Separate Droplets Research Articles

Bioaerosol sampling and bioanalysis: Applicability of the next generation impactor for quantifying Legionella pneumophila in droplet aerosols by flow cytometry

Bioaerosol generation, sampling, and cultivation-independent quantification of pathogenic bacteria play a crucial role in studying dose-response effects of Legionella pneumophila. Here, the Next Generation Impactor (NGI), initially created for pharmaceutical inhaling studies, was assessed for its potential to sample airborne bioaerosols and to separate size-dependent wet droplets by incrementally increasing the airflow speed. This stainless-steel sampler was shown in this study to be suitable for sampling prior to cultivation-independent analysis of pathogen-containing bioaerosols using washable cups. The applicability was studied by quantifying the total and intact cell count of L. pneumophila by flow cytometry after being dispersed into a droplet aerosol. Our results demonstrate a high total sampling efficiency of 95.5% ± 11.8% despite a lower biological sampling efficiency of 59.7% ± 16.5% for dry aerosols. However, by elevating the relative humidity (RH) to 100% in a liquid aerosolization unit, the biological sampling efficiency increased to over 90% for L. pneumophila. More than 50% of the cells were found in stage 1 using the liquid aerosolization unit. In comparison, 80% of the cells were sampled in stages 4–6 at 30% RH. Specifically, while at 100% RH, the droplet size mattered, at 30% RH, the size distribution of dry particles, in this case L. pneumophila, was relevant due to evaporation processes, which explains the size differences. These findings indicate the potential of the NGI for further exploration and application in studying other aerosol-borne pathogens, especially concerning the size distribution of wet droplets, viability, or effect-based bioanalysis.

An ultra high-throughput, massively multiplexable, single-cell RNA-seq platform in yeasts.

Yeasts are naturally diverse, genetically tractable, and easy to grow such that researchers can investigate any number of genotypes, environments, or interactions thereof. However, studies of yeast transcriptomes have been limited by the processing capabilities of traditional RNA sequencing techniques. Here we optimize a powerful, high-throughput single-cell RNA sequencing (scRNAseq) platform, SPLiT-seq (Split Pool Ligation-based Transcriptome sequencing), for yeasts and apply it to 43,388 cells of multiple species and ploidies. This platform utilizes a combinatorial barcoding strategy to enable massively parallel RNA sequencing of hundreds of yeast genotypes or growth conditions at once. This method can be applied to most species or strains of yeast for a fraction of the cost of traditional scRNAseq approaches. Thus, our technology permits researchers to leverage "the awesome power of yeast" by allowing us to survey the transcriptome of hundreds of strains and environments in a short period of time and with no specialized equipment. The key to this method is that sequential barcodes are probabilistically appended to cDNA copies of RNA while the molecules remain trapped inside of each cell. Thus, the transcriptome of each cell is labeled with a unique combination of barcodes. Since SPLiT-seq uses the cell membrane as a container for this reaction, many cells can be processed together without the need to physically isolate them from one another in separate wells or droplets. Further, the first barcode in the sequence can be chosen intentionally to identify samples from different environments or genetic backgrounds, enabling multiplexing of hundreds of unique perturbations in a single experiment. In addition to greater multiplexing capabilities, our method also facilitates a deeper investigation of biological heterogeneity, given its single-cell nature. For example, in the data presented here, we detect transcriptionally distinct cell states related to cell cycle, ploidy, metabolic strategies, and so forth, all within clonal yeast populations grown in the same environment. Hence, our technology has two obvious and impactful applications for yeast research: the first is the general study of transcriptional phenotypes across many strains and environments, and the second is investigating cell-to-cell heterogeneity across the entire transcriptome.

Separate and joint clustering characteristics of large-Stokes-number sprays subjected to turbulent co-flows

Separate and joint droplets, clusters, and voids characteristics of sprays injected in a turbulent co-flow are investigated experimentally. Simultaneous Mie scattering and interferometric laser imaging for droplet sizing along with separate hotwire anemometry are performed. The turbulent co-flow characteristics are adjusted using zero, one or two perforated plates. The Taylor-length-scale-based Reynolds number varies from 10 to 38, and the Stokes number estimated based on the Kolmogorov time scale varies from 3 to 25. The results show that the mean length scale of the clusters normalized by the Kolmogorov length scale varies linearly with the Stokes number. However, the mean void length scale is of the order of the integral length scale. It is shown that the number density of the droplets inside the clusters is approximately 7 times larger than that in the voids. The ratios of the droplets number densities in the clusters and voids to the total number density are independent of the test conditions and equal 5.5 and 0.8, respectively. The joint probability density function of the droplets diameter and clusters area shows that the droplets with the most probable diameter are found in the majority of the clusters. It is argued that intensifying the turbulence broadens the range of turbulent eddy size in the co-flow which allows for accommodating droplets with a broad range of diameters in the clusters. The results are of significance for engineering applications that aim to modify the clustering characteristics of large-Stokes-number droplets sprayed into turbulent co-flows.

Performance evaluation of downhole oil–water separators in wells that use DWL technique using computational fluid dynamics: influence of velocities and flow rates

A major issue in many oil fields is the production of undesirable water from oil wells. One of the most important causes of unwanted water is water coning. This phenomenon may be leading to a decreasing oil production rate, an increasing water cut, and consequently high production costs. Downhole water loop (DWL) is a relatively new and effective technique to control water coning. Even though many studies have shown how effective the DWL approach is in reducing the problem of water cones, the issue of oil droplets escaping the drainage zone might damage the injection area and perhaps cause blockage. It is suggested to use the downhole oil–water separator (DOWS) approach to separate oil droplets from the water stream based on the difference in densities. This article gives a numerical analysis of DOWS in two stages. In order to confirm that the simulator could faithfully simulate this sort of separator, the findings of the employed simulator were first compared with the preceding analytical solutions. Then the impact of inlet velocities and flow rates was discussed numerically for seven scenarios in the second stage. The results showed that a high inlet velocity encourages the formation of oil droplets as a result of the mixture stream colliding with the separator walls, whereas a low inlet velocity produced undesirable results because the oil droplets remained dispersed in the water stream (the separation efficiency was 30.6% less than the high-velocity condition). In the following case, a novel design based on expanding the mixture input area and changing the mixture inlet and outlet points was presented to lessen the impact of mixture inlet velocity. The separation efficiency was improved by 38.65% as a result of this approach. Finally, the discussion's findings about the effect of mixture flow rates at the separator's inlet and upper outlet showed that the inlet rate has a bigger impact on separator performance than the upper outlet rate. The outcomes of this research and the numerical models can be utilized to enhance the system-level design, better understand this kind of separator, and increase its efficacy.

Fundamentals and Manipulation of Bare Droplets and Liquid Marbles as Open Microfluidic Platforms

Microfluidics, as one of the most valuable analytical technologies of this century, has played an important role in various fields. Particularly, out-of-channel microfluidics, often referred to as open microfluidics (OMF) has recently drawn wide research attention among scholars for its great potential in convenient manual intervention. Much recent research has been geared toward bare droplets and particle-armed droplets (namely liquid marbles, LMs), which could serve as independent systems in OMF. Their versatile applications include but are not limited to nanomaterials preparation, energy harvesting, cell culture and environment monitoring. These applications are mainly attributed to the excellent independence, low reagent consumption and short reaction time of separate droplets and LMs. In addition, more operation features, such as diverse handling options, flexible controllability and high precision, further enable droplets and LMs carrying small liquid biochemical samples to be manipulated in an open environment freely. Considering the emergence of important research on bare droplets and LMs, this paper systematically reviews the state of the art in the fundamentals and manipulation of the two novel platforms under the frame of OMF. First, the intrinsic property of bare droplets on solid substrates, especially on superhydrophobic ones, is discussed, followed by the formation mechanism of nonwetting LMs and the effect of coating particles on LMs’ performance. Then, friction obstacles and actuation principles raised in driving droplets and LMs are further analyzed theoretically. Subsequently, several classical types of manipulation tasks for both droplets and LMs, namely transportation, coalescence, mixing and splitting, are discussed with a focus on key techniques to accomplish the tasks aforementioned. Finally, the fundamental and manipulation similarities and differences between bare droplets and LMs are summarized and future developments towards droplet- or LM-based microreactors and microsensors are recommended accordingly.

Design of gas-liquid two-phase separation device with application in solar hydrogen production system

Currently, solar thermochemical energy conversion technology has attracted more and more attention because of the increasing global need for clean fuel and chemical energy demand. The thermochemical hydrogen production technology uses solar radiation with concentrated high-density as a high-temperature heat source to produce hydrogen by decomposing water through two-step cycle redox reactions. It is an environment-friendly technology based on artificial photosynthesis utilizing water vapor as the reaction gas. However, limited by the separation efficiency, current gas-liquid separation devices cannot output stable high-purity water vapor and sophisticate the experimental processes. In this research, intensive numerical investigations were carried out on the widely-used corrugated plate steam separators. The structural parameters are designed by the multi-objective optimization method combining the artificial neural network and the genetic algorithm. Nine optimized structures are designed by adding hydrophobic hooks, streamlined, and reducing the plate distance optimization methods. The results give engineering application conditions of different optimized separators. The streamlined single-hook corrugated plate separator with rounded corners exhibited the best separation efficiency under the heat state condition, which is 97.27%. It can also completely separate droplets over 28.5 μm. The applicability of the cyclone steam separators indicated that it is more suitable for pretreatment. The benchmark experimental system was built for the measurement of the separation efficiency resulting in only a 0.73% error. The designed steam separator was successfully applied to the solar thermochemical hydrogen production experiment, which ensures its practicability and pertinence in the process of solar fuel synthesis.

Manipulation, aggregation, fusion and separation of droplets using laser-induced Marangoni force

Micro-scale control of liquid/droplet motion is crucial for chemical and biochemical analysis. There are several methods to manipulate droplet motion such as the Marangoni effect which can be triggered by introducing temperature gradients on suspended droplets in mineral oil.In this study, a focused continuous wave (CW) laser beam was used to induce the Marangoni force to separate, fuse, aggregate, and control droplets. Droplets experience a force due to an interfacial tension gradient near the locally heated area created by the laser beam. The work is done on a chamber and a microchannel platform.In order to fuse water droplets, we used an optical fiber (200-µm core and 220-µm glass cladding, which has a 0.065 numerical aperture (NA)) to direct focused laser beams into the oil medium, where the droplets were first moved to the heat source and then stopped at this point and merged a second time. Also, for the first-time droplet separation for different radii of 47 and 55 in the microchannel and droplet aggregation in the chamber was performed by the Marangoni effect. We have also examined the behavior of the droplets in relation to their size and distance from the hot spot.By controlling the incident laser power, we can manipulate the droplet to either fuse, separate or aggregate.

Estimating the liquid jet breakdown height using dimensional analysis with experimental evidence

When opening a sink or pouring water from a bottle an interesting and unintuitive physical phenomenon occurs: the regular cylindrical jet breaks into droplets at a certain height, which changes once the initial conditions of the falling jet change , thus two distinct regions are observable: a steady stream of water at high flow and separate droplets at low flow . In this paper, we found and experimentally tested a model that correlates the parameters of the phenomenon mentioned above. We analyzed how the breakdown height of the jet changes with three initial parameters: jet radius, liquid density, and surface tension. We propose a mathematical model for the relationship between the diameter of the liquid stream and the height at which it breaks into droplets , consisting of a quadratic dependency . There was a good fit between experimental data and the model with a correlation coefficient exceeding 0.95. Finding and exploring this way to analyze fluid mechanics might help understand the fundamental correlation between the parameters involved and design more lucrative industrial techniques in fields such as oil extraction or printing.

Spatial scales of competition and a growth-motility trade-off interact to determine bacterial coexistence.

The coexistence of competing species is a long-lasting puzzle in evolutionary ecology research. Despite abundant experimental evidence showing that the opportunity for coexistence decreases as niche overlap increases between species, bacterial species and strains competing for the same resources are commonly found across diverse spatially heterogeneous habitats. We thus hypothesized that the spatial scale of competition may play a key role in determining bacterial coexistence, and interact with other mechanisms that promote coexistence, including a growth-motility trade-off. To test this hypothesis, we let two Pseudomonas putida strains compete at local and regional scales by inoculating them either in a mixed droplet or in separate droplets in the same Petri dish, respectively. We also created conditions that allow the bacterial strains to disperse across abiotic or fungal hyphae networks. We found that competition at the local scale led to competitive exclusion while regional competition promoted coexistence. When competing in the presence of dispersal networks, the growth-motility trade-off promoted coexistence only when the strains were inoculated in separate droplets. Our results provide a mechanism by which existing laboratory data suggesting competitive exclusion at a local scale is reconciled with the widespread coexistence of competing bacterial strains in complex natural environments with dispersal.

Continuous coalescence and separation of oil-in-water emulsion via polyacrylonitrile nanofibrous membrane coalescer

Coalescence separation is an energy-efficient, physical separation method to enable the reuse of oil from oil-in-water (O/W) emulsions, which are widely found in industrial wastewater. However, traditional coalescers are generally ineffective in separating fine, emulsified oil droplets. Here, we applied the polyacrylonitrile (PAN) nanofibrous membrane possessing a three-dimensional network structure and high porosity to separate oil droplets smaller than 10 µm. We demonstrated that oil pieces floated on the surface of the discharged fluid. The continuous separation conducted under a flow rate of 40 mL/min was steady and with a separation ratio greater than 99.9% and a pressure drop of less than 25 kPa. In addition, an analysis of the amount of oil during the continuous operation indicated that the oil droplets did not form a cake layer, which would otherwise foul the membrane and hinder its long-term use. Moreover, the continuous separation of the surfactant-stabilized O/W emulsion with a SPAN20 concentration of 2 wt% in dodecane exhibited a high performance comparable to that of the surfactant-free emulsion. In conclusion, the PAN nanofibrous membrane exhibited excellent performances for the coalescence of fine oil droplets, demonstrating the industrial applicability of nanofibrous membranes for continuous O/W emulsion coalescence and separation.

Combinatorial perturbation sequencing on single cells using microwell-based droplet random pairing

Combinatorial drug therapy reduces drug resistance and disease relapse, but informed drug combinations are lacking due to the high scale of possible combinations and the relatively simple phenotyping strategies. Here we report combinatorial perturbation sequencing (CP-seq) on single cells using microwell-base droplet random pairing. CP-seq uses oligonucleotides to barcode drugs, encapsulates drugs and cells in separate droplets, and pairs cell droplets with two drug droplets randomly on a microwell array chip to complete combinatorial drug treatment and barcode-tagging on cells. The subsequent single-cell RNA sequencing simultaneously detects the single-cell transcriptomes and drug barcodes to demultiplex the corresponding drug treatment. The microfluidic droplet operations had robust performance, with the overall utilization rate of the microwells being up to 83%. We then progressively validated the CP-seq by performing single-drug treatments and then combinatorial-drug treatments, confirming the CP-seq's capability in the collection and analysis of drug-perturbed transcriptomes. Leveraging the advantage of droplet microfluidics in massive multiplexing, the CP-seq represents a great technology for combinatorial perturbation screening with high throughput and comprehensive profiling.

Numerical Simulation of Ammonia-Water Solution Based Heat Absorber

This article provides an insight into the numerical simulation of an ammonia-water solution-based plate heat absorber, which is a crucial part of an absorption chiller. These chillers could be used as part of a stratified chilled-water storage tank configuration for coupling to a small modular reactor. The common approach utilized in the process of designing the chiller is to call the absorber a "black box" without considering the processes inside. It follows that the resulting design must be highly oversized to ensure reliable operation of the system. This article focuses on the obstacles that needs to be overcome in order to simulate the processes inside the absorber, such as stream breakup into separate droplets or absorption of ammonia. Unfortunately, we do not have any experimental data we could use to validate our simulations and thus this article should be looked at as a "proof of concept" and a possible guideline for simulations of similar phenomenon.

Flow field analysis and performance evaluation of a hydrocyclone coalescer

ABSTRACT Hydrocyclones are extensively applied in oil-water separation for fluid purification. However, it is difficult for a hydrocyclone to separate tiny oil droplets. Therefore, the coalescence of oil droplets plays an important role in enhancing the separation performance of hydrocyclone. In this study, an innovative hydrocyclone coalescer (HCC) was designed to enhance the separation of de-oiling hydrocyclone. The population balance model was carried out to simulate the distribution characteristic of oil droplet size in the HCC. High speed video was utilized to study the coalescence process qualitatively. Furthermore, an improved particle size analysis experimental system was designed to evaluate the coalescence performance quantitatively. The effects of inlet flow rate, oil concentration and water viscosity on the coalescence of oil droplets in HCC were analyzed. Results show that the optimum inlet flow is 3.9 m3/h, and the oil droplets with mean diameter 0–200 μm at the inlet of HCC can be enlarged to 502.54 μm at the outlet. When the viscosity of water increases from 1.03 mPa·s to 5.56 mPa·s, the mean diameter decreases from 502.5 μm to 382.4 μm. The HCC shows obvious coalescence performance under different operation and fluid parameters, which can contribute to enhancing the separation precision of hydrocyclones.

Preparation and properties of a novel rejuvenator-loaded fiber for asphalt pavement

Rejuvenator encapsulation is a promising method to efficiently deliver rejuvenator to the interior of asphalt pavement, contributing to the development of smart pavement with excellent self-healing ability. In this study, the rejuvenator-loaded fiber, namely the fiber encapsulating rejuvenator, was prepared using a self-assembled microfluidic device. The encapsulation mechanism was explored, and the key preparation parameters were proposed. Then, the properties of the prepared fiber were investigated comprehensively using multiple test methods, including the optical digital microscope, uniaxial tensile strength (UTS) test, Fourier transform infrared (FTIR) spectra analysis and thermo-gravity analysis. Test results showed that the rejuvenator was successfully encapsulated in separate droplets inside the fiber with “egg box” structure shell. With the increase of internal phase flux, the rejuvenator droplet gradually expanded in volume, making its shape change from sphericity to ellipsoid and jet. According to the mechanical requirement on the rejuvenator-loaded fiber during asphalt pavement construction, the optimal preparation parameters were recommended as sodium alginate concentration of 2.5%, calcium chloride concentration of 2.0%, external phase flux of 20.0 ml/h, internal phase flux of 0.2 ml/h, and titanium dioxide was selected as the shell additive. The addition of titanium dioxide in the shell improved the mechanical property and thermal stability of the fiber, but reduced the relative content of encapsulated rejuvenator.

Chemical design of self-propelled Janus droplets

Chemical design of self-propelled Janus droplets

Programmable droplet manipulation and wetting with soft magnetic carpets

Significance A set of magnetically responsive, soft hairs, which form a soft magnetic carpet, can be infused with a liquid to achieve switchable wetting. Applying a pattern of magnetic field results in a reconfigurable wetting pattern on the soft magnetic carpet. Combining this switchable wetting with a travelling magnetic field wave can allow us to spatially manipulate droplets. The efficiency of the droplet manipulation depends on the size and the contact angle of the droplet, which allows a pathway to sort and separate different droplets. Temporal and spatial control over multiple droplets allows us to conduct droplet reactions, which has a potential to be used for automated analytical testing and screening.

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

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

Comparing features in metallurgical interaction when applying different techniques of arc and plasma surfacing of steel wire on titanium

This paper reports a study into the regularities of interphase interaction, features in the formation of intermetallic phases (IMPs), and defects when surfacing steel on titanium in four ways: P-MAG, CMT, plasma surfacing by an indirect arc with conductive wire, and PAW. A general tendency has been established in the IMP occurrence when surfacing steel on titanium by all the considered methods. It was determined that the plasma surfacing technique involving an indirect arc with conductive wire is less critical as regards the IMP formation. That makes it possible to obtain an intermetallic layer of the minimum thickness (25...54 μm) in combination with the best quality in the formation of surfaced metal beads. Further minimization of the size of this layer is complicated by a critical decrease in the heat input into the metal, which gives rise to the capability of the surfaced metal to be collected in separate droplets. The formation of TiFe2, TiFe, and the α-Fe phase enriched with titanium in different percentage compositions has been observed in the transition zone of steel surfacing on titanium under different techniques and modes of surfacing. The study has shown the possibility of formation, in addition to the phases of TiFe2 and TiFe, the Ti2Fe phase at low heat input. The technique of plasma surfacing by an indirect arc with conductive wire minimizes the thermal effect on the base metal. When it is used at the border of the transition of the layer of steel surfaced on titanium, the phase composition and structure of the layers in some cases approach the composition and structure of the transition zone of the original bimetallic sheet "titanium-steel" manufactured by rolling. A layer up to 5 μm thick is formed from the β phase with an iron concentration of 44.65 % by weight and an intermetallic layer up to 0.2...0.4 μm thick, close in composition to the TiFe phase. The next step in minimizing the IMP formation might involve the introduction of a barrier layer between titanium and steel.

Design and analysis of de-oiling coalescence hydrocyclone

ABSTRACT De-oiling hydrocyclones are extensively applied in oilfield wastewater purification for fluid separation, because of their efficient and rapid processing performance. However, it is difficult for a hydrocyclone to separate tiny oil droplets owing to the inadequate centrifugal force. A type of coalescence hydrocyclone (CHC) is designed based on the principle of centrifugal separation and hydraulic droplet collision coalescence. The structure, coalescence theory, and separation principle of the CHC are introduced. Based on the Euler–Euler method, the population balance model (PBM) is applied to a continuous equation to simulate the distributions of the velocities, oil volume fraction, and oil droplet size in the CHC. The simulation method is verified by conducting particle image velocimetry tests in a polymethyl methacrylate hydrocyclone. The results indicate that the CHC can improve the separation performance by enlarging the oil droplet size by collision coalescence before entering the hydrocyclone. The results of separation efficiency experiment indicate that the CHC can not only improve the oil–water separation efficiency but also clearly enhance the processing capability. The optimal inlet flow rate is 5.5 m3·h-1 and the split ratio is 25%. The feasibility of the structure design and the reliability of the separation performance are validated by experiments.

High diversity droplet microfluidic libraries generated with a commercial liquid spotter

Droplet libraries consisting of many reagents encapsulated in separate droplets are necessary for applications of microfluidics, including combinatorial chemical synthesis, DNA-encoded libraries, and massively multiplexed PCR. However, existing approaches for generating them are laborious and impractical. Here, we describe an automated approach using a commercial array spotter. The approach can controllably emulsify hundreds of different reagents in a fraction of the time of manual operation of a microfluidic device, and without any user intervention. We demonstrate that the droplets produced by the spotter are similarly uniform to those produced by microfluidics and automate the generation of a ~ 2 mL emulsion containing 192 different reagents in ~ 4 h. The ease with which it can generate high diversity droplet libraries should make combinatorial applications more feasible in droplet microfluidics. Moreover, the instrument serves as an automated droplet generator, allowing execution of droplet reactions without microfluidic expertise.