Drop Formation Research Articles

Inkjet printing of sustainable ZTO/AlOx thin film transistors

Abstract Even though printed metal oxide thin film transistors (TFTs) have been a central topic of research in the past decade, the most notable results still require scarce elements such as gallium and indium, or high annealing temperatures (≥ 400 °C) when used non-critical raw materials such as zinc and tin.
In this work, safe, abundant and inexpensive materials such as zinc, tin and aluminum are explored to reach low-cost thin films and devices with both the semiconductor and dielectric layers deposited by inkjet printing and annealed at lower temperatures (300 °C). Alumina (AlOx) and zinc tin oxide (ZTO) inks containing a theoretical optimal V% of ethylene glycol (EG) were optimized for production of uniform and reproducible AlOx/ZTO thin film layers. Common ink parameters (such as the reverse Ohnesorge, capillary, Webber and Reynolds numbers) were evaluated and compared with relevant literature on inkjet drop formation mechanisms. Inks within theoretical optimal parameter values were printing optimized in terms of drops per inch, number of layers, UV substrate surface activation, print speed, and post annealing. A high-quality dielectric of two alumina layers was printed, having a breakdown field above 2.93 ± 0.33 MV.cm-1, and a dielectric constant of 7.74 ± 0.73 at 1 kHz. Thin film transistors (TFTs) of inkjet printed (IJP) ZTO/AlOx layers were produced with a maximum IOn/IOff ratio of 103 and a saturation mobility of 2.2 cm2.V-1.s‑1. This approach not only advances the field of printed electronics but also addresses concerns related to material scarcity, thermal budget, and production costs.

Electrospray modes of liquids in electrohydrodynamic atomization: A review

Liquid is sprayed from a capillary tube and further disperses into fine drops in various means, when subjected to an externally electric field, where the process of liquid jet formation and breakup into drops is usually named as electrohydrodynamic atomization or electrospray (ES). Electrospray has been extensively applied into many fields because uniform and highly charged drops, easy controllability in size and motion, and various ES modes are available to match the requirements of various applications. In present work, recent progresses in theory and numerical work to explain electrospray structure and drop formation were summarized. According to the geometry of liquid ejection and its further disintegration, main ES modes including dripping, micro-dripping, spindle, cone-jet, multi-jet, and simple-jet have been designated. The transformation of ES modes due to variation of electric potential, liquid flow rate, and physical parameters, the formation of curved liquid surface, and jet fragmentation behavior in these ES modes were also reviewed, as well as generated drops dynamics. In a rational range of flow rate, dripping, micro-dripping, spindle, cone-jet, multi-jet modes successively emerge with an increase in electric potential, and otherwise, an irregular instability may occur. In addition, the simple jet mode occurs in a relatively large flow rate. The insight into ES modes may fully understand mechanism and technology of electrospray and further promote more extensive application in industrial fields.

Dynamic behavior of melt electrospinning of blended polypropylene

Melt electrospinning is a promising process for fiber production without the need for solvents and with potential applications in various fields. In this study, we investigated the dynamic behavior of melt electrospinning under different blending ratios and process conditions. We used high melt flow index polypropylene and low molecular weight polypropylene, which were blended to lower the melt viscosity, and fibers were successfully manufactured through the melt electrospinning process. The effects of blending ratio and applied voltage on jet and drop formation, as well as fiber morphology, were examined. The results showed that blending low-molecular-weight polypropylene significantly influenced the jet and drop areas, leading to fluctuations in jet morphology. The size of the applied high voltage also had a high effect on the fiber diameter. Additionally, the viscosity reduction achieved through blending allowed for continuous jet formation and improved fiber production. These results provide valuable insights into controlling the process parameters and blending ratios in melt electrospinning, enabling the establishment of stable electrospinning conditions and precise control of fiber diameter.

Investigation of the insoluble impurities' impact on flow boiling heat transfer in aluminum microchannel heat exchangers

Microchannel flat-tube heat exchangers are known for their high heat transfer efficiency and compact size. In practical applications, the predominantly adverse influence of insoluble impurities on the condensation process necessitates further exploration into the underlying mechanisms affecting the flow boiling process. The effect of common insoluble impurities on the flow boiling of R410A refrigerant in a microchannel flat-tube heat exchanger has been investigated, and variation of the impurity volume fraction on heat transfer, mass transfer, pressure drop, and bubble formation are analyzed. Additionally, an adaptive modification method for the mass transfer factor is proposed. The numerical model of flow boiling heat transfer in a microchannel is validated through experimental data and empirical correlations. Thermo-hydraulic performance evaluation incorporates efficiency index and area goodness ratio metrics. Results reveal that the presence of insoluble impurities complicates the boiling heat transfer mechanism by influencing bubble evolution and multiphase flow patterns. Air impurities at a volume fraction not exceeding 5% prove beneficial for enhancing flow boiling efficiency in microchannels; however, a 38.5% decrease in efficiency index is observed with 1% oil impurities present. Optimal thermo-hydraulic performance is achieved with approximately 2%–3% water impurities.

Size and velocity of jet drops produced by bursting bubbles at the interface of a water jet

Bursting bubbles at the free surface of aerated faucet water jets may spread pathogens through the released droplets. Many studies focused on the production of jet drops from bursting bubbles at a planar interface, particularly for the first jet drop. The extent to which previous findings apply to bubbles in aerated jets remains unknown. In this study, we produce a wide range of bubble size distributions within different jet diameters and characterize the diameter and velocity of jet drops released from individually bursting bubbles. Several similarities with the planar case are recovered, such as the overall dependence of the jet drop diameter and bursting dynamics on the bubble diameters and the formation of secondary jet drops. However, we observe asymmetries in the ejection of the droplets, and droplets ejected horizontally appear to have the highest ejection velocity among all jet drops. By modeling the evolution of the ejected drops for the different bubble size distributions, we find that for a mean Laplace number Labub=ρwσwRbubμw2≲6×104, a fraction of the drops ejected can become airborne. Droplets deposit within 9 cm for a mean Labub≲2.1×104 and within 33 cm for a mean 2.1×104≲Labub≲1.8×105 from a faucet jet, assuming a countertop situated 20 cm below the faucet outlet. A bubble size distribution with a mean Labub of 6×104 would minimize both the risk of airborne pathogen transmission and that resulting from surface contamination.

Formation of sodium-alginate droplets in an X-microdevice: Characterization of the pinching efficiency

Experiments and simulations are used jointly to gain a comprehensive insight into the pinching mechanism that generates alginate droplets in an X-microdevice operating in a hydrodynamic flow-focusing configuration. The X-microdevice is fed with an aqueous alginate solution into one inlet channel, while sunflower oil and Span80 are fed into the other two inlet channels. The use of the adaptive mesh refinement and volume of fluid method allows accurate tracking of the interface in numerical simulations. The sensitivities of numerical predictions to the contact angle and the surface tension are estimated through dedicated sets of simulations. Subsequently, numerical simulations and experiments are compared for different flow rates with a satisfactory agreement. We observe that the pinch-off mechanism may lead to the formation of several satellite drops in addition to the main droplet. A pinching performance indicator is suggested based on the amount of alginate that is encapsulated in the main droplet. The effect of operating conditions on the pinching efficiency, frequency, and droplet diameter is discussed to provide valuable information to optimize the droplets production. The pinching efficiency is closely related to the length and diameter of the liquid thread. At low flow rates, a short liquid thread is observed. This leads to the formation of few satellites and, thus, to high pinching efficiency but low droplet production. Increasing the dispersed-phase flow rate slightly reduces the efficiency but significantly increases the production.

Spray-assisted drop formation liquid-phase microextraction for the determination of sertraline in environmental water samples with matrix-matching calibration in GC–MS

Sertraline is used as an antidepressant drug for the treatment of psychiatric disorders, including anxiety and depression. In the current study, a simple and effective method was developed for the sensitive monitoring of sertraline in water samples using a GC–MS system. The spray-assisted droplet formation liquid-phase microextraction (SADF-LPME) method was used as a sample preparation method for the enrichment of analytes. Accordingly, dichloromethane was used as an extraction solvent and easily dispersed into a sample/standard solution using a lab-made modified spray device without using a dispersing solvent. The significant factors affecting the SADF-LPME efficiency, including sample pH, mixing conditions, extraction solvent type, and spray cycle, were univariately optimized to ascertain the extraction performance and applicability of the system. Under the optimized conditions, the plotted calibration curve of the method was linear in the range of 100.2–2011.7 µg/kg (mass-based standard preparation) with a good correlation coefficient (R2) of 0.9997. The detection and quantification limits of method were found to be 37.5 and 125 µg/kg, respectively. Validation of the method was successfully carried out using different tap water samples and applying a matrix-matching calibration strategy. The acceptable percent recoveries were recorded between 77.3 and 133.7%, with high repeatability. The recommended method is an alternative and fast extraction method with several advantages, including a simple experimental process, good dispersibility, and fast and superior extraction performance. It can be readily applicable to the monitoring and quantification of sertraline in tap water samples with good precision and accuracy.

Shell-Core Microbeads Loaded with Probiotics: Influence of Lipid Melting Point on Probiotic Activity.

Probiotics have many beneficial physiological activities, but the poor stability during storage and gastrointestinal digestion limits their application. Therefore, in this study, a novel type of shell-core microbead for loading probiotics was prepared through high-precision concentric drop formation technology using gelatin as the shell material and lipids as the core material. The microbeads have a regular spherical structure, uniform size, low moisture content (<4%) and high probiotic activity (>9.0 log CFU/g). Textural testing showed that the hardness of the medium-chain triglyceride microbeads (MCTBs), cocoa butter replacer microbeads (CBRBs) and hydrogenated palm oil microbeads (HPOBs) increased gradually (319.65, 623.54, 711.41 g), but their springiness decreased (67.7, 43.3, 34.0%). Importantly, lipids with higher melting points contributed to the enhanced stability of probiotics during simulated digestion and storage. The viable probiotic counts of the HCTBs, CBRBs and HPOBs after being stored at 25 °C for 12 months were 8.01, 8.44, and 8.51 log CFU/g, respectively. In the simulated in vitro digestion process, the HPOBs resisted the destructive effects of digestive enzymes and gastric acid on probiotics, with a reduction in the probiotic viability of less than 1.5 log CFU/g. This study can provide new ideas for the preparation of intestinal delivery probiotic foods.

Piezoelectric-synchronized step emulsification for facile generation of microdroplet library with fluid-independent drop size regulation regime

Microdroplets play a crucial role in various applications based on microfluidics, including biomedicine, materials synthesis, and analytical chemistry. However, there is still an urgent need for a microdroplet preparation method that is simple in design, precise in droplet size control and meanwhile independent of the properties of the fluid. Here, we present a piezoelectric-synchronized step emulsification method. The drop formation process can be synchronized by the introduced periodic vibration via the piezoelectric element, which occurs in a specific frequency range determined by a dimensionless parameter. The competing between the step emulsification regime and the piezoelectric-triggered local flow rate fluctuation leads to various microscopic flow behavior. A novel instantaneous jetting regime is found to be responsible for the extended achievable drop size range. By combining the piezoelectric step emulsification and the XY stage control, we achieve facile production of microdroplet and hydrogel microsphere library in well plates, which is promising to be integrated as a low-cost drop-generating technique into bioassay instruments.

Ground-based cloud microphysical observations at Mount Lu in the East Asian monsoon region from 2015 to 2020

Ground-based cloud microphysical observations were continuously conducted at Mount (Mt.) Lu site from 2015 to 2020, which is located in the East Asian monsoon areas of eastern China. The statistical characteristics of cloud microphysics under different meteorological conditions were analyzed by using visibility, cloud droplet and raindrop size distribution data, and meteorological variables. The mean cloud droplet number concentration (Nc), liquid water content (LWC) and effective diameter (De) are 151 cm−3, 0.08 g m−3 and 11.4 μm, respectively. Nc and LWC observed at Mount Lu are lower than the observation results of cloud from other mountain stations all over the world. Broader cloud droplet spectra are correlated with higher temperatures and lower wind speeds. The clouds are classified into nonprecipitating, lightly-raining and raining clouds. Statistics show that lightly-raining and raining clouds account for 66% of all clouds. Nc and LWC of lightly-raining (drizzling) clouds are highest, while spectral width of raining clouds is largest. Spectral dispersion of raining clouds converges to the narrow range of 0.4–0.7. Notably, medium sized cloud droplets (11–40 μm) promote the formation of large cloud droplets (40–50 μm, pre-drizzle size) and drizzle drops which initiate the auto-conversion from condensation to collision-coalescence growth. This study relying on in-situ continuous cloud observation from mountain station are helpful to understand cloud microphysical structures in East Asian monsoon region, and fitting parameters also provide observational evidence for numerical models.

Improving Supercooled Water Forecast Through Real‐Time Aerosol Input: A Case Study

AbstractAccurately simulating and forecasting supercooled water has been crucial for addressing the threat of aircraft icing. This study utilized the Weather Research and Forecast model and Aerosol‐Aware Thompson‐Eidhammer microphysics (TE14) scheme to simulate supercooled water properties. Three high‐resolution experiments were conducted to explore the impact of increased model resolution and different aerosol initial conditions. The synoptic‐scale characteristics and cloud extent were well‐matched between observations and the model simulation, which established a background for supercooled water comparisons. Microphysical characteristics of supercooled droplets and the formation of supercooled large drops demonstrated the TE14 scheme's reasonable simulation of supercooled water microphysics under different aerosol loadings. In situ aircraft measurements were used to validate the simulated supercooled water properties. Results highlighted the sensitivity of supercooled water simulation to aerosol number concentration via droplet activation in the scheme. The choice for the aerosol initial condition could result in a significant underestimation or overestimation of supercooled water number concentration, consequently leading to biased estimations of droplet size. Incorporating real‐time forecast aerosol data improved the simulation by increasing cloud droplet number concentration and reducing droplet size. These findings underscored the importance of aerosols via droplet activation in accurately simulating cloud water properties and emphasized their role in forecasting aircraft icing hazards.

Three-phase equilibria of hydrates from computer simulation. II. Finite-size effects in the carbon dioxide hydrate.

In this work, the effects of finite size on the determination of the three-phase coexistence temperature (T3) of the carbon dioxide (CO2) hydrate have been studied by molecular dynamic simulations and using the direct coexistence technique. According to this technique, the three phases involved (hydrate-aqueous solution-liquid CO2) are placed together in the same simulation box. By varying the number of molecules of each phase, it is possible to analyze the effect of simulation size and stoichiometry on the T3 determination. In this work, we have determined the T3 value at 8 different pressures (from 100 to 6000bar) and using 6 different simulation boxes with different numbers of molecules and sizes. In two of these configurations, the ratio of the number of water and CO2 molecules in the aqueous solution and the liquid CO2 phase is the same as in the hydrate (stoichiometric configuration). In both stoichiometric configurations, the formation of a liquid drop of CO2 in the aqueous phase is observed. This drop, which has a cylindrical geometry, increases the amount of CO2 available in the aqueous solution and can in some cases lead to the crystallization of the hydrate at temperatures above T3, overestimating the T3 value obtained from direct coexistence simulations. The simulation results obtained for the CO2 hydrate confirm the sensitivity of T3 depending on the size and composition of the system, explaining the discrepancies observed in the original work by Míguez et al. [J. Chem Phys. 142, 124505 (2015)]. Non-stoichiometric configurations with larger unit cells show a convergence of T3 values, suggesting that finite-size effects for these system sizes, regardless of drop formation, can be safely neglected. The results obtained in this work highlight that the choice of a correct initial configuration is essential to accurately estimate the three-phase coexistence temperature of hydrates by direct coexistence simulations.

Numerical study of drop dynamics for inkjet based 3D printing of pharmaceutical tablets

Interest in 3D printing has been growing rapidly especially in pharmaceutical industry due to its multiple advantages such as manufacturing versatility, personalization of medicine, scalability, and cost effectiveness. Inkjet based 3D printing gained special attention after FDA’s approval of Spritam® manufactured by Aprecia pharmaceuticals in 2015. The precision and printing efficiency of 3D printing is strongly influenced by the dynamics of ink/binder jetting, which further depends on the ink’s fluid properties. In this study, Computational Fluid Dynamics (CFD) has been utilized to study the drop formation process during inkjet-based 3D printing for piezoelectric and thermal printhead geometries using Volume of Fluid (VOF) method. To develop the CFD model commercial software ANSYS-Fluent was used. The developed CFD model was experimentally validated using drop watcher setup to record drop progression and drop velocity. During the study, water, Fujifilm model fluid, and Amitriptyline drug solutions were evaluated as the ink solutions. The drop properties such as drop volume, drop diameter, and drop velocity were examined in detail in response to change ink solution properties such as surface tension, viscosity, and density. A good agreement was observed between the experimental and simulation data for drop properties such as drop volume and drop velocity.

Multi-component electro-hydro-thermodynamic model with phase-field method. I. Dielectric

We derive a multi-component electro-hydro-thermodynamic (EHTD) model for both leaky and perfect dielectric materials via the principle of energy dissipation. Differing from previous electro-hydrodynamic (EHD) models focusing on fluid mechanics, the electrochemical potential expression is revised and the electric field related term is added to the mass and momentum conservation equations. Resulting from this new correction, we obtain a generalized electro-hydro-thermodynamic stress tensor including the effect of Kortweg and Maxwell stresses. We observe the magnificent impact of the electric field on the thermodynamic equilibrium of the system in two aspects: (i) phase diagram modified by the electric field; (ii) electric field induced surface tension decrease/increase. In addition, the proposed model is validated and shows well conformity with previous analytical solutions in literature. As exemplary applications, we perform phase-field simulations to study the ternary droplet coalescence and spinodal decomposition and observe several typical morphological transformations, such as satellite drop formation and Quincke rotation.

Influence of surface and edge profile of a spinning disc on its atomization characteristics in direct drop mode

A spinning disc in direct drop regime is useful for contacting applications using one stream as drops. Here, we presenta systematic probe into the effect ofseveral edge and surface modification strategies on droplet characteristics. The characteristics of interest in this study are mean sizes of primary and secondary drops and their spread around respective mean values, and the evenness of circumferential distribution of drops. Exposure controlled static imaging is used to obtain blur free images in high resolution. Concentric grooving on surface offered stable film under limited flow condition, improves circumferential distribution, and significantly eliminates secondary drop formation. Serration at the disc edge controls the pitch of the drop detachment points, a feature naturally unique to only ligament mode. A new scale named maldistribution index (MI) is proposed to quantify circumferential distribution of released droplets.

Collision of two drops moving in the same direction

The collision dynamics of two drops of the same liquid moving in the same direction has been studied numerically. A wide range of radius ratios of trailing drop and leading drop (Rr) and the velocity ratios (Ur) have been deployed to understand the collision outcomes. A volume of fluid based open-source fluid flow solver, Basilisk, has been used with its adaptive mesh refinement feature to capture the nuances of the interface morphology. The simulations are analyzed for the evolving time instances. Different collision outcomes, such as coalescence and reflexive separation with and without the formation of satellite drops, have been observed for various combinations of Ur and Rr. The study analyzes the evolution of kinetic energy and surface energy before and after the collision for plausible outcomes. The collision outcomes are depicted on a regime map with Ur−Rr space, highlighting distinct regimes formed due to variations in relevant governing parameters.

DETERMINATION OF THE DROP SIZE AND DISTRIBUTIONS IN SWIRL INJECTION IN CROSS FLOWS, IMPINGING, AND EFFERVESCENT INJECTORS

We have extended the primary atomization analysis to swirl injection in cross flows, impinging, and effervescent injectors. Using the integral form of the conservation equations, the drop size can be expressed in terms of injection and fluid parameters, the main variable being the liquid and gas velocities. Using the measured velocities as inputs to this &lt;i&gt;D&lt;/i&gt;&lt;sub&gt;32&lt;/sub&gt;-equation, good agreements with experimental data are found for the drop size in the three spray geometries. Underlying physical mechanisms for the drop formation are also revealed from the analysis. The aerodynamic interaction between the swirl spray and cross flow results in reduction in momentum, with a corresponding decrease in kinetic energy that appears as surface tension of energy of many small droplets. Similarly, cancellation of the lateral momentum in impinging jets and internal deceleration in effervescent injectors are the key primary atomization routes. The use of the analytical drop size-velocity correlation has also been demonstrated for swirl sprays in cross flows. Therefore, this approach can be used to predict the drop size and distributions in different spray geometries, with appropriate changes in the velocity input terms and fluid properties.

Live Imaging of 3D Hanging Drop Arrays through Manipulation of Light-Responsive Pyroelectric Slippery Surface and Chip Adhesion.

Three-dimensional (3D) hanging drop cell culture is widely used in organoid culture because of its lack of selection pressure and rapid cell aggregation. However, current hanging drop technology has limitations, such as a dependence on complex microfluidic transport channels or specific capillary force templates for drop formation, which leads to unchangeable drop features. These methods also hinder live imaging because of space and complexity constraints. Here, we have developed a hanging drop construction method and created a flexible 3D hanging drop construction platform composed of a manipulation module and an adhesion module. Their harmonious operation allows for the easy construction of hanging drops of varying sizes, types, and patterns. Our platform produces a cell hanging drop chip with small sizes and clear fields of view, thereby making it compatible with live imaging. This platform has great potential for personalized medicine, cancer and drug discovery, tissue engineering, and stem cell research.

The Role of Binders for Water-Based Anode Dispersions in Inkjet Printing

Binders play a pivotal role in the production and the operation of lithium-ion batteries. They influence a number of key dispersion characteristics and battery parameters. In the light of growing interest in additive manufacturing technologies, binders were found to decisively govern the processability due to the induced complex non-Newtonian behavior. This paper examines the relevance of various binder derivatives for aqueous graphite dispersions that can be employed in inkjet printing. Two different carboxymethyl cellulose (CMC) derivatives with strongly deviating molecular weights were employed. The impact of the inherent polymer characteristics on the processability and the electrode characteristics were explored. Therefore, miscellaneous studies were carried out at the dispersion, the electrode, and the cell levels. The results revealed that the CMC with the lower molecular weight affected most of the studied characteristics more favorably than the counterpart with a higher molecular weight. In particular, the processability, encompassing drop formation and drop deposition, the cohesion behavior, and the electrochemical characteristics, were positively impacted by the low-molecular-weight CMC. The adhesion behavior was enhanced using the high-molecular-weight CMC. This demonstrates that the selection of a suitable binder derivative merits close attention.

Drop model of integer and fractional quantum Hall effects

In this paper, we present a drop model for integer and fractional quantum Hall effects (FQHE). We show that the two-dimensional electron gas breaks up into regions with filling factors [Formula: see text] and [Formula: see text] in the disk geometry, and the formation of drops with a finite number of electrons is possible. Sequences of filling fractions are constructed on the basis of experimental data. For all sequences, there are initial FQHE states, which correspond to a drop with five electrons. The remaining FQHE states are composite states of a drop with five electrons and one or more pairs of electrons.