Crystallization Of Droplets Research Articles

Optical properties of different crystal structures under evaporative crystallization

We investigate the behavior of evaporative crystallization of a fluorescent dye droplets on the substrates with different contact angles. Evaporation of the dye drop lead to smaller crystals at the centre of the droplet. In the case of on the glass substrate, two distinct microcrystalline morphologies of the recrystallized deposits – hexagonal and stick/rod shaped have been observed. This indicates that the evaporation driven crystallization is highly dependent on the wettability of the substrate. The sizes of crystals decrease on increasing the contact angle of the substrate. The photoluminescence (PL) studies indicate that the hexagonal crystals have higher emission compared to rod-shaped crystals. PL decay measurements also show distinct lifetimes for the two shapes. The self-assembly leading to the formation of distinct crystal morphologies along with their individual optical properties different from the parent material is highly interesting to the optical materials research.

Variations of interfacial thermal conductance at melting and crystallization of an indium micro-particle in contact with a solid

The heat transfer between a micrometer-sized particle, as used in laser-assisted additive manufacturing, and a substrate strongly depends on the variations in interfacial thermal conductance (ITC), among other thermophysical parameters of the sample and substrate. Variations of ITC were measured on a millisecond time scale during fast melting and crystallization of an indium micro-sized sample with a mass of about 1 ng. Fast scanning nanocalorimetry was simultaneously applied with high-speed infrared thermography. The ITC between the sample and the sensor membrane was obtained. Therefore, the evolution of the temperature difference at the sample/membrane interface during fast melting and crystallization of the micro-sized indium droplet was measured. An unusual effect of gradual variation of ITC in the melting experiment was found. The method can be applied for ITC measurements during fast processes with 0.26 ms resolution. The quantification of ITC allows, for example, the optimization of melting during additive manufacturing.

Microfluidic formation of crystal-like structures.

Crystal-like structures find application in several fields ranging from biomedical engineering to material science. For instance, droplet crystals are critical for high throughput assays and material synthesis, while particle crystals are important for particles and cell encapsulation, Drop-seq technologies, and single-cell analysis. Formation of crystal-like structures relies entirely on the possibility of manipulating with great accuracy the micrometer-size objects forming the crystal. In this context, microfluidic devices offer versatile tools for the precise manipulation of droplets and particles, thus enabling fabrication of crystal-like structures that form due to hydrodynamic interactions among droplets or particles. In this review, we aim at providing an holistic representation of crystal-like structure formation mediated by hydrodynamic interactions in microfluidic devices. We also discuss the physical origin of these hydrodynamic interactions and their relation to parameters such as device geometry, fluid properties, and flow conditions.

A new model for chromitite formation in ophiolites: Fluid immiscibility

Although the involvement of hydrous fluids has been widely invoked in formation of podiform chromitites in ophiolites, there is lack of natural evidence to signify the role and mechanism of fluids. In this study, a new model for the genesis of podiform chromitite is proposed on basis of revisits of comprehensive petrological, mineralogical and geochemical results of the well-preserved Kizildag ophiolite and the well-characterized Luobusa chromite deposit. In this model, ascending magmas intruding oceanic lithospheric mantle would presumably form a series of small magma chambers continuously connected by conduits. Tiny chromite nuclei would collect fluids dispersed in such magmas to form nascent droplets. They tend to float upward in the magma chamber and would be easily transported upward by flowing magmas. Chromite-rich droplets would be enlarged via coalescence of dispersed droplets during mingling and circulation in the magma chamber and/or transport in magma conduits. Crystallization of the chromite-rich liquid droplets would proceed from the margin of the droplet inward, leaving liquid entrapped within grains as precursor of mineral inclusions. With preferential upward transportation, immiscible chromite-rich liquids would coalesce to a large pool in a magma chamber. Large volumes of chromite would crystallize in situ , forming podiform chromitite and resulting in fluid enrichment in the chamber. The fluids would penetrate and compositionally modify ambient dunite and harzburgite, leading to significant fractionations of elemental and isotopic compositions between melts and fluids from which dunite and chromitite respectively formed. Therefore, fluid immiscibility during basaltic magma ascent plays a vital role in chromitite formation.

Exploration of the natural waxes-tuned crystallization behavior, droplet shape and rheology properties of O/W emulsions

Lipid crystallization in O/W emulsions is essential to control the release of nutrients and to food structuring. While few information is involved in adjusting and controlling the performance of emulsions by adjusting oil phase crystallization behavior. We herein developed a novel strategy for designing lipid crystallization inside oil droplets by natural waxes to modify the O/W emulsion properties. Natural waxes, the bio-based and sustainable materials, displayed a high efficiency in modifying the crystallization behavior, droplet surface and shape, as well as the overall performance of emulsions. Specifically, waxes induced the formation of a new hydrocarbon chain distances of 3.70 and 4.15 Å and slightly decreased the lamellar distance (d001) of the single crystallites, thus forming the large and rigid crystals in droplets. Interestingly, these large and rigid crystals in droplets tended to penetrate the interface film, forming the crystal bumps on the droplet surface and facilitating non-spherical shape transformation. The presence of rice bran wax (RW) and carnauba wax (CW) induced the droplet shape into ellipsoid and polyhedron shape, respectively. Furthermore, the uneven interface and non-spherical shape transformation promoted the crystalline droplet-droplet interaction, fabricating a three-dimensional network structure in O/W emulsions. Finally, both linear and nonlinear rheology strongly supported that waxes enhanced the crystalline droplet-droplet interaction and strengthened the network in O/W emulsions. Our findings give a clear insight into the effects of adding natural waxes into oil phase on the crystalline and physical behavior of emulsions, which provides a direction for the design and control of emulsion performance.

Experiments to understand crystallization of levitated high temperature silicate melt droplets under low vacuum conditions

We report experiments on crystallization of highly undercooled forsterite melt droplets under atmospheric and sub-atmospheric pressure conditions. Experiments have been conducted under non-contact conditions using the principles of aero-dynamic levitation. Real time dynamics of solidification, along with the transient evolution of surface textures, have been recorded using high speed camera for three cooling rates. These images have been matched with the time-tagged temperature data to understand the effect of pressure conditions and cooling rates on the crystallization dynamics. Compared to normal pressure, relatively higher levels of undercooling could be achieved under sub-atmospheric conditions. Results showed a strong dependence of surface textures on pressure conditions. For any externally employed cooling rate, relatively small length scale morphological textures were observed under sub-atmospheric conditions, in comparison to those achieved under ambient conditions. The observed trends have been explained on the basis of influence of pressure conditions on recalescence phenomenon and the rate at which latent heat of crystallization gets dissipated from the volume of the molten droplet. Sub-atmospheric experiments have also been performed to reproduce one of the classical chondrule textures, namely the rim + dendrite double structure. Possible formation conditions of this double structure have been discussed vis-à-vis those reported in the limited literature. To the best of our knowledge, the reported study is one of the first attempts to reproduce chondrules-like textures from highly undercooled forsterite melt droplets under sub-atmospheric non-contact conditions.

Molecular Dynamics Study on Cooling and Crystallization of Water Droplets on Solid Surfaces with Various Wettability

Molecular Dynamics Study on Cooling and Crystallization of Water Droplets on Solid Surfaces with Various Wettability

Analysis of Freeze-Thaw Behavior of Double (W1/O/W2) Emulsions by Differential Scanning Calorimetry: Effects of Inner Salt Concentration and Solid Fat Content

This work is focused on the study of freeze-thaw behavior of double (W1/O/W2) emulsions by the application of a cooling-heating-cooling cycle by differential scanning calorimetry. Emulsions were prepared with sodium caseinate as hydrophilic emulsifier in outer aqueous (W2) phase and sunflower oil (SO) and/or interesterified vegetable fat (VF) plus polyglycerol polyricinoleate as lipophilic emulsifier in lipid phase. The effects of sodium chloride concentration in inner aqueous (W1) phase and solid fat content in lipid phase were analyzed. In all cases, W1 phase froze at lower temperature than W2 phase because higher undercooling was required for the crystallization of inner water droplets. In the absence of VF, the system with low salt concentration showed water diffusion from undercooled W1 phase to frozen W2 phase at the first cooling stage, due to the lower vapor pressure of ice. However, at the second cooling stage, this phenomenon was not observed and partial recovery of inner water was detected, probably because of an osmotic effect. The increase of salt concentration allowed a higher retention of inner water after freezing of W2 phase, attributed to the lowered vapor pressure of W1 phase. The loss of inner water was also restrained or prevented by the presence of VF in lipid phase due to the immobilization of water droplets within a fat crystal network. The crystallization behavior of SO was related to inner water quantity and VF content. This study could be useful for the formulation of W1/O/W2 emulsions with enhanced freeze-thaw stability.

Future warming exacerbated by aged-soot effect on cloud formation

Clouds play a critical role in modulating the Earth’s radiation balance and climate. Anthropogenic aerosol particles that undergo aging processes, such as soot, aid cloud droplet and ice crystal formation and thus influence the microphysical structure of clouds. However, the associated changes in cloud radiative properties and climate effects remain uncertain and are largely omitted in climate models. Here we present global climate simulations of past and future effects of both ozone-aged soot particles acting as cloud condensation nuclei and sulfuric acid-aged soot particles acting as ice-nucleating particles on the structure and radiative effects of clouds. Under pre-industrial conditions, soot aging led to an increase in thick, low-level clouds that reduced negative shortwave effective radiative forcing by 0.2 to 0.3 W m−2. In the simulations of a future, warmer climate under double pre-industrial atmospheric carbon dioxide concentrations, soot aging and compensating cloud adjustments led to a reduction in low-level clouds and enhanced high-altitude cirrus cloud thickness, which influenced the longwave radiative balance and exacerbated the global mean surface warming by 0.4 to 0.5 K. Our findings suggest that reducing emissions of soot particles is beneficial for future climate, in addition to air quality and human health. Aged soot particles in the atmosphere enhance future warming through their influence on cloud formation and thus Earth’s radiation balance, according to global climate simulations.

Sessile Microdroplet‐Based Writing Board for Patterning of Structural Colored Hydrogels

AbstractThe patterning of structural colored materials has a significant impact on various applications such as flexible displays, anti‐counterfeiting patches, colorimetric sensors, etc. Herein, a sessile microdroplet‐based writing board is presented to pattern magnetochromatic hydrogels with abundant structural colors and improved optical performance. It is demonstrated that predesigned hydrophilic patterns on a hydrophobic writing board can capture a mixture of polymer and Fe3O4@SiO2 magnetic nanoparticles inks with a spatial resolution of ≈100 pin per 1 cm2 while retaining magnetic field responsibility to the lower limit of 84 Gs. The inks are self‐partitioned into microdroplet arrays, which would in situ transform into structural colored hydrogels within a short time via thiol‐Michael addition. In contrast to conventional evaporation induced assembly of colloidal photonic crystals in sessile droplets, the resulting structural colored hydrogel microarrays show not only good stability and optical adjustability but tunable morphologies. In addition, the introduction of the microfluidic mixing and ink dispensing system greatly shortens the time interval from the polymer mixing to sessile droplet generation, circumvents the challenge of short operation time for the self‐crosslinking ink components, and enables the direct handwriting of high quality structural colored patterns.

Pathway of orientational symmetry breaking in crystallization of short n-alkane droplets: A molecular dynamics study.

We carry out molecular dynamics simulations by using an all-atom model to study the nucleation and crystallization of n-alkane droplets under three-dimensional and quasi-two-dimensional conditions. We focus on the development of orientational order of chains from a random state to a neatly ordered one. Two new methods, the map of symmetry breaking and the information entropy of chain orientations, are introduced to characterize the emerge and remelting phenomena of a primary nucleus at the early stage of crystallization. Stepwise nucleation, as well as the surface induced nucleation, of large droplets is observed. We elucidate the kinetic process of the formation of a primary nucleus and the rearrangement of every single molecule involved in a primary nucleus. We found that density fluctuation and orientational preordering are coupled together and occur simultaneously in nucleation. Our results show the pathway of orientational symmetry breaking in the crystallization of n-alkane droplets that are heuristic for the deeper understanding of the crystallization in more complex molecules such as polymers.

Hygroscopic properties and compositional evolution of internally mixed sodium nitrate-amino acid aerosols

Abstract Although nitrates and amino acids are ubiquitous in the atmosphere, the interactions of amino acids with nitrates on the hygroscopicity of aerosols are still not clear. We studied the hygroscopic properties and compositional evolution of three atmospherically relevant species, sodium nitrate (NaNO3), glycine and L-alanine (alanine). The investigations on the NaNO3, glycine, alanine and their internally NaNO3/amino acid mixed particles with molar ratios of 3:1, 1:1 and 1:3 were conducted using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The mixed NaNO3/glycine droplets with molar ratios of 3:1, 1:1 and 1:3 exhibited efflorescence transition at 52.3%, 62.6% and 63.2%RH, respectively. For the NaNO3/alanine mixed systems with molar ratios of 3:1, 1:1 and 1:3, the efflorescence relative humidity (ERH) was measured to be 50.2%, 59.8% and 69.3%, respectively. These results suggested that in each of the systems studied the addition of amino acids to aerosols could promote the crystallization of mixed droplets. However, the higher deliquescence relative humidity (DRH) with increased fraction of glycine for the mixed NaNO3/glycine (3:1, 79.2%RH; 1:1, 86.3%RH; 1:3, 86.5%RH) also indicated that glycine could inhibit the deliquescence phase transition of mixed systems. In the case of NaNO3/alanine systems, the DRH for 3:1 and 1:3 mixed particles was 78.2% and 82.7% while no deliquescence transition occurred for the 1:1 mixed particles. The hygroscopic properties of mixed NaNO3/amino acids droplets were modified due to the formed amino acid-NaNO3 complex salts from the interactions of amino acids with NaNO3 in aerosols during dehydration process. The discrepancies in water content for the mixed NaNO3/amino acids with molar ratios of 1:1 and 1:3 between dehydration and hydration processes at high RH could be attributed to the crystallization of amino acid-NaNO3 complex salts during dehydration and the residual amino acids.

Unveiling the importance of process parameters on droplet shrinkage and crystallization behaviors of easily crystalline material during spray drying

This study investigated droplet shrinkage and crystallization behaviors of easily crystalline mannitol model material. Different sized droplets were generated from feeds of different solid contents and dried into uniform microparticles via a microfluidic jet spray dryer. The droplet shrinkage behavior was characterized by comparing the size of dried microparticles and initially atomized droplets. Morphology and polymorphs of the microparticles were analyzed via SEM and XRD. Droplet shrinkage and crystallization behaviors were shown to be closing related to size, morphology, and polymorph of the spray dried microparticles. Droplets with small size or low solid content followed perfect shrinkage behavior, while droplets with larger sizes or higher solid contents demonstrated less shrinkage due to the earlier precipitation of a crust. Dense, partially hollow, or hollow spherical particles with different polymorphs (mixture of α- and β-mannitol or fully β-mannitol) were obtained depending on the process parameters, indicating the occurrence of different crystallization behaviors.

The dependence of evaporation and crystallization kinetics on dynamic and thermal background

AbstractIn technical problems there is often the need to simultaneously describe both non‐stationary evaporation and non‐stationary crystallization of droplets and films. Poor wettability of the wall and high heat fluxes lead to the film rupture and the formation of pools, dry spots, droplets. To date, there are no well‐developed methods for calculating crystallization and evaporation in the presence of the factors. Evaporation and crystallization of a drop are shown to fundamentally differ from those of a thin layer. The rate of evaporation prior to crystallization controls the crystallization kinetics. The evaporation and crystallization rates for the film (under identical conditions) are significantly higher than for the drop. The difference in the thickness of the diffusion and dynamic boundary layers affects the evaporation rate of an aquatic salt solution. For correct simulation of evaporation, it is necessary to take into account the thicknesses of the thermal, diffusion and concentration boundary layers.

Interfacial microdroplet evaporative crystallization on 3D printed regular matrix platform

AbstractDroplet evaporative crystallization on microscale heterogeneous surface is a vivid topic in chemical engineering, bioengineering, nanomaterials, and so on. Here, 3D printed interfacial matrix platform with regular pillar convexity and tunnel structure is fabricated to reveal the mechanism of the interfacial micro droplet crystallization. Element‐based rotation volume model is established to simulate the concentration and nucleation barrier distribution during the microscale process. Sodium urate monohydrate and NaCl crystallization on the pillar convex structure both confirm that confined capillary flow in the micro droplet and initial nucleation condition dominate the nucleation, growth control and particle distribution. Droplet crystallization stretches over the tunnel structure reveal an interesting phenomenon that two regions possessing distinct‐different nucleation barriers can isolated obtain the crystal particles from nanoscale to even millimeter scale. The fabricated platform and the capillary circulation transfer theory unfold a potential approach to harvest high value‐added crystals with specific morphology and desire sizes distribution.

Non-Ostwald Behavior of Disperse Systems in Evaporation and Crystallization of Droplets of Water–Organic Solutions

This Letter describes experiments with aqueous solutions of organic substances demonstrating a non-Ostwald behavior under which the stability of small droplets during evaporation and crystallization is higher than that of large droplets. Such a behavior has been described earlier for aqueous solutions of some inorganic salts. It is shown that the non-Ostwald behavior has a common thermodynamic nature with Ostwald ripening and should be observed in disperse systems with a complex chemical composition. The features of reproduction of the non-Ostwald behavior related to the surface activity of organic substances in aqueous solutions are described. The studied regularities can be used upon preparation of solutions of organic and bioorganic substances with a concentration significantly higher than their solubility under normal conditions, as well as for the formation of narrow size distributions in different spray processes.

Crystallization kinetics of pentaerythritol tetranitrate (PETN) thin films on various materials

The nature of the crystal growth process in explosives can dramatically impact their safety and performance. Thin films are a commonly used tool for investigating the fundamental crystallization behavior in many systems, and the interfacial physics between a crystallizing species and the substrate can significantly affect many factors associated with the crystal growth process. In this work, atmospheric vapor deposition was used to prepare thin films of supercooled PETN droplets on the surfaces of copper, gold, and silicon. The gold and copper surfaces were prepared on silicon substrates using ultra-high vacuum vapor deposition. Crystallization of the supercooled PETN droplets was induced by scanning the surface of each substrate type with an atomic force microscope upon which crystallization occurred in the form of compact, circularly shaped dendrites reminiscent of spherulites. All three substrates were characterized relative to their respective surface roughness and surface energy. The surface energy was assessed from contact angle measurements with three liquids: water, ethylene glycol, and dodecane. High-resolution, time-lapse images of the crystal growth process were acquired under high magnification on each material surface, and the crystal growth rates were measured based on the radial distance of “ring” features that appeared in the crystal growth patterns after inducing changes in the substrate temperature. The growth rates were used to determine the Arrhenius activation energy of crystal growth on each surface, and the results indicate that there is a significant correlation between the surface energy and the crystallization behavior of the supercooled PETN droplets.

Tritoroidal particle rings formation in open microfluidics induced by standing surface acoustic waves.

In this paper, the particle movements in a sessile droplet induced by standing surface acoustic waves (SSAWs) are studied. Tritoroidal particle rings are formed under the interaction of acoustic field and electric field. The experimental results demonstrate that the electric field plays an important role in patterning nanoparticles. The electric field can define the droplet shape due to electrowetting. When the droplet approximates a hemisphere, the acoustic radiation force induced by SSAWs drives the particles to form tritoroidal particle rings. When the droplet approximates a convex plate, the drag force induced by acoustic steaming drives the particle to move. The results will be useful for better understanding the nanoparticle movements in a sessile droplet, which is important to explain the mechanism that SSAWs enhance reaction and crystallization in droplet.

Rotons and Bose condensation in Rydberg-dressed Bose gases

We investigate the ground-state properties and excitations of Rydberg-dressed bosons in both three and two dimensions, using the hypernetted-chain Euler-Lagrange approximation, which accounts for correlations and thus goes beyond the mean field approximation. The short-range behavior of the pair distribution function signals the instability of the homogeneous system towards the formation of droplet crystals at strong couplings and large soft-core radius. This tendency to spatial density modulation coexists with off-diagonal long-range order. The contribution of the correlation energy to the ground-state energy is significant at large coupling strengths and intermediate values of the soft-core radius while for a larger soft-core radius the ground-state energy is dominated by the mean-field (Hartree) energy. We have also performed path integral Monte Carlo simulations to verify the performance of our hypernetted-chain Euler-Lagrange results in three dimensions. In the homogeneous phase, the two approaches are in very good agreement. Moreover, Monte Carlo simulations predict a first-order quantum phase transition from a homogeneous superfluid phase to the quantum droplet phase with face-centered cubic symmetry for Rydberg-dressed bosons in three dimensions.

The crystallization behavior of the aqueous solution of CaCl2 salt in a drop and a layer

Non-isothermal evaporation during crystallization of CaCl2 salt in a droplet and a thin layer on a hot wall has been investigated experimentally. The growth of salt crystal hydrates (CaCl2·2H2O) on the interface has been studied. It has been found that the change in the initial salt concentration leads to different crystallization rates. The crystallization rate on the droplet interface is many times lower than for a thin layer. The description of crystallization in the salt solution droplet should take into account the crystallization anisotropy, which is associated with the direction of crystallization. The crystallization rate along the contact line of the droplet is many times higher than in the direction of the droplet radius. For a long time of crystallization, the area of the crystal film (outside the drop) increases several times. Four characteristic modes of crystallization to a drop of salt solution have been distinguished. When modeling crystallization, it is necessary to take into account multiple changes in the growth rate of salt crystallohydrates over time, as well as the anisotropic nature of crystallization.