Droplet Composition Research Articles

Understanding the formation of ultrafine maltodextrin particles under simultaneous convective drying and antisolvent vapour precipitation

Research on simultaneous antisolvent-vapour-induced precipitation and convective drying of a solute-containing droplet was extensively conducted since this technique was introduced. However, the internal droplet compositions, which were suggested to be related to the formation of particle morphologies, had not been explored. Herein, the ethanol-vapour-induced precipitation of multi-solvent droplets containing maltodextrin as the solute was used to analyse internal droplet compositions. The droplet mass and diameter profiles were obtained via an established single-droplet drying experiment, which mimicked the spray drying of droplets. Analysis revealed that the antisolvent concentration increased with time and was higher than solvent concentration towards the end of the process. It is interesting to find out that the final particle morphology was profoundly impacted by the ambient ethanol humidity and also how spontaneous the subsequent drying was during ethanol-vapour-induced precipitation of the solutes. The formation of the porous structure was favoured with the occurrence of spontaneous vaporization once the ethanol was present for precipitation. Therefore, low ethanol humidity (20% ERH in this study) was sufficient. In contrast, higher ethanol humidity (>70% ERH) was preferable to produce spherical particles. This study provides an insight into particle engineering to unveil the internal droplet conditions and physical phenomena during this unique process.

The Lipid Droplet Knowledge Portal: A resource for systematic analyses of lipid droplet biology.

Lipid droplets (LDs) are organelles of cellular lipid storage with fundamental roles in energy metabolism and cell membrane homeostasis. There has been an explosion of research into the biology of LDs, in part due to their relevance in diseases of lipid storage, such as atherosclerosis, obesity, type 2 diabetes, and hepatic steatosis. Consequently, there is an increasing need for a resource that combines datasets from systematic analyses of LD biology. Here, we integrate high-confidence, systematically generated human, mouse, and fly data from studies on LDs in the framework of an online platform named the "Lipid Droplet Knowledge Portal" (https://lipiddroplet.org/). This scalable and interactive portal includes comprehensive datasets, across a variety of cell types, for LD biology, including transcriptional profiles of induced lipid storage, organellar proteomics, genome-wide screen phenotypes, and ties to human genetics. This resource is a powerful platform that can be utilized to identify determinants of lipid storage.

Molecular Determinants of Selectivity in Disordered Complexes May Shed Light on Specificity in Protein Condensates.

Biomolecular condensates challenge the classical concepts of molecular recognition. The variable composition and heterogeneous conformations of liquid-like protein droplets are bottlenecks for high-resolution structural studies. To obtain atomistic insights into the organization of these assemblies, here we have characterized the conformational ensembles of specific disordered complexes, including those of droplet-driving proteins. First, we found that these specific complexes exhibit a high degree of conformational heterogeneity. Second, we found that residues forming contacts at the interface also sample many conformations. Third, we found that different patterns of contacting residues form the specific interface. In addition, we observed a wide range of sequence motifs mediating disordered interactions, including charged, hydrophobic and polar contacts. These results demonstrate that selective recognition can be realized by variable patterns of weakly defined interaction motifs in many different binding configurations. We propose that these principles also play roles in determining the selectivity of biomolecular condensates.

ЭКОЛОГИЧЕСКИЕ АСПЕКТЫ ОПТИМИЗАЦИИ ПРИМЕНЕНИЯ СРЕДСТВ ЗАЩИТЫ РАСТЕНИЙ

Within the “From Field to Counter” Strategy framework, the European Parliament calls for a review of the procedure for the admission of plant protection products (PPP) in the EU. The aim is to strengthen control over the PPP use and reduce their use. The development of energy- and resource-saving agrochemical technologies for the PPP use implies designing monodisperse spray devices for specific chemicals, specifying their consumption rates per unit area, and selecting compatible spray equipment and relevant agricultural technologies. The elaboration of spray technology requires a fundamentally new approach to its testing and determining the dispersed composition of spray droplets. To elaborate an innovative methodology for optimizing the operation of spraying devices based on the dispersive analysis of spray droplets, the authors have developed and manufactured a test bench that provides a representative aerosol sampling. Express analyzers of spraying quality have been developed, made in the form of cards with dimensions 90 by 40 mm or tape 40 mm wide and 3 m long, impregnated with a solution of potassium hexacyanoferrate (III) at a concentration of 5…7%. A computer program has been made for counting and ranking spray drops in a real-time mode. The article presents study results on the optimization of several parameters: the consumption rates of the products and the hydraulic medium, the density (concentration) of the power fluid droplets on the surface of the treatment object, the dispersed composition of the spray droplets (the droplet size, the degree of productivity polydispersity and the possibility of adjusting the technological process parameters). The developed experimental complex and the technology of experimental testing of spraying devices will facilitate comparative tests of spraying devices.

Electrodynamic balance-mass spectrometry reveals impact of oxidant concentration on product composition in the ozonolysis of oleic acid.

The chemical and physical properties of atmospheric aerosol particles change upon oxidative ageing, influencing their interaction with radiation, their propensity to serve as nuclei for cloud condensation and ice formation, and their adverse effects on human health. The investigation of atmospheric aerosol oxidation processes is complicated by low oxidant concentrations and long timescales, which are difficult to represent in laboratory studies. Experimental work often attempts to compensate for short timescales with elevated concentrations of oxidative agents, assuming that the ageing progress depends only on the oxidant exposure, i.e. on the product of oxidant concentration and time, [Ox] × t, and not on [Ox] or t independently. The application of electrodynamic balance-mass spectrometry of single particles allows the validity of this assumption to be investigated, since it provides information on the molecular composition of aerosol particles for a wide range of reaction durations under well-defined oxidation conditions. Here, we demonstrate the capabilities of a new setup on levitated oleic acid droplets reacting with ozone at mixing ratios of 0.2 and 15 ppm, i.e. spanning almost two orders of magnitude in [Ox]. We show that the reactive removal of oleic acid can be accurately expressed as a function of ozone exposure [Ox] × t, whereas the product concentrations depend on [Ox] and t independently. As the underlying reason for the breakdown of the exposure metric, we suggest a competition between evaporation of volatile first-generation products and their accretion reactions with reactive Criegee intermediates, converting them into low-volatility dimers and oligomers. This hypothesis is supported by kinetic model simulations using the aerosol process model KM-SUB, which explicitly resolves the competition between evaporation and secondary chemistry as a function of the experimental timescale and ozone mixing ratio. The model successfully reproduces final product distributions. The findings are further supported by the recorded changes of droplet sizes during oxidation. As a heuristic, the breakdown of the exposure metric in a chemical reaction system is possible, when competition between first- and second-order processes of reactive intermediates determines important system properties.

Numerical analysis on temporal size change of expiratory droplets by considering component variation

When conducting computational fluid dynamics (CFD) simulations to investigate the evaporation characteristics of respiratory particles, the over-simplification of droplet compositions may cause inaccuracies in the results. Although some researchers have conducted parametric studies on droplet components, an investigation using CFD simulation is still lacking. Therefore, this study aimed to determine the effect of different components on the temporal size change of expiratory droplets using CFD simulation. Two droplet sizes (10 μm and 100 μm) were selected, and two types of component combinations were considered, both with a volume fraction of 98.2% for water and 1.8% for non-volatile parts. In Scenario 1, the non-volatile part is composed of NaCl (density: 2200 kg/m3, molecular weight: 58.5 kg/kmol), whereas in Scenario 2, the non-volatile part is composed of NaCl, KCl, lactate, and protein (density: 1000 kg/m3, average molecular weight: 293 kg/kmol). Computations were conducted under constant temperature (25 °C) and different relative humidity (0 and 90%). The results showed that the equilibrium size and equilibrium time were strongly dependent on the droplet components. In subsequent investigations, the effects of different droplet components should be considered in the CFD simulations to obtain more accurate results.

Drying of virus-containing particles: modelling effects of droplet origin and composition

Background and purposeVirus-containing aerosol droplets emitted by breathing, speech or coughing dry rapidly to equilibrium with ambient relative humidity (RH), increasing in solute concentration with effects on virus survival and decreasing in diameter with effects on sedimentation and respiratory uptake. The aim of this paper is to model the effect of ionic and macromolecular solutes on droplet drying and solute concentration.MethodsDeliquescence-efflorescence concepts and Kohler theory were used to simulate the evolution of solute concentrations and water activity in respiratory droplets, starting from efflorescence data on mixed NaCl/KCl aerosols and osmotic pressure data on respiratory macromolecules.ResultsIn NaCl/KCl solutions total salt concentrations were shown to reach 10-13 M at the efflorescence RH of 40-55%, depending on the K:Na ratio. Dependence on K:Na ratio implies that the evaporation curves differ between aerosols derived from saliva and from airway surfaces. The direct effect of liquid droplet size through the Kelvin term was shown to be smaller and restricted to the evolution of breath emissions. Modelling the effect of proteins and glycoproteins showed that salts determine drying equilibria down to the efflorescence RH, and macromolecules at lower RH.ConclusionDifferences in solute composition between airway surfaces and saliva are predicted to lead to different drying behaviour of droplets emitted by breathing, speech and coughing. These differences may influence the inactivation of viruses.

Controlling composition of coexisting phases via molecular transitions

Phase separation and transitions among different molecular states are ubiquitous in living cells. Such transitions can be governed by local equilibrium thermodynamics or by active processes controlled by biological fuel. It remains largely unexplored how the behavior of phase-separating systems with molecular transitions differs between thermodynamic equilibrium and cases in which the detailed balance of the molecular transition rates is broken because of the presence of fuel. Here, we present a model of a phase-separating ternary mixture in which two components can convert into each other. At thermodynamic equilibrium, we find that molecular transitions can give rise to a lower dissolution temperature and thus reentrant phase behavior. Moreover, we find a discontinuous thermodynamic phase transition in the composition of the droplet phase if both converting molecules attract themselves with similar interaction strength. Breaking the detailed balance of the molecular transition leads to quasi-discontinuous changes in droplet composition by varying the fuel amount for a larger range of intermolecular interactions. Our findings showcase that phase separation with molecular transitions provides a versatile mechanism to control properties of intracellular and synthetic condensates via discontinuous switches in droplet composition.

Controlled self-assembly of microgels in microdroplets

Microgels with embedded distinct compartments are robust tools for creating different physiochemical scaffolding conditions by co-encapsulation of various cargoes. This work presents a robust, rapid, and low-cost approach for one-step fabrication of multicompartmental microgels using droplet-based microfluidic systems. After selective modification of microchannels wettability using a simple and reliable patterning approach, double emulsion (DE) droplets are generated with desired number, size and composition of internal precursor core droplets. Upon gelation, the microgels confined in each oil droplet self-assemble, followed by their rapid release from oil droplet. By tuning the droplet generation and crosslinking parameters, complex microgels with desired structure and composition are fabricated to demonstrate the potential of the method for flexible production of codded microgels. The DE approach applied here enables accurate confinement of target compartments, provides a clog-free on-chip gelation, and more importantly offers high biocompatibility due to rapid release of microgels from unfavorable reagents. Implementation of different hydrogels such as alginate, agarose, and gelatin methacryloyl further demonstrates the robustness of presented method which is not limited to a specific material or gelling condition. This method can provide new opportunities in many biomedical applications from tissue engineering to drug delivery and high-throughput multiplex bioanalysis.

Fragmentation of heated droplets of coal-water slurries containing petrochemicals

This research presents experimental findings on the fragmentation of droplets of coal-water slurries containing petrochemicals heated on a substrate (300–600 °C), in an air flow (450–550 °C), and in a tubular muffle furnace (500–700 °C). The fuels were composed of water, coal, coal processing waste (filter cakes), used industrial turbine oil, sawdust, nut shells, and stabilizers (neonol, starch, and tween). Before ignition, heated droplets behaved in three possible ways: gradual shrinking due to moisture evaporation; significant surface deformation when subjected to heating and droplet breakup with large fragments separating from it; full breakup of a droplet into small fragments. We recorded the droplet breakup delay times and integral characteristics of secondary fragments (number, size, and surface area) in comparison with the same parameters of the initial droplet. We also established the impact of a set of factors (temperature, heating scheme, and component composition of droplets) on the above characteristics. Approximations were obtained for the dependences established to be used for mathematical modeling. Finally, the findings were compared with the earlier established characteristics of similar processes studied in experiments with emulsion droplets and two-component immiscible droplets containing liquid combustible and noncombustible components.

Study of the influence of the increased carbon content in electrodes on structure and properties of the welding seam during welding of 110G13 steel

The object of research is the effect of the carbon-forming component of coated electrodes for welding and surfacing of Gadfield steel (110G13L and analogs) on the structure and properties of the weld. One of the most problematic areas in the welding and surfacing of high-carbon steel is the high irregularity of the rod and coating melting rates. Therefore, the non-melted part of the coating is literally poured into the weld pool, which leads to significant chemical and structural inhomogeneity of the welded metal. The main hypothesis of the study is the assumption that it is possible to increase the homogeneity of the deposited metal by changing the conditions for the transition of carbon from the electrode to the weld pool by using an electrode rod made of carbon steel. In the course of the study, electrode rods with different carbon contents were used. With an increase in the carbon content in the composition of the electrode rod, the fluidity of the drops increased, which contributed to a decrease in the strength of the welding current without harm to the welding and technological characteristics. This allows to reduce the generation of heat in the base metal, that is an effective measure to prevent hot cracks in the weld metal and heat affected zone Studies of the composition of the electrode metal droplets and the weld material showed that with an increase in the carbon content in the electrode rod from 0.08 % to 0.8 %, the carbon content in the droplets increases from 0.3 % to 0.97 %. The carbon content in the weld metal is 1.1 %. The assimilation of manganese by a drop increases with an increasing of coating and the droplet interaction time. A significant increasing in the rate of coating melting was obtained. This is due to the fact that the concomitant decrease in the content of graphite in the coating contributes to a decrease in the refractoriness of the electrode coating. The use of high carbon steels for the manufacturing of electrode rods for welding and surfacing of Gadfield steel improves the properties of the welded metal and sanitary and hygienic parameters.

Size conservation emerges spontaneously in biomolecular condensates formed by scaffolds and surfactant clients

Biomolecular condensates are liquid-like membraneless compartments that contribute to the spatiotemporal organization of proteins, RNA, and other biomolecules inside cells. Some membraneless compartments, such as nucleoli, are dispersed as different condensates that do not grow beyond a certain size, or do not present coalescence over time. In this work, using a minimal protein model, we show that phase separation of binary mixtures of scaffolds and low-valency clients that can act as surfactants—i.e., that significantly reduce the droplet surface tension—can yield either a single drop or multiple droplets that conserve their sizes on long timescales (herein ‘multidroplet size-conserved’ scenario’), depending on the scaffold to client ratio. Our simulations demonstrate that protein connectivity and condensate surface tension regulate the balance between these two scenarios. The multidroplet size-conserved scenario spontaneously arises at increasing surfactant-to-scaffold concentrations, when the interfacial penalty for creating small liquid droplets is sufficiently reduced by the surfactant proteins that are preferentially located at the interface. In contrast, low surfactant-to-scaffold concentrations enable continuous growth and fusion of droplets without restrictions. Overall, our work proposes one thermodynamic mechanism to help rationalize how size-conserved coexisting condensates can persist inside cells—shedding light on the roles of protein connectivity, binding affinity, and droplet composition in this process.

Raman Study on Lipid Droplets in Hepatic Cells Co-Cultured with Fatty Acids

The purpose of the present study was to investigate molecular compositions of lipid droplets changing in live hepatic cells stimulated with major fatty acids in the human body, i.e., palmitic, stearic, oleic, and linoleic acids. HepG2 cells were used as the model hepatic cells. Morphological changes of lipid droplets were observed by optical microscopy and transmission electron microscopy (TEM) during co-cultivation with fatty acids up to 5 days. The compositional changes in the fatty chains included in the lipid droplets were analyzed via Raman spectroscopy and chemometrics. The growth curves of the cells indicated that palmitic, stearic, and linoleic acids induced cell death in HepG2 cells, but oleic acid did not. Microscopic observations suggested that the rates of fat accumulation were high for oleic and linoleic acids, but low for palmitic and stearic acids. Raman analysis indicated that linoleic fatty chains taken into the cells are modified into oleic fatty chains. These results suggest that the signaling pathway of cell death is independent of fat stimulations. Moreover, these results suggest that hepatic cells have a high affinity for linoleic acid, but linoleic acid induces cell death in these cells. This may be one of the causes of inflammation in nonalcoholic fatty liver disease (NAFLD).

A Bimodal Fluorescence-Raman Probe for Cellular Imaging.

Biochemical changes in specific organelles underpin cellular function, and studying these changes is crucial to understand health and disease. Fluorescent probes have become important biosensing and imaging tools as they can be targeted to specific organelles and can detect changes in their chemical environment. However, the sensing capacity of fluorescent probes is highly specific and is often limited to a single analyte of interest. A novel approach to imaging organelles is to combine fluorescent sensors with vibrational spectroscopic imaging techniques; the latter provides a comprehensive map of the relative biochemical distributions throughout the cell to gain a more complete picture of the biochemistry of organelles. We have developed NpCN1, a bimodal fluorescence-Raman probe targeted to the lipid droplets, incorporating a nitrile as a Raman tag. NpCN1 was successfully used to image lipid droplets in 3T3-L1 cells in both fluorescence and Raman modalities, reporting on the chemical composition and distribution of the lipid droplets in the cells.

Unraveling Structural Details in Ga-Pd SCALMS Systems Using Correlative Nano-CT, 360° Electron Tomography and Analytical TEM

We present a comprehensive structural and analytical characterization of the highly promising supported catalytically active liquid metal solutions (SCALMS) system. This novel catalyst shows excellent performance for alkane dehydrogenation, especially in terms of resistance to coking. SCALMS consists of a porous support containing catalytically active low-melting alloy particles (e.g., Ga-Pd) featuring a complex structure, which are liquid at reaction temperature. High-resolution 3D characterization at various length scales is required to reveal the complex pore morphology and catalytically active sites’ location. Nano X-ray computed tomography (nano-CT) in combination with electron tomography (ET) enables nondestructive and scale-bridging 3D materials research. We developed and applied a correlative approach using nano-CT, 360°-ET and analytical transmission electron microscopy (TEM) to decipher the morphology, distribution and chemical composition of the Ga-Pd droplets of the SCALMS system over several length scales. Utilizing ET-based segmentations of nano-CT reconstructions, we are able to reliably reveal the homogenous porous support network with embedded Ga-Pd droplets featuring a nonhomogenous elemental distribution of Ga and Pd. In contrast, large Ga-Pd droplets with a high Ga/Pd ratio are located on the surface of SCALMS primary particles, whereas the droplet size and the Ga/Pd ratio decreases while advancing into the porous volume. Our studies reveal new findings about the complex structure of SCALMS which are required to understand its superior catalytic performance. Furthermore, advancements in lab-based nano-CT imaging are presented by extending the field of view (FOV) of a single experiment via a multiple region-of-interest (ROI) stitching approach.

Experimental Investigations on the Ignition Delay Time of Freely Falling Liquid Fuel Droplets

The ignition delays of freely falling liquid fuel droplets in a high-temperature environment were determined experimentally as a function of the surrounding parameters and droplet composition. Two different groups of fuels have been categorized based on the viscosity and volatility of each fuel. In the first group, for diesel and kerosene, the ignition delay time decreases with increasing system temperature due to low viscosity and thereby high volatile nature of fuels. Whereas, in the second group, C-heavy oil and blended renewable fuel shows an increase in the ignition delay time with increasing the system temperature and thereby shows the negative temperature coefficient (NTC) behavior due to high viscosity and low volatile characteristics of those fuels. In the case of low viscosity carbon residue fuels with low ignition temperature, they may vaporize early and decrease in the ignition delay time. But for high viscosity carbon residue fuels and with high ignition temperature, it may prolong the vaporization time and thereby physical delay. Evidently, the physical parameters and therefore the physical delay are the predominant factors in the NTC behavior of such high hydrocarbon liquid fuel droplets.

Active coacervate droplets are protocells that grow and resist Ostwald ripening

Active coacervate droplets are liquid condensates coupled to a chemical reaction that turns over their components, keeping the droplets out of equilibrium. This turnover can be used to drive active processes such as growth, and provide an insight into the chemical requirements underlying (proto)cellular behaviour. Moreover, controlled growth is a key requirement to achieve population fitness and survival. Here we present a minimal, nucleotide-based coacervate model for active droplets, and report three key findings that make these droplets into evolvable protocells. First, we show that coacervate droplets form and grow by the fuel-driven synthesis of new coacervate material. Second, we find that these droplets do not undergo Ostwald ripening, which we attribute to the attractive electrostatic interactions and translational entropy within complex coacervates, active or passive. Finally, we show that the droplet growth rate reflects experimental conditions such as substrate, enzyme and protein concentration, and that a different droplet composition (addition of RNA) leads to altered growth rates and droplet fitness. These findings together make active coacervate droplets a powerful platform to mimic cellular growth at a single-droplet level, and to study fitness at a population level.

The disassembly of lipid droplets in Chlamydomonas.

Lipid droplets (LDs) are ubiquitous and specialized organelles in eukaryotic cells. Consisting of a triacylglycerol core surrounded by a monolayer of membrane lipids, LDs are decorated with proteins and have myriad functions, from carbon/energy storage to membrane lipid remodeling and signal transduction. The biogenesis and turnover of LDs are therefore tightly coordinated with cellular metabolic needs in a fluctuating environment. Lipid droplet turnover requires remodeling of the protein coat, lipolysis, autophagy and fatty acid β-oxidation. Several key components of these processes have been identified in Chlamydomonas (Chlamydomonas reinhardtii), including the major lipid droplet protein, a CXC-domain containing regulatory protein, the phosphatidylethanolamine-binding DTH1 (DELAYED IN TAG HYDROLYSIS1), two lipases and two enzymes involved in fatty acid β-oxidation. Here, we review LD turnover and discuss its physiological significance in Chlamydomonas, a major model green microalga in research on algal oil.

Coal-water slurry atomization in a new pneumatic nozzle and combustion in a low-power industrial burner

A new pneumatic nozzle for spraying coal-water fuel based on the near-wall and cumulative jets and Coanda effect has been tested. The mechanisms and characteristics of CWS spraying and combustion have been investigated. To prepare the CWS, Kuznetsk oxidized coal of grade D (long-flame) was used in proportion to water of 55/45. The disperse composition of water and CWS droplets was measured at the nozzle outlet using the shadow photography method. The characteristic size of liquid CWS droplets in the ignition region is 20 µm. At the same time, the flow contains coal particles with a size of about 100 µm. This size of particles is sufficient for efficient combustion. The principle possibility of efficient joint combustion of CWS and pulverized coal fuel with the help of the developed burner is shown at the uncooled fire setup with an uncooled 5-MW furnace. The experiments were carried out at a power of 1 MW and water content in CWS of 45%. NOx emissions meet the MPC requirements for coal-fired boilers. Emissions of other substances are close to zero even with suboptimal operating and design parameters. The results obtained can be used in numerical simulation of the processes of CWS dispersion and combustion. Further work should be aimed at optimizing operating parameters in application to industrial conditions and at developing practical recommendations for boiler design.

Simulation of evaporation of lower alcohols binary droplets

This paper presents the simulation results of evaporation process of lower alcohols - ethanol (E), butanol (B) and their binary mixtures individual droplets with 2 mm droplet initial size in hot air (T∞ = 440 ÷ 675K) and atmospheric pressure. The evaporating droplets size, composition and temperature histories are obtained using descrete-component approach to describe different initial composition fuel mixtures heat-mass transfer processes. The comparative analysis of obtained data allowed to propose a possible mechanism of multicomponent fuel mixtures droplets evaporation and explain some of predicted features in main process characteristics behavior.