Nucleation Of Water Research Articles

High‐Speed 3D Imaging of Multiphase Systems: Applying SCAPE Microscopy to Analog Experiments in Volcanology and Earth Sciences

AbstractMultiphase suspensions are complex systems where microscopic interactions between suspended bubbles, particles, and liquids can significantly alter bulk behavior. Observing the internal mechanics of such suspensions can help constrain the dynamics of natural multiphase flows. To capture these internal processes at high speed and in three dimensions, we propose the use of Swept Confocally Aligned Planar Excitation (SCAPE) microscopy in analog experiments. This imaging technique, developed for neuroscience and biology, uses a sweeping light sheet to illuminate and image fluorophores within a sample. We performed experiments using water and various oils as the liquid phases, glass or PMMA particles for solids, and air or CO2 for gas, which we imaged at rates >50 volumes per second, over a volume size of ∼1 × 1 × 0.4 mm. We focused on three case studies: (1) bubble nucleation, growth, and rise in sparkling water, where we found that bubble detachment from angular PMMA particles left residual bubbles that also grew and detached, generating more bubbles compared to smooth particles; (2) flow of immiscible liquids (water droplets suspended in canola oil) in a porous matrix of PMMA beads, which highlighted the importance of pore and throat sizes on droplet velocities; and (3) injection of air bubbles into concentrated suspensions of glass beads or crushed PMMA particles in a refractive‐index‐matched liquid, which revealed particle motion and strong alterations of the bubble shape. We conclude that SCAPE microscopy is a powerful tool to study the dynamics of multiphase systems.

Effect of an oscillating magnetic field on the inhibition of ice nucleation and its application for supercooling preservation of fresh-cut mango slices

The present study was aimed to examine the effect of oscillating magnetic fields (OMFs) at different intensities (up to 100 mT) on the extended water supercooling. The exterior supercooling chamber with specialized air circulation was invented for validation of the influence of OMF without any heat involvement. The pendulum experiment demonstrated that water tended to move in a direction opposite to the applied OMF due to diamagnetic repulsion, and the magnitude of the displacement increased proportionally with increases in the OMF intensities. Supercooling probability results indicated that OMF intensities of 50 mT inhibited ice nucleation in supercooled water when stored at the temperature of −11 °C, whereas OMF intensities exceeding 100 mT induced freezing. In this respect, the OMF at the field strength of 50 mT was applied for the supercooling preservation of fresh-cut mango slices, which were preserved in a supercooled state at −5 °C for up to 7 days. The quality assessment, such as weight loss and firmness, indicated that the supercooling preservation potentially extended the shelf-life of fresh-cut mangoes while maintaining their original quality. • The intensity of OMF was a significant factor affecting the supercooling probability of water. • OMF intensities of 50 mT potentially inhibited ice nucleation. • The supercooled state of mango slices was extended at −5 °C with the OMF treatment. • Supercooling preservation extended the shelf-life of mango samples without freezing damage.

Ice nucleation in high alternating electric fields: Effect of electric field strength and frequency.

Icing is a severe problem for many technical systems such as aircraft or systems for high-voltage power transmission and distribution. Ice nucleation in water droplets is affected by several influencing factors like impurities or the liquid temperature, which have been widely investigated. However, although an electric field affects nucleation, this influence has been far less investigated and is still not completely understood. The present work is focused on the influence of high alternating electric fields on ice nucleation in sessile water droplets, which is examined for a systematic variation of the electric field frequency and strength. All experiments used to determine the influence of a single parameter like the electric field strength or frequency are performed with the same set of droplets to ensure well-defined conditions and a high repeatability of the procedure. For each parameter variation a large number of nucleation events is observed and analyzed. Droplet survival curves and the nucleation site density are used to analyze the experiments and to determine the influence of the electric field on ice nucleation. Especially for high electric field strengths, a significant influence on nucleation is observed. Some droplets freeze earlier, which leads to a higher median nucleation temperature. On the other hand, the lowest temperature required to freeze all droplets is almost constant compared to the reference case without an electric field. It is shown that not all droplets are affected by the electric field in the same way, but the influence of the electric field on ice nucleation is rather of singular nature. In addition, the frequency of the applied electric field has an impact on the nucleation behavior. The present experimental data quantitatively demonstrate the effect of an electric field on ice nucleation and improves our understanding of heterogeneous nucleation of supercooled water subjected to high alternating electric fields.

Demonstration of neutron radiation-induced nucleation of supercooled water.

We present here direct evidence for neutrons causing nucleation of supercooled water. Highly purified water (20 nm filtration) is cooled to well below freezing (as low as -20 °C) with a radioactive calibration source of neutrons/gamma-rays either present or removed during each of many control cooling runs for the same volume of water. When it is primarily neutrons irradiating the sample bulk, the non-equilibrium freezing point (also known as the "supercooling point") is, on average, +0.7 °C warmer than the control equivalent, with a statistical significance of greater than 5 Sigma, with systematic uncertainty included. This effect is not observed with water in the presence of gamma-rays instead of neutrons. While these neutrons should have theoretically had sufficient energy to mount the energy barrier, corroborating our results, their raising of supercooling temperature has never been reported experimentally to the best of our knowledge. The potential to use deeply supercooled solutions, not only water, as metastable detectors for radiation and perhaps dark matter or neutrino physics presents now a new avenue for exploration.

Suppression of ice nucleation in supercooled water under temperature gradients

Understanding the behaviours of ice nucleation in non-isothermal conditions is of great importance for the preparation and retention of supercooled water. Here ice nucleation in supercooled water under temperature gradients is analyzed thermodynamically based on classical nucleation theory (CNT). Given that the free energy barrier for nucleation is dependent on temperature, different from a uniform temperature usually used in CNT, an assumption of linear temperature distribution in the ice nucleus was made and taken into consideration in analysis. The critical radius of the ice nucleus for nucleation and the corresponding nucleation model in the presence of a temperature gradient were obtained. It is observed that the critical radius is determined not only by the degree of supercooling, the only dependence in CNT, but also by the temperature gradient and even the Young’s contact angle. Effects of temperature gradient on the change in free energy, critical radius, nucleation barrier and nucleation rate with different contact angles and degrees of supercooling are illustrated successively. The results show that a temperature gradient will increase the nucleation barrier and decrease the nucleation rate, particularly in the cases of large contact angle and low degree of supercooling. In addition, there is a critical temperature gradient for a given degree of supercooling and contact angle, at the higher of which the nucleation can be suppressed completely.

Puffing/micro-explosion in rapeseed oil/water droplets: The effects of coal micro-particles in water

The paper is focused on detailed experimental investigation of puffing and micro-explosions in composite water/rapeseed oil droplets in the presence of lignite and bituminous coal micro-particles in water. Gas temperature was measured using a high speed National Instruments 9219 for data collection and an S-type thermocouple. Video recording of droplet micro-explosions was performed using a Phantom Miro M310 high-speed camera. Droplets with radii in the range 1–2 mm were placed in a hot chamber with air velocities 3–7 m/s and temperatures up to 600 °C. The time to puffing/micro-explosion and average radii of child droplets generated during puffing and micro-explosions are shown to decrease with increasing gas temperature. The presence of bituminous coal led to a visible decrease in these radii. The observed times to puffing/micro-explosion were interpreted in terms of the recently developed model of the phenomenon based on the assumption that a single spherical water sub-droplet is located in the centre of a spherical fuel droplet. The time to puffing/micro-explosion in this model is associated with the time instant when the temperature at the water/fuel interface reaches the water nucleation temperature. The model predicts a decrease in time to puffing/micro-explosion in agreement with experimental observations. The effect of coal particles on this time is shown to be weak in agreement with observations at gas temperatures above 300 °C. It is shown that the times to puffing predicted by the model are close to those predicted by a simpler model in which these times are identified with the time instants when the temperature at the water/fuel interface reaches the boiling temperature of water.

Zn2+-Pb2+-doped calcite shrub fabrics: Abiotic morphogenesis of travertine-like dripstone encrustation at the Jersey Zinc Mine, southeastern British Columbia

A cm-thick calcite dripstone on the floor of the abandoned Jersey Zinc Mine in southeastern British Columbia, western Canada, consists of a mixture of shrub and radial fibrous elongated columnar crystal fabrics that resulted from Zn2+ and Pb2+ doping of the calcite crystallographic lattice structure. These heavy metal elements were sourced from sulfide mineralized veins in the overlying limestone beds. Zn2+ and Pb2+ substitution for Ca2+ reduced the size of the calcite crystal structure, impacting configuration of the calcite crystal fabrics. Lower concentration levels of dopants resulted in a radial fibrous elongated columnar crystal fabric with high inter-crystalline porosity. Increased levels of Zn2+ and Pb2+ dopants resulted in a crystal splitting process forming the shrub fabric. Growth of normally flat rhombohedral face on the external surface of the dripstone encrustation was disrupted by mixtures of isotropic and anisotropic growth rates. Inhibited growth rates resulted in early stage crystal splitting processes, forming parallel arrays of precursor crystallites aligned as step-down micro-terraces separated by dam-like micro-barrage partitions with normal growth rates. Shrub fabrics developed below the encrustation surface as ion-laden dripwater films infiltrated the 20% to 25% inter-crystalline porosity. This early stage of crystal splitting transitioned into a shrub fabric substrate, each consisting of fan-shaped crystal arrays distributed along a main stem, all in optical continuity. Extreme levels of Zn2+ dopant resulted in split crystal formation of micro-spherulites on the external surface of the dripstone. Spherulite neomorphism occurred, resulting in replacement of the crystallites by an individual calcite spar during envelopment by the columnar crystal domain fabric. The spheroid forms were preserved within the columnar fabric as spheroid zones of Zn-calcite and outlined by microcrystalline ferroan calcite. The shrub fabrics have morphological similarity to dendritic branching shrubs commonly associated with biotic and abiotic travertine and some biotic tufa deposits, which form under very different depositional conditions. Abiotic Zn2+-Pb2+ dopants absorbed into the calcite crystal structure of this mine floor encrustation precluded the necessity for carbonate precipitation from supersaturated carbonate water or precursor microbial induced nucleation sites, unlike similar travertine and tufa shrub fabrics elsewhere.

Heterogeneous nucleation of water vapor on different types of black carbon particles

Abstract. The heterogeneous nucleation of water vapor on insoluble particles affects cloud formation, precipitation, the hydrological cycle, and climate. Despite its importance, heterogeneous nucleation remains a poorly understood phenomenon that relies heavily on empirical information for its quantitative description. Here, we examine the heterogeneous nucleation of water vapor on different types of soots as well as cloud drop activation of different types of soots, including both pure black carbon particles and black carbon particles mixed with secondary organic matter. We show that the recently developed adsorption nucleation theory quantitatively predicts the nucleation of water and droplet formation upon particles of the various soot types. A surprising consequence of this new understanding is that, with sufficient adsorption site density, soot particles can activate into cloud droplets – even when completely lacking any soluble material.

Homogeneous water nucleation: Experimental study on pressure and carrier gas effects.

Homogeneous nucleation of water is investigated in argon and in nitrogen at about 240 K and 0.1 MPa, 1 MPa, and 2 MPa by means of a pulse expansion wave tube. The surface tension reduction at high pressure qualitatively explains the observed enhancement of the nucleation rate of water in argon as well as in nitrogen. The differences in nucleation rates for the two mixtures at high pressure are consistent with the differences in adsorption behavior of the different carrier gas molecules. At low pressure, there is not enough carrier gas available to ensure the growing clusters are adequately thermalized by collisions with carrier gas molecules so that the nucleation rate is lower than under isothermal conditions. This reduction depends on the carrier gas, pressure, and temperature. A qualitative agreement between experiments and theory is found for argon and nitrogen as carrier gases. As expected, the reduction in the nucleation rates is more pronounced at higher temperatures. For helium as the carrier gas, non-isothermal effects appear to be substantially stronger than predicted by theory. The critical cluster sizes are determined experimentally and theoretically according to the Gibbs-Thomson equation, showing a reasonable agreement as documented in the literature. Finally, we propose an empirical correction of the classical nucleation theory for the nucleation rate calculation. The empirical expression is in agreement with the experimental data for the analyzed mixtures (water-helium, water-argon, and water-nitrogen) and thermodynamic conditions (0.06 MPa-2 MPa and 220 K-260 K).

AFM imaging of extracellular ice nucleators.

Ice nucleators are substances that can initiate nucleation of pure water at and above -10 °C.Some plant pathogens possess a gene which encodes for a protein that acts as an ice nucleator, activity of which is enhanced when it is combined with the sugar and lipid components from the cell membrane. This matter retains its ice nucleation activity even after it is detached from the cell wall, and is termed extracellular ice nucleator (ECIN). In this paper, surface morphology of ECINs was investigated using atomic force microscopy (AFM) in tapping mode. ECINs were immobilized onto polyelectrolyte multilayers using the layer by layer deposition method. Effect of layer build-up, method of ECIN production, and polyelectrolytes used for multilayer fabrication were investigated. Globular and rod-like structures were observed on the AFM images of the nano-thin ECIN layers. Activity of ECINs, tested in food solutions in earlier studies, was retained when applied as a nano-thin layer onto a silicon wafer surface. Protein aggregate sizes decreased when higher centrifugation speeds were applied, and ice nucleation activity also decreased. Nucleation occurred faster and at higher temperatures when substrates were immersed in solutions of higher ECIN concentration, whereas number of bilayers formed did not have a significant effect. Higher concentration ECIN dipping solutions also led to the formation of thicker and denser ECIN layers as observed via AFM imaging. PRACTICAL APPLICATION: This study demonstrates the properties of nano-thin ECIN layers, which can crystallize pure water into ice at higher temperatures and in shorter time. Accelerating ice nucleation can potentially be utilized to freeze liquids in shorter time hence using less energy, or improve frozen foods' stability against the risk of cold chain breakage.

Effects of an oscillating magnetic field on ice nucleation in aqueous iron‐oxide nanoparticle dispersions during supercooling and preservation of beef as a food application

AbstractThis study was aimed to explore the effects of an oscillating magnetic field (OMF) on the ice nucleation behavior of distilled water (DW) and iron‐oxide nanoparticle dispersion (IND) during supercooling. The magnetic field intensity and distribution of the OMF produced by Helmholtz coils were predicted using COMSOL. It was hypothesized that the ferric nanoparticles in the IND would promote the heterogeneous ice nucleation, and the OMF could inhibit the nucleation process by rotating the particles. The supercooling probability of IND was significantly increased by 36% under the OMF at the ambient temperature of −10°C. However, the OMF also enhanced the supercooling stability of DW by 32%, suggesting that it could induce the dipolar movements of water molecules via water diamagnetism and create the induced electric fields, subsequently suppressing the occurrence of ice nucleation within DW as well. As an extended application, fresh beef was preserved in a supercooled state with the OMF treatment and its supercooled state was effectively extended for a week at the temperature of −4°C. The supercooling preservation potentially prolonged the shelf life of meat with no significant changes in drip loss, color, and bacterial growth for up to a week in this study.Practical applicationsRecently, the application of an oscillating magnetic field (OMF) has attracted considerable interest in the food preservation industry because the OMF is supposed to control ice nucleation during the freezing process. The present study demonstrated that the OMF treatment potentially suppressed ice nucleation in water and aqueous iron‐oxide nanoparticle dispersion. As a case study, beef steaks were preserved at subzero temperatures with the OMF treatment and they were successfully supercooled at −4°C for up to 7 days. The supercooling technology based on the OMF allowed to maintain the meat quality for an extended period while preventing bacterial growth. This novel technology can be integrated into a commercial refrigeration system and ensure the prolonged shelf life of various food products.

Transparent Photothermal Metasurfaces Amplifying Superhydrophobicity by Absorbing Sunlight.

Imparting and maintaining surface superhydrophobicity has been receiving significant research attention over the last several years, driven by a broad range of important applications and enabled by advancements in materials and surface nanoengineering. Researchers have investigated the effect of temperature on droplet-surface interactions, which poses additional challenges when liquid nucleation manifests itself, due to ensuing condensation into the surface texture that compromises its antiwetting behavior. Maintaining surface transparency at the same time poses an additional and significant challenge. Often, the solutions proposed are limited by working temperatures or are detrimental to visibility through the surface. Here we introduce a scalable method employing plasmonic photothermal metasurface composites, able to harvest sunlight and naturally heat the surface, sustaining water repellency and transparency under challenging environmental conditions where condensation and fogging would otherwise be strongly promoted. We demonstrate that these surfaces, when illuminated by sunlight, can prevent impalement of impacting water droplets, even when the droplet to surface temperature difference is 50 °C, by suppressing condensate formation within the texture, maintaining transparency. We also show how the same transparent metasurface coating could be combined and work collaboratively with hierarchical micro- and nanorough textures, resulting in simultaneous superior pressure-driven impalement resistance and avoidance of water nucleation and related possible frosting in supercooled conditions. Our work can find a host of applications as a sustainable solution against impacting water on surfaces such as windows, eyewear, and optical components.

Cellulose-Based Superhydrophobic Surface Decorated with Functional Groups Showing Distinct Wetting Abilities to Manipulate Water Harvesting.

Inspired by the distinct functions of desert beetles with efficient droplet nucleation and lotus leaves with excellent droplet removal, an integrated method is presented for the design of a superhydrophobic surface decorated with hydrophilic groups that can efficiently nucleate and remove water droplets. We constructed a cellulose-based superhydrophobic surface containing numerous olefin terminal groups by solvent exchange and spray coating. This surface is different from most of the reported biomimicking water harvesting surfaces that rely on complicated lithography and micropatterning techniques requiring special instruments. The obtained superhydrophobic surface was further modified using various thiol compounds via a thiol-ene reaction to manipulate the water harvesting property. The modified surfaces containing hydrophobic groups (e.g., 1-octadecanethiol and 1H,1H,2H,2H-perfluorodecanethiol) or a strong hydrophilic group (e.g., 3-mercaptopropionic acid and 6-mercapto-1-hexanol) exhibited insufficient fog collecting abilities due to poor water droplet nucleation or strong water adhesion. By contrast, the modified surface decorated with moderately hydrophilic amino groups combines the advantages of biological surfaces with distinct wetting features (such as fog-harvesting beetles and water-repellent lotus leaves), resulting in accelerated water nucleation and less compromise of the water removal efficiency. Molecular dynamic simulations revealed that the efficient droplet nucleation is attributed to the hydrophilic amino groups whereas the rapid droplet removal is due to the maintained superhydrophobicity of the amino group-modified surface. This strategy of decorating a superhydrophobic surface with moderately hydrophilic functional groups provides insight into the manipulation of droplet nucleation and removal for water collection efficiency.

Surface water formation on the natural surface under supersaturation: from local water balance to air pollutant deposition

Heterogeneous nucleation and subsequent growth of surface water occur on hydrophobic natural substrates under supersaturation; however, this basic physical relationship has been explained only empirically as yet. In order to derive a new method to determine supersaturation at the canopy–air interface, we considered the parameters that contribute to surface water formation (SWF) and examined their importance by field observations at an urban site in the period 2015–2017. We found that both the interfacial and vertical temperature differences ranged 1–3 K and that they were necessary but not sufficient for supersaturated condensation on natural surfaces. Excess supply of moisture must exist and continuously contribute to the growth of the condensed water nuclei, which may originate from external sources such as atmospheric advection. Under the additional moisture supply, SWF appeared not only on the ground soil but also on the vegetation canopy at heights of 1–2 m. We also found that the SWF plays a role in the removal of ground-level air pollutants. The removal efficiency for [SO42− + NO3−] of the deposition flux was estimated as ~ 0.3 mmol (per [Ca2+] meq)/m2(per leaf area) during SWF.

Molecular insight into the interfacial chemical functionalities regulating heterogeneous calcium-arsenate nucleation

Heterogeneous nucleation induced by natural organic matter (NOM) can lower the energy barrier for calcium arsenate (Ca-As) precipitation, which aids in immobilizing arsenate (AsⅤ). However, it remains unclear how certain chemical functionalities of NOM affect Ca-As nucleation at the molecular scale. By analyzing changes in the local supersaturation and/or interfacial energy, the present work investigates the Ca-As heterogeneous nucleation kinetics and mechanisms on functional-group–modified model surfaces.Mica surfaces modified by functional groups of amine (NH2), hydroxyl (OH), or carboxyl (COOH) through self-assembled monolayers were used to investigate how chemical functionalities affect the Ca-As heterogeneous nucleation, in which the distributions of formation kinetics and size (as measured by the change in particle height) of nucleated Ca-As particles were measured by using in situ atomic force microscopy. In a parallel analysis, a quartz-crystal microbalance with dissipation was used to detect the buildup of Ca2+ and/or HAsO42− ions at the solid–fluid interface. PeakForce quantitative nanomechanical mapping and dynamic force spectroscopy using functional-group–modified tips made it possible to calculate the binding energies holding functional groups to Ca-As particles. Nucleated Ca-As particles were characterized by using Raman spectroscopy and high-resolution transmission electron microscopy.The results indicate that the height of amorphous Ca-As particles formed on a modified mica surface may be ranked in descending order as NH2 > OH > bare mica > COOH, as determined by the buildup of Ca2+ and HAsO42− ions at the solid–fluid interface and the decrease of interfacial energy due to the functional groups. These nanoscale observations and molecular-scale determinations improve our understanding of the roles played by chemical functionalities on NOM in immobilizing dissolved As through heterogeneous nucleation in soil and water.

Non-segregated crystalline state of dilute glycerol aqueous solution.

When a dilute aqueous solution freezes at 1 atm, it is segregated into water-rich ice Ih and solute-rich freeze-concentrated glassy solution. A similar segregation is observed at the crystallization of homogeneous glassy aqueous solutions by heating. The influence of solutes on the nucleation of solvent water and the solute discharge process from the crystalline ice are not clear. In this study, I made a homogeneous dilute glassy glycerol aqueous solution (0.07 mol fraction) using pressure liquid cooling vitrification (PLCV), measured the specific volume and the sample temperature during the compression and decompression processes, and examined the polyamorphic and crystallization behaviors. It is found that the sample crystallized slightly above the crystallization temperature is amorphized homogeneously under pressure, and that the amorphized sample is equivalent to the homogeneous glassy sample made by PLCV. This indicates that glycerol solutes in the crystalline sample are dispersed homogeneously and the crystalline sample does not segregate. These experimental results suggest that nucleation does not involve segregation and that crystal growth induces segregation. The discovery of the non-segregated crystalline state has an implication in not only the understanding of crystallization of glassy ice in meteorology and planetary physics but also the application to cell thawing techniques in cryobiology and food engineering.

Surface roughness affects early stages of silica scale formation more strongly than chemical and structural properties of the substrate

Precipitation of amorphous silica (SiO2) in geothermal power plants has been shown to occur via homogeneous nucleation in the separated water as well as heterogeneous nucleation on pre-existing surfaces. While the factors facilitating homogeneous nucleation are well known, the effect of surface properties on the heterogeneous pathway are less well understood. We investigated the precipitation of amorphous silica onto different surfaces by placing coupons of opal (= mirroring previously deposited silica), volcanic glass (= common reservoir rocks) and corrosion-resistant carbon steel (= geothermal pipelines) inside the pipelines of the Hellisheiði power plant (SW-Iceland) where they were in contact with a silica-supersaturated geothermal liquid (800 ppm SiO2, 60–120 °C) for up to 10 weeks. Our results showed that the similarities in chemical composition and structure of opal and volcanic glass to the amorphous silica were less important in facilitating nucleation than the rough surface of the carbon steel. However, once the nuclei had formed, their growth was independent of the surface material and only controlled by deployment length, temperature and the concentration of monomeric silica in the separated water. Thus, over time a continuous, botryoidal silica layer formed on all coupons. This suggests that surface properties are not crucial in developing better mitigation strategies against amorphous silica scaling.

Onset and critical radius of heterogeneous bubble nucleation

In this work, the onset of heterogeneous bubble nucleation is studied using molecular dynamics (MD) simulations and experiments. In MD simulations, heterogeneous bubble nucleation is initiated in liquid argon by partially heating a platinum surface. Multiple simulations are run by varying the width and temperature of the heated part of the surface; each simulation results in either a collapsing, stable or growing bubble for which Gibbs free energy is estimated and compared. These results atomistically confirm that a critical radius of nucleation exists for heterogeneous nucleation. Based on these simulations, an analytical model is developed to predict the critical width required for bubble nucleation at the nanoscale. Experiments are also conducted on the onset of bubble nucleation in water on a silicon-dioxide surface.

Nanoclusters and amorphous ice flakes built from water dimers

The water-solid interaction is fundamentally important for understanding and controlling the structures of interfacial water. Here we study the initial stage of water adsorption and nucleation on a Cd(0001) surface, through a combination of low temperature scanning tunnelling microscopy (STM) experiments and first-principles density-functional theory (DFT) calculation. Water is found to aggregate into various clusters with the dominant of water dimers. Particularly, the amorphous ice nanoflakes are built exclusively from water dimers. Driven by the electric field from a STM tip, the water dimers can hop across the surface, detach from a cluster with subsequent attaching to another, or rotate or diffuse within the amorphous ice nanoflakes. DFT calculations demonstrate that the ultrahigh stability of water dimers results from the adsorption-induced enhancement of dipole moment of water.

Comparative analysis of nuclear waste solidification performance models: Spent ion exchanger-cement based wasteforms

Solidification performance for cement based radioactive wasteforms was investigated and linked to the hydraulic performance using mechanistic and empirical models. Within this context, the short-term developments of the compressive strength, porosity, and permeability of cement based matrices of varying water content were assessed. For matrices of low-water content, diffusion reaction is the dominant solidification mechanism due to super-saturation of CSH phases. As the water content increases, nucleation and growth reaction controls the process. The nature of the immobilization of inorganic ion exchangers and polymer modification in cement based matrices and its effect on the relative change in the compressive strength and permeability were investigated. The reductions in the solidification performance for cement-inorganic exchanger wasteforms were attributed to the excess amount of Ettringite in case of alumina exchangers and to the reduction in the hydrated phases formation for the rest of the inorganic exchangers. The permeability of the alumina-cement wasteform is fairly constant up to 16 % loading, whereas this behavior is noted up to 10 % loading of the rest of the inorganic exchanger and absent for organic exchangers-modified cement wasteforms.