a general proposed antimicrobial mechanism via the generation of reactive oxygen species (ROS) was provided.CONCLUSIONThe fabricated Ag/PES membranes can perform a dual function of complete microbial inactivation and ultrafiltration of polluted water to provide better quality water with reduced membrane fouling. © 2021 Society of Chemical Industry (SCI).

The Direct Cause of Amplified Wettability: Roughness or Surface Chemistry?

Higher contact angles or amplified wettability observed on surfaces of rough solid materials are typically expressed as a function of a physical dimension (roughness factor). Herein, we present a simple experimental approach that demonstrates that roughness may only magnify the inherent surface chemistry that seems to have direct influence on surface wettability. We investigate gradual change in surface chemistry (hydrophobisation) of rough and smooth glass surfaces, from a very low concentration (10−7 M) of dichlorodimethylsilane, DCDMS through various intermediate hydrophilic/hydrophobic states to when the surfaces are maximally hydrophobised with DCDMS at 0.1 M. The wettability of the modified glasses was studied by water contact angle measurements using drop shape analysis system (DSA). The data obtained indicate a deviation from Wenzel model, with the functionalized rough glass surfaces showing higher reactivity towards DCDMS when compared to the smooth glass surfaces, indicating that the two surfaces are not chemically identical. Our study reveals that just like transforming a solid material to powder, a well-divided glass (rough) surface may not only exhibit a greater surface area than the smooth counterpart as rightly predicted by the Wenzel model, but seems to be bloated with functional groups (–OH or –CH3) that can amplify surface interaction when such functional species dominate the solid surface.

Influence of surface modification of titanium implants on improving osseointegration: An in vitro study

Statement of problemThe effect of aging and the surface treatment of implants on osseointegration needs to be evaluated. PurposeThe purpose of this in vitro study was to evaluate the effects of aging and the surface treatment of titanium with ultraviolet (UV) radiation and fibroblast growth factor (FGF) on hydrophilicity and cell growth and thus on osseointegration. Material and methodsA total of 28 specimens were divided into 2 groups to measure hydrophilicity (n=14) and cell growth (n=14). Each group was further divided into 4 groups according to surface modification. These include the control group (CG) (nascent specimens), aged group (AG) (nascent specimens aged for 4 weeks), photofunctionalized group (PG) (aged specimens UV-A treated), and mimed group (MG) (aged specimens UV-A and FGF2 treated). The PG and MG specimens were treated with UV-A light for 40 minutes. The biomimetic surface modification was performed for MG. Hydrophilicity was measured by using the contact angle in relation to the surface of titanium disks with the help of a drop shape analyzing device (KRUSS), and cell growth was measured by calculating the number of stem cells per cm2 with the help of a scanning electron microscope (SEM). The data obtained were subjected to statistical analysis with a statistical software program (α=.05). ResultsThe lowest contact angle values were found in PG (13.52 ±0.90 degrees) and the highest in AG (70.54 ±1.72 degrees). The highest number of cells per cm2 (2880 ±99.33) were found for MG, and the lowest number of cells per cm2 (760 ±9.17) for AG. ConclusionsAging decreased the hydrophilicity and cell adhesion, migration, and growth on the titanium surface. UV treatment improved the hydrophilicity, cell adhesion, migration, and growth for both CG and AG. FGF2 treatment increased the cell adhesion, migration, and growth for CG, AG, and PG.

Influence of surface structures on wettability

Wettability of solid surfaces is a key parameter for many industrial applications of solid materials. The wettability is influenced not only by the nature of the material but also by the existence of surface structures. Crucial influence of the oriented surface structures on the shape of liquid drop was observed in this study. Observed differences in value of contact angle measured on the metal surface at two perpendicular directions were 19° for water and 23° for diiodomethane. These surface structures can significantly influence liquid and heat transfer on structured surfaces.

Research of the effect of droplets deformation on the radar characteristics of rains

The results of calculations of the radar characteristics of rains for the averaged spectra of drops specific to the North Caucasus are presented. The results are obtained under the assumption that the droplets are deformed when falling in clouds and precipitation, taking the form of a flattened spheroid. For comparison, the radar characteristics calculated by the Mi algorithm for spherical droplets are given. For individual large droplets, which under the influence of an electric field can take extreme sizes, the reflectivity are also calculated. The analysis of the obtained results showed that when reconstructing the microstructural characteristics of hail clouds and precipitation at high intensities, it is necessary to take into account the shape of drops.

Ellipsoidal drop impact on a single-ridge superhydrophobic surface

A water drop impacting on a superhydrophobic surface exhibits a complete bounce after a certain residence time bounded by a theoretical time scale. Recent studies have demonstrated that the residence time is modified below the time scale through an asymmetric bouncing on a ridge surface. However, previous studies still assumed initially spherical shapes of drops, focusing on a high impact velocity for a desirable residence time. Herein, we propose asymmetric bouncing dynamics of ellipsoidal drops on a single-ridge superhydrophobic surface to create synergistic cooperation between the initial drop shapes and the ridge structures. Numerical simulations demonstrate the feasibility of reducing the residence time by approximately 55% using a volume-of-fluid method, compared with a conventional drop impact on flat surfaces. We examine how the drop's ellipticity and impact velocity affect the spreading, retraction, and splitting and interpret the underlying mechanism behind the residence time reduction by quantifying the evolutions of the shape and axial momenta of the drops. We also predict the bouncing directions of the drops and the effect of the off-centred distances and ridge sizes in the height and width on the residence time. These findings are expected to illuminate the fundamentals of asymmetric bouncing on a ridge and provide beneficial guidance to strategies such as self-cleaning and anti-icing.

The role of oscillation in ellipsoidal drop impact on a solid surface

Ellipsoidal shapes of drops can significantly modify the impact dynamics and suppress the rebound by inducing symmetry breaking in the mass and momentum distributions compared to the axisymmetric dynamics of typical drops. However, the previous works have assumed that the drop oscillation at the moment of impact only slightly affects the post-dynamics although the oscillation must be involved in the spreading. Here, we study the impact dynamics of the oscillating ellipsoidal drops on non-wetting surfaces as a function of the ellipticity, oscillation phase, and Weber number (We) experimentally and numerically. The spreading dynamics show notable hysteretic features in the maximal spreading diameters at the four regions of the oscillation phase. The hysteresis appears more prominently in prolate drops than in oblate drops and becomes remarkably suppressed at the four phases as We increases. Momentum analysis shows that the phases for shaping the drops spherically can drive higher asymmetry in the horizontal momenta than the other phases for shaping the drops ellipsoidally. The momentum asymmetry in the horizontal axes indicates that the oscillation phase as well as the ellipticity can play an important role in altering the hydrodynamics and reducing the bounce magnitude.

Hydrodynamic model of blood flow in major arteries pulsing in various modes.

Traditionally, the arteries in mammals are viewed as the tubes with elastic wall, whose elasticity could be slowly (during a minute) tuned to change its diameter thereby regulating regional blood supply. Recent findings showed that an artery is a much more sophisticated organ, which can change elasticity of vascular wall within a fraction of a second during a cardiac cycle due to activation of its smooth muscles manifested by generation of arterial action potentials. The rapid variations in elasticity of vascular wall resulted in three basic modes of arterial pulsing: passive, active, and intermediate. The latter is characterized by counteraction of dilation force of arterial pressure and the contractile one of smooth muscle in arterial wall, which can result in seemingly "rigid" artery of constant diameter. The prevalence of any of these forces results in active or passive pulsing modes. Existence of various pulsing modes raises the question of their effect on the main function of blood vessels, i.e., the transport of blood. The aim of this study is to assess the effect of various modes of arterial pulsing on hydraulic impedance of major arteries. The linearized Navier-Stokes equation was employed to develop a model of pulsatile flow of viscous incompressible fluid at small velocity via a conduit artery with the walls of variable or constant elasticity. An essential feature of the developed model is the shape of variable pressure drop applied to the ends of arterial segment, which simulates the real changes in arterial pressure during the heartbeat. Here, it is modeled by periodic (systolic) positive bell-shaped impulses with maxima corresponding to systolic arterial pressure, while the minimal plateau level refers to diastolic arterial pressure. The model assesses the changes in arterial hydraulic impedance during a cardiac cycle relatively to the stable level corresponding to constant blood flow driven by persistent pressure drop. Within intermediate variety of pulsing modes between the active and passive ones, the approximation of rigid arterial segment with infinite elasticity of arterial wall showed that hydraulic impedance in rigid artery is not constant due to inertial properties of the flowing blood. In passive pulsing mode characterized with constant elasticity of arterial wall, the diameter of artery changes in parallel with systolic pressure applied to the ends of arterial segment. At this, the overall change of hydraulic resistance is negative. In active pulsing mode, elasticity of arterial wall varies at different phase shifts relative to arterial pressure due to periodic contractions and relaxation of the smooth muscles in arterial wall. An important feature of active mode is possibility to decrease the hydraulic impedance during the front of arterial pressure. Various experimental modes of artery pulsing can be mathematically simulated. The passive and active modes of pulsing as well as a broad variety of intermediate pulsing modes with various phase shifts between arterial pressure and its diameter result in potency of the arteries to tune its performance in order to meet the regional circulatory requirements. The model showed that active arterial pulsing can diminish the arterial hydraulic impedance and contribute to the work needed for circulation thereby helping the pumping action of the heart.

Axisymmetric Drop Shape Analysis using a low-cost home-made setup

Surface science and engineering gained an increasing importance in recent years, due to the potential benefit they can offer in many applications. An important parameter in this field is the surface wettability, that is in general evaluated by the contact angle. One of the most accurate techniques to measure this quantity is the axisymmetric drop shape analysis, based on the fitting of the theoretical Laplace-Young profile to the contour of experimental drops. In this paper the performance of a simple, low-cost setup – that can be built “at home” – to apply this technique is assessed, also including a detailed analysis about the influence of the most important parameters to set in the procedure. The latter aspect was evaluated by using computer-generated drop profiles and pictures, to have “realistic” images, but for drops of known properties. The experimental setup was built using a desk, a table lamp, a medical syringe, a support for the samples and a “bridge” camera. Measurements were performed on smooth and rough textile surfaces and the results were compared with previous measurements taken with a professional setup. From the comparison it can be affirmed that the performance of the home-made setup is very satisfactory.

Approximating stationary deformation of flat and toroidal drops in compressional viscous flow using generalized Cassini ovals

Viscous drops, subject to a linear flow in an immiscible viscous fluid, deform. When the resulting drop shape is simple the problem can be addressed by an asymptotic approach or by approximating the deformation using known simple shapes. When the resulting deformation is more complex, the problem is usually addressed numerically. In this paper, we address the problem of drops that are deforming in an axisymmetric compressional (bi-axial extensional) flow. Yielded shapes are flat drops, flat drops with dimples and toroidal drops. The latter two are highly unstable. We propose to approximate the solution of this problem, approximating the shapes by using generalized Cassini ovals, defined herein. The analysis reproduced the branches with shapes of stationary stable flat drops and stationary unstable toroidal drops, available from numerical calculation. Furthermore, it predicts the point of loss of stability of the flat drop to exhibit the transition branch that leads into the formation of the toroidal shapes, and shows that this branch shows stationary, yet unstable, flat drops with ever growing dimples up to collapse.

Acoustic Levitation: A Novel Approach to Study the Physical Properties of Blood in Normal Subjects and in Patients with Sickle Cell Disease

Acoustic levitation is a novel technique which we have developed for the purpose of measuring physical properties of blood, plasma and red cells in a non-contact setting, which eliminates issues and concerns related to the interaction of blood with non-physiological surfaces. Figure 1 shows a levitated blood drop between the ultrasound transducer and reflector. By exciting drop shape oscillation, we can study its vibrational behavior and infer its viscoelastic properties.Whole blood samples were collected from volunteers in tubes containing Ethylenediaminetetraacetic acid (EDTA) as anticoagulant. Patients' samples were studied using left-over material after a clinically-ordered CBC had been performed. Samples with different hematocrit (Hct) were obtained in the same subject, by removing or adding autologous plasma after centrifugation.To calibrate the device, we compared the results obtained by our instrument with the blood viscosity determination provided by a cone-plate rotational rheometer (HR-2, Hybrid rheometer - TA Instrument). Figure 2 (Left) shows the results from levitator and rotational rheometer.We also compared normal samples with samples of patients with sickle cell disease (SCD) over a wide range of Hct values, obtained by addition or removal of autologous plasma. As shown in Figure 2 (Right), for any given Hct the viscosity measurements obtained by the levitation device were greater in blood of patients with sickle cell disease compared with normal controls.For each sample of blood from patients with sickle cell disease, we assessed viscosity with the levitation device at different values of Hct (autologous plasma addition or removal) and were able to determine the slope of this regression line. We also compared the viscosity value determined at an arbitrary Hct value of 55% among all the clinical samples collected from patients with SCD. As shown in Figure 3, when these data were analyzed as a function of the fetal Hb content of each blood sample (obtained from the total Hb value of the unmodified clinical sample and the % of Hb F determined by HPLC), a clear negative correlation emerged between total Hb F values (in g/dl) and viscosity, measured as either the slope of the regression line or the value at a fixed Hct of 55%. The clinical samples included several patients treated with hydroxycarbamide, showing an important correlation between higher values of Hb F and lower blood viscosity.These studies demonstrate that acoustic levitation is a non-contact technique which can be successfully used to measure physical properties of human blood. We show that viscosity measurements obtained with this new device compare very favorably with traditional rotational viscometer. Furthermore, this new technology can reproducibly measure viscosity over a wide range of Hct values and for any given Hct, it shows that the viscosity of samples from patients with SCD is greater than normal controls. We also show that our measurement is sensitive enough to detect variation in viscosity associated with different absolute values of fetal Hb in blood, and more specifically showing lower viscosity with higher Hb F values, opening the possibility that this technique could be used to determine changes in viscosity associated with hydroxycarbamide therapy in patients with sickle cell disease. [Display omitted] DisclosuresAnsari Hosseinzadeh:National Science Foundation: Research Funding. Brugnara:National Science Foundation: Research Funding. Holt:National Science Foundation: Research Funding.

The shape of two-dimensional and three-dimensional drops on flat and curved hydrophilic substrates: variational, numerical and molecular dynamics simulation investigations

The shape of two-dimensional and three-dimensional drops on flat and curved hydrophilic substrates: variational, numerical and molecular dynamics simulation investigations

Neutron drop trapped in axially deformed external fields

The neutron drop is firstly investigated in an axially symmetric harmonic oscillator (ASHO) field, whose potential strengths of different directions can be controlled artificially. The shape of the neutron drop will change from spherical to oblate or prolate according to the anisotropy of the external field. With the potential strength increasing in the axial direction, the neutron prefers to occupy the orbital perpendicular to the symmetry axis. On the contrary, the neutron likes to stay in the orbital parallel to the symmetry axis when the potential strength increases in the radial direction. Meanwhile, when the potential strength of one direction disappears, the neutron drop cannot bind together. These investigations are not only helpful to simulate the properties of neutrons in finite nuclei but also provide the theoretical predictions to the future artificial operations on the nuclei like the ultracold atom system, for a deeper realization of quantum many-body systems.

Study of early time dynamics of drop spreading in different surrounding pressure

The initial spreading phenomena of oil droplets on a partially wettable surface under various surrounding pressures was conducted through an experimental investigation outlined in this study. The gauge pressure of the surrounding medium was varied stepwise in the range from atmospheric pressure to 30 MPa. Upon contact with the surface, spreading alters the total energy of the system. The timescale for this process is very fast and the spreading involves the motion of the three-phase contact line established at the junction of the droplet, the substrate and the surrounding medium. In this study, the early time dynamics of different grades of oil drops spreading on PTFE substrates were examined utilizing high-speed imaging and drop shape analysis. Results show that the temporal evolution of the spreading radius closely resembles a power law where the empirically obtained exponent, α, was calculated for different surrounding pressures. Observations of instantaneous drop spreading reveal that spreading occurs through three distinct regimes: an initial spreading regime, a short transition regime and a viscous regime. In the inertial regime of the early time dynamics, spreading radius scales as r~tα where the spreading exponent, α, decreases with the increase of pressure. In addition, pressure influences the onset of the transition regime, the contact line speed, and the contact angle during the initial wetting process.

The role of drop shape in impact and splash

The impact and splash of liquid drops on solid substrates are ubiquitous in many important fields. However, previous studies have mainly focused on spherical drops while the non-spherical situations, such as raindrops, charged drops, oscillating drops, and drops affected by electromagnetic field, remain largely unexplored. Using ferrofluid, we realize various drop shapes and illustrate the fundamental role of shape in impact and splash. Experiments show that different drop shapes produce large variations in spreading dynamics, splash onset, and splash amount. However, underlying all these variations we discover universal mechanisms across various drop shapes: the impact dynamics is governed by the superellipse model, the splash onset is triggered by the Kelvin-Helmholtz instability, and the amount of splash is determined by the energy dissipation before liquid taking off. Our study generalizes the drop impact research beyond the spherical geometry, and reveals the potential of using drop shape to control impact and splash.

MEASURING COMPLEX FOR STUDYING EVAPORATION OF LIQUID DROPS ON A SUBSTRATE

The measuring equipment is a hardware-software complex consisting of a capacitive measuring device for the thickness of a lying drop, a digital microscope and a coordinate device. The equipment makes it possible to “scan” the drop and obtain the data of the height, drop shape, and the line of contact of the liquid phase with the surface that change during evaporation.

Preparation of Polyetherimide Nanoparticles by a Droplet Evaporation-Assisted Thermally Induced Phase-Separation Method.

The droplet evaporation effect on the preparation of polyetherimide (PEI) nanoparticles by thermally induced phase separation (TIPS) was studied. PEI nanoparticles were prepared in two routes. In route I, the droplet evaporation process was carried out after TIPS. In route II, the droplet evaporation and TIPS processes were carried out simultaneously. The surface tension and shape parameters of samples were measured via a drop shape analyzer. The Z-average particle diameter of PEI nanoparticles in the PEI/dimethyl sulfoxide solution (DMSO) suspension at different time points was tested by dynamic light scattering, the data from which was used to determine the TIPS time of the PEI/DMSO solution. The natural properties of the products from both routes were studied by optical microscope, scanning electron microscope and transmission electron microscope. The results show that PEI nanoparticles prepared from route II are much smaller and more uniform than that prepared from route I. Circulation flows in the droplet evaporation were indirectly proved to suppress the growth of particles. At 30 °C, PEI solid nanoparticles with 193 nm average particle size, good uniformity, good separation and good roundness were obtained. Route I is less sensitive to temperature than route II. Samples in route I were still the accumulations of micro and nanoparticles until 40 °C instead of 30 °C in route II, although the particle size distribution was not uniform. In addition, a film structure would appear instead of particles when the evaporation temperature exceeds a certain value in both routes. This work will contribute to the preparation of polymer nanoparticles with small and uniform particle size by TIPS process from preformed polymers.

Drying crack patterns of sessile drops with tuned contact line

Drying cracks formed in the deposits of films, paints, and coatings make the deposits failure and limit the corresponding applications. Extensive experimental attempts and theoretical understanding have been made to discover the underlying mechanisms and avoid cracks in the cases of uniform films. However, crack formation from drying drops is greatly complicated due to the strong coupling of the mass, internal flow and geometry constriction by the presence of the contact line, resulting in the heterogeneity of the deposit thickness. Interestingly, the complex physicochemical influences from colloidal particle, solution, surroundings can be geometrically reflected by the motion of the contact line, while the effect on crack formation is still lack of investigations. Hence, in this paper, we propose a model system to examine the dynamical motion of the contact line and correlate the corresponding mechanism of crack formation. The wettability of supporting substrates are successfully tuned in order to control the drop shapes with different contact angles, i.e. from hydrophilic to hydrophobic. Three drying regimes are recognized as pinned, stick-slip and receding by tuning the mobility of the contact line. The correlation between the crack spacing and the local thickness of deposits near the contact line is found as approximately linear, which is qualitatively discussed in the analysis of the scaling law. Finally, suppression of the cracks deposits are practically realized by freely moving contact line on the slippery substrates in receding cases with a wide range of suspension concentration.

Rain attenuation prediction based on theoretical method with realistic drop shape for millimeter-wave radio in tropical region

This paper aims to investigate the effects of drop shape on rain attenuation prediction based on the theoretical approach. By comparing the predicted rain attenuation with the measurement results obtained in Skudai, Malaysia, the theoretical method based model utilizing the knowledge of scattering properties and raindrop-size distributions are found to produce better prediction results than the widely-used empirical ITU-R model, particularly at high rain rate. At 26 GHz and 38 GHz, results calculated using realistic drop shape were found to yield lower RMSE than using spherical shape.

Manipulation of toroidal-spiral particles internal structure by fluid flow

We report on the precise manipulation of the fine structures of toroidal-spiral particles (TSPs) generated by a self-assembly process of droplet sedimentation at low Reynolds numbers in a miscible bulk solution followed by solidification. The biocompatible polymeric TSP can serve as a device for drug delivery and in vivo therapeutic cell expansion, activation, and delivery, for which highly tunable and reproducible structures are essential to design dosages and release kinetics. TSP formation can be divided into two stages: initial infusion of the drop vs its subsequent sedimentation, deformation, and entrainment of the surrounding bulk solution. The infusion rate affects the drop shape and tail length. These two features represent crucial initial conditions for subsequent shape evolution, which determines the overall morphology of the TSP and fine structure of the internal channel. Our computer simulations of drop dynamics add a new capability to the swarm-of-Stokeslets technique: unequal viscosities of the drop and bulk phases (i.e., non-unit viscosity ratio). During sedimentation, the density difference between the droplet and the bulk solution played a more pronounced role than the viscosity ratio, which was revealed both by experimental observations and numerical simulations. Understanding the fundamental hydrodynamics and developing a flow map will ultimately aid in the design of TSPs with tunable empty channels toward drug delivery and cell encapsulation.