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To accurately predict the film thickness distribution during dynamic spraying performed with air guns and support accordingly the development of intelligent spray painting, the spray problem was analyzed numerically. In particular, the Eulerian-Eulerian approach was employed to calculate the paint atomization and film deposition process. Different spray heights, spray angles, spray gun movement speeds, spray trajectory curvature radii, and air pressure values were considered. Numerical simulation results indicate that the angle of spray painting significantly affects the velocity of droplets near the spray surface. With an increase in the spraying angle, spraying height and spray gun movement speed, the maximum film thickness decreases to varying degrees, and the uniformity of the film thickness also continuously worsens. When the spray gun moves along an arc trajectory, at smaller arc radii, the film thickness on the inside of the arc is slightly greater than that on the outside, but the impact on the maximum film thickness is minimal. Increasing air pressure expands the coating coverage area, results in finer atomization of paint droplets, and leads to a thinner and a more uniform paint film. However, if the pressure is too high, it can cause paint splattering. Using the orthogonal experimental method, multiple sets of simulation calculations were conducted, and the combined effects of spraying height, spray angle, and spray gun movement speed on the film thickness distribution were comprehensively analyzed to determine optimal configurations. Finally, the reliability of the numerical simulations was validated through dynamic spray painting experiments. [ABSTRACT FROM AUTHOR]

Magnetic fluids, also known as ferrofluids, are versatile functional materials with a wide range of applications. These applications span from industrial uses such as vacuum seals, actuators, and acoustic devices to medical uses, including serving as contrast agents for magnetic resonance imaging (MRI), delivering medications to specific locations within the body, and magnetic hyperthermia for cancer treatment. The use of a non-wettable immiscible liquid substrate to support a layer of magnetic fluid opens up new possibilities for studying various fluid flows and related instabilities in multi-phase systems with both a free surface and an interface. The presence of two deformable boundaries within a ferrofluid layer significantly reduces the critical magnetic field strength required to transform the layer into an organized system of drops or polygonal figures evolving according to the intensity, frequency and direction of the considered magnetic field. This paper experimentally investigates this problem by assuming a uniform magnetic field perpendicular to the surface. This specific subject has not been previously explored experimentally. The critical magnetic field intensity required to destabilize the ferrofluid layer is determined based on the layer's thickness and the fluid's initial magnetic susceptibility. It is demonstrated that the critical magnetic field strength needed to disrupt the initially continuous ferrofluid layer increases with the layer's thickness. Conversely, an increase in the ferrofluid's magnetic susceptibility results in a decrease in the critical magnetic field strength. The emerging droplet structures are analyzed in terms of the number of drops, their size, and the periodicity of their arrangement. The number of droplets formed depends on the initial thickness of the layer, the presence or absence of a stable rupture in the upper layer, and the rate at which the magnetic field strength is increased to the critical value. A characteristic viscous time is proposed to evaluate the decomposition of the ferrofluid layer, which depends on the duration of the magnetic field's application. The experimental data on the instability of a ferrofluid layer on a liquid substrate are compared with the theoretical results from the study of "magnetic fluid sandwich structures" conducted by Rannacher and Engel. This comparison highlights the similarities and differences between experimental observations and theoretical predictions, providing a deeper understanding of the behavior of ferrofluid layers under the influence of magnetic fields. [ABSTRACT FROM AUTHOR]

The effects of two cokes with different reactivity on the lump ore's metallurgical properties and coke's solution loss are investigated under the high‐temperature load reduction. The work used an improved test device for softening‐melting and dropping characteristics of iron ores in both CO2 and CO2H2O atmospheres. The deterioration behavior of highly reactive cokes is expounded under hydrogen‐rich conditions. High‐reactivity cokes under hydrogen‐rich conditions are more favorable for enhancing the breathability of charge and the penetration of the coke layer. However, it increased the thickness of the softening zone. High‐reactivity cokes had obvious internal and external reaction gradients. The solution loss reaction mostly occurred on the surface, with selectivity. The longitudinal stacking height, layer number, and order degree in the carbon structure decreases after the reaction. The carbon‐structure difference weakens between the shell and core. The enhancement of coke's reactivity, however, results in the significant loss of coke powders on its surface. Unreduced FeO and refractory Fe2SiO4 are more likely to appear in the droplets, which is not conducive to the reduction of Fe and the generation of slag crust in the furnace. The difficulty in separating lump ores and cokes is aggravated, and more iron‐containing charge remain in the furnace. [ABSTRACT FROM AUTHOR]

Novel experimental data have been presented on the influence of the surface tension of a liquid on the dispersity of droplets in the spray cone of an ejection atomizer with forward and swirling gas feeds. The droplet-size distributions were measured with the optical method of small angles of the indicatrix of scattering. A decrease of nearly 10–17% in the median diameter of droplets of distilled water in the spray cone has been demonstrated with reduction in the coefficient of surface tension of water as a result of adding surfactants to it. [ABSTRACT FROM AUTHOR]

Droplet-based microfluidics exhibit numerous benefits leading to relevant innovations and many applications in various fields. The precise handling of droplets in capillaries, including droplet formation, manipulation, and separation, is essential for successful operation. Only a few reports are known concerning the separation of segmented flows, particularly the continuous separation of droplets, which is of high interest regarding the control of biochemical and chemical reactions or other applications where the contact time of the involved phases is crucial. Here, the separation must be flexible and adjusted to different flow parameters, such as the surface tension, the volumetric flow rates, and their ratios. This contribution presents two novel open-source approaches based on additive manufacturing and mechanical deforming for continuous liquid–liquid separation under various flow conditions. The Laplace pressure is the driving force for the separation, which is adjusted to the flow conditions by adapting the distance of pinning points provided by the design of the devices. Details of the device design and experimental setup are shown along with limitations to promote further development and to increase availability for researchers. With the right parameters, sophisticated separations can be realized by inexpensive laboratory equipment and simple control of them. It was found that the distance between the pinning points needs to enlarged for increasing volumetric flow rates and reduced for higher viscosities of the continuous phase respectively higher amounts of the dispersed phase. The open source approach of this article expands the exploration space in addition to commercially available phase separators only available to a selected group of people. [ABSTRACT FROM AUTHOR]

The current study focuses on spray cooling applied to the heat exchange components of a cooling tower. An optimization of such processes is attempted by assessing different spray flow rates and droplet sizes. For simplicity, the heat exchanger of the cooling tower is modeled as a horizontal round tube and a cooling tower spray cooling model is developed accordingly using a computational fluid dynamics (CFD) software. The study examines the influence of varying spray flow rates and droplet sizes on the heat flow intensity between the liquid layer on the surface of the cylindrical tube and the surrounding air, taking into account the number of nozzles. It is observed that on increasing the spray flow strength, the heat flow intensity and extent of the liquid film in the system are enhanced accordingly. Moreover, the magnitude of droplet size significantly impacts heat transfer. A larger droplet size decreases evaporation in the air and enhances the deposition of droplets on the round tube. This facilitates the creation of the liquid film and enhances the passage of heat between the liquid film and air. Increasing the number of nozzles, while maintaining a constant spray flow rate, results in a decrease in the flow rate of each individual nozzle. This decrease is not favorable in terms of heat transfer. Graphic Abstract [ABSTRACT FROM AUTHOR]

Compared with the conventional emulsification method, droplets generated within microfluidic devices exhibit distinct advantages such as precise control of fluids, exceptional monodispersity, uniform morphology, flexible manipulation, and narrow size distribution. These inherent benefits, including intrinsic safety, excellent heat and mass transfer capabilities, and large surface‐to‐volume ratio, have led to the widespread applications of droplet‐based microfluidics across diverse fields, encompassing chemical engineering, particle synthesis, biological detection, diagnostics, emulsion preparation, and pharmaceuticals. However, despite its promising potential for versatile applications, the practical utilization of this technology in commercial and industrial is extremely limited to the inherently low production rates achievable within a single microchannel. Over the past two decades, droplet‐based microfluidics has evolved significantly, considerably transitioning from a proof‐of‐concept stage to industrialization. And now there is a growing trend towards translating academic research into commercial and industrial applications, primarily driven by the burgeoning demands of various fields. This paper comprehensively reviews recent advancements in droplet‐based microfluidics, covering the fundamental working principles and the critical aspect of scale‐up integration from working principles to scale‐up integration. Based on the existing scale‐up strategies, the paper also outlines the future research directions, identifies the potential opportunities, and addresses the typical unsolved challenges. [ABSTRACT FROM AUTHOR]

Liquid metals, particularly non‐toxic gallium‐based alloys, have emerged as promising materials for future soft electronics due to their unique properties, including fluidity, excellent electrical and thermal conductivities, and surface reactivity. They demonstrate adaptability, responsivity, and self‐healing abilities, offering a platform for innovative electronic devices. Embodied in a droplet form factor, gallium‐based liquid metal droplets (LMDs) combine the traits of liquid metals with the advantages of miniaturized structures, including high surface tension, high surface area, high mobility, and surface functionalization. This review discusses the inherent properties of LMDs, which have driven substantial research interest across various fields, such as sensors, robotics, electronic circuits, energy harvesters, drug delivery, and microfluidics systems, among others. Effective fabrication and processing techniques are detailed for LMDs, illustrating their role in applications previously challenging with conventional materials, such as reconfigurable, self‐healing, and transient electronics. Existing challenges and future directions in this growing field are discussed. This extensive review seeks to further the understanding of LMDs and their potential, offering a roadmap for their journey from a niche interest to a key material in various electronic devices. [ABSTRACT FROM AUTHOR]

Acoustically activated perfluoropropane droplets (PD) formulated from lipid encapsulated microbubble preparations produce a delayed myocardial contrast enhancement that preferentially highlights the infarct zones (IZ). Since activation of PDs may be temperature sensitive, it is unclear what effect body temperature (BT) has on acoustic activation (AA). We sought to determine whether the microvascular retention and degree of myocardial contrast intensity (MCI) would be affected by BT at the time of intravenous injection. We administered intravenous (IV) PD in nine rats following 60 min of ischemia followed by reperfusion. Injections in these rats were given at temperatures above and below 36.5°C, with high MI activation in both groups at 3 or 6 min following IV injection (IVI). In six additional rats (three in each group), IV PDs were given only at one temperature (<36.5°C or ≥36.5°C), permitting a total of 12 comparisons of different BT. Differences in background subtracted MCI at 3-6 min post-injection were compared in the infarct zone (IZ) and remote zone (RZ). Post-mortem lung hematoxylin and eosin (H&E) staining was performed to assess the effect potential thermal activation on lung tissue. Selective MCI within the IZ was observed in 8 of 12 rats who received IVI of PDs at <36.5°C, but none of the 12 rats who had IVI at the higher temperature (p < 0.0001). Absolute MCI following droplet activation was significantly higher in both the IZ and RZ when given at the lower BT. H&E indicated significant red blood extravasation in 5/7 rats who had had IV injections at higher BT, and 0/7 rats who had IV PDs at <36.5°C. Selective IZ enhancement with AA of intravenous PDs is possible, but temperature sensitive. Thermal activation appears to occur when PDs are given at higher temperatures, preventing AA, and increasing unwanted bioeffects. [ABSTRACT FROM AUTHOR]

Gallium (Ga)-based liquid metals (LMs), as an emerging functional material, stand out among many candidates due to their combination of fluidic and metallic attributes, and they have extensively attracted the attention of academic researchers. When fabricated into droplet form, these metals are imbued with many fantastic characteristics, such as a high specific surface area and self-healing properties. Additionally, Ga-based liquid metal droplets (LMDs) achieve higher response accuracy to external stimuli, satisfying the demands of many applications requiring micro-size and precise stimulus-responsivity. Herein, we focus on reviewing the properties of Ga-based LMs and their droplets, the fabrication strategies of metal droplets, their stimulus-response motion under different external fields, and their applications in microfluidic systems, biomedical applications, and micromachines. To further advance the development of responsive Ga-based LMDs, the future outlooks with key challenges related to their further applications are also presented here. [ABSTRACT FROM AUTHOR]

Abstract To detect the contaminate of faucets in hospitals and the splash during hand washing, and to explore the reasonable layout of hand washing pools. Two faucets with roughly the same spatial layout in the ICU of a third-class first-class general hospital were selected, and the farthest splashing distance and specific splashing points were measured by color paper. Samples were detected by ATP detection technology and routine microbial detection method, and the contaminate of faucets was analyzed. After 72 h of daily hand-washing activities, the furthest distance to the splash point was about 100 cm around the faucet, and the place 40–110 cm around the faucet was contaminated seriously. The farthest distance that the splash point reached was about 80 cm around the faucet with the center of the circle, and the area 40–60 cm around the faucet was heavily contaminated. The distance from the water outlet of the long handle and the short handle faucet to the detection point had a high negative correlation (r = − 0.811, P

Accurate and flexible control of droplets is essential in many industrial applications, such as water harvesting, chemical assays, and biological detection. Magnetic force‐based methods have been broadly exploited to fulfill the goals due to the advantage of non‐contact, easy control, and long‐range navigation. Nevertheless, it still suffers from some challenges, such as sample fouling, and the paradox between the droplet efficient motion and the large volume. Here a ferrofluid‐based liquid spring to achieve contamination‐free and fast droplet transportation on non‐wetting solid surfaces is proposed. The liquid spring is based on the actuation of a ferrofluid droplet in an external uniform magnetic field. The actuation enables the liquid spring to propel tiny objects, including the non‐magnetic miscible droplets and water‐repellent solid particles, with adjustable motion velocity. Furthermore, the magnetic force, applied on the ferrofluid via an additional permanent magnet, makes it possible to navigate the liquid spring in a programmable way. With the aid of the liquid spring, the single or multiple droplets/solid particles advancing, on‐demand droplets coalescence, and out‐of‐plane droplet motion are achievable. [ABSTRACT FROM AUTHOR]

Salt particles generated by aerosol generator are commonly used in air filtration test. As a common phenomenon, the number of generated particles increases with the salt concentration in the atomization solution. Thus far, the dependence of the particle number on the concentration of the atomization solution is not fully understood. In this study, two hypotheses were proposed to explain this phenomenon: i) a single droplet generates multiple solid particles, and the generated particle number is influenced by the salt concentration, and ii) the original droplet number increases with an increase in the salt concentration of the atomization solution. By observing the particle formation process of the levitated millimeter-scale NaCl droplet, one droplet was found to generate one particle in free air. However, whether these results are applicable to micrometer-scale droplets remains to be determined. In situ measurements were performed to detect the size distributions of the original droplets generated by the atomization solutions with various salt concentrations. A more concentrated atomization solution induced a higher number of original droplets. Particle formation patterns of droplets on glass substrates and filaments were demonstrated. Traditional observation methods for droplet drying are unsuitable for studying the particle formation of atomized droplets because of the large difference in droplet size and the existence of external forces. [ABSTRACT FROM AUTHOR]

The authors have proposed different models of deformation of droplets and bubbles in regular and non-Newtonian fluids depending on Weber, Morton, and Reynolds numbers. Consideration has been given to a geometric interpretation of the issues of deformation with the aim of evaluating the surface and volume of a deformed droplet. The influence of asphalt and resin material contained in heavy oils on the degree of deformation of the droplets in them has been evaluated. Models of deformation of droplets and bubbles in regular and non-Newtonian fluids have been developed. It has been noted that the change in the shape of droplets in heavy oils is slight owing to their high viscosity. A comparison of the proposed models of deformation of droplets with the existing experimental data and with other models has been made. [ABSTRACT FROM AUTHOR]

An experimental investigation and a mathematical simulation of the gravitational stratification of a polydisperse water–oil emulsion in a rectangular cell have been performed. Histograms of the size distribution of droplets in the initial emulsion have been obtained using the approach based on the analysis of the images of an emulsion sample, made on an optical microscope at different magnifications. The concentration distributions of droplets along the height of the cell have been constructed using results of the digital processing of the photos of the emulsion, obtained in the experiment on its gravitational stratification. A methodology of numerical simulation of the stratification of a polydisperse emulsion system, based on the representation of this system as a set of quasi-monodisperse subsystems and on the combined solution of the equations for the sedimentation of droplets different in size in the one-liquid approximation, is proposed. [ABSTRACT FROM AUTHOR]

This work explores the manipulation method for controlling the dynamic behavior of impacting droplets using surface patterns. By designing and implementing four radially patterned surfaces with strategically positioned obstacles, the study reveals the direct correlation between surface patterns and droplet behavior upon impact. The experimental results demonstrate that, the maximum stretching length of the droplet after impact is significantly inhibited due to the enhanced viscous dissipation of the droplet on these patterned surfaces. Furthermore, the formation of satellite droplets delays and the number of satellite droplets also significantly decreases. Through an analysis of energy distribution during the impact process, we concluded that the surface energy and kinetic energy of the droplets exhibit a linear growth relationship with We0.25, whereas the dissipated energy We0.5. As the number of obstacles increases, the viscosity dissipation of the droplet enhances during the impact, resulting in a decrease in the kinetic energy and surface energy. Consequently, the droplets become more resistant to breaking, resulting in a reduced formation of satellite droplets. Therefore, the special designed surface patterns can be expected to manipulate the stretching shape, stretching length of the droplet, and formation of satellite droplets after impacting. The findings provide valuable insights into the manipulation and control of droplet dynamics, offering potential applications in various fields such as surface engineering, anti-icing and liquid-based technologies. [ABSTRACT FROM AUTHOR]

There has been significant interest in researching droplet transport behavior on composite wetting surfaces. However, current research is primarily focused on modifying individual droplets and lacks an in‐depth investigation into high‐precision droplet storage. This study introduces a "billiard ball" droplet transport and storage platform (TSP) with differentiated areas. Within this platform, the volume of droplets stored in the area reaches a consistent threshold through droplet "scrambling," inspired by the water‐gathering behavior of spiders. The TSP involves connecting two regions of different sizes using a three‐dimensional stepped wedge angle structure. However, this connection is not seamless, leaving a 2‐mm gap between the regions. This gap is intentionally designed to enable continuous droplet transfer while preventing any static migration. Through systematic experimental and simulation analysis, we investigated the influence of superhydrophilic pattern structures and parameters on quantitative droplet storage. We established a functional relationship between the pattern area and the stored volume, and analyzed the intrinsic mechanism of droplet collision separation. This enabled us to achieve on‐demand quantitative droplet storage and autonomize the storage process. The "billiard ball" droplet transport–storage platform proposed in this study holds promising applications in the fields of biomedical and organic chemistry. [ABSTRACT FROM AUTHOR]

Spreading of liquids on soft solids often occurs intermittently, i.e., the liquid's wetting front switches between sticking and slipping. Studies of this so-called stick-slip wetting on soft solids mostly are confined within quasi-static or forced spreading conditions. In these situations, because the sticking duration is set much larger than the viscoelastic relaxation time of the solid, a ridge is persistently and fully developed at the wetting front as the soft solid yields to the liquid's surface tension. The sticking duration and spreading velocity, therefore, were shown to have little impact to the contact angle change required for stick-to-slip transitions. For unsteady wetting of soft solids, a commonly encountered but largely unexplored situation, we hypothesize that the stick-to-slip transition is controlled not only by a combination of sticking duration and the spreading velocity, but also by an increasing depinning threshold caused by the growing ridge at the wetting front. We performed unsteady wetting experiment on soft solids by letting water droplets spread freely on soft solid surfaces of various stiffness. We capture both the stick-slip spreading behavior and growing wetting ridges using synchronous high-speed imaging and high-speed interferometry. Recorded data of liquid spreading and solid deforming at the wetting front were analyzed to shed light on the relation between stick-slip characteristics and the growing wetting ridge. We find that intermittent wetting on a soft solid surface results from a competition between three key factors: liquid inertia, capillary force change during sticking, and growing pinning force caused by the solid's viscoelastic response. We theoretically formulate their quantitative contributions to predict how stick-to-slip transitions occur, i.e., how the contact angle change and sticking duration depend on the liquid's spreading velocity and the solid's viscoelastic characteristics. This provides a mechanistic understanding and methods to control unsteady wetting phenomena in diverse applications, from tissue engineering and fabrication of flexible electronics to biomedicine. [ABSTRACT FROM AUTHOR]

Giant cells of characean algae provide an excellent platform for testing different techniques to explore cytoplasmic streaming, electrophysiological behaviour, intercellular communication, and drug delivery methods. In this study, we successfully applied nematic emulsions based on 5CB to visualise the shuttle flow in cells' cytoplasm. Additionally, we demonstrate the compatibility of the liquid crystal material with the intracellular environment. [ABSTRACT FROM AUTHOR]

Two-phase flows under microgravity conditions play a crucial role in Space technology and science. Studying the behavior of dispersed droplets suspended in a gas flow and their influence on the characteristics of the carrier flow is the main task of computational modeling of turbulent two-phase flows. To understand the features and predict the behavior of such flows, along with experimental studies, it is necessary to develop mathematical models, which adequately describe all the basic physical and chemical processes in a gas-droplet environment at different scales. In this paper we obtain solutions for the problem of two droplets collision, using solutions for cumulative jets, and propose droplet collision outcome criterion. This research will focus on the process of two interacting droplets coalescence into one and coalescence with subsequent separation into two or more droplets. A semi-analytical method has been developed for application of the solution of the cumulative jet problem to the problem of droplet collision. A differential equation has been obtained that describes the following possible outcomes of droplet collision: coalescence and coalescence with subsequent separation. A criterion for determining the outcome of on-head droplet collision has been obtained. In accordance with the developed criterion, the number and size of formed droplets are obtained. The effect of collision on moving droplet evaporation in a heated atmosphere was regarded. • Solutions for the problem of two droplets collision and fragmentation are obtained. • A differential equation has been obtained that describes droplet coalescence or atomization. • A criterion for droplet fragmentation has been obtained. • The effect of collision on moving droplet evaporation in a heated atmosphere was regarded. [ABSTRACT FROM AUTHOR]

Though single droplet impact dynamics was extensively investigated, the complex hydrodynamics involved in the simultaneous interaction of droplets with a loosely held dense solid particle on a hydrophobic substrate has received less attention. In this paper, the authors report the impingement response of a water droplet colliding on a non-fixed spherical steel particle placed on a hydrophobic surface and the subsequent creation of a particle-laden compound droplet. Utilizing the kinetic energy of the water drop, the heavy metal bead is picked up from the surface during the droplet bouncing. Here, a dense metal spherical mass is located on a hydrophobic substrate having contact angle, θ c = 140 ° and drop collides with a Weber number range of 8.20 ≤ We ≤ 38.07. During the droplet spreading, a thin film is developed between the particle and the hydrophobic plate due to capillary action and the particle is engulfed inside the droplet while it recoils, thereby a compound droplet is created. For instance, during the rebound of a composite drop, the metal bead, having one-third the mass of the droplet, is elevated to a height of 2.5 times its diameter at We = 24.5. Phenomenological models are developed for the prediction of compound droplet rebound height and the minimum Weber number required for the composite drop creation, and it exhibited good accord with experimental observations. These results shed more light on the self-cleaning mechanism involving dense particles and provided a promising strategy for the production of a solid–liquid composite droplet. [ABSTRACT FROM AUTHOR]

Background: Acoustically activatable perfluoropropane droplets (PD) can be formulated from commercially available microbubble preparations. Diagnostic transthoracic ultrasound frequencies have resulted in acoustic activation (AA) predominately within myocardial infarct zones (IZ). Objective: We hypothesized that the AA area following acute coronary ischemia/reperfusion (I/R) would selectively enhance the developing scar zone, and target bioeffects specifically to this region. Methods: We administered intravenous PD in 36 rats and 20 pigs at various stages of myocardial scar formation (30 minutes, 1 day, and 7 days post I/R) to determine what effect infarct age had on the AA within the IZ. This was correlated with histology, myeloperoxidase activity, and tissue nitrite activity. Results: The degree of AA within the IZ in rats was not associated with collagen content, neutrophil infiltration, or infarct age. AA within 24 hours of I/R was associated with increased nitric oxide utilization selectively within the IZ (P <.05 compared with remote zone). The spatial extent of AA in pigs correlated with infarct size only when performed before sacrifice at 7 days (r =.74, P <.01). Conclusions: Acoustic activation of intravenous PD enhances the developing scar zone following I/R, and results in selective tissue nitric oxide utilization. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic (EHD)-induced droplet emission is an efficient method for the production of micron- and submicron-sized droplets in technological applications. Existing studies propose several scaling laws to determine the size of the emitted droplet. However, they have usually focused on the tip streaming phenomena of a droplet when subjected to a uniform electric field. In most applications, a non-uniform distribution of the electric field is created owing to the nozzle-to-plate configuration. Here, we employ an arbitrary Lagrangian-Eulerian method to demonstrate the mechanism of the first droplet emission from an electrified liquid meniscus with a fixed volume hanging at the nozzle tip. The critical condition when tip streaming occurs is determined using our numerical results. A phase diagram in terms of the electric field and initial liquid volume is presented to obtain the commonly used jetting mode. The effects of the liquid volume, electric field strength and electrical conductivity of the liquid on the processes of jet formation and breakup are further investigated. We find a particularly non-monotonic dependence of the size of the emitted droplet on the electrical conductivity. These findings could be useful for generating microdroplets and improving injection frequency in EHD printing technology. [ABSTRACT FROM AUTHOR]

Asymmetric mechanical transducers have important applications in energy harvesting, signal transmission, and micro-mechanics. To achieve asymmetric transformation of mechanical motion or energy, active robotic metamaterials, as well as materials with asymmetric microstructures or internal orientation, are usually employed. However, these strategies usually require continuous energy supplement and laborious fabrication, and limited transformation modes are achieved. Herein, utilizing wettability patterned surfaces for precise control of the droplet contact line and inner flow, we demonstrate a droplet-based mechanical transducer system, and achieve multimodal responses to specific vibrations. By virtue of the synergistic effect of surface tension and solid-liquid adhesion on the liquid dynamics, the droplet on the patterned substrate can exhibit symmetric/asymmetric vibration transformation when the substrate vibrates horizontally. Based on this, we construct arrayed patterns with distinct arrangements on the substrate, and employ the swarm effect of the arrayed droplets to achieve three-dimensional and multimodal actuation of the target plate under a fixed input vibration. Further, we demonstrate the utilization of the mechanical transducers for vibration management, object transport, and laser modulation. These findings provide a simple yet efficient strategy to realize a multimodal mechanical transducer, which shows significant potential for aseismic design, optical molding, as well as micro-electromechanical systems (MEMS). Asymmetric mechanical transducers are pivotal in various applications; however, conventional methods demand continuous energy and intricate fabrication. Here, the authors demonstrate a droplet-based mechanical transducer utilizing wettability-patterned surfaces, enabling precise control of droplet dynamics. [ABSTRACT FROM AUTHOR]

Extensive research has demonstrated the potential of cell viscoelastic properties as intrinsic indicators of cell state, functionality, and disease. For this, several microfluidic techniques have been developed to measure cell viscoelasticity with high-throughput. However, current microchannel designs introduce complex stress distributions on cells, leading to inaccuracies in determining the stress--strain relationship and, consequently, the viscoelastic properties. Here, we introduce a novel approach using hyperbolic microchannels that enable precise measurements under a constant extensional stress and offer a straightforward stress--strain relationship, while operating at a measurement rate of up to 100 cells per second. We quantified the stresses acting in the channels using mechanical calibration particles made from polyacrylamide (PAAm) and found that the measurement buffer, a solution of methyl cellulose and phosphate buffered saline, shows strain-thickening following a power law up to 200 s-1. By measuring oil droplets with varying viscosities, we successfully detected changes in the relaxation times of the droplets and our approach could be used to get the interfacial tension and viscosity of liquid--liquid droplet systems from the same measurement. We further applied this methodology to PAAm microgel beads, demonstrating the accurate recovery of Young's moduli and the near-ideal elastic behavior of the beads. To explore the influence of altered cell viscoelasticity, we treated HL60 human leukemia cells with latrunculin B and nocodazole, resulting in clear changes in cell stiffness while relaxation times were only minimally affected. In conclusion, our approach offers a streamlined and time-efficient solution for assessing the viscoelastic properties of large cell populations and other microscale soft particles. [ABSTRACT FROM AUTHOR]

This study delves into the dynamics of generating microdroplets by impacting a droplet onto a micropore on superhydrophobic copper substrates. It identifies the necessary impact velocities for single microdroplet formation for each micropore and characterizes microdroplet size in relation to micropore diameter. The results underscore the significant role of viscosity, especially as the diameter of the micropore decreases. For micropores measuring 400 μm, an increase in viscosity up to 8 cP does not alter the critical impact velocities, while smaller diameters of 50 and 100 μm see a notable change in critical velocities with even minor increases in viscosity. Remarkably, the diameter of the microdroplet remains consistent regardless of changes in the liquid viscosity or impact velocity. This research showcases two practical uses of single microdroplets: printing on paper and fabricating microbeads. The insights gained from these findings pave the way for advancements in printing technology and microfabrication techniques. [ABSTRACT FROM AUTHOR]

The present work aims to investigate the effect of surface topology and wettability on the impacting droplet dynamics at different flow conditions. A multiphase lattice Boltzmann method (LBM) is employed for the simulation of interfacial dynamics. Firstly, the results obtained based on the present method for some benchmark two-phase flow problems are validated. Then, three surface topologies, including a flat substrate, semicircular cavity, and semicircular bump, are considered to get insight into the physical treatment of the impacting droplet. The present study shows that although the surface topology affects the spreading and rebounding processes of the impacting droplet, the hydrophilicity plays a significant role in the final form of the liquid phase and dictates a similar treatment for all the studied topologies. Considering different sizes for the bump, it is found that the shape of the droplet deforms almost the same immediately after the impaction for all the bump sizes and the spreading process is not affected by the wettability. However, the receding dynamics is significantly affected by the bump size and the wetting condition of the bump surface. It is found that the contact time is minimized by increment the bump size and hydrophobicity of the surface. [ABSTRACT FROM AUTHOR]

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Abstract Thouless charge pumps are quantum mechanical devices whose operation relies on topology. They provide the means for transporting quantum matter in space lattices with a single quantum precision. Contrasting space crystals that spontaneously break a continuous spatial translation symmetry and form crystals in space, time crystals have emerged as novel states of matter that organise into time lattices and spontaneously break a discrete time translation symmetry. The utility of Thouless pumps that enable topologically protected quantised transport of electrons and neutral atoms in spatial superlattices leads to the question if corresponding devices exist for time crystals. Here we show that topological pumps can be realised for time solids by transporting droplets of a liquid forward and backward in time lattices and we measure the topological index that characterises such pumping processes. By exploiting a synthetic time dimension, classical time crystals can circumvent the quantum tunnelling that underpins Thouless charge pumps. Our results establish topological pumping through time instead of space and pave the way for applications of time crystals. Key Points Periodically driven fluid droplets can be made to bounce persistently in a gravitational field and may undergo spontaneous time translation symmetry breaking forming classical time crystals. These classical time crystals can be pumped from one time site to another, and this pumping process is characterised by a topological index. Our observations establish a classical temporal counterpart to Thouless pumping of quantum particles in space lattices.

Understanding the intricate functions of membrane proteins is pivotal in cell biology and drug discovery. The composition of the cell membrane is highly complex, with different types of membrane proteins and lipid species. Hence, studying cellular membranes in a complexity-reduced context is important to enhance our understanding of the roles of these different elements. However, reconstitution of membrane proteins in an environment that closely mimics the cell, like giant unilamellar vesicles (GUVs), remains challenging, often requiring detergents that compromise protein function. To address this challenge, we present a novel strategy to manufacture GUVs from styrene maleic acid lipid particles (SMALPs) that utilises surfactant-stabilised droplets as a template. As a first step towards the incorporation of membrane proteins, this work focusses on the conversion of pure lipid SMALPs in GUVs. To evaluate the method, we produced a new form of SMA linked to fluorescein, referred to as FSMA. We demonstrate the assembly of SMALPs at the surfactant-stabilised droplet interface, resulting in the formation of GUVs when released upon addition of a demulsifying agent. The released vesicles appear similar to electroformed vesicles imaged with confocal light microscopy, but a fluorescein leakage assay and cryo-TEM imaging reveal their porous nature, potentially as a result of residual interactions of SMA with the lipid bilayer. Our study represents a significant step towards opening new avenues for comprehensive protein research in a complexity-reduced, yet biologically relevant, setting.

Arcing is a mechanism of dust production and erosion in fusion devices. The masses and velocities of tungsten (W) particles produced by arcing is of special interest given that W is used as wall material in current experimental devices and is planned for use in new machines such as ITER. This work presents a new technique for evaluation of the parameters of particles produced by vacuum arcs in laboratory conditions based on direct observation with a high-speed video camera. Tracking of particle trajectory provides a measurement of velocity and angle of emission. Additionally, the emitted thermal radiation of the particles is measured and its evolution over time is compared with a model of its cooling in order to obtain a measurement of size and temperature at the moment of emission for each individual particle. Surprisingly, temperature measurements reveal the production of initially solid particles. The newly established video technique allows automated measurement of a high number of particles in order to obtain distributions of the particle parameters.

3D droplet-based bioprinting technology is an innovative and time-saving additive manufacturing method, which enables spatial patterning of biological materials and biochemical and living cells for multiple clinical and research applications. Understanding the criteria that control droplet spreading behavior during droplet impact is of great importance in controlling printing resolution and optimizing the printing performance. In this experimental work, the spreading of 3D printed cell-laden droplets was studied with side and bottom view images. The droplets contain 1 × 10 7 cells/ml input cell concentration and corresponding Φ = 0.52 % cell volume fraction and impact onto a flat hydrophilic substrate, a pre-printed droplet, and a pre-printed thin liquid film. The cell-laden droplet impact morphology, the maximum spreading factor, and the cell distribution under different printing conditions (89 < W e < 365 , 174 < R e < 414) in a 3D bioprinting process were characterized. It was found that on the hydrophilic flat substrate, the cells homogeneously distributed into a disk structure. The maximum spreading factor, β max , can be well described by the correlation formulas based on the energy balance and volume conservation. A power-law scaling formula was found to describe the maximum spreading in terms of the Weber number for cell-laden droplet impact on both pre-printed droplets and thin liquid films, where β max ∝ W e 0.25 . Input cell concentration, up to 1 × 10 7 cells/ml, was found to have negligible effect on the maximum droplet spreading factor in a 3D bioprinting process. [ABSTRACT FROM AUTHOR]

Freezing impinged water droplets on glass surfaces cause serious problems such as reduced visibility of traffic lights and surveillance cameras. Droplets in the air associated with these issues are often at subzero temperatures. However, experimental results on the freezing of precooled impinged droplets are limited. In this study, we measured the freezing of precooled and impinged water droplets on cold glass surfaces. Two types of lattice-patterned microscale grooves were formed on glass surfaces to reduce the contact area of droplets and growth of frosts, which contributed to droplet freezing. In addition, the surfaces were coated with a silane coupling agent to further reduce the contact area. We analyzed the images of droplets captured using a high-speed video camera. The results of the linear relationships between the frozen droplet height, freezing front velocity, and freezing time (for the impinged droplets) indicated that the grooves and coating were effective in retarding the freezing of impinged droplets. This retardation was more evident for frost-free glass surfaces, and it was less evident for precooled droplets. Moreover, a simple heat transfer analysis was conducted to effectively estimate the overall heat flux and freezing front velocity. The sublimation of frost (adjacent to the impinged droplets) and supercool elimination of the precooled droplets significantly contributed to the heat flux and caused an increase in the freezing front velocity. [ABSTRACT FROM AUTHOR]

Interactions at the interface between atmospheric pressure plasmas and liquids are being investigated to address applications ranging from nanoparticle synthesis to decontamination and fertilizer production. Many of these applications involve activation of droplets wherein the droplet is fully immersed in the plasma and synergistically interacts with the plasma. To better understand these interactions, two-dimensional modeling of radio frequency (RF) glow discharges at atmospheric pressure operated in He with an embedded lossy dielectric droplet (tens of microns in size) was performed. The properties of the sheath that forms around the droplet were investigated over the RF cycle. The electric field in the bulk plasma polarizes the dielectric droplet while the electron drift in the external electric field is shadowed by the droplet. The interaction between the bulk and sheath electric fields produces a maximum in E/N (electric field/gas number density) at the equator on one side of the droplet where the bulk and sheath fields are aligned in the same direction and a minimum along the opposite equator. Due to resistive heating, the electron temperature Te is maximum 45° above and below the equator of the droplet where power deposition per electron is the highest. Although the droplet is, on the average, negatively charged, the charge density on the droplet is positive on the poles and negative on the equator, as the electron motion is primarily due to diffusion at the poles but due to drift at the equator. [ABSTRACT FROM AUTHOR]

Multiphase Navier–Stokes simulations of liquid metal droplets colliding with solid plasma-facing components are carried out in conditions representative of magnetic confinement fusion devices. The flow dynamics of the spreading liquid are examined to assess the relative importance of various physical processes in the impact energy budget. Contributions from the initial droplet surface energy and the solidification-induced momentum sink are shown to be of great importance in determining the final geometry of the frozen spatter. Semi-empirical scaling laws available in the literature are adapted to provide robust predictions of the flattening ratio that can be extrapolated to general fusion-relevant impact scenarios.

AbstractThis study enhances the understanding of virus removal efficiency by filters, crucial for predicting respiratory disease transmission risk and guiding outbreak prevention. Current research often neglects the survival behaviour of pathogens. Addressing this, our research develops a novel approach anchored in medical experimental data. A mathematical model was established to depict the dynamic changes in particulate concentration within non-centralized air-conditioned rooms, considering indoor and outdoor concentrations, natural ventilation, and filter dynamics. The model’s reliability was affirmed through particle and aerosolized pathogen filtration experiments, showing an R2 value over 0.99, indicating strong agreement with empirical data. Analysis of filter operation, both with and without infection sources during epidemics, reveals that the use of split air conditioners and filters significantly reduces pathogen concentration. Pathogens trapped in filters undergo natural decay, considerably lowering transmission risk compared to airborne states. This research offers a scientifically grounded, precise methodology for evaluating respiratory disease transmission risks, contributing substantially to public health management.

In recent years, liquid–solid triboelectric nanogenerator (LSTENG) has attracted great attention. However, its low average power density and long charging time limit the practical application of this technique. Here, for the first time, a liquid–solid triboelectric nanogenerator combined with external charge‐pumping method (ECP‐LSTENG) is proposed. Compared to traditional LSTENGs, a charge storage capacitor is added in this ECP‐LSTENG to store the output charges from the pumping generator. Then, a charge extraction capacitor is formed by the spreading and shrinking processes of falling droplet, while the charging and discharging process between charge storage and extraction capacitors can generate displacement current output for external circuit. Meanwhile, it is found that a special charged droplets adhesion phenomenon happens at the liquid–solid interface, which seriously hinders the continuous output of ECP‐LSTENG. To overcome this limitation, a special coaxial deceleration commutation component is designed to ensure continuous output of the ECP‐LSTENG. Finally, the peak power density of a droplet (50 µL) reaches 231.8 W m−2, surpassing the highest research record to date by 1.43 times. This ECP‐LSTENG provides a different approach for the future development of large‐scale integrated raindrop generators for efficient raindrop energy harvesting. [ABSTRACT FROM AUTHOR]

Manipulating oil droplets in an aqueous solution is highly desirable for organic multiphase liquid separation. Despite substantial works in the realm of organic multiphase liquid manipulation and separation, the ultrafast transportation and efficient and precise separation of these liquids, especially those with varied surface tensions, encounters significant challenges due to little driving forces. To address this issue, a semi-conical structure with pine-needlelike features and incorporated wedge-shaped grooves is fabricated, which could support the ultrafast transport and separation of organic droplets. For pre-wetted superhydrophobic surfaces, organic liquids with lower surface tension can be transported at a speed of 305.6 mm/s. The Laplace pressure difference caused by the conical structure determines the direction of transport of organic liquids, and the capillary force caused by flat wedge-shaped grooves increases the transport speed of organic droplets on the surface. Based on the characteristics of "differential" transportation and directional transportation, the separation of mixed organic liquids is realized. This biomimetic design concept will pave a path for microfluidics, liquid manipulation, and the separation of various organic liquids. [ABSTRACT FROM AUTHOR]

The total evaporation rate due to a volatile capillarity-dominated droplet diffusively evaporating into the surrounding gas is a critically important quantity in industrial and engineering applications such as Q/OLED screen manufacturing. However, the analytical expression in terms of integrals in toroidal coordinates can be unwieldy in applications, as well as expensive to compute. Therefore, simple yet highly accurate approximate solutions are frequently used in practical settings. Herein we present a new approximate form that is both accurate and fast to compute, but also retains the correct asymptotic behaviour in the key physical regimes, namely hydrophilic and superhydrophobic substrates, and a hemispherical droplet. We illustrate this by comparison to several previous approximations and, in particular, illustrate its use in calculating droplet lifetimes, as well as approximating the local evaporative flux. [ABSTRACT FROM AUTHOR]

The transportation and control of microfluidics have an important influence on the fields of biology, chemistry, and medicine. Pump systems based on the electrocapillary effect and room-temperature liquid metal droplets have attracted extensive attention. Flow rate is an important parameter that reflects the delivery performance of the pump systems. In the systems of previous studies, cylindrical structures are mostly used to constrain the droplet. The analysis and quantitative description of the influence of voltage frequency, alternating voltage, direct current voltage bias, and solution concentration on the flow rate are not yet comprehensive. Furthermore, the systems are driven by only one droplet, which limits the increase in flow rate. Therefore, a pump with a cuboid structure is designed and the droplet is bound by pillars, and the flow rate of the pump is increased by more than 200% compared with the cylindrical pump. For this structure, the mechanism of various factors on the flow rate is analyzed. To further enhance the flow rate, a pump system with multi-droplets is proposed. Moreover, the expression of flow velocity of the solution on the surface of each droplet and the relationship between the flow rate, alternating voltage, and the number of droplets are deduced. Finally, the potential of applying the multi-droplet cuboid pump system in drug delivery and analytical chemistry is demonstrated. Additionally, the core of the pump, the droplet area, is modularized, which breaks the overall structural limitations of the liquid metal pump and provides ideas for pump design. [ABSTRACT FROM AUTHOR]

An approach based on the direct numerical solution of the Boltzmann kinetic equation is proposed to take into account the influence of homogeneous nucleation on the mass transfer intensity in the evaporation/condensation (recondensation) problem. On the basis of the comparison between the scales of the formation time of a critical-size droplet and the time of supersaturation propagation, it is shown that it is possible to describe the considered problem in two stages, i.e., without taking into account the influence of droplets at the first stage and with taking into account their influence at the second stage. The calculation results show that, in the case of immobile droplets, there is a strong influence of bulk condensation on the intensity of the evaporation/condensation process. [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional compound droplet collision numerical model is established by using volume of fluid. The morphological evolution of compound hollow droplets affected by high-speed solid droplet was studied in detail. Parameterized analysis is conducted on the velocity VS, center distance ϕ , and diameter ζ of high-speed small droplets. Through the analysis of the compound droplets flow field, it is found that the broken mode of compound droplets is caused by the increase in Pn (dimensionless pressure) and θ (velocity angle). The results show that the surface Pn of compound droplets is positively correlated with the velocity VS of high-speed small droplets, while there is a more complex relationship with the dimensionless center distance ϕ and dimensionless diameter ζ. When the values of ϕ and ζ are appropriate, Pn can reach its maximum value. The broken mode of compound droplets can be divided into three categories: shear deformation, shear crushing, and violent crushing. [ABSTRACT FROM AUTHOR]

Droplet coalescence process is important in many applications and has been studied extensively when two droplets are surrounded by gas. However, the coalescence dynamics would be different when the two droplets are surrounded by an external viscous liquid. The coalescence of immiscible droplets in liquids has not been explored. In the present research, the coalescence of two immiscible droplets in low- and high-viscosity liquids is investigated and compared with their miscible counterparts experimentally. The coalescence dynamics is investigated via high-speed imaging, and theoretical models are proposed to analyze the growth of the liquid bridge. We find that, the liquid bridge r evolves differently due to the constraint from the triple line in the bridge region, which follows r ∝ t 2 / 3 for low-viscosity surroundings. While for high-viscosity surroundings, the liquid bridge grows at a constant velocity u r which varies with the surrounding viscosity μ s as u r ∝ μ s 1 / 2. In the later stage of the bridge growth, the bridge evolution again merges with the well-established power-law regime r ∝ t 1 / 2 , being either in low or high-viscosity liquids. Moreover, a new inertia-viscous-capillary timescale is proposed, which unifies the combined influence of inertia, viscous, and capillary forces on the evolution of the liquid bridge in liquid environments, highlighting the joint role of inertia and viscous resistance in the coalescence process. [ABSTRACT FROM AUTHOR]