Nucleation Of Water Research Articles

Cavitation Nuclei Regeneration in a Water-Particle Suspension.

Bubble nucleation in water induced by boiling, gas supersaturation, or cavitation usually originates from preexisting gas cavities trapped into solid defects. Even though the destabilization of such gas pockets, called nuclei, has been extensively studied, little is known on the nuclei dynamic. Here, nuclei of water-particle suspensions are excited by acoustic cavitation, and their dynamic is investigated by monitoring the cavitation probability over several thousand pulses. A stable and reproducible cavitation probability emerges after a few thousand pulses and depends on particle concentration, hydrophobicity, and dissolved gas content. Our observations indicate that a stable nuclei distribution is reached at a later time, different from previously reported nuclei depletion in early time. This apparent paradox is elucidated by varying the excitation rate, where the cavitation activity increases with the repetition period, indicating that the nuclei depletion is balanced by spontaneous nucleation or growth of nuclei. A model of this self-supporting generation of nuclei suggests an origin from dissolved gas adsorption on surfaces. The method developed can be utilized to further understand the spontaneous formation and distribution of nanosized bubbles on heterogeneous surfaces.

Ice-Crystal Nucleation in Water: Thermodynamic Driving Force and Surface Tension. Part I: Theoretical Foundation.

A recently developed thermodynamic theory for the determination of the driving force of crystallization and the crystal–melt surface tension is applied to the ice-water system employing the new Thermodynamic Equation of Seawater TEOS-10. The deviations of approximative formulations of the driving force and the surface tension from the exact reference properties are quantified, showing that the proposed simplifications are applicable for low to moderate undercooling and pressure differences to the respective equilibrium state of water. The TEOS-10-based predictions of the ice crystallization rate revealed pressure-induced deceleration of ice nucleation with an increasing pressure, and acceleration of ice nucleation by pressure decrease. This result is in, at least, qualitative agreement with laboratory experiments and computer simulations. Both the temperature and pressure dependencies of the ice-water surface tension were found to be in line with the le Chatelier–Braun principle, in that the surface tension decreases upon increasing degree of metastability of water (by decreasing temperature and pressure), which favors nucleation to move the system back to a stable state. The reason for this behavior is discussed. Finally, the Kauzmann temperature of the ice-water system was found to amount , which is far below the temperature of homogeneous freezing. The Kauzmann pressure was found to amount to , suggesting favor of homogeneous freezing on exerting a negative pressure on the liquid. In terms of thermodynamic properties entering the theory, the reason for the negative Kauzmann pressure is the higher mass density of water in comparison to ice at the melting point.

Cluster Formation at Extreme Supersaturations: Nucleation versus Barrierless Transition.

We study the process of cluster formation at extreme supersaturations and identify the temperature-supersaturation domain where evaporation can be neglected resulting in a barrierless process with kinetics dominated by the dimer formation. The cluster size distribution obeys the coalescence equation with the pressure-temperature-dependent association rate coefficients ki,j. In view of the crucial role played by kinetics under these extreme conditions, the values of these coefficients calculated within the free molecular collision model are insufficient for the prediction of the nucleation rate and cluster distribution. An alternative is the use of ki,j obtained from the ab initio calculations. We apply these considerations to the analysis of recent water nucleation experiments in the postnozzle flow of a Laval nozzle. Theoretical predictions of nucleation rate are in an excellent agreement with experiment. At the same time, there is a discrepancy in the densities of small clusters. The latter can be attributed to the difference in ki,j extracted from the experimental data and those resulted from the ab initio calculations.

Visualization of Droplet Nucleation on Patterned Hybrid Surfaces

Abstract Hydrophobic-hydrophilic hybrid surfaces have the potential to enhance and optimize condensation heat transfer. The optimum design of hybrid surfaces has been shown to greatly improve heat transfer performance when compared to that of pure hydrophobic or hydrophilic surfaces. However, challenges remain related to the manufacture of hybrid patterns on large area samples. Here, we develop and visualize a simple stamping method to pattern surfaces for well-defined hydrophobic and hydrophilic regions. The reversible control of adhesion of patterned Polydimethylsiloxane (PDMS) stamps was utilized to form arrays of hydrophilic regions on HTMS (Heptadecafluoro-(tetrahydrodecyl) Trimethoxysilane). To visualize the nucleation behavior, we utilized optical microscopy. Water condensation on the hybrid surfaces resulted in nucleation of droplets that initiated on the hydrophilic patterns. The visualizations shown here not only demonstrate the spatial control of heterogeneous nucleation of water, but present design guidelines for the development of scalable hybrid surfaces for the study of controlled droplet nucleation phenomena and to enable the control of droplet distribution and density during dropwise condensation.

Extraction of monomer-cluster association rate constants from water nucleation data measured at extreme supersaturations

We utilize recently reported data for water nucleation in the uniform postnozzle flow of pulsed Laval expansions to derive water monomer association rates with clusters. The nucleation experiments are carried out at flow temperatures of 87.0 K and 47.5 K and supersaturations of lnS ∼ 41 and 104, respectively. The cluster size distributions are measured at different nucleation times by mass spectrometry coupled with soft single-photon ionization at 13.8 eV. The soft ionization method ensures that the original cluster size distributions are largely preserved upon ionization. We compare our experimental data with predictions by a kinetic model using rate coefficients from a previous ab initio calculation with a master equation approach. The prediction and our experimental data differ, in particular, at the temperature of 87.0 K. Assuming cluster evaporation to be negligible, we derive association rate coefficients between monomer and clusters purely based on our experimental data. The derived dimerization rate lies 2-3 orders of magnitude below the gas kinetic collision limit and agrees with the aforementioned ab initio calculation. Other than the dimerization rate, however, the derived rate coefficients between monomer and cluster j (j ≥ 3) are on the same order of magnitude as the kinetic collision limit. A kinetic model based on these results confirms that coagulation is indeed negligible in our experiments. We further present a detailed analysis of the uncertainties in our experiments and methodology for rate derivation and specify the dependency of the derived rates on uncertainties in monomer and cluster concentrations.

Plasmonic Bubble Nucleation and Growth in Water: Effect of Dissolved Air.

Under continuous laser irradiation, noble metal nanoparticles immersed in water can quickly heat up, leading to the nucleation of so-called plasmonic bubbles. In this work, we want to further understand the bubble nucleation and growth mechanism. In particular, we quantitatively study the effect of the amount of dissolved air on the bubble nucleation and growth dynamics, both for the initial giant bubble, which forms shortly after switching on the laser and is mainly composed of vapor, and for the final life phase of the bubble, during which it mainly contains air expelled from water. We found that the bubble nucleation temperature depends on the gas concentration: the higher the gas concentration, the lower the bubble nucleation temperature. Also, the long-term diffusion-dominated bubble growth is governed by the gas concentration. The radius of the bubbles grows as R(t) ∝ t1/3 for air-equilibrated and air-oversaturated water. In contrast, in partially degassed water, the growth is much slower since, even for the highest temperature we achieve, the water remains undersaturated.

Crystallization Kinetics of Water on Bare, Hydrogenated, and Hydroxylated Si(100) and Si(111) Surfaces Studied by RHEED, TOF-SIMS, and TPD

Nucleation and growth processes of water deposited onto Si(100) and (111) substrates were investigated in terms of the influences of hydrogenation and hydroxylation of the surface, as well as high-energy electron-beam irradiation. On the hydrogenated Si(100) substrate, randomly oriented ice Ic crystallites grow by heating a monolayer of amorphous solid water (ASW) to ca. 150 K after agglomeration into droplets at T > 80 K. In contrast, nucleation of the ASW monolayer is strongly prohibited on the hydroxylated Si(100) substrates; crystallites are formed in the multilayer regime out-of-registry with the substrate as a result of spontaneous nucleation. The epitaxial growth is quenched on the hydroxylated Si(100) surface (bare Si(100)-(2 × 1) surface) because water molecules bound tightly to the substrate via hydrogen bonds (weak chemical bonds) control the ice nucleation in contrast to the physisorbed water species. On the other hand, the epitaxial growth (nonepitaxial growth) of ice is observed even at 100 ...

Effect of ultrasound on the nucleation temperature of water with varied air contents

Ultrasonic cavitation is shown to hamper the supercooling required for the nucleation of water. To elucidate the mechanism of nucleation of ice under ultrasonic cavitation, ultrasound waves were applied to supercooled water with oxygen contents of 4.06, 4.48, 4.95, 5.62, and 6.34 mg L−1. Ultrasonic waves were intermittently applied at temperatures below 0 °C. Nucleation temperatures were measured under different experimental conditions. The maximum nucleation temperature (−3.66 ± 0.39 °C) was observed for a water sample containing 4.95 mg L−1 oxygen, at 319 W power (electric power of ultrasound). At 319 W, the intensity of cavitation in this water sample was less than that at higher power. It is concluded that compared with the effect of pressure produced by cavitation, the effect of heat produced by cavitation is significant during the nucleation of water with high-intensity ultrasonic cavitation.

Inversely modeling homogeneous H<sub>2</sub>SO<sub>4</sub> − H<sub>2</sub>O nucleation rate in exhaust-related conditions

Abstract. The homogeneous sulfuric acid–water nucleation rate in conditions related to vehicle exhaust was measured and modeled. The measurements were performed by evaporating sulfuric acid and water liquids and by diluting and cooling the sample vapor with a sampling system mimicking the dilution process occurring in a real-world driving situation. The nucleation rate inside the measurement system was modeled inversely using CFD (computational fluid dynamics) and the aerosol dynamics code, CFD-TUTMAM (Tampere University of Technology Modal Aerosol Model for CFD). The nucleation exponents for the concentrations of sulfuric acid and water and for the saturation vapor pressure of sulfuric acid were found to be 1.9±0.1, 0.50±0.05, and 0.75±0.05, respectively. These exponents can be used to examine the nucleation mechanisms occurring in exhaust from different combustion sources (internal combustion engines, power plant boilers, etc.) or in the atmosphere. Additionally, the nucleation rate can be expressed with the exponents as a function of the concentrations of sulfuric acid and water and of temperature. The obtained function can be used as a starting point for inverse modeling studies of more complex nucleation mechanisms involving extra compounds in addition to sulfuric acid and water. More complex nucleation mechanisms, such as those involving hydrocarbons, are observed with real vehicle exhaust and are also supported by the results obtained in this study. Furthermore, the function can be used to improve air quality models by using it to model the effect of sulfuric acid-emitting traffic and power generation on the particle concentration in urban air.

Heterogeneous ice nucleation correlates with bulk-like interfacial water.

Establishing a direct correlation between interfacial water and heterogeneous ice nucleation (HIN) is essential for understanding the mechanism of ice nucleation. Here, we study the HIN efficiency on polyvinyl alcohol (PVA) surfaces with different densities of hydroxyl groups. We find that the HIN efficiency increases with the decreasing hydroxyl group density. By explicitly considering that interfacial water molecules of PVA films consist of "tightly bound water," "bound water," and "bulk-like water," we reveal that bulk-like water can be correlated directly to the HIN efficiency of surfaces. As the density of hydroxyl groups decreases, bulk-like water molecules can rearrange themselves with a reduced energy barrier into ice due to the diminishing constraint by the hydroxyl groups on the PVA surface. Our study not only provides a new strategy for experimentally controlling the HIN efficiency but also gives another perspective in understanding the mechanism of ice nucleation.

Development of Corn-Oil Ester and Water Mixture Phase Change Materials for Food Refrigeration Applications

This research aims to investigate development of corn-oil ester and water mixtures as novel solid-liquid phase change material candidates for chilled and frozen food refrigeration applications. Thermal properties of both water and its mixture with corn-oil ester were tested by DSC and T-history methods. The results showed that corn oil could mix well in water solutions. Phase transition temperatures of the mixtures were lower than those of individual water. Corn-oil ester in the mixtures was acted as a nucleate agent and it was able to lower freezing point and to trigger ice nucleation in water which could diminish super-cooling. Addition of corn oil ester by 5% to 35% in water solutions could decrease freezing temperature from 0°C down to respectively -3.5°C to -28°C. The PCM candidates were also found to have excellent thermal properties that could fulfill requirements of thermal energy storage systems for food refrigeration applications.

Non-equilibrium crystallization pathways of manganese oxides in aqueous solution

Aqueous precipitation of transition metal oxides often proceeds through non-equilibrium phases, whose appearance cannot be anticipated from traditional phase diagrams. Without a precise understanding of which metastable phases form, or their lifetimes, targeted synthesis of specific metal oxides can become a trial-and-error process. Here, we construct a theoretical framework to reveal the nanoscale and metastable energy landscapes of Pourbaix (E-pH) diagrams, providing quantitative insights into the size–dependent thermodynamics of metastable oxide nucleation and growth in water. By combining this framework with classical nucleation theory, we interrogate how solution conditions influence the multistage oxidation pathways of manganese oxides. We calculate that even within the same stability region of a Pourbaix diagram, subtle variations in pH and redox potential can redirect a non-equilibrium crystallization pathway through different metastable intermediates. Our theoretical framework offers a predictive platform to navigate through the thermodynamic and kinetic energy landscape towards the rational synthesis of target materials.

High-speed imaging of ice nucleation in water proves the existence of active sites.

Understanding how surfaces direct nucleation is a complex problem that limits our ability to predict and control crystal formation. We here address this challenge using high-speed imaging to identify and quantify the sites at which ice nucleates in water droplets on the two natural cleavage faces of macroscopic feldspar substrates. Our data show that ice nucleation only occurs at a few locations, all of which are associated with micron-size surface pits. Similar behavior is observed on α-quartz substrates that lack cleavage planes. These results demonstrate that substrate heterogeneities are the salient factor in promoting nucleation and therefore prove the existence of active sites. We also provide strong evidence that the activity of these sites derives from a combination of surface chemistry and nanoscale topography. Our results have implications for the nucleation of many materials and suggest new strategies for promoting or inhibiting nucleation across a wide range of applications.

Energetics of ice nucleation in mesoporous titania using positron annihilation spectroscopy.

The low temperature behavior of water and kinetics of ice nucleation in titania mesopores have been probed by positron annihilation lifetime spectroscopy as a function of pore filling. It is revealed that water undergoes complete freezing at around 220 K when more than 50% of the pore volume is filled and such freezing is hindered at lower hydration levels. A model describing progressive trapping of positronium by ice nuclei in liquid water during the phase transition is employed to estimate the energy associated with the nucleation under confinement. It is observed that the energy for ice nucleation in confinement is less than the activation energy for nucleation in bulk water because of the surface assisted nucleation inside the pore. Interestingly, energy for nucleation is seen to decrease with the lowering of hydration level and ascribed to the curtailed hydrogen bonding network of water at lower pore filling.

Water nucleation at extreme supersaturation.

We report water cluster formation in the uniform postnozzle flow of a Laval nozzle at low temperatures of 87.0 and 47.5 K and high supersaturations of lnS ∼ 41 and 104, respectively. Cluster size distributions were measured after soft single-photon ionization at 13.8 eV with mass spectrometry. Critical cluster sizes were determined from cluster size distributions recorded as a function of increasing supersaturation, resulting in critical sizes of 6-15 and 1, respectively. Comparison with previous data for propane and toluene reveals a systematic trend in the nucleation behavior, i.e., a change from a steplike increase to a gradual increase of the maximum cluster size with increasing supersaturation. Experimental nucleation rates of 5 · 1015 cm-3 s-1 and 2 · 1015 cm-3 s-1 for lnS ∼ 41 and 104, respectively, were retrieved from cluster size distributions recorded as a function of nucleation time. These lie 2-3 orders of magnitude below the gas kinetic collision limit assuming unit sticking probability, but they agree very well with a recent prediction by a master equation model based on ab initio transition state theory. The experimental observations are consistent with barrierless growth at 47.5 K, but they hint at a more complex nucleation behavior for the measurement at 87.0 K.

First laboratory results of supersaturated water nucleation characteristics at low temperatures

Researchers report nucleation rates and trends in nucleation cluster size of extremely supersaturated water vapor.

A theoretical study on the activation of insoluble particles in atmospheric conditions

A theoretical analysis for the description of insoluble particles activation in the atmosphere has been performed using as framework the classical theory of heterogeneous nucleation. In the current work a model for heterogeneous nucleation for one-component and two-component gaseous systems was presented taking into account the process of surface diffusion during nucleating embryo formation. The theory predicts higher nucleation rates compared to the classical theory of heterogeneous nucleation and consequently higher probability of particle activation. The model including the effect of surface diffusion shows a qualitative agreement with experimental results of heterogeneous nucleation of water at different substrates. In addition, the process of heterogeneous nucleation of the sulphuric acid – water system on the surface of insoluble spherical aerosol particles in atmospheric conditions has been examined. Insoluble particle activation is depended on several factors such as the concentration of the participating vapours, the ambient temperature, the chemical composition and particle size. Our results show that activation of insoluble particles is an energetically favourable process under specific conditions in the atmosphere.

Homogeneous nucleation of nano size H2O bubbles and their growth to micro size in rhyolite melts

Volcanism accompanies transfer of volatiles such as H2O and CO2 from the Earth interior to the atmosphere. The underlying process for transfer of the volatiles is magma degassing. As magma rises toward the Earth surface, the volatiles in silicate melts become supersaturated due to decompression of magma so that nucleation of volatile-bearing bubbles and subsequent growth of the bubble occur. In this study, bubble nucleation rate of water in rhyolite melts above 1000 K, which determines the style of the eruption of the magma, is calculated by using molecular cluster model. Calculation results indicate that the homogeneous nucleation of water in the rhyolite melts is possible when the supersaturation pressure exceeds 110 MPa and the number density of bubbles formed increases as increase in the degree of the supesaturation. Growth of bubble formed from the critical cluster was also calculated and the results were compared with observed bubble sizes. When the bubble number density is greater than 1015/m3, depletion of the concentration of volatiles hinders further growth of bubbles.

Unexpected formation of sII methane hydrate in some water-in-oil emulsions: Different reasons for the same phenomenon

The structures of methane hydrate obtained from water emulsions in oils of four types, n-heptane and n-decane were studied. Surfactant Span 80 was used to stabilize emulsions of water in n-heptane and n-decane. Hydrate synthesis was carried out by two methods, namely rapid cooling of a water-in-oil emulsion saturated with methane and long-term isothermal holding of this emulsion. It was shown that different methods of hydrate preparation may result in formation of gas hydrates with different structures. Rapid cooling of three of these emulsions (in two oils and n-heptane) saturated with methane to a temperature below −35 °C leads not only to the formation of the expected methane hydrate of cubic structure I (sI) but also to the cubic structure II (sII) hydrate. In case of oils, the formation of the hydrates in the emulsions seemed to occur at a temperature below the pour point of the corresponding oil. Experiments were carried out with the cooling rate about 14 °C/min at initial methane pressures near 12, 10 and 7 MPa. More detailed investigation showed that in two of these emulsions (in one oil and n-heptane) only sI hydrate is formed during long-term synthesis at 1 °C and methane pressure of 12 MPa. The formed sII hydrate must be metastable. In the case of the emulsion in second oil, the formation of sII hydrate can be related either to the kinetic factor (the formation of metastable hydrate) or to the presence of propane and butanes in the corresponding oil in rather high concentrations. The reason of the metastable phase appearance in the systems under consideration is most likely to be that Span 80 and some kinds of crude oil can inhibit nucleation of sI gas hydrate at the oil – water interface. Thus, some emulsions saturated with methane can be overcooled to a temperature at which the nucleation of sII hydrate is preferable. The data obtained are of interest to understand mechanisms of gas hydrate inhibition/promotion and may provide fresh insight into the influence of crude oils and surfactants on gas hydrate nucleation in water – oil – gas systems.

Unusual examples of methane hydrate nucleation in bilayer water–oil systems

Visual investigation of the nucleation and growth of methane hydrate in a bilayer system of water and oil revealed hydrate nucleation to proceed not only on the water–oil contact surface but also beyond this boundary on the contact surface of water with glass.