Small Droplets Research Articles

Compression and fracture of ordered and disordered droplet rafts.

We simulate a two-dimensional array of droplets being compressed between two walls. The droplets are adhesive due to an attractive depletion force. As one wall moves toward the other, the droplet array is compressed and eventually induced to rearrange. The rearrangement occurs via a fracture, where depletion bonds are quickly broken between a subset of droplets. For monodisperse, hexagonally ordered droplet arrays, this fracture is preceded by a maximum force exerted on the walls, which drops rapidly after the fracture occurs. In small droplet arrays a fracture is a single well-defined event, but for larger droplet arrays, competing fractures can be observed. These are fractures nucleated nearly simultaneously in different locations. Finally, we also study the compression of bidisperse droplet arrays. The addition of a second droplet size further disrupts fracture events, showing differences between ideal crystalline arrays, crystalline arrays with a small number of defects, and fully amorphous arrays. These results are in good agreement with previously published experiments.

The Development and Analysis of a Multistage Spraying Method for Liquids in an Ultrasonic Field

Spraying various liquids (primarily aqueous solutions of various substances) is widely used in various technological processes. For most of them, high dispersibility and a narrow droplet size distribution are essential. Ultrasonic spraying allows these parameters to be achieved. However, the higher the dispersity of droplets produced by ultrasonic spraying, the lower the spray productivity. To solve this problem, we propose a method of multistage spraying, consisting of the generation of a large number of particles of large initial size (to ensure high productivity) and their subsequent destruction by propagation in a periodic ultrasonic field (to ensure small droplet sizes at high productivity). To experimentally determine the capabilities of this technique, a tubular emitter in the shape of a cylinder with a stepped-variable cross-section was designed. The configuration of the ultrasonic field inside the emitter (22.2 kHz; 182 dB) implements three-stage spraying (the number of sputtering stages corresponds to the number of anti-nodes along the emitter axis). The effectiveness of the proposed and developed technique, suitable for the generation of droplets smaller than 40 µm, with performance exceeding the known ultrasonic spray techniques by at least 10-fold, was confirmed in the course of the conducted research.

Field experimental study of high expansion foam coverage after LNG leakage

With the rapid development of the world’s natural gas industry, LNG (Liquefied Natural Gas) has received widespread attention as a clean energy source. However, the leakage accidents of LNG are usually accompanied by safety hazards such as explosions, low temperatures, and phase transitions. In this study, the field experiment is carried out to cover LNG leakage pool with HEF (High-Expansion Foam). In the process of LNG leakage, when the ambient temperature at the bottom of the reservoir drops to about − 82.3 °C (the critical temperature of LNG), the ambient temperature would rise briefly due to the effect of phase transition. Meanwhile, the temperature distribution of different vertical and horizontal positions in the reservoir during the process of leakage is analyzed. Besides, it is also found that the density of the spilled vapor is much lower than that of the air, but the water in the surrounding air encounters the cryogenic vapor to condense into small droplets, the small droplets entrap part of the flammable gas during the process of settling to the ground, therefore, the flammable vapor still shows a heavy gas effect. During the initial period of HEF coverage, evaporation from the liquid pools accelerates, resulting in a 386% increase in peak concentration of methane above the reservoir. Nevertheless, when HEF application is maintained an effective thickness, it can effectively reduce the methane vapor concentration downstream of the reservoir near the surface to less than 1/2 LFL (1/2 of the Lower Flammability Limit). In general, the large-scale field experiments have far-reaching engineering significance and reference value for the occurrence and emergency treatment of LNG leakage accidents under actual working conditions.

Quasi-Static Fracture Toughness and Damage Monitoring in Liquid Metal Reinforced Hybrid Composites

An experimental study is performed to investigate the quasi-static fracture toughness and damage monitoring capabilities of liquid metal (75.5% Gallium/24.5% Indium) reinforced intraply glass/carbon hybrid composites. Two different layups (G-0, where glass fibers are along the crack propagation direction; C-0, where carbon fibers are along the crack propagation direction) and two different weight percentages of liquid metal (1% and 2%) are considered in the fabrication of the composites. A novel four-probe technique is employed to determine the piezo-resistive damage response under mode-I fracture loading conditions. The effect of layups and liquid metal concentrations on fracture toughness and changes in piezo-resistance response is discussed. The C-composite without liquid metal demonstrated higher fracture toughness compared to that of the G-composite due to carbon fiber breakage. The addition of liquid metal decreases the fracture initiation toughness of both G- and C-composites. Scanning electron microscopy images show that liquid metal takes the form of large liquid metal pockets and small spherical droplets on the fracture surfaces. In both C- and G-composites, the peak resistance change of composites with 2% liquid metal is substantially lower than that of both no-liquid metal and 1% liquid metal composites.

Droplet supercooling in marine icing tests

Droplet supercooling in marine icing tests is studied theoretically using established correlations for convection and evaporation. The effect of freestream turbulence on heat and mass transfer is included through an empirical modification to the Nusselt and Sherwood numbers. Droplets are shown to cool following a modified exponential decay, with the trajectory length and shape determined by a thermal mixing length and a cooling exponent. The space needed for supercooling is shown to increase with (droplet diameter)1.8, and also depend on wind speed, injection speed and ambient temperature. Turbulence at realistic offshore levels shortens cooling distances by up to 50%. A reanalysis shows that previous marine icing tests have typically reached supercooling higher than 80% of cooling potential for small droplets up to 100–200 μm, and possibly up to 300–400 μm in long setups at low wind speeds if boosted by turbulence or a contracting tunnel; larger droplets have been significantly undercooled compared to field conditions.

Studying the photothermal activation of polydopamine-shelled, phase-change emulsion droplets into microbubbles using small- and ultra-small-angle neutron scattering

Polydopamine-shelled perfluorocarbon (PDA/PFC) emulsion droplets are promising candidates for medical imaging and drug delivery applications. This study investigates their phase transition into microbubbles under near-infrared (NIR) illumination in situ using small- and ultra-small-angle neutron scattering (SANS and USANS) and contrast variation techniques. Supported by optical microscopy, thermogravimetric analysis, and ultrasound imaging, SANS and USANS results reveal rapid phase transition rates upon NIR illumination, dependent on PFC content and droplet size distribution. Specifically, perfluoropentane droplets rapidly transform into bubbles upon NIR irradiation, whereas perfluorohexane droplets exhibit greater resistance to phase change (bulk boiling points = 30 °C and 60 °C, respectively). Furthermore, smaller emulsion droplets with unimodal distribution resist NIR-triggered phase changes better than their bimodal counterparts. This observation is attributable to the lower boiling points of large emulsion droplets (lower Laplace pressure than smaller droplets) and the faster photothermal heating rates due to their thicker polydopamine shells. The insights gained from these techniques are crucial for designing phase-change emulsions activated by NIR for photothermal therapies and controlled drug delivery.

Formulation of Emulsion Paint Derived from Waste Expanded Polystyrene as a Binder

Emulsion paint, also known as water-based paint, is a type of paint that consists of small water droplets suspended in a binder. The binder, typically made of acrylic or vinyl acetate polymers, acts as a film-forming agent that holds the pigments and other additives together. Emulsion paint was formulated from waste expanded polystyrene as a binder. The formulated emulsion paint which underwent a three-staged process had a pH of 7.82, density of 1.31 g/cm3, the drying time was 15-20 and 85-90 minutes for the set to touch and set to hard drying times respectively, viscosity of 10.4 Cp. The formulated paint exhibited good adhesion, tackiness, opacity, flexibility and stability properties. The paint also possessed good resistance to blistering; which indicates that it has good external exposure resistance and thus; can perform well when exposed to environmental conditions such as rain and sun. Effects of concentration on viscosity, density, melting point, refractive index, moisture uptake, turbidity, elongation at break and water solubility were studied for the polystyrene binder to ascertain for its suitability. Fourier transform infrared spectrophotometer was employed to characterized the binder. This investigation revealed favourable properties of a conventional emulsion paint inherent in the formulated polystyrene binder derived emulsion paint such as, drying time, moisture uptake, water solubility.

Emotion estimation of people wearing masks using machine learning

Coronavirus (COVID-19) is the infectious agent responsible for the transmission of SARS (severe acute respiratory syndrome). When an infected person coughs, talks, or breathes, it spreads as small droplets of fluid from the mouth and nose of the infected person. Sanitary masks help prevent the spread of the virus from the person wearing the mask to others. This new behavior may cause a number of problems in interpersonal interactions. The goal of this paper is the emotion estimation of masked faces. It presents two major parts. At the first level, we created a system for identifying sanitary masks, using CNN. At the second one, we developed an emotion estimation system in order to estimate the classification rates of a masked face. It consists of three steps: face element detection, feature point localization, and classification. We used the well-known Viola and Jones algorithm in order to achieve the first step. We used several techniques to estimate emotions (SVM, KNN and deep learning). We made comparisons of the obtained results. Particular attention is also given to the effect of face masks on the performance of various methods.

Succinylated starch emulsified Eugenol and Carvacrol nanoemulsions improved digestive stability, bio-accessibility and Salmonella typhimurium inhibition

The ultrasonically processed Eugenol (EU) and Carvacrol (CAR) nanoemulsions (NE) were successfully optimized via response surface methodology (RSM) to achieve broad spectrum antimicrobial efficacy. These NE were prepared using 2 % (w/w) purity gum ultra (i.e., succinylated starch), 10 % (v/v) oil phase, 80 % (800 W) sonication power, and 10 min of processing time as determined via RSM. The second order Polynomial method was suitable to RSM with a co-efficient of determination >0.90 and a narrow polydispersity index (PDI) ranging 0.12–0.19. NE had small droplet sizes (135.5–160 nm) and low volatility at high temperatures. The EU & CAR entrapment and heat stability (300 °C) confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Further, the volatility of EU & CAR NE was 18.18 ± 0.13 % and 12.29 ± 0.11 % respectively, being lower than that of bulk/unencapsulated EU & CAR (i.e., 23.48 ± 0.38 % and 19.11 ± 0.08 %) after 2 h at 90 °C. Interestingly, both EU & CAR NE showed sustained release behaviour till 48 h. Their digest could inhibit Salmonella typhimurium (S. typhimurium) via membrane disruption and access to cellular machinery as evident from SEM images. Furthermore, in-vivo bio-accessibility of EU & CAR in mice serum was up to 80 %. These cost-effective and short-processed EU/CAR NE have the potential as green preservatives for food industry.

Experimental study on droplet and bioaerosol emissions from flushing a squat toilet

Toilet flushing can produce pathogen-laden aerosols and may pose a serious concern for the transmission of diseases. The emission of bioaerosols from flushing a squat toilet has not been thoroughly examined in the literature. In this study, we conducted pilot measurements to quantify the emission of airborne microorganisms during the flushing of a squat toilet. A full-scale custom-built squat toilet with a typical flushing system was designed and built. The aerosolized droplets and microbes emitted after a single flushing were measured and quantified. Three bacteria (Escherichia coli, Pseudomonas alcaligenes, and Salmonella enterica) and two viruses (bacteriophage MS2 and P22) were tested. The results suggest that a single flush can generate a large number of small droplets in the air. The total emission number of droplets within 0.3–10 μm per flush was 5.72 × 105±1.93 × 105 of which 96 % were smaller than 2 μm. We observed a linear correlation between the number of emitted bioaerosols and the amount of microorganisms introduced into the toilet bowl. The quantified data also shows that flushing-induced airborne microorganism emission strength (a normalized parameter) varied significantly with the sizes of microorganisms. Overall, the emission strengths of viruses were significantly higher than those of the tested bacteria. The mean emission strength of P22 and MS2 per flush was 33.5 times higher than the average emission strength of the three tested bacteria. This work provides valuable data on the bioaerosol emission by flushing a squat toilet, which is essential for developing control measures and evaluating the risk of pathogen exposure.

Preparation of magnetic oil-based gel microspheres containing di(2-ethylhexyl)phosphoric acid for extraction of scandium ions at low concentrations in aqueous solutions

Extraction of low-concentration rare earths is one of the important paths for the sustainability of the rare earth industry. The research and development of materials suitable for the extraction of rare earth ions at low concentrations is of great significance. Currently, the application of solvent extraction in the rare earth production industry is highly mature. However, it is not economical to use it for the extraction of low concentration rare earths with problems of phase separation and organic phase loss. This work innovatively proposes to encapsulate the extractant and diluent in magnetic oleogel microspheres, which are obtained by solubilizing magnetic poly (phenyl divinylbenzene)(PS-DVB) microspheres with the extractant and diluent.. The magnetic PS-DVB microspheres of 3 ∼ 16 μm were prepared by suspension polymerisation, followed by encapsulation of di(2-ethylhexyl)phosphoric acid (D2EHPA) and dichloroethane in magnetic PS-DVB microspheres using emulsion swelling, and then magnetic oil-based gel microspheres containing D2EHPA with a particle size of 10 ∼ 32 μm were obtained. The magnetic oil-based gel microspheres containing D2EHPA consist of about 96 wt% liquid phase and about 4 wt% solid phase, with D2EHPA accounting for more than 4.19 wt%. The magnetic oil-based gel microspheres are very close to small oil droplets and are superparamagnetic. The magnetic oil-based gel microspheres containing D2EHPA could completely extract 60 ppm of scandium ions(Sc3+) under the conditions of O:A = 1:50,1:60,1:70, and the extraction equilibrium times were 6, 9 and 12 min, respectively. This extractant encapsulation scheme inherits the selectivity of traditional extractants while simultaneously preserving the advantages of rapid extraction by solvent extraction.

INVESTIGATING ABSORPTION EFFECTS ON OIL DROPLETS IN ENHANCED OIL RECOVERY: A FORCE ANALYSIS APPROACH

This research aims to analyze the forces that affect oil droplets to illustrate that augmenting the mass of an oil droplet fosters favorable conditions for interaction between displaced and displacing fluids. This, in turn, impedes the bypassing of the displacing fluid around the oil droplets. In this investigation, the concept of augmenting the mass of an oil droplet is realized through absorption phenomena, employing coated spinel oxide (cobalt ferrite oxide) nanoparticles (CFO NPs). The synthesis of CFO NPs was successfully carried out in the laboratory using a sol-gel technique, followed by coating with a surfactant and lauric acid. The coated spinel oxide NPs underwent characterization using IR, XRD, and XRF techniques. The procedures started with the calculation of capillary force restrictions for small and large oil droplets. Furthermore, practical experiments involving oil droplets on glass plates at a 30° angle were conducted for different scenarios: without water injection, with water injection, and during the “absorption effect” of CFO NPs. The findings revealed that a large oil droplet exhibits lower capillary pressure restrictions compared to a small oil droplet, with a disparity of 0.02 m/s2 . Consequently, it is comparatively easier for large oil droplets to become free than small ones. Moreover, a large oil droplet exhibits faster movement than small oil droplets due to gravitational effects in the absence of any injections. During the water injection scenario, the water droplets were unable to displace the oil droplet; instead, they passed through the passage beside and above the oil droplet consistently with an increase in the amount of water droplets. However, in the coated CFO NPs scenario, absorption of the coated CFO NPs onto the oil droplet was observed. This resulted in the aggregation of oil molecules, augmenting the gravity of the oil droplet and creating favourable conditions for its displacement. Notably, no water bypass beside the oil droplet was observed in this scenario, unlike the water scenario. Additionally, the aggregation of oil molecules induced corner flow, providing conducive conditions for microemulsion formation, altering wettability, modifying residual oil saturation, and enhancing injection performance. Euler’s equation was employed to analyse corner flow, indicating that the level of oil deformation increases with the rising rotation velocity, potentially leading to an increased recovery factor.

Study on Marangoni explosion of binary mixtures in liquid layer

In this work, the process of forming micro-droplets due to instability and fragmentation after short chain alcohol solution spreads on the surface of oil layers is studied. Based on the free energy theory of the liquid-liquid interface, the relationship between the binary mixtures spreading on the surface of the liquid layer is derived, and the concentration range of short chain alcohol solution spreading as a thin film on the surface of the oil layer is calculated from the Hiskovsky formula. The Malangoni flow caused by the difference in evaporation rate between the center and edge of the droplet film perturbs the boundary of the liquid film, causing finger-shaped liquid columns to grow at the edge when the droplet spreads to its maximum. In this work, the expression for the critical wavelength and maximum wavelength of boundary instability are derived based on the perturbation model, and the reason for finger shaped liquid column fragmentation is explained based on the Plateau Rayleigh instability. A concentric cylindrical shell liquid column model is established to simplify the calculation and predict the location range of “droplet explosion” of droplets with different viscosity ratios on the liquid layer. Through theoretical calculations and experimental verification, it is found that the alcohol solution fragmented into small droplets within a length range of 4.51–5.98 times the width of the liquid column. This study provides theoretical guidance for existing application fields such as film forming technology and coating technology. The hypotheses, assumptions, and simplified models preliminarily verified experimentally provide solutions for some technical difficulties in the research fields of micro reactions and nanoparticle preparation in chemical industry.

Laboratory investigation of dodecylbenzene diffusion from submarine cables

Oil-filled submarine cables have come to dominate the reliable delivery of electrical power today, but oil leakage still remain a challenge. This work focuses on the exploring of spill behavior of dodecylbenzene (DDB) after leakage and the detection of DDB. Static and dynamic spill model were established to study the spreading and migration behavior of underwater DDB. In still water, the spilled oil droplets can quickly reach the uniform floating speed of 0.13 m s-1 with no significant change under different oil spill rates. DDB can be dispersed as small droplets in seawater, which the diameter of DDB droplets increased from 60 nm to 200 nm with the increase of the concentration from 10 ppm to 1000 ppm. This study suggests a research basis for finding the leakage point of submarine cables, and explores the way for detection of DDB.

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 <i>D</i><sub>32</sub>-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.

Droplet size affects the degree of separation between fluorescence-positive and fluorescence-negative droplet populations in droplet digital PCR.

In droplet digital polymerase chain reaction (ddPCR) tests, a single sample solution is divided into many water-in-oil droplets. At the endpoint of PCR amplification, individual droplets are classified as either fluorescence-positive (FL(+)) or fluorescence-negative (FL(-)) droplets based upon their fluorescence amplitudes. Populations of FL(+) and FL(-) droplets can be seen in the histogram of fluorescence amplitude. The absolute copy number of a target molecule can be calculated from the fraction of FL(+) droplets relative to the total droplet number analyzed using Poisson statistics. It is crucial that the population of FL(+) droplets can be distinctly separated from that of the FL(-) droplets for accurately estimating the FL(+) droplet fraction and the absolute copy number. However, the distinct separation of the two populations is often impaired in actual ddPCR tests. Although many factors have been suggested to affect population separation, no study has addressed whether the droplet size influences the degree of separation. In this study, we compared the degrees of separation for ddPCR runs with three different droplet sizes. The experimental results showed an increasing degree of separation with decreasing droplet size. This discovery will potentially guide researchers to use smaller droplets in ddPCR to achieve higher accuracy and precision.

3D printing in microfluidics: experimental optimization of droplet size and generation time through flow focusing, phase, and geometry variation.

Droplet-based microfluidics systems have become widely used in recent years thanks to their advantages, varying from the possibility of handling small fluid volumes to directly synthesizing and encapsulating various living forms for biological-related applications. The effectiveness of such systems mainly depends on the ability to control some of these systems' parameters, such as produced droplet size and formation time, which represents a challenging task. This work reports an experimental study on tuning droplet size and generation time in a flow-focusing geometry fabricated with stereolithography 3D printing by exploring the interplay of phase and geometrical parameters. We produced droplets at different low flow rates of continuous and dispersed phases to assess the effect of each of these phases on the droplets' size and formation time. We observed that smaller droplets were produced for high viscosity oil and water phase, along with high flow rates. In addition, changing the microfluidics channels' width, and morphology of the orifice has shown a similar effect on droplet size, as shown in the case of high-viscosity solutions. The variation of the bifurcation angle shows a noticeable variation in terms of the achieved droplet size and formation time. We further investigated the impact of modifying the width ratio of the continuous and dispersed phases on droplet formation.

Abnormal condensation of water vapour at ambient temperature.

The homogeneous condensation of water vapor at ambient temperature is studied using molecular dynamics simulation. We reveal that there is a droplet size at the nanoscale where water droplets can be stabilized in the condensation process. Our simulations show that the growth of water droplets is dominated by collision and coagulation between small water droplets after nucleation. This process is found to be accompanied by exceptionally fast evaporation such that droplet growth is balanced by evaporation when water droplets grow to a critical size, approximately 12.5 Å in radius, reaching a stable size distribution. The extremely high evaporation rate is attributed to the curvature dependence of surface tension. Surface tension shows a significant decrease with decreasing droplet size below 20 Å, which causes the total free energy of nanoscaled water droplets to rise after collision and coagulation. Consequently, water droplets have to shrink via fast evaporation. The curvature dependence of surface tension is related to the dielectric ordering of water molecules near the surface of water droplets. Owing to fast evaporation, secondary condensation occurs, and many small water clusters form, ultimately exhibiting a bimodal distribution of water-droplet size.

Performance of Azolla pinnata fern protein hydrolysates as an emulsifier and nutraceutical ingredient in an O/W emulsion system and their effect on human gut microbiota and mammalian cells.

This study investigated the dual potential of Azolla pinnata fern protein hydrolysates (AFPHs) as functional and nutraceutical ingredients in an oil/water emulsion system. The AFPH-stabilised emulsion (AFPH-E) displayed a small and uniform droplet distribution and was stable to aggregation and creaming over a wide range of pH (5-8), salt concentrations ≤ 100 mM, and heat treatment ≤ 70 °C. Besides, the AFPH-E possessed and maintained strong biological activities, including antihypertensive, antidiabetic, and antioxidant, under different food processing conditions (pH 5-8; NaCl: 50-150 mM, and heat treatment: 30-100 °C). Following in vitro gastrointestinal digestion, the antihypertensive and antioxidant activities were unchanged, while a notable increase of 8% was observed for DPPH. However, the antidiabetic activities were partially reduced in the range of 5-11%. Notably, AFPH-E modulated the gut microbiota and short-chain fatty acids (SCFAs), promoting the growth of beneficial bacteria, particularly Bifidobacteria and Lactobacilli, along with increased SCFA acetate, propionate, and butyrate. Also, AFPH-E up to 10 mg mL-1 did not affect the proliferation of the normal colon cells. In the current work, AFPH demonstrated dual functionality as a plant-based emulsifier with strong biological activities in an oil/water emulsion system and promoted healthy changes in the human gut microbiota.

Looking for QGP signatures in ultraperipheral PbPb collisions

Ultraperipheral collisions of relativistic heavy ion beams lead to a diverse set of photon-nucleus (photonuclear) interactions. The measurements of particles and their interaction produced in photonuclear reactions can shed light on the QCD dynamics of these novel, extremely asymmetric colliding systems, with energies between those available at RHIC and the LHC. Previous studies by ATLAS indicate significant elliptic and triangular flow coefficients in these events [1]. Thus, it is imperative to check these events for other potential QGP signatures including radial flow, strangeness enhancement, and enhanced baryon/meson production. This proceeding presents the measurement of charged hadron yields in photonuclear collisions using 5.02 TeV Pb+Pb data collected in 2018 by ATLAS, with a dedicated photo-nuclear event trigger. The charged hadron yields are presented as a function of pseudorapidity and transverse momentum in different categories of event multiplicity. The results are compared with 5.02 TeV p+Pb data collected in 2016 by ATLAS, at the same event multiplicities. The results are also compared with calculations from DPMJET and hydrodynamic-based models. These comparisons enable detailed characterizations of photonuclear collision properties, including the photon energy distribution, and whether small QGP droplets may be formed.