Nucleation In Aqueous Solutions Research Articles

Ice nucleation in aqueous solutions of short- and long-chain poly(vinyl alcohol) studied with a droplet microfluidics setup

Poly(vinyl alcohol) (PVA) has ice binding and ice nucleating properties. Here, we explore the dependence of the molecular size of PVA on its ice nucleation activity. For this purpose, we studied ice nucleation in aqueous solutions of PVA samples with molar masses ranging from 370 to 145000g mol-1, with a particular focus on oligomer samples with low molar mass. The experiments employed a novel microfluidic setup that is a follow-up on the previous WeIzmann Supercooled Droplets Observation on a Microarray (WISDOM) design by Reicher et al. The modified setup introduced and characterized here, termed nanoliter Bielefeld Ice Nucleation ARraY (nanoBINARY), uses droplet microfluidics with droplets (96 ± 4) µm in diameter and a fluorinated continuous oil phase and surfactant. A comparison of homogeneous and heterogeneous ice nucleation data obtained with nanoBINARY to those obtained with WISDOM shows very good agreement, underpinning its ability to study low-temperature ice nucleators as well as homogeneous ice nucleation due to the low background of impurities. The experiments on aqueous PVA solutions revealed that the ice nucleation activity of shorter PVA chains strongly decreases with a decrease in molar mass. While the cumulative number of ice nucleating sites per mass nm of polymers with different molar masses is the same, it becomes smaller for oligomers and completely vanishes for dimer and monomer representatives such as 1,3-butanediol, propan-2-ol, and ethanol, most likely because these molecules become too small to effectively stabilize the critical ice embryo. Overall, our results are consistent with PVA polymers and oligomers acting as heterogeneous ice nucleators.

Which Surface Is More Scaling Resistant? A Closer Look at Nucleation Theories for Heterogeneous Gypsum Nucleation in Aqueous Solutions.

Developing engineered surfaces with scaling resistance is an effective means to inhibit surface-mediated mineral scaling in various industries including desalination. However, contrasting results have been reported on the relationship between scaling potential and surface hydrophilicity. In this study, we combine a theoretical analysis with experimental investigation to clarify the effect of surface wetting property on heterogeneous gypsum (CaSO4·2H2O) formation on surfaces immersed in aqueous solutions. Theoretical prediction derived from classical nucleation theory (CNT) indicates that an increase of surface hydrophobicity reduces scaling potential, which contrasts our experimental results that more hydrophilic surfaces are less prone to gypsum scaling. We further consider the possibility of nonclassical pathway of gypsum nucleation, which proceeds by the aggregation of precursor clusters of CaSO4. Accordingly, we investigate the affinity of CaSO4 to substrate surfaces of varied wetting properties via calculating the total free energy of interaction, with the results perfectly predicting experimental observations of surface scaling propensity. This indicates that the interactions between precursor clusters of CaSO4 and substrate surfaces might play an important role in regulating heterogeneous gypsum formation. Our findings provide evidence that CNT might not be applicable to describing gypsum scaling in aqueous solutions. The fundamental insights we reveal on gypsum scaling mechanisms have the potential to guide rational design of scaling-resistant engineered surfaces.

Multiple pathways of crystal nucleation in an extremely supersaturated aqueous potassium dihydrogen phosphate (KDP) solution droplet

Solution studies have proposed that crystal nucleation can take more complex pathways than previously expected in classical nucleation theory, such as formation of prenucleation clusters or densified amorphous/liquid phases. These findings show that it is possible to separate fluctuations in the different order parameters governing crystal nucleation, that is, density and structure. However, a direct observation of the multipathways from aqueous solutions remains a great challenge because heterogeneous nucleation sites, such as container walls, can prevent these paths. Here, we demonstrate the existence of multiple pathways of nucleation in highly supersaturated aqueous KH2PO4 (KDP) solution using the combination of a containerless device (electrostatic levitation), and in situ micro-Raman and synchrotron X-ray scattering. Specifically, we find that, at an unprecedentedly deep level of supersaturation, a high-concentration KDP solution first transforms into a metastable crystal before reaching stability at room temperature. However, a low-concentration solution, with different local structures, directly transforms into the stable crystal phase. These apparent multiple pathways of crystallization depend on the degree of supersaturation.

Probing the Mechanisms Underlying Electrolyte-Assisted Nucleation Enhancement of dl-Alanine

The effects of common electrolytes (including inorganic acids, bases, and salts) on dl-alanine nucleation in aqueous solutions have been systematically investigated via measurement of nucleation induction times. It is observed that all the electrolytes examined in this study considerably shorten the induction times, suggesting that they greatly enhance dl-alanine nucleation. It is hypothesized that, in solution, an electrolyte assists the formation of the head-to-tail chains of dl-alanine molecules. Such head-to-tail chains, structurally matching dl-alanine crystal packing, act as favorable precursors for dl-alanine nucleation and play a great role in enhancing the nucleation, highlighting the importance of prenucleation phenomena.

Mineral coatings modulate β-TCP stability and enable growth factor binding and release

β-Tricalcium phosphate (β-TCP) is an attractive ceramic for bone tissue repair because of its similar composition to bone mineral and its osteoconductivity. However, compared with other ceramics β-TCP has a rapid and uncontrolled rate of degradation. In the current study β-TCP granules were mineral coated with the aim of influencing the dissolution rate of β-TCP, and also to use the coating as a carrier for controlled release of the growth factors recombinant human vascular endothelial growth factor (rhVEGF), modular VEGF peptide (mVEGF), and modular bone morphogenetic protein 2 peptide (mBMP2). The biomineral coatings were formed by heterogeneous nucleation in aqueous solution using simulated body fluid solutions with varying concentrations of bicarbonate (HCO3). Our results demonstrate that we could coat β-TCP granules with mineral layers possessing different dissolution properties. The presence of a biomineral coating delays the dissolution rate of the β-TCP granules. As the carbonate (CO32−) content in the coating was increased the dissolution rate of the coated β-TCP also increased, but remained slower than the dissolution of uncoated β-TCP. In addition, we showed sustained release of multiple growth factors, with release kinetics that were controllable by varying the identity of the growth factor or the CO32− content in the mineral coating. Released rhVEGF induced human umbilical vein endothelial cell (HUVEC) proliferation, and mVEGF enhanced migration of mouse embryonic endothelial cells in a scratch wound healing assay, indicating that each released growth factor was biologically active.

Umbrella sampling study of crystal nucleation in aqueous solutions of globular proteins

Umbrella sampling study of crystal nucleation in aqueous solutions of globular proteins

Parameterizations for ice nucleation in biological and atmospheric systems

Ice nucleation is an important process in numerous environmental systems such as atmospheric aerosol droplets or biological tissues. Here we analyze two widely used approaches for describing homogeneous ice nucleation in aqueous solutions with respect to their applicability to heterogeneous ice nucleation processes: the lambda approach and the water-activity-based approach. We study experimentally the heterogeneous ice nucleation behaviour of mineral dust particles and biological ice nuclei (Snomax; Pseudomonas syringae) in aqueous solutions as a function of solute concentration for various solutes (sulfuric acid, ammonium sulfate, glucose, and poly(ethylene glycol) with two different molar masses of 400 and 6000 g mol(-1)). We show that the ice nucleation temperature and the corresponding lambda values depend on both the type of ice nucleus and the type of solute, while the water-activity-based approach depends only on the type of ice nucleus when the solution water activity is known. Finally, we employ both approaches to the study of ice nucleation in biological systems such as the supercooling point of living larvae and insects. We show that the behaviour of freeze tolerant and freeze avoiding species can be described using the two approaches and we discuss how the analysis can be used to interpret experimental results of the freezing behaviour of living species.

Microfluidic Droplet Method for Nucleation Kinetics Measurements

In this work, we developed a microfluidic equivalent of the classical droplet method for investigating nucleation kinetics. Our microfluidic device allows us to store hundreds of droplets of small volume ( approximately 100 nL) and to accurately control their temperature. We also monitor directly all the stored droplets, and thus perform statistical measurements on a large number of nucleation events. In the case of aqueous solutions of potassium nitrate, we manage to investigate nucleation kinetics and polymorphs and quantify the influence of impurities. The use of small droplets is crucial in such experiments, since it allows the sample to reach high supersaturations and to separate all the nucleation events. Moreover, we compare our results to the classical nucleation theory, and we demonstrate unambiguously using direct observations of the droplets that nucleation in aqueous solutions of potassium nitrate always occurs using heterogeneous mechanisms.

Heterogeneous Ice Nucleation in Aqueous Solutions: the Role of Water Activity

Heterogeneous ice nucleation experiments have been performed with four different ice nuclei (IN), namely nonadecanol, silica, silver iodide and Arizona test dust. All IN are either immersed in the droplets or located at the droplets surface. The IN were exposed to various aqueous solutions, which consist of (NH4)2SO4, H2SO4, MgCl2, NaCl, LiCl, Ca(NO3)2, K2CO3, CH3COONa, ethylene glycol, glycerol, malonic acid, PEG300 or a NaCl/malonic acid mixture. Freezing was studied using a differential scanning calorimeter and a cold finger cell. The results show that the heterogeneous ice freezing temperatures decrease with increasing solute concentration; however, the magnitude of this effect is solute dependent. In contrast, when the results are analyzed in terms of the solution water activity a very consistent behavior emerges: heterogeneous ice nucleation temperatures for all four IN converge each onto a single line, irrespective of the nature of the solute. We find that a constant offset with respect to the ice melting point curve, Deltaaw,het, can describe the observed freezing temperatures for each IN. Such a behavior is well-known for homogeneous ice nucleation from supercooled liquid droplets and has led to the development of water-activity-based ice nucleation theory. The large variety of investigated solutes together with different general types of ice nuclei studied (monolayers, ionic crystals, covalently bound network-forming compounds, and a mixture of chemically different crystallites) underlines the general applicability of water-activity-based ice nucleation theory also for heterogeneous ice nucleation in the immersion mode. Finally, the ice nucleation efficiencies of the various IN, as well as the atmospheric implication of the developed parametrization are discussed.

Ice nucleation in solutions and freeze-avoiding insects—homogeneous or heterogeneous?

This article challenges the common view that solutions and cold-hardy freeze-avoiding insects always freeze by heterogeneous nucleation. Data are presented to show that the nucleation temperatures of a variety of solutions and freeze-avoiding insects are a function of the water volume as described by the data previously published by Bigg in 1953. The article also points out that the relationships between melting point depression and depression of nucleation temperature are different for samples undergoing homogeneous nucleation and those undergoing heterogeneous nucleation. Aqueous solutions and freeze-avoiding insects display a relationship like that of homogeneously nucleated samples. It is also argued that the identity of the “impurities” assumed to cause heterogeneous nucleation in aqueous solutions and insects is obscure and that the “impurities” have features which make their existence rather unlikely.

Ice nucleation in aqueous solutions of poly[ethylene glycol] with different molar mass

Homogeneous ice nucleation was investigated in aqueous solutions of poly[ethylene glycol] (PEG) with a molar mass between 300 and 6000 g mol−1. Experiments were performed with a differential scanning calorimeter using emulsified aqueous PEG solutions with concentrations of 0–44 wt %. Equilibrium phase transition temperatures are determined and discussed, in particular the simultaneous occurrence of metastable and stable eutectic temperatures. The observed homogeneous freezing temperatures of ice reveal a continuous increase in the supercooling of PEG solutions with increasing molar mass of the PEG. The freezing behavior was investigated within the framework of water-activity-based ice nucleation theory. The latter predicts that homogeneous ice nucleation in aqueous solutions is independent of the nature of the solute, but depends only on the water activity of the solution. Water activity data of various PEG solutions in the stable and supercooled range were compared. It was found that the water activity of PEG solutions decreases with decreasing temperature. This trend is stronger for the PEGs of larger molar mass, and can explain why solutions of larger PEGs supercool more readily. Our study shows that the predictions of water-activity-based ice nucleation theory are consistent with the observed freezing behavior and with the thermodynamic properties of PEG solutions. It is also in agreement with the suggestion of a thermodynamic control of ice nucleation in aqueous systems due to the existence of a liquid phase spinodal.

Crystal Phase Control for Titanium Dioxide Films by Direct Deposition in Aqueous Solutions

Crystalline titanium dioxide (TiO2) was directly grown on a substrate via heterogeneous nucleation in aqueous solutions with titanyl sulfate at near room temperature. The crystal phase of TiO2 films was essentially determined by the initial pH value and the Ti concentration of the precursor solutions. The rutile and anatase phases were produced in the solutions around their thermodynamic equilibrium conditions between Ti(IV) ionic species and the solid phases. The effect of the deposition rate on the crystal phases was not dominant in this system. On the other hand, the morphology of the TiO2 products was influenced by the reaction rate controlled with the properties of anions as a ligand for titanium cations. Homogeneous rutile and anatase films consisting of highly oriented needlelike crystals were obtained with a relatively slow deposition rate.

Fabrication of Rutile TiO2 Foils with High Specific Surface Area via Heterogeneous Nucleation in Aqueous Solutions

Abstract Rutile TiO2 foils with high specific surface area were fabricated through heterogeneous nucleation on substrates in acidic aqueous solutions of titanyl sulfate. Rutile crystals were directly deposited even at a near room temperature in the solutions at the conditions around the boundary between the Ti(IV) soluble species and the TiO2 crystal in the phase stability diagram of the Ti(IV)-H2O system.

Water activity as the determinant for homogeneous ice nucleation in aqueous solutions

The unique properties of water in the supercooled (metastable) state are not fully understood. In particular, the effects of solutes and mechanical pressure on the kinetics of the liquid-to-solid phase transition of supercooled water and aqueous solutions to ice have remained unresolved. Here we show from experimental data that the homogeneous nucleation of ice from supercooled aqueous solutions is independent of the nature of the solute, but depends only on the water activity of the solution--that is, the ratio between the water vapour pressures of the solution and of pure water under the same conditions. In addition, we show that the presence of solutes and the application of pressure have a very similar effect on ice nucleation. We present a thermodynamic theory for homogeneous ice nucleation, which expresses the nucleation rate coefficient as a function of water activity and pressure. Recent observations from clouds containing ice are in good agreement with our theory and our results should help to overcome one of the main weaknesses of numerical models of the atmosphere, the formulation of cloud processes.

Synthesis and Conformational Preferences of a Potential beta-Sheet Nucleator Based on the 9,9-Dimethylxanthene Skeleton.

A 4,5-disubstituted-9,9-dimethylxanthene-based amino acid (10) has been synthesized for incorporation into peptide sequences which have a propensity to adopt beta-sheet structure. Molecular dynamics studies support the FT-IR and NMR results which demonstrate that amides based on this residue utilize the NH and the C=O from the xanthene residue to form an intramolecular hydrogen bond (13-membered ring), unlike the previously studied dibenzofuran-based amino acid residues in which the NH and the C=O of the attached amide groups participate in intramolecular hydrogen bonding (15-membered ring). Interestingly, residue 10 derivatized as a simple amide prefers to adopt a trans conformation where the aliphatic side chains are placed on opposite sides of the plane of the 9,9-dimethylxanthene ring system. This is different than the conformational preferences of the dibenzofuran-based amino acids which adopt a cis conformation that is preorganized to nucleate beta-sheet formation. It will be interesting to see how these conformational differences effect nucleation in aqueous solution.

Amorphous silica coating on α-alumina particles

Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.

A Study of Heterogeneous Nucleation in Aqueous Solutions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA Study of Heterogeneous Nucleation in Aqueous SolutionsC. B. Richardson and Tamara D. SnyderCite this: Langmuir 1994, 10, 7, 2462–2465Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/la00019a072RIGHTS & PERMISSIONSArticle Views436Altmetric-Citations42LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (503 KB) Get e-Alerts Get e-Alerts

Present-day understanding of crystal growth from aqueous solutions

Recent results on the kinetics of crystal growth from aqueous solutions are reviewed, with the emphasis placed on the KDP group of crystals. Elementary parameters of spiral growth are discussed. Nonlinear dependences of step velocity on supersaturation, incompatible with the Burton-Cabrera-Frank theory, are analysed, and a new more general theory is presented. Morphological stability of stepped vicinal faces is considered, with due account of the influence of solution hydrodynamics and impurities. New experiments are described, in which reproducible growth of the ADP dipyramidal face by two-dimensional (2D) nucleation is found. Effective step energy is deduced. At low supersaturations the preferential 2D nucleation is demonstrated to occur on active sites, whereas at high supersaturations the 2D nucleation seems to be homogeneous. Secondary nucleation in aqueous solutions is analysed. New experiments demonstrating a direct correlation between secondary nucleation and basic crystal cracking are described and discussed. Therefore, the achievement of high supersaturations and thus high growth rates is closely related to high crystal perfection, and vice versa. Selected achievements in biological crystallization, primarily in nucleation and growth of protein, viruses and other crystals built up of large molecules or colloidal particles, are briefly discussed.

Growth rate dispersion in small crystals and its relation to mosaic spread

High mosaic spread is a common feature of a number of complex materials (such as certain zeolites and protiens) for which the preparation of large single crystals is prohibited. In one previous systematic study, a direct correlation between growth rate and mosaic spread was found for very small crystals of sodium chlorate. This work has attempted to explore the generality of the effect by extending measurements to a wider range of simple materials. Small crystals (5–200 μm) of ammonium dihydrogen phosphate (ADP), sodium chlorate and sucrose, generated by secondary nucleation in aqueous solution, have been grown under constant conditions of supersaturation. A wide dispersion of growth rates was observed for each material using optical microscopy. A number of individual crystals of known growth rate were successfully retrieved from solution and an assessment of the mosaic spread of each crystal was made using synchroton radiation Laue diffraction at Daresbury Laboratory. All of the crystals produced diffraction patterns comprising small, sharp spots, indicative of low mosaic spread ( <0.5°). No correlation was found between growth rate and mosaic spread for these relatively simple structures. In addition, individual crystals of sucrose have also been examined immediately after creation in solution and subsequently grown-on at constant supersaturation. The Laue patterns obtained for each crystal, both before and after growth, exhibited low mosaic spread, yet each crystal grew at different rate. It is suggested that radiation damage can account for the previously published discrepancies, and acceptable radiation doses are calculated for the determination of mosaic spread in these materials.

Precipitation of Strontium Sulphate

AbstractPrecipitation of unseeded supersaturated aqueous solutions of SrSO4 and growth of SrSO4 crystals at the size of approximately 20 μm were studied. Within the examined range of supersaturations, i.e. Sa &lt; 16, the nucleation in aqueous solutions is controlled by the heterogeneous nucleation mechanism. The induction period of precipitation depends on the rates of both the nucleation and growth of the formed nuclei. The growth of SrSO4 crystals in supersaturated solutions at S ⪅ 5.6 is of the 2nd order with respect to the concentration and at temperatures 25 ÷ 45°C the process is controlled by the surface reaction mechanism. The number of crystals in the precipitated slurry is decreasing rapidly as a result of the Ostwald maturing.