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Single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) is a high-throughput method for the multiplexed analysis of nanoparticles (NPs). However, matrix interferences are a significant challenge that must be overcome for accurate NP sizing and number concentration determination. In online microdroplet calibration, multi-element droplet standards are mixed with nebulized aerosols from a NP-containing sample in a dual-sample introduction system before entering the ICP. Microdroplet standards are used to determine absolute sensitivities and calibrate the mass amount(s) of analyte element(s) in particle events. A plasma-uptake standard is added to NP-containing samples to account for variations in the nebulization and transport efficiency of aerosols into the plasma, which are used in the determination of particle number concentrations (PNCs). Since the microdroplets experience the same plasma conditions as analyte NPs, this creates a matrix-matched calibration. We studied the efficacy of online microdroplet calibration for the quantification of NPs in three organic matrices: ethanol, acetone, and acetonitrile. Organic solvents can cause a pronounced increase in sample uptake and cause plasma-related signal attenuation for nanoparticle measurements. Online microdroplet calibration corrects for both effects without the use of nanoparticle standards. Our results demonstrate accurate NP sizing and PNC determinations in organic matrices up to 98% (v/v), even when these matrices caused signals to be attenuated up to 35-times and nebulizer transport efficiencies to be up to four-times higher than that of a pure water matrix., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

The high-speed impact of liquid microdroplets has emerged as a promising method to eliminate nanoparticle contaminants from semiconductor wafer surfaces. However, existing experimental studies have primarily focused on evaluating their own nozzles for removing particles larger than 50 nm, which does not align with the current research roadmap where the target particles' size decreases down to sub-10 nm. As it is more challenging to remove smaller particles, there is a strong need to better understand droplet's spreading behavior in relation to the detachment of particles from a surface. Nonetheless, there remains a lack of experimental evidence to validate existing models or a scarcity of numerical simulation studies, mainly due to the practical difficulties associated with single droplet experiments. Hence, in this study, we conduct a series of numerical simulations to investigate the time-dependent spreading behavior of the droplet, together with collecting local velocity data at the attached particle position. The local velocity data is then integrated to an existing model to predict the effective cleaning diameter for each impact condition. Starting from the free-fall dropwise impaction, we develop a single-microdroplet cleaning system by minimizing the number of sprayed droplets and capturing their behavior using a high-speed camera (HSC), with aims of validating the model predictions and numerical simulations. Finally, we provide a contour plot for a prior prediction of the effective cleaning diameter from the impaction conditions of microdroplets. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

We report a novel method to conduct heterogeneous reactions using aqueous-ionic liquid Janus microdroplets as a series of isolated bi-phasic microreactors where AgCl@polyaniline core–shell nanoparticles are successfully synthesized accompanied by polyaniline nano-needles, and enhanced visualization of reaction progression through the color changes in Janus droplets is achieved. [ABSTRACT FROM AUTHOR]

Polymer microparticle synthesis based on the surface‐templated method is a simple and environmentally friendly method to produce various microparticles. Unique particles with different compositions can be fabricated by simply annealing a polymer on a liquid‐repellent surface. However, there are hurdles to producing particles of homogeneous sizes with large quantities and varying the shape of particles. Here, a new approach to synthesizing multiple polymer microparticles using micropatterns with wettability contrast is presented. Polymer microparticles are formed in two steps. First, a layer of poly(sodium‐4‐styrenesulfonate) is deposited on the hydrophilic regions by dipping and withdrawing this micropattern from a polymer solution, and an array of microdroplets is formed. A dewetting‐inducing layer on the pattern is introduced, and then target polymer patches are sequentially generated on it. By annealing over Tg, the contact line of the target polymer patch is freely receded, creating a particle form. The size and shape of the microparticle can be controlled by varying the micropatterns. In addition, it is demonstrated that microparticles made of polymer blends or polymer/nanoparticle composite are easily produced. This versatile method offers the potential of surface‐templated synthesis to tailor polymer microparticles with different sizes, shapes, and functionalities in various research and applications. [ABSTRACT FROM AUTHOR]

Droplet evaporation and dissolution phenomena are pervasive in both natural and artificial systems, playing crucial roles in various applications. Understanding the intricate processes involved in the evaporation and dissolution of sessile droplets is of paramount importance for applications such as inkjet printing, surface coating, and nanoparticle deposition, etc. In this study, we present a demonstration of electrochemical investigation of the dissolution behaviour in sub-nL droplets down to sub-pL volume. Droplets on an electrode have been studied for decades in the field of electrochemistry to understand the phase transfer of ions at the oil–water interface, accelerated reaction rates in microdroplets, etc. However, the impact of microdroplet dissolution on the redox activity of confined molecules within the droplet has not been explored previously. As a proof-of-principle, we examine the dissolution kinetics of 1,2-dichloroethane droplets (DCE) spiked with 155 μM decamethylferrocene within an aqueous phase on an ultramicroelectrode (r = 6.3 μm). The aqueous phase serves as an infinite sink, enabling the dissolution of DCE droplets while also facilitating convenient electrical contact with the reference/counter electrode (Ag/AgCl 1 M KCl). Through comprehensive voltammetric analysis, we unravel the impact of droplet dissolution on electrochemical response as the droplet reaches minuscule volumes. We validate our experimental findings by finite element modelling, which shows deviations from the experimental results as the droplet accesses negligible volumes, suggesting the presence of complex dissolution modes. [ABSTRACT FROM AUTHOR]

Overcoming the oxygen diffusion limit of approximately 200 µm remains one of the most significant and intractable challenges to be overcome in tissue engineering. The fabrication of hydrogel microtissues and their assembly into larger structures may provide a solution, though these constructs are not without their own drawbacks; namely, these hydrogels are rapidly degraded in vivo, and cells delivered via microtissues are quickly expelled from the area of action. Here, we report the development of an easily customized protocol for creating a protective, biocompatible hydrogel barrier around microtissues. We show that calcium carbonate nanoparticles embedded within an ECM-based microtissue diffuse outwards and, when then exposed to a solution of alginate, can be used to generate a coated layer around the tissue. We further show that this technique can be fine-tuned by adjusting numerous parameters, granting us full control over the thickness of the hydrogel coating layer. The microtissues' protective hydrogel functioned as hypothesized in both in vitro and in vivo testing by preventing the cells inside the tissue from escaping and protecting the microdroplets against external degradation. This technology may provide microtissues with customized properties for use as sources of regenerative therapies. [ABSTRACT FROM AUTHOR]

Polycaprolactone nanoparticles (NPs) were produced in the co‐flow glass capillary device with 250μm tip dimension. NPs size was 990 nm for continuous phase velocity, and uc=0.05m/s and 426 nm for uc=0.2m/s. The droplet formation process in the co‐flow microchannel was also simulated using computational fluid dynamic (CFD). Employing a digital image analysis technique, a cut‐off value of 0.81 for the dispersed phase volume fraction was proposed for the determination of droplet size. A scenario was expressed for NP formation from micro‐droplets. Moreover, after conducting 27 CFD simulations, a dimensionless exponential form correlation was proposed for droplet size estimation. In this generalized map, there were three distinct regions based on the relative capillary numbers of continuous to dispersed phases. It was revealed that at a constant dispersed phase velocity, by increasing the continuous phase velocity, more small NPs are formed. The results show that the ratio of micro‐droplets to NPs size was between 735 and 755. [ABSTRACT FROM AUTHOR]

Spontaneous emulsification, resulting from the assembly and accumulation of surfactants at liquid–liquid interfaces, is an interfacial instability where microdroplets are generated and diffusively spread from the interface until complete emulsification. Here, it is shown that an external magnetic field can modulate the assembly of paramagnetic nanoparticle surfactants (NPSs) at liquid–liquid interfaces to trigger an oversaturation in the areal density of the NPSs at the interface, as evidenced by a marked reduction in the interfacial tension, γ, and corroborated with a magnetostatic continuum theory. Despite the significant reduction in γ, the presence of the magnetic field does not cause stable interfaces to become unstable. Upon rapid removal of the field, however, an explosive ejection of a plume of microdroplets from the surface occurs, a dynamical interfacial instability which is termed explosive emulsification. This explosive event rapidly reduces the areal density of the NPSs to its pre‐field level, stabilizing the interface. The ability to externally suppress or trigger the explosive emulsification and controlled generation of tens of thousands of microdroplets, uncovers an efficient energy storage and release process, that has potential applications for controlled and directed delivery of chemicals and remotely controlled soft microrobots, taking advantage of the ferromagnetic nature of the microdroplets. [ABSTRACT FROM AUTHOR]

• The revelation of the evaporation and solidification mechanism of microdroplets. • Modeling of evaporative microdroplets across scales. • Propose a modified set of boundary conditions to control the evaporation rate. • Optimize the cured morphology using vacuum drying system. Inkjet printing is already regarded as a transformative technique for producing organic light-emitting diodes (OLED) due to its low cost, high material utilization, and short procedure. However, the application of printed OLED has been severely limited by the appearance fault of cured microdroplets. The process of microdroplets evaporation is complicated and hard to monitor experimentally since it spans the nano and micro scales. In this work, a hybrid 3D lattice Boltzmann (LB) model coupled with the Langevin equation model is used to study the evaporation and solidification mechanism of microdroplets in the pit. During the microdroplets evaporation process, the nanoparticles (NPs) are primarily affected by the internal field of microdroplets and the falling liquid level. The internal field will bring the NPs inside the microdroplets to the edge of pit, while the falling liquid level causes the NPs to fall vertically. Based on this law, we propose a modified set of boundary conditions to control the evaporation rate. The slower the evaporation rate, the more NPs gather around the edge. The maximum particle uniformity of 68.27 % is achieved with an evaporation coefficient of 0.85. Ultimately, we successfully achieved a uniform and flat morphology of the cured microdroplets by making the microdroplets evaporate at varying speeds. The mechanism of the evaporation and the solidification of microdroplets in pits are revealed, which is of great significance to the application of printed OLED technology. [ABSTRACT FROM AUTHOR]

In this work, we investigated the orientation and the polarization of ZnO nanoparticles, which serve as building blocks of highly monodisperse microspheres, using a droplet microfluidic-assisted synthesis method. We observe, for the first time, a square lattice organization of liquid microdroplets, in a steady state, at the oil/water interface. Such square organization reveals clearly a dipolar organization of ZnO nanoparticles at the surfaces of droplets at the early stage of ZnO nanocrystal aggregation and microsphere formation. We discuss different models of organization of ZnO nanoparticles and show that the well-known tip-streaming effect in droplets in microfluidics explains the reason for the obtained dipolar droplets. The square organization is illustrated and explained. [ABSTRACT FROM AUTHOR]

Aqueous microdroplets strongly attach to metallic needles with superhydrophobic sides and flat hydrophilic tips. Such needles can be made surface‐enhanced Raman spectroscopy (SERS)‐active by adsorbing a layer of densely packed and uniform plasmonic nanoparticles onto the hydrophilic tip. The resulting particle‐tipped needles allow dual enhancement of the Raman signals from microdroplets of low concentration analytes by combining analyte enrichment through solvent evaporation and plasmonic SERS enhancement. The combination of small sample volume, preconcentration, and SERS allows extremely low total amounts of analytes to be detected. Here, we show that with crystal violet as the model analyte, the limit of detection can reach 2 pg. The method can be readily used to fabricate superhydrophobic needles tipped with different types of plasmonic colloidal nanoparticles for enhanced Raman analysis, for example, silver cube tipped needles could be used to detect as little as 2.5 ng of trinitrotoluene. [ABSTRACT FROM AUTHOR]

Laser-microdroplet interactions influence the quality of nanoparticle deposition on a substrate. When a microdroplet and its impinging spot are heated, the microdroplet can evaporate gently, boil immediately after impingement, or bounces back inhibiting the deposition process. The interaction between a laser and droplets carrying semiconductor and metal nanoparticles is studied for different laser powers. The results indicate that the laser is refocused by the droplets, and deposition of nanoparticles and formation of nanofeatures are achieved under certain conditions. On the other hand, when the laser power exceeds a critical value, heating up the substrate at a specific temperature, microdroplets bounce back from the substrate, except for the cases of liquids with low reflectance coefficient and high absorption coefficient, where a new laser-spraying regime is observed. [ABSTRACT FROM AUTHOR]

In this paper, an additive manufacturing process has been used to deposit nanoparticles on a substrate. In this innovative technique called the nano-electrospray laser deposition process, droplets of various nanosuspensions are dispensed onto a silicon substrate where subwavelength structures and bouncing droplets have been observed. An analytical model is presented for determining the temperature distribution in the substrate by considering the microdroplet as a ball lens. This lens continuously changes the focus of the laser beam as the droplet travels toward the substrate. The laser is either defocused or focused on the substrate forming locally decreased or enhanced heating near the center of the laser beam depending on the distance of the droplet from the substrate. It is found that the enhancement in heating differs for the nanosuspensions since their optical properties are different. The subwavelength structures determined from the post-pulse temperature qualitatively match with the experimental results. The steady end-period temperature is also compared with the experimentally observed temperature for bouncing droplets and the temperatures are in good agreement. [ABSTRACT FROM AUTHOR]

For the first time, the molecular bands of the C 2 species were detected in the single-bubble sonoluminescence spectra of aqueous colloidal suspensions of graphite nanoparticles (≤ 50 nm) obtained by ultrasonic dispergation upon multi-bubble sonolysis. The registration of these bands indicates that graphite nanoparticles enter the moving cavitation bubble together with solution microdroplets, where they are decomposed in the nonequilibrium plasma that occurs during ultrasonic vibrations into small fragments, including C 2 radicals. Based on the conventional mechanism for the formation of fullerenes at the arc-discharge synthesis, starting from C 2 , under plasma conditions, we suggest that these framework molecules are synthesized in a cavitation bubble during single-bubble sonolysis of graphite nanoparticles. Indeed, the presence of the C 60 and C 70 fullerenes was registered in the accumulated sonolysis products of samples of suspensions of graphite nanoparticles with the chromatographic and mass-spectrometric techniques. [Display omitted] • Graphite nanoparticles (∼20 nm) were subjected to moving single-bubble sonolysis • Lines of C 2 molecule are detected in the spectrum of moving single-bubble sonoluminescence • Assembly С 2 → С 60 /C 70 in the bubble's plasma is assumed • The assumption is confirmed with mass-spectrometric detection of the fullerene products of sonolysis (С 60 /C 70) [ABSTRACT FROM AUTHOR]

The article titled "Formation of Giant Unilamellar Vesicles Assisted by Fluorinated Nanoparticles" presents a new technique for creating giant unilamellar vesicles (GUVs) that contain transmembrane proteins. The researchers used silica nanoparticles to stabilize microdroplets, which then served as templates for the formation of GUVs. The resulting GUVs could be easily released through centrifugation. This technique provides a valuable tool for the artificial cell community. [Extracted from the article]

Supercritical antisolvent precipitation (SAS) has been successfully used to produce microparticles and nanoparticles of controlled size and distribution either as a single precipitates or by coprecipitation of two or more compounds. SAS coprecipitation process has produced different particles morphologies and, differently from the single compound SAS precipitation, process mechanisms involved have never been elucidated and the effectiveness of the technique has been verified only in some cases. In this work, the mechanisms proposed in SAS coprecipitation are critically discussed and general indications about coprecipitation efficiency are given, based on several experimental evidences and on the possible underlying nucleation, growth and drying mechanisms. The most effective and reliable SAS coprecipitation resulted from the formation of microdroplets and their subsequent drying. [ABSTRACT FROM AUTHOR]

Abstract: Liquid crystalline tactoids are anisotropic microdroplets existing in isotropic phases. We studied the structure and evolution of tactoids in the presence of doping nanoparticles by electron microscopy at the resolution of individual mesogens and observed size‐selective exclusion effects of liquid crystalline tactoids on foreign nanoparticles. We applied this principle to the separation of polymer nanospheres, gold nanoparticles, and magnetic nanoparticles by size. These results indicate a new way to size‐selectively separate nanoparticles using lyotropic liquid crystals, in which nanoparticles smaller than a threshold size will be selectively transferred from the disordered phase into the ordered phase by tactoids during the phase separation process. [ABSTRACT FROM AUTHOR]

Abstract: Creating an intelligent artificial cell wall to endow fabricated cells with more advanced functionalities is highly desirable. Here, an efficient and cytocompatible approach to generate a type of viable artificial cell wall based on direct self‐assembly of coacervate microdroplets on individual cellular surface is developed, which can protect the fabricated cell against various external stresses and can then prolong the storage of the fabricated cells over two months. Moreover, as a type of viable artificial cell wall, it can not only help the fabricated cell sequester nutrients or functionalized substances such as catalase, or iron oxide nanoparticles actively from the solution which then makes the fabricated cell more versatile but also allows the fabricated cell proliferate. Significantly, the artificial cell wall also shows heritable behavior that can reserve its protection to as far as the third‐generation daughter cell. Undoubtedly, such an illustrated artificial cell wall provides a conceptually new and promising technique toward the cell‐based research as well as application of next generation. [ABSTRACT FROM AUTHOR]

Manipulation of arrayed tiny droplets is important in liquid dispersion, liquid transportation, bioassays, nucleation, integrated electronics, and various lab experiments that require delivering precise and minute volumes of droplets. Liquid dispensed from a small orifice or split from surface patterns are typical methods, but the acquired droplet diameters are similar to that of the nozzle and pattern. Here we demonstrate that tiny droplets with dimensions much smaller than the pattern can be arrayed advantageously through designing a Laplace pressure pattern based on conical morphology and wetting heterogeneity. The pattern could selectively resist liquid's motion and drive the capillary bridge breaking of macrodrop into arrayed tiny droplets at wettability boundaries. Arrayed picoliter droplets can be acquired on a submillimeter-scaled pattern with a feature size of several hundred micrometers. Through regulating the conical morphologies and the wetting heterogeneity, the volume and number of tiny droplets can be accurately controlled. As a paradigm, adopting droplets of nanoparticle dispersion, various arrayed functional assemblies can be fabricated. This integration of conical morphology and wetting heterogeneity offers a powerful kit for patterned microdroplets quantitative and locational manipulation and opens a new avenue to achieve functional units in a facile and high-throughput way. [ABSTRACT FROM AUTHOR]

The optical spectra of nanostructured patterns with different degrees of order, obtained by dehydration self-assembly of nanoparticles in solution microdroplets placed on a planar substrate, have been analyzed. The reflectance spectrum of the best-ordered pattern contains a characteristic peak, the position of which is determined by the average lattice period in the layer. It is shown that the height of this peak depends on the degree of order of the pattern structure. Patterns with different degrees of order have been simulated using a software for modeling the self-assembly process, which takes into account the properties of particles, substrate, and solvent, as well as the contact line dynamics during solvent evaporation. A peak occurs in the reflectance spectrum due to the resonance Rayleigh scattering in the ordered layer. The described technique for optical diagnostics can be used to analyze the degree of particle order in a pattern. [ABSTRACT FROM AUTHOR]

We investigated the possibility of using charged luminescent nanoparticles as nanoprobes for studying the evolution scenarios of surface and internal structure of slowly evaporating free (light-absorbing) microdroplets of suspension. Three concentrations (1, 10 and 50 mg/ml) of luminescent nanoparticles were used. Single microdroplets were kept in a linear electrodynamic quadrupole trap and the luminescence was excited with a CW IR laser with an irradiance of ∼50 W/mm2. Since the microdroplet acted as an optical spherical resonance cavity, the interaction of nanoparticles with light both reflected and modified the internal light field mode structure. Depending on the nanoparticle concentration used, it led, among others, to a very significant increase in modulation depth and narrowing of spherical cavity resonance maxima (morphology dependent resonances – MDRs) observed both in luminescence and scattering, the abrupt changes in the ratio between the luminescence and the scattering and the bi-stability in luminescence signal. The observed phenomena could be attributed to the interaction of optical MDRs with nanoparticle lattice shells forming and changing their structure at the microdroplet surface. In this way, the formation and collapse of such lattices could be detected. [Display omitted] [ABSTRACT FROM AUTHOR]

A method to monitor the level of oxygen in microdroplets is presented. Optical sensor nanoparticles are dispersed in the aqueous phase of the microfluidic droplets for culturing bacteria. The oxygen sensor nanoparticles consist of phosphorescent indicator dye embedded in poly(styrene-block-vinylpyrrolidone) nanobeads. The nanoparticles are excitable by red light and emit in the near-infrared spectra region which minimizes background fluorescence from biological matter. The biocompatibility of the nanoparticles was proven. Nanoparticles sensors were read out by adapted miniaturized oxygen meters. The instruments can be easily integrated into the microfluidic system by placing it next to the tubing and measuring through the tubing wall. The phosphorescence lifetime-based measurement circumvents the drawbacks of intensity-based measurements and enables the determination of the absolute oxygen concentration in individual moving droplets. The technique can also be used for monitoring the growth of bacteria in microdroplets. We demonstrate simultaneous measurement of concentration of oxygen and optical density (OD) from micro cultures of E. coli and M. smegmatis. [ABSTRACT FROM AUTHOR]

An acoustic levitator was used to determine the drying kinetics and behavior of microdroplets of colloidal polymer latex dispersions. It was possible to measure the kinetic behavior of evaporation rate, droplet surface temperature, and droplet/particle aspect ratio for two polymers at two different volume fractions of dispersed phase, ϕ. A drying air temperature of 60 °C, a relative humidity of 1 %, and a flow rate of 0.5 L/min through the levitator chamber were used. Under these conditions Eudragit NE 30 D was dried above its minimum film-forming temperature and a critical point of drying could be detected from sharp changes in surface temperature and droplet/particle shape. The drying rate depended inversely on ϕ which increases continually during drying. Aquacoat was dried below its minimum film-formation temperature, and a two-step change in particle/droplet shape and surface temperature was observed. Although the nanoparticles of Aquacoat form an interfacial film at the first step, this does not substantially reduce drying rate. Only the second step change in surface temperature was accompanied by a decrease in drying rate as the surface film is now sufficiently condensed but not fused. The levitator detects therefore a differentiated picture of the changes taking place in drying rate, surface temperature, and droplet/particle. [ABSTRACT FROM AUTHOR]

Intrinsic differences in the molecular sequestration of folded and unfolded proteins within poly(diallyldimethylammonium) (PDDA)/poly(acrylate) (PAA) coacervate microdroplets are exploited to establish membrane-free microcompartments that support protein refolding, facilitate the recovery of secondary structure and enzyme activity, and enable the selective uptake and exclusion of folded and unfolded biomolecules, respectively. Native bovine serum albumin, carbonic anhydrase, and α-chymotrypsin are preferentially sequestered within positively charged coacervate microdroplets, and the unfolding of these proteins in the presence of increasing amounts of urea results in an exponential decrease in the equilibrium partition constants as well as the kinetic release of unfolded molecules from the droplets into the surrounding continuous phase. Slow refolding in the presence of positively charged microdroplets leads to the resequestration of functional proteins and the restoration of enzymatic activity; however, fast refolding results in protein aggregation at the droplet surface. In contrast, slow and fast refolding in the presence of negatively charged PDDA/PAA droplets gives rise to reduced protein aggregation and misfolding by interactions at the droplet surface to give increased levels of protein renaturation. Together, our observations provide new insights into the bottom-up design and construction of self-assembling microcompartments capable of supporting the selective uptake and refolding of globular proteins. [ABSTRACT FROM AUTHOR]

In this paper, nanoparticle enhanced laser-induced breakdown spectroscopy (NELIBS) was applied to the elemental chemical analysis of microdrops of solutions with analyte concentration at subppm level. The effect on laser ablation of the strong local enhancement of the electromagnetic field allows enhancing the optical emission signal up to more than 1 order of magnitude, enabling LIBS to quantify ppb concentration and notably decreasing the limit of detection (LOD) of the technique. At optimized conditions, it was demonstrated that NELIBS can reach an absolute LOD of few picograms for Pb and 0.2 pg for Ag. The effect of field enhancement in NELIBS was tested on biological solutions such as protein solutions and human serum, in order to improve the sensitivity of LIBS with samples where the formation and excitation of the plasma are not as efficient as with metals. Even in these difficult cases, a significant improvement with respect to conventional LIBS was observed. [ABSTRACT FROM AUTHOR]

Controlled crystallization is very important for crystal growth. The electrospray (ES) technique has attracted great interest thanks to its advantages of facile manipulation of micrometer droplets and the generation of fine and charged droplets with very narrow size dispersion. In this work, nanocrystals with cubic shapes with 32 nm edges were successfully grown from ultra-dilute NaCl solution (1 µg mL-1) on a millisecond timescale by an ES technique. Dispersed and charged microdroplets were created by ES. In the process, an increase in ion strength and built-in electric field in microdroplets promoted nucleation and growth. Moreover, solvent evaporation increased solute and charge concentration and decreased the size of the microdroplets, which had a further effect on nucleation and growth. The morphologies of crystals were the competitive results of ion strength and evaporation. Fortunately, these physicochemical properties can be controlled facilely by adjusting the ES parameters. This report suggests potential application of ES technology for controllable crystallization of pharmaceuticals, proteins, etc. [ABSTRACT FROM AUTHOR]

Condensate microdrop self-propelling (CMDSP) surfaces have attracted intensive interest. However, it is still challenging to form metal-based CMDSP surfaces. We design and fabricate a type of copper-based CMDSP porous nanoparticle film. An electrodeposition method based on control over the preferential crystal growth of isotropic nanoparticles and synergistic utilization of tiny hydrogen bubbles as pore-making templates is adopted for the in situ growth of cerium oxide porous nanoparticle films on copper surfaces. After characterizing their microscopic morphology, crystal structure and surface chemistry, we explore their CMDSP properties. The nanostructure can realize the efficient ejection of condensate microdrops with sizes below 50 μm. [ABSTRACT FROM AUTHOR]

This article addresses steady flow of Maxwell nanofluid induced by an exponentially stretching sheet subject to convective heating. The revised model of passively controlled wall nanoparticle volume fraction is taken into account. Numerical solutions of the arising non-linear boundary value problem (BVP) are obtained by using MATLAB built-in function bvp4c. Simulations are performed for various values of embedded parameters which include local Deborah number, Prandtl number, Biot number, Brownian motion parameter and thermophoresis parameter. The results are consistent with the previous studies in some limiting cases. It is found that velocity decreases and temperature increases when the local Deborah number is increased. Moreover the influence of Brownian diffusion on temperature and heat transfer rate is found to be insignificant. [ABSTRACT FROM AUTHOR]

Nanometer-sized magnetic stirring bars containing Pd nanoparticles (denoted as Fe3O4-NC-PZS-Pd) for heterogeneous catalysis in microscopic system were prepared through a facile two-step process. In the hydrogenation of styrene, Fe3O4-NC-PZS-Pd showed an activity similar to that of the commercial Pd/C catalyst, but much better stability. In microscopic catalytic systems, Fe3O4-NC-PZS-Pd can effectively stir the reaction solution within microdrops to accelerate mass transfer, and displays far better catalytic activity than the commercial Pd/C for the hydrogenation of methylene blue in an array of microdroplets. These results suggested that the Fe3O4-NC-PZS-Pd could be used as nanoscale stirring bars in nanoreactors. [ABSTRACT FROM AUTHOR]

The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, herein it is demonstrated that adsorbate-driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface-driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as 'Janus-like' microparticles. By using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field. [ABSTRACT FROM AUTHOR]

A high-rate, continuous synthesis of functional nanomaterials using a home engineered reactor is reported. The reactor is able to produce low-cost, kilogram-scale BaTiO3 nanopowders with a nanocrystalline particle size less than 30 nm at mild temperatures (<100 °C) and ambient pressure. Nebulization and collision of warm microdroplets (60-80 °C) of Ba(OH)2 and Ti(O-nBu)4 very quickly result in total hydrolysis and subsequent conversion to BaTiO3, yielding 1.3 kg/day of high purity, highly crystalline nanoparticles (25-30 nm). This synthesis procedure also enables high-rate production of TiO2 anatase (2.9 kg/day). It therefore provides a general platform for processing and scaling up of functional inorganic nanomaterials under very mild conditions. [ABSTRACT FROM AUTHOR]

The helium-assisted evaporation of pure, saline, and nanoparticle (NP)-containing microdroplets (∅droplet = 40–50 μm) at ambient conditions was studied. To quantify the liquid-to-gas mass transfer water droplets experience during evaporation, their sizes were monitored in different sections of a custom-made transport system, corresponding to increasing residence times after production. Drying times specified this way turned out to be approximately three times faster than values achievable by heavier gases such as argon which is commonly chosen as the carrier gas for subsequent NP analysis by inductively-coupled plasma mass spectrometry (ICP-MS). Furthermore, residues of saline droplets doped with well-defined amounts of an acidified calcium standard solution were classified by light scattering (LS) and scanning electron microscopy (SEM) indicating nearly complete desolvation over transport distances of a few tens of centimeters if helium or argon–helium mixtures were supplied. Mass transfer rates along droplet trajectories simulated on the basis of computational fluid dynamics (CFD) were found to be consistent with measured ones which proved the applicability of the evaporation model used, thus allowing an optimization of user-defined transport systems without the need for a time-consuming adaptation by trial-and-error. The analytical capabilities of helium-assisted evaporation as an alternative to conventional approaches employing argon-only-based set-ups operated at elevated temperatures were, in addition, demonstrated by ICP-quadruple (Q)MS of gold NPs. Therefore, NP-containing droplets were delivered through an either horizontally or vertically arranged transport assembly both resulting in over-all throughputs of 90 to 100%. [ABSTRACT FROM AUTHOR]

A prototype inductively coupled plasma time-of-flight mass spectrometer (ICPTOFMS) for time resolved measurements of transient signals in the microsecond regime is described in this work. Analytical figures of merit for the prototype are given for both liquid nebulization and single droplet introduction and are compared to a conventional quadrupole-based ICPMS using the same ICP source and vacuum interface. Quasi-simultaneous detection at a time resolution of 33 μs of the prototype ICPTOFMS allows multi-isotope monitoring of short signals (200–500 μs duration) generated from individual droplets and particles. The capabilities of the instrument for the analysis of single nanoparticles are studied using microdroplets consisting of a multi-element standard solution and containing 114 nm Au particles. The detection efficiencies for Ag and Au, calculated from the response of individual droplets and particles, are similar to those of the quadrupole-based instrument and amount to 1.3 × 10−6 ions per atom and 3.1 × 10−6 ions per atom, respectively. The sizes of the smallest detectable Ag, Au and U metallic nanoparticles are estimated to be 46 nm, 32 nm and 22 nm, respectively. Furthermore, time shifts of the signals of different elements within single droplets were observed. These new results demonstrate the advantage of the temporal resolution of the instrument for studying processes taking place in the plasma on the μs-time scale. [ABSTRACT FROM AUTHOR]

This work presents the fabrication and characterization of a dielectric microdroplet thermal interface material (TIM). Glycerin droplets, 1 μL, were tested as TIMs in this study. Copper nanoparticles having a diameter of 25 nm were dispersed in glycerin at different volume fractions to enhance its thermal conductivity. An increase of 57.5 % in the thermal conductivity of glycerin was measured at a volume fraction of 15 %. A minimum thermal interface resistance of 30.37 mmK/W was measured for the glycerin microdroplets at a deformed droplet height of 10.2 μm. Good agreement between experimental measurements and the predictions of a model based on Maxwell's equation of rules of mixtures was obtained. The effect of nanoparticles' size on the effective thermal conductivity of glycerin was studied. Nanoparticles with diameters of 60-80 and 300 nm were dispersed in glycerin at a volume fraction of 5 %, and their results were compared to those of the 25 nm particles. [ABSTRACT FROM AUTHOR]

Abstract: Particles produced by low-temperature desolvation of monodisperse microdroplets of analyte standard solution and nanoparticle suspensions in argon were collected on Si-wafers and studied applying scanning electron microscopy and X-ray microprobe techniques. At desolvation temperatures of about 150°C, the particles from standard solutions are most often spherical and solid with good reproducibility and the analyte elements together with the unavoidable accompanying elements from trace contamination seem to be homogeneously distributed in the particles. However, there are surprising exceptions, particularly at higher temperatures, where analyte elements are separated in the particle by reduction or crystallization, as shown with Au and Ca standard solutions, respectively. Drying droplets of a diluted suspension of 250nm gold particles at 200°C revealed another interesting result, the production of relatively stable concave balloons of ∼3µm in diameter including the Au particles. The balloon sheath was formed of compounds made of the contaminant elements in the suspension. The morphology of the particles is discussed in consideration of the Peclet number, the ratio of evaporation rate to analyte diffusion coefficient. The consequences of particle size and morphology for calibration purposes in nanoparticle characterization by ICP spectrometry are discussed. [Copyright &y& Elsevier]

The structure of water in water-in-oil microemulsions used to synthesize oxalate precusor nanoparticles for the production of YBa2Cu3O7−x (YBCO) superconductor powder has been studied by FTIR–ATR spectroscopy of the O&z.sbnd;H stretching band. Two initial microemulsions are mixed together and nanoparticles are formed by a precipitation reaction in the cores of the reverse micelles of the resulting microemulsion. The shapes of the water O&z.sbnd;H stretching bands for the microemulsions before and after the reaction exhibit noticeable differences when normalized at their peaks. These differences have been quantified by decomposing the water O&z.sbnd;H stretching band into three components corresponding to water molecules with different types of hydrogen bonding. In the microemulsion after the precipitation and formation of oxalate precusor nanoparticles, the structure of water is characterized with an increased fraction of bound water. These bound water molecules are also connected with stronger H-bonds. We propose that upon synthesis of the precursor nanoparticles, the observed water structure changes are due to a thin water layer formed around the newly synthesized nanoparticles. [Copyright &y& Elsevier]

• Laser engineering of microbial systems is an effective precise method of bioprinting. • However, pressure jumps during printing process can cause damage to biomaterial. • The amplitude of pressure jumps was evaluated in the 1–100 MHz range. • Pressure jumps of 0.02–5 kbar appear when using a Ti film and 0.02–10 kbar for Cr. • At E > 15 μJ the optoacoustic conversion efficiency for a Cr film is higher than for Ti. Laser printing with gel microdroplets containing living organisms is a promising method for microbiology, biotechnology, and medicine. The transfer of small volumes of the gel occurs due to the absorption of a short laser pulse in a thin metal film of the donor plate. During the transfer process, laser printing generates pressure jumps that can cause damage and loss of biological material. Therefore, the assessment of these jumps is important for studying the influence of physical factors on the transferred living systems and improving the technology of laser printing with biomaterials. In the course of laser printing, laser pulses with a wavelength of 1064 nm, energy 7–120 µJ, duration of 4–30 ns with a laser beam diameter of 30 µm were applied to Ti and Cr films of glass donor slides. Experimental estimates of the emerging jumps were carried out on the basis of measurements of the acoustic pressure in the far zone in the range of 1–100 MHz using a hydrophone based on a lithium niobate crystal. It was found that in the operating range of laser energies E = 15–30 μJ in a gel layer with a thickness of 200 μm on the donor plate, pressure jumps from 20 bar to 5 kbar appeared when using an absorbing Ti film and from 20 bar to 10 kbar for a Cr film. The high efficiency of optoacoustic conversion for Cr films is explained by the better adhesion of this metal to the glass surface. [ABSTRACT FROM AUTHOR]

Tumor blood vessels are chaotic and abundantly distributed, owing to their heterogeneity. Therefore, imaging techniques which reveal abnormalities of tumor vasculature play significant roles in both mechanistic and clinical diagnostic tumor studies. Photoacoustic (PA) imaging uses the intrinsic characteristics of hemoglobin, to acquire tumor hemodynamic information, while ultrasound (US) imaging provides information about tumoral vessel structures and blood flow. To improve the imaging contrast performance, hydrogel-based microdroplets were designed for both US blood flow and PA imaging in this study. The microdroplets served as carriers for PA contrast agent solution in the innermost part while oil and hydrogel formed the inner and outer layers of the droplets. In vitro experiments firstly demonstrated the dual modality contrast effects of the microdroplets on US flow determination and PA imaging. In vivo experiments were then carried out in both healthy nude mice and nude mice with subcutaneous tumor to validate the contrast effects and to monitor the duration of contrast effects in animals. Using the dual-modality microdroplets, we were able to obtain distinct edges of tumor and blood flow mapping of the tumor microvascular with improved sensitivity up to 11.09 dB for PA and 6.69 dB for US flow. Besides, the in vivo evaluation with microdroplets showed US flow enhancement for more than 60 min. Therefore, the microdroplets are able to provide the contrast effects for both US flow and PA in a relative long duration and have potential to be applied in the tumor related diagnoses and studies. [ABSTRACT FROM AUTHOR]

Gold nanoparticles coated with a poly(N‐isopropylacrylamide) (pNIPAM) shell undergo reversible dis/assembly below and above the critical temperature of 32 °C. Loading these particles into microdroplets at high density creates light‐driven artificial chromatophores. Triggering the nanoparticle assembly gives dramatic color changes from nanoparticle localization at the base of the droplets, resembling zebrafish melanophores. These reversible chromatophore states can be switched by both bulk and optical heating, explored here in individual microdroplets and in large cm2 areas of close‐packed droplets. Illuminating chromatophores off‐center with a tightly focused beam results in droplet locomotion via two separate mechanisms, Marangoni interfacial shear and gas bubble propulsion, depending on optical power. [ABSTRACT FROM AUTHOR]