High Supersaturation Research Articles

Manipulating the crystallization kinetics and morphology of gypsum, CaSO4·2H2O via addition of citrate at high levels of supersaturation and the effect of high salinity

Citrate ion possesses the right structure to be strongly bound on specific crystal faces of gypsum, CaSO4·2H2O, which results in an increase in the induction time of precipitation, and changes the structure and morphology of the solid. The inhibition of the precipitation kinetics of gypsum, in the stoichiometric reaction of Na2SO4 and CaCl2 was investigated in aqueous solutions with high supersaturation (0.1 M initial reactant concentrations). The induction time was found to be the longest when the inhibitor was present in fully deprotonated form in the solution (pH > 5). The inhibition effect levels off with the increasing inhibitor concentrations (ca. 3 mM). As a result of citrate binding, on the basis of SEM measurements, the morphology of the crystals change from rod-like to plate-like. Addition of high concentration of NaCl (mimicking seawater conditions) was found to facilitate the inhibition, but from the morphological studies, the inhibition mechanism of citrate appears to change under hypersaline conditions (relative to systems without added electrolyte.) From UV and IR spectroscopic measurements, it was found that the inhibitor ended up in the mother liquor after the completion of the precipitation reaction.

Modulation of evaporation-affected crystal motion in a drying droplet by saline and surfactant concentrations

Crystallization of evaporating droplets has attracted intense interests thanks to its broad applications in bioengineering, coating technologies and pharmaceutical industries. We investigate the effects of saline and surfactant concentrations on the evaporative dynamics and crystallization patterns of sessile droplets. The droplet exhibits three regimes during evaporation. In regime I, the droplet transits from pinning to depinning, and then the commence of crystallization near the contact line launches regime II, during which the crystal exhibits more or less inward motion. In regime III, the crystal becomes immobilized until the evaporation completes. In the surfactant-free saline droplet, the crystal exhibits a weak gathering motion towards the center at a low saline concentration, resulting in the mild discrete crystalline deposition. Whereas the crystal movability is highly enhanced that they gather as a chunk at a high saline concentration, resulting from the larger droplet contact angle and higher supersaturation at the beginning of crystallization, and the higher liquid-vapor surface tension. These factors increase the horizontal component of the capillary force and solutal Marangoni force which drive crystals inwards. In the presence of surfactant, the crystals stay almost immobilized in regime II compared to the ones of the surfactant-free droplet, leading to discrete crystal morphologies. Surfactant reduces the liquid-vapor surface tension and the contact angle at the beginning of crystallization which are responsible for the smaller inward driving force.

Development and Application of a Wide Dynamic Range and High Resolution Atmospheric Aerosol Water-Based Supersaturation Condensation Growth Measurement System

The supersaturated condensation of atmospheric aerosol is important in the study of mechanisms of cloud condensation and even heavy air pollution. The existing technology cannot realize accurate dynamic control of wide range supersaturation, so it is difficult to study condensation growth characteristics of nanoparticles through different levels of supersaturation. Here, a supersaturated condensation growth measurement system with three-stage microscope pipes was developed. The resolution of supersaturated condensation system is 0.14, within the range of 0.92 to 2.33 after calibration. Stabilization time is only about 80 s for saturation range 0.92–1.01, which helps to control saturation rapidly, and the control deviation of saturation is no more than 0.06. Measurement of different supersaturated condensation growth control conditions showed that, the particle size increased significantly compared with hygroscopic growth at high humidity. For single-component particles, the increase in size increased to a similar size at the same saturation, with a difference within 7.4%. The increase in size for ammonium sulfate (AS) increased by 13.4–30.2% relative to that of glucose. For the mixed-component, the increase in size decreased about 15.9–25.0% with the increase of the glucose. Because the glucose coating on the surface of AS have hindered particle growth. This also shows that atmospheric ultrafine particles, especially inorganic salt particles, will rapidly grow into larger particles under supersaturated conditions such as increased environmental humidity, thus having some impact on environmental pollution and climate change.

Total dissolved gases induced tolerance and avoidance behaviors in pelagic fish in the Yangtze River, China

Total dissolved gas (TDG) supersaturation caused by dam operations can cause fish gas bubble disease (GBD) and even fish kill. Few studies have examined the effects on pelagic species. Here, we examined the tolerance and avoidance characteristics of silver carp (Hypophthalmichthys molitrix), a pelagic fish widely distributed in the Yangtze River basin in China, under stress caused by TDG supersaturation. Silver carp had an average mortality rate of 7.5% ± 1.8%, 92.5% ± 1.8%, and 97.5% ± 1.8% under 130%, 140% and 150% TDG supersaturation for 72 h of exposure, respectively. The average median lethal time (LT50) of silver carp was 18.1 h and 8.0 h under 140% and 150% TDG supersaturation, respectively. Bubbles and congestion appeared in the fins, gills and skin of silver carp. Silver carp can detect and avoid high TDG supersaturation. Significant avoidance behaviors were displayed by silver carp and the final avoidance rate was over 80% under 130% or above TDG conditions. The results of this study indicate that 130% TDG supersaturation triggered silver carp avoidance behaviors, and can be considered as the tolerance threshold.

Voltage losses in zero-gap alkaline water electrolysis

Reducing the gap between the electrodes and diaphragm to zero is an often adopted strategy to reduce the ohmic drop in alkaline water electrolyzers for hydrogen production. We provide a thorough account of the current–voltage relationship in such a zero-gap configuration over a wide range of electrolyte concentrations and current densities. Included are voltage components that are not often experimentally quantified like those due to bubbles, hydroxide depletion, and dissolved hydrogen and oxygen. As is commonly found for zero-gap configurations, the ohmic resistance was substantially larger than that of the separator. We find that this is because the relatively flat electrode area facing the diaphragm was not active, likely due to separator pore blockage by gas, the electrode itself, and or solid deposits. Over an e-folding time-scale of ten seconds, an additional ohmic drop was found to arise, likely due to gas bubbles in the electrode holes. For electrolyte concentrations below 0.5 M, an overpotential was observed, associated with local depletion of hydroxide at the anode. Finally, a high supersaturation of hydrogen and oxygen was found to significantly increase the equilibrium potential at elevated current densities. Most of these voltage losses are shown to be easily avoidable by introducing a small 0.2 mm gap, greatly improving the performance compared to zero-gap.

Ultra-fast growth of cuprate superconducting films: Dual-phase liquid assisted epitaxy and strong flux pinning

Cuprate superconductors are key candidate materials toward high energy-efficient devices. Improving their growth rate and performance under magnetic fields are indispensable for achieving even higher efficiency. For the first time, we demonstrated the ultra-high rate up to 100 nm/s in the growth of dual-phase cuprate superconducting film (EuBa2Cu3O7-BaHfO3). The growth rate achieved is two orders of magnitude higher than that at lab-scale and was also the highest on record to our best knowledge. Epitaxial growth mechanism assisted by the transient liquid phase is proposed, as evidenced by formation of Eu2BaCuO5 and Ba–Cu–O metastable phases under high supersaturation conditions. The high growth rate results in formation of mixed defective landscape, consisting of short nanorods, nanoparticles and naturally formed defects (e.g., staking faults). Due to such unique microstructure, we confirm that weak Jc anisotropy is dominated by random pinning mechanism. Contribution of isotropic and anisotropic Jc to Jctotal also varies with temperatures and magnetic field strength, which is a consequence of evolution of dominant pinning in film. As a result, the in-field current carrying capacity is significantly enhanced (exceeding 430 A/4 mm-width at 4.2 K, 18 T, B//c), being among the top tier of commercialized superconductor materials. This study establishes the correlation between ultra-high growth rate and flux pinning behaviors, which provides feasibility of dramatically improvement of production efficiency with the low price-performance ratio of future high temperature superconductor.

Using the near field optical trapping effect of a dielectric metasurface to improve SERS enhancement for virus detection

In this paper, we report the effect of optical trapping on the enhancement factor for Raman spectroscopy, using a dielectric metasurface. It was found that a higher enhancement factor (up to 275%) can be obtained in a substrate immersed in water, where particles are freee to move, compared to a dried substrate, where the particles (radius r=9 nm, refractive index n=1.58) are fixed on the surface. The highest enhancement is obtained at low concentrations because, this case, the particles are trapped preferentially in the regions of highest electric field (hotspots). For high concentrations, it was observed that the hotspots become saturated with particles and that additional particles are forced to occupy regions of lower field. The dielectric metasurface offers low optical absorption compared to conventional gold substrates. This aspect can be important for temperature-sensitive applications. The method shows potential for applications in crystal nucleation, where high solute supersaturation can be achieved near the high-field regions of the metasurface. The high sensitivity for SERS (surface-enhanced Raman spectroscopy) at low analyte concentrations makes the proposed method highly promising for detection of small biological particles, such as proteins or viruses.

Concomitant Polymorphism and Nucleation Control of DL‐Methionine Through Antisolvent Crystallization

AbstractThe concomitant polymorphism of the sulfur‐containing essential amino acid DL‐methionine was revealed, and α‐ and β‐polymorphic forms were separated from aqueous solution through antisolvent crystallization with ethanol as antisolvent. The addition of different volume fractions of ethanol into the mother solution reduces the solubility of DL‐methionine in double‐distilled water and in turn proportionately generates a range of supersaturation levels. This induces the nucleation of a stable β‐polymorph at low supersaturation levels, a mixture of α‐ and β‐ polymorphs at intermediate supersaturation levels, and a metastable α‐form at high supersaturation levels. Needle‐shaped α‐polymorphs and platy‐shaped β‐polymorphs were well distinguished through in‐situ optical microscopic analysis and their structural confirmation was done by X‐ray diffraction analysis.

Synthesis of uniform nanometer-thick graphite film on polycrystalline Ni substrate with ultrafine grains

When a polycrystalline Ni foil is used as the substrate for the chemical vapor deposition synthesis of multilayer-graphene or nanometer-thick graphite films (NGFs), these films always exhibit uneven morphologies and qualities on Ni grains with different orientations. In this study, we fabricated a carbon-supersaturated Ni foil (ss-Ni foil) to function as a carbon source through an ultrafast cooling process (∼180 °C/s), while an additional Ni film was sputtered on the ss-Ni foil to act as a buffer layer and a new surface for NGF growth. By re-annealing the Ni film/ss-Ni foil system at a low temperature (∼650–800 °C) within a short duration, NGF can rapidly form on the Ni film owing to the high supersaturation degree of the ss-Ni foil. The grain growth of the Ni film is limited by the low-temperature growth process, and the ultrafine grains of Ni film averaged the grain orientation effect from the Ni foil. The NGF formed on the Ni film/ss-Ni foil showed a significant improvement in thickness and quality uniformity, and we studied the influences of Ni film thickness as well as re-annealing temperature and time on the diffusion of carbon in the Ni film/ss-Ni foil system and summarized the growth mechanism.

A Lagrangian Cloud Model for the Study of Marine Fog

A large-eddy simulation model is coupled with a Lagrangian cloud model to study marine fog. In this model, aerosols and droplets are treated from a Lagrangian frame of reference, in contrast to the traditional bulk and bin microphysical models. Droplet growth via condensation is governed by Kohler theory and environmental conditions local to the droplet. Coupling to the vapour and temperature fields of the flow ensures mass, momentum, and energy conservation between the air and droplet phases. Based on the recent C-FOG field campaign, a simulation is performed which highlights the benefits and potential of this type of model. By initializing the simulation with the measured aerosol size distribution and making assumptions about the chemical composition of the multiple peaks, the simulations provide a clear explanation for the observed bimodal droplet distribution during C-FOG: high supersaturation levels cause condensational growth of nearly all coarse-mode aerosols (presumed to be composed of marine salt), as well as a large number of accumulation model aerosols (presumed to be of continental origin with a lower hygroscopicity). The largest peak in the resulting droplet distribution is created from coarse-mode aerosols with high hygroscopicity, while the secondary peak is only possible due to the limited impact of the largest peak on saturation levels inside the fog. Thus, for the simulated levels of supersaturation, it is the limited number of coarse-mode aerosols which is responsible for the emergence of a larger second peak.

Determination of nucleation kinetics from the induction time of 1,1-diamino-2,2-dinitroethylene (FOX-7) in DMSO/Water

Elucidation of the crystal nucleation process can provide guidance for controlling crystal size and quality. To understand the nucleation process of 1,1-diamino-2,2-dinitroethylene (FOX-7), the induction time and nucleation kinetics of FOX-7 were studied using a turbidity method in a binary solvent system (DMSO ​+ ​water, xDMSO ​= ​0.3364) under cooling crystallization conditions. Using the CrystalSCAN system, the induction time was determined at a range of temperatures (325.05, 335.25, 343.15, 348.15, and 354.65 ​K) and supersaturations (S) (1.20, 1.22, 1.24, 1.27, 1.30, 1.32, 1.35, 1.37), and it was found that induction time decreases as supersaturation increases. The system displayed a homogeneous nucleation mechanism at high supersaturation ratios (≥1.27) and heterogeneous nucleation at low supersaturation ratios, below 1.25. The FOX-7 crystal exhibited a continuous growth mechanism, as inferred from the value of the surface entropy factor (f). The induction time data were analyzed using the classical nucleation theory to calculate the interfacial energy (γ) and various nucleation parameters, including the radius of the critical nucleus (r∗), critical free energy of the nucleus (ΔG∗), molecular number of the critical nucleus (i∗), and the nucleation rate (J). The morphology of FOX-7 crystals changed negligibly with varying temperature and supersaturation, while the average particle size decreased with an increase in supersaturation and a decrease in temperature.

Crystal growth inhibition of gypsum under normal conditions and high supersaturations by a copolymer of phosphino-polycarboxylic acid

Scale formation is a bottleneck of most industrial and domestic water equipment, in particular, of oilfield water systems. Therefore, high-performance and environmentally-benign chemical scale inhibitors are highly needed. Phosphino-polycarboxylic acid (PPCA) is a low-in-phosphorous scale inhibitor with high inhibition efficiency, but its synthesis and performance analyses have been rarely disclosed. In this work for the first time, a PPCA copolymer is synthesized by a simple method based on free radical polymerization of acrylic acid and phosphinic acid monomers and directly employed for gypsum scale inhibition. The formation of PPCA was verified by FTIR and 31PNMR spectroscopies, and then its inhibition performance was evaluated by the complexometric determination of the Ca2+ concentration. The PPCA (2.5 ppm) showed 100% inhibition efficiency at a saturation index of 0.31 at the room temperature and without pH regulation after 24 h with practically no detectable gypsum crystallites even after two months, while the commercial ATMP showed a low inhibition efficiency of 30%. The Field Emission Scanning Microscopy (FESEM) images of the PPCA-inhibited and uninhibited samples revealed that the typical gypsum microfibers are distorted and reduced in size significantly in the inhibited sample. At a still higher saturation index of 1.47 (saturation ratio of 10), the inhibition efficiency of PPCA reduced to 16% and 24% for two dosages of 2.5 and 10 ppm which was attributed to the higher ion activity coefficients at the extremely high ionic strength, and hence, a much higher thermodynamic driving force. The rate constants for these two high supersaturation conditions and low PPCA dosages were also calculated and discussed.

Chemical vapor deposition of clean and pure MoS2 crystals by the inhibition of MoO3−x intermediates

A sublimated sulfur vapor versus evaporated MoO3 vapor with transition from low to high sulfur supersaturation would cause different CVD products transformed from MoS2–MoO3−x composites to clean and pure MoS2 crystals accordingly.

Molecular dynamics simulations of homogeneous nucleation of liquid phase in highly supersaturated propylene glycol vapors

The homogeneous nucleation rate of the liquid phase from a supersaturated propylene glycol vapor is a key factor in aerosol formation from condensation aerosol generators. The droplet nucleation rate is difficult to measure experimentally at high supersaturations. This paper demonstrates the feasibility of using classical Molecular Dynamics (MD) simulations to describe the nucleation of propylene glycol from the vapor phase in air at 320 and 343 K. After an initial induction period, nucleation was observed in many of the scenarios studied here. The classical nucleation theory underestimates the nucleation rate compared to the MD simulation results at high supersaturations. However, a kinetic model that assumed no free energy barrier to nucleation had better agreement with the MD predictions at extremely high supersaturations. For systems where a quasi-steady state was reached during the simulation, it is possible to determine the nucleation free energy as a function of cluster size. From this analysis it is found that the MD simulations predict over a factor of two larger critical clusters and about 50% higher free energy barriers than the classical nucleation theory.

Experimental constraints on nonskeletal CaCO3 precipitation from Proterozoic seawater

Abstract Precambrian carbonates record secular variations in the style of CaCO3 nucleation and growth, yet the geochemical conditions recorded by some enigmatic textures remain poorly quantified. Here, we performed CaCO3 nucleation experiments in synthetic seawater in order to constrain the mineralization pathways of synsedimentary calcite microspar cement, a prolific component of Proterozoic carbonates. We found that dissolved PO4 above ∼12 μmol/L (µM) inhibits the nucleation of aragonite and calcite and permits the formation of an amorphous Ca-Mg carbonate (ACMC) precursor once CaCO3 supersaturation (Ωcal) is ≥ 45. Depending on seawater Mg/Ca, ACMC then rapidly recrystallizes to monohydrocalcite and/or calcite. This precipitation mechanism is consistent with sedimentological, petrographic, and geochemical characteristics of Proterozoic synsedimentary calcite microspar cement, and it suggests that kinetic interactions among common seawater ions may open nontraditional CaCO3 mineralization pathways and sustain high CaCO3 supersaturation.

Role of Thermodynamics and Kinetics in the Composition of Ternary III-V Nanowires

We explain the composition of ternary nanowires nucleating from a quaternary liquid melt. The model we derive describes the evolution of the solid composition from the nucleated-limited composition to the kinetic one. The effect of the growth temperature, group V concentration and Au/III concentration ratio on the solid-liquid dependence is studied. It has been shown that the solid composition increases with increasing temperature and Au concentration in the droplet at the fixed In/Ga concentration ratio. The model does not depend on the site of nucleation and the geometry of monolayer growth and is applicable for nucleation and growth on a facet with finite radius. The case of a steady-state (or final) solid composition is considered and discussed separately. While the nucleation-limited liquid-solid composition dependence contains the miscibility gap at relevant temperatures for growth of InxGa1−xAs NWs, the miscibility gap may be suppressed completely in the steady-state growth regime at high supersaturation. The theoretical results are compared with available experimental data via the combination of the here described solid-liquid and a simple kinetic liquid-vapor model.

Partitioning of surfactant into drug-rich nanodroplets and its impact on drug thermodynamic activity and droplet size

The excipients present in an amorphous solid dispersion (ASD) are essential functional additives that ultimately influence the drug release performance and absorption. Herein, the effect of a polymer, hypromellose (HPMC), and three chemically diverse surfactants, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and polyoxyethylene sorbitan monooleate (Tween 80, Tween), on the size and stability of the colloidal ketoprofen (KTP)-rich phase generated by liquid-liquid phase separation was evaluated. In addition, the impact of the excipients on the thermodynamic activity of KTP at concentrations in excess of the amorphous solubility was evaluated. Dynamic light scattering measurements showed that using surfactant alone did not effectively suppress coarsening of the KTP-rich phase. In contrast, the combined use of surfactant and HPMC maintained the KTP-rich droplet size at around 200 nm, which was smaller than in HPMC solutions without surfactant. Solution nuclear magnetic resonance spectroscopy revealed that HPMC distributed into the KTP-rich phase, leading to a reduced thermodynamic activity of KTP, and a consequent decrease in the maximum achievable aqueous phase concentration. Moreover, substantial amounts of both CTAB and Tween distributed into the KTP-rich phase from the aqueous phase, while SDS remained predominantly in the aqueous phase. The combined use of HPMC with CTAB or Tween resulted in a further decrease in the thermodynamic activity of KTP relative to in the presence of HPMC alone, due to the mixing of both HPMC and surfactant with the KTP-rich phase. In contrast, the addition of SDS did not reduce the thermodynamic activity of KTP because of the limited distribution of SDS into the KTP-rich phase. A reduction in KTP thermodynamic activity translated to a decreased supersaturation and hence a reduction in the maximum achievable membrane flux. The present study illustrates the complex effects of surfactant and polymer on drug thermodynamic activity, factors which should be considered when optimizing ASD formulations to maximize oral drug absorption. Ideally, excipients that do not substantially impact drug thermodynamic activity should be selected, in particular for drugs where achieving high supersaturation is critical to drive their absorption.

Kinetics and mechanistic aspects of removal of heavy metal through gas-liquid sulfide precipitation: A computational and experimental study

The production of fine particles from extremely high supersaturation has challenged the application of sulfide precipitation in treating heavy metal wastewater due to the difficulty of solid-liquid separation. To this end, a gas-liquid sulfide precipitation reactor for the removal of Cu2+ was designed by controlling the mass transfer and supersaturation levels during sulfidation processes. Particularly, a computational fluid dynamics (CFD) model of the reactor, integrating sulfidation reaction kinetics with two-phase flow hydrodynamics, was first built, followed by examining the effects of H2S(g) bubble diameter and flow rate. Based on the CFD simulation, the rate-limiting step of the gas-liquid sulfide precipitation reaction is the gas-liquid mass transfer process. Either reducing H2S(g) bubble diameter or increasing H2S(g) flow rate can result in the control of reaction rate and supersaturation level in the system. In order to validate the CFD simulations, we measured Cu2+ concentrations during the sulfidation process with the batch experiments. The agreement between computational and experimental results indicated that our mechanistic model can provide a protocol for the design and optimization of the reaction system, allowing one to visualize the time-dependent reaction process and evaluate the performance of a reactor.

Determination of the metastable zone and induction time of thiourea for cooling crystallization

Abstract The solubility, metastable zone width (MSZW), and induction time of thiourea for cooling crystallization were experimentally determined in the temperature range of 283–323 K. The solubility data could be well described by the Apelblat equation model as lnx = −99.55 + 1071.66/T + 16.27lnT. The determinations of the effects of various stirring and cooling rates indicated that the MSZW increased with increasing and decreasing cooling and stirring rates, respectively. Furthermore, the induction times at various temperatures and supersaturation ratios were also measured. The results indicated that homogeneous nucleation could occur at high supersaturation, whereas heterogeneous nucleation was more likely to occur at low supersaturation. Based on the classical nucleation theory and induction period data, the calculated solid–liquid interfacial tensions of thiourea in deionized water at 302.46 and 312.58 K were 2.86 and 2.94 mJ⋅m−2, respectively.

Synthesis and polymorph controlling of calcite and aragonite calcium carbonate nanoparticles in a confined impinging-jets reactor

In this article, a confined-impinging-jets reactor (CIJR) was designed and tested successfully for the synthesis of calcium carbonate nanoparticles using the reactive precipitation method. The proposed CIJR comprised of two opposed nozzles placed in a cylindrical chamber. Effects of various operating and design parameters such as supersaturation, feed flow rate, nozzle diameter, reactor diameter, operating temperature, and surface-active agents on the mean particle size, particle size distribution, and the polymorphs of calcium carbonate nanoparticles were investigated carefully. By changing the supersaturation, reactor diameter, jets velocity, operating temperature, and the nozzle diameter, a wide range of calcium carbonate nanoparticles with mean particle sizes of smaller than 40 nm to larger than 160 nm was synthesized. Mixing intensity and control of parameters decrease the mean particle size and increase selectivity to the synthesis of calcite or aragonite nanoparticles compared to other synthesis devices. The use of high supersaturation values and nozzle diameter of 500 μm in the presence of sodium dodecyl sulfate surfactant result in the synthesis of nanoparticles with a mean particle size of 34 nm and a weight percentage of about 80 % of aragonite phase.