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Properties of crystalline and amorphous materials are characterized by the underlying long-range and local crystalline order. Deformations and defects are structural hallmarks of plasticity, ice formation, and crystal growth mechanisms. Partitioning topological networks into constituent crystal building blocks, which is the basis of topological identification criteria, is an intuitive approach for classification in both bulk and confinement. However, techniques reliant on the convex hull for assigning orientations of component units fail for non-convex blocks. Here, we propose a new framework, called Topological Unit Matching (TUM), which exploits information from topological criteria for an efficient shape-matching procedure. TUM is a general family of algorithms, capable of quantifying deformations and unambiguously determining grains of bulk and confined ice polymorphs. We show that TUM significantly improves the identification of quasi-one-dimensional ice by including deformed prism blocks. We demonstrate the efficacy of TUM by analyzing supercooled water nanoparticles, amorphous ice, and phase transitions in an ice nanotube. We also illustrate the superiority of TUM in resolving topological defect structures with minimal parameterization.

Low-density amorphous ice (LDA) is of paramount importance not only for fields such as astronomy, meteorology and biology from a scientific point of view, but also for technological applications like cryo-scanning electron microscopy and electron-beam lithography utilizing ice resists. Recent advances in LDA have been reviewed, focusing on its formation and crystallization processes. The specific aspects of this review include: (a) the LDA formation methods and the corresponding required conditions, (b) the measurement principles of the density, thermal conductivity and the growth rate of LDA, (c) the monitoring of the phase transformation, (d) the transformation kinetics of LDA to crystalline ice. Finally, open questions as well as future challenges relating to LDA are discussed.

We report on the freezing behavior of the AOT reverse micelles studied by molecular dynamics (MD) simulation. Structural and thermodynamic properties of the micelle have been investigated in nonpolar medium at the temperature range from 300 to 150 K. Aggregation number and the water to surfactant ratio were constant (NAOT = 32, ω = 10). The freezing temperature of water in micelle core was found to be lower than that in bulk water. There are three types of water in the AOT reverse micelle freezing process: liquid water at high temperature, 5-membered rings of glassy water, and solid state water at temperature lower than 200 K. The water molecules in ionic shells and oil molecules demonstrated liquid state during the simulation. Sodium counterions have moved from the micelle core into the surface and back during the simulation forming clathrate-like structure.

In this study, the structure of nanoconfined ice and its behavior during the melting process have been investigated. For this purpose, deionized water was inserted into the pores of the ordered carbon structures CMK-3 and CMK-8 having pores of different diameters. The first set of experiments was performed using differential scanning calorimetry (DSC), from which the melting transition temperature of the confined ice was determined. In order to investigate the structure of ice formed inside the mesopores, wide-angle X-ray scattering was used. The measurements were performed at temperatures from 173 K up to and above the pore melting point for each system. The results of the XRD experiments showed features characteristic of both hexagonal, Ih, and cubic, Ic, ice at temperatures below the melting point. The structure of the confined ice corresponds to disordered stacking ice layers, ice Isd, and our results agree well with recent simulations of X-ray diffraction of such ice crystals by Murray and co-workers.

In-situ NMR spin-lattice relaxation measurements were performed on several vapor deposited ices. The measurements, which span more than 6 orders of magnitude in relaxation times, show a complex spin-lattice relaxation pattern that is strongly dependent on the growth conditions of the sample. The relaxation patterns change from multi-timescale relaxation for samples grown at temperatures below the amorphous-crystalline transition temperature to single exponential recovery for samples grown above the transition temperature. The slow-relaxation contribution seen in cold-grown samples exhibits a temperature dependence, and becomes even slower after the sample is annealed at 200K. The fast-relaxation contribution seen in these samples, does not seem to change or disappear even when heating to temperatures where the sample is evaporated. The possibility that the fast relaxation component is linked to the microporous structures in amorphous ice samples is further examined using an environmental electron scanning microscope. The images reveal complex meso-scale microporous structures which maintain their morphology up to their desorption temperatures. These findings, support the possibility that water molecules at pore surfaces might be responsible for the fast-relaxation contribution. Furthermore, the results of this study indicate that the pore-collapse dynamics observed in the past in amorphous ices using other experimental techniques, might be effectively inhibited in samples which are grown by relatively fast vapor deposition.

Climatic signals in deep ice cores, particularly from ion concentrations, may be affected by the diffusion of liquid solution along grain boundaries of ice. Such solutions include sulfates. Because of the difficulty of detecting sulfate liquids in the ice matrix, we must infer the phase of the sulfates from the ice temperature and inclusion properties. In this study, we use micro-Raman spectroscopy to determine the phase of three sulfate micro-inclusions in the Dome Fuji ice core at 2798.5 m depth. Using a temperature-ramp test, we find a peak position at 984 cm−1 and a change in the full width at half maximum of the SO stretching mode that identifies the sulfate in the micro-droplets. Considering the peak position and full width at half maximum of sulfate inclusions, we argue that the sulfate would have existed as a micro-droplet liquid on an air-clathrate hydrate in the ice. Additionally, the increase in the low frequencies of the Raman spectrum below 30 cm−1 that we detect can be generally used to identify liquids in natural ice. Our investigation also indicates that the surface of air-clathrate hydrates in ice is a preferred location for liquid micro-inclusions. Copyright © 2016 John Wiley & Sons, Ltd.

Three different characterization tests namely, ice adhesion strength, drop freezing time and a newly developed ice accretion method were applied to surfaces which were commonly used in anti-icing research such as aluminum, stainless steel, copper, styrene butadiene rubber, polypropylene and polytetrafluoroethylene in order to investigate the effect of their water wettability and surface free energies on their anti-icing performances. It was found that ice adhesion strengths increased and drop freezing times decreased with the increase of the total surface free energies and decrease of the water contact angles on these surfaces similar to previously published reports however, no direct relationship was found between the ice accretion results and solid wettability, surface free energies and the reasons were discussed in terms of heterogeneous nucleation mechanisms.

Ice films formed at mineral surfaces are of widespread occurrence in nature and are involved in numerous atmospheric and terrestrial processes. In this study, we studied thin ice films at surfaces of 19 synthetic and natural mineral samples of varied structure and composition. These thin films were formed by sublimation of thicker hexagonal ice overlayers mostly produced by freezing wet pastes of mineral particles at -10 and -50 °C. Vibration spectroscopy revealed that thin ice films contained smaller populations of strongly hydrogen-bonded water molecules than in hexagonal ice and liquid water. Thin ice films at the surfaces of the majority of minerals considered in this work [i.e., metal (oxy)(hydr)oxides, phyllosilicates, silicates, volcanic ash, Arizona Test Dust] produced intense O-H stretching bands at ∼3400 cm(-1), attenuated bands at ∼3200 cm(-1), and liquid-water-like bending band at ∼1640 cm(-1) irrespective of structure and composition. Illite, a nonexpandable phyllosilicate, is the only mineral that stabilized a form of ice that was strongly resilient to sublimation in temperatures as low as -50 °C. As mineral-bound thin ice films are the substrates upon which ice grows from water vapor or aqueous solutions, this study provides new constraints from which their natural occurrences can be understood.

Ice crystals in the atmosphere nucleate from supercooled liquid water and grow by vapor uptake. The structure of the ice polymorph grown has strong impact on the morphology and light scattering of the ice crystals, modulates the amount of water vapor in ice clouds, and can impact the molecular uptake and reactivity of atmospheric aerosols. Experiments and molecular simulations indicate that ice nucleated and grown from deeply supercooled liquid water is metastable stacking disordered ice. The ice polymorph grown from vapor has not yet been determined. Here we use large-scale molecular simulations to determine the structure of ice that grows as a result of uptake of water vapor in the temperature range relevant to cirrus and mixed-phase clouds, elucidate the molecular mechanism of the formation of ice at the vapor interface, and compute the free energy difference between cubic and hexagonal ice interfaces with vapor. We find that vapor deposition results in growth of stacking disordered ice only under conditions of extreme supersaturation, for which a nonequilibrium liquid layer completely wets the surface of ice. Such extreme conditions have been used to produce stacking disordered frost ice in experiments and may be plausible in the summer polar mesosphere. Growth of ice from vapor at moderate supersaturations in the temperature range relevant to cirrus and mixed-phase clouds, from 200 to 260 K, produces exclusively the stable hexagonal ice polymorph. Cubic ice is disfavored with respect to hexagonal ice not only by a small penalty in the bulk free energy (3.6 ± 1.5 J mol(-1) at 260 K) but also by a large free energy penalty at the ice-vapor interface (89.7 ± 12.8 J mol(-1) at 260 K). The latter originates in higher vibrational entropy of the hexagonal-terminated ice-vapor interface. We predict that the free energy penalty against the cubic ice interface should decrease strongly with temperature, resulting in some degree of stacking disorder in ice grown from vapor in the tropical tropopause layer, and in polar stratospheric and noctilucent clouds. Our findings support and explain the evolution of the morphology of ice crystals from hexagonal to trigonal symmetry with decreasing temperature, as reported by experiments and in situ measurements in clouds. We conclude that selective growth of the elusive cubic ice polymorph by manipulation of the interfacial properties can likely be achieved at the ice-liquid interface but not at the ice-vapor interface.

The coexistence of the amorphous structure and crystalline hexagonal structure of ice near its melting point at normal pressure is confirmed by comparing the diffraction patterns of diffuse X-ray scattering for different amorphous structures. The diffuse X-ray scattering at an ice sample maintained at a temperature of–10°C is continuously recorded for a long time. Continual variations in the nature of diffuse scattering until its complete disappearance are revealed. The disappearance of diffuse scattering indicates the metastability of amorphous ice near its melting point with a lifetime of about 15 days.

The glass transitions of low-density amorphous ice (LDA) and high-density amorphous ice (HDA) are the topic of controversial discussions. Understanding their exact nature may be the key to explaining the anomalies of liquid water but has also got implications in the general context of polyamorphism, the occurrence of multiple amorphous forms of the same material. We first show that the glass transition of hydrogen-disordered ice VI is associated with the kinetic unfreezing of molecular reorientation dynamics by measuring the calorimetric responses of the corresponding H2O, H2(18)O, and D2O materials in combination with X-ray diffraction. Well-relaxed LDA and HDA show identical isotopic-response patterns in calorimetry as ice VI, and we conclude that the glass transitions of the amorphous ices are also governed by molecular reorientation processes. This "reorientation scenario" seems to resolve the previously conflicting viewpoints and is consistent with the fragile-to-strong transition from water to the amorphous ices.

We present an overview of recent static and time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state, as well as of crystalline and amorphous ice forms. The structure and dynamics of the complex hydrogen-bond network formed by water molecules in the bulk and interphases are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed, from conventional infrared and Raman spectroscopy to femtosecond pump-probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. Additionally, we discuss novel approaches, such as two-dimensional sum-frequency generation, three-dimensional infrared, and two-dimensional Raman terahertz spectroscopy. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and energetics emerges. Furthermore, we outline future perspectives of vibrational spectroscopy for water researches.

Using molecular dynamics simulation, we investigate the phase behavior of water confined in graphene nanocapillaries at room temperature (300 K). Here, the lateral pressure Pzz is used as the primary controlling variable, and its effect on the behavior of trilayer water is systematically studied. Three (meta)stable trilayer (TL) crystalline/amorphous ice phases, namely, TL-ABAI, TL-ABA, and TL-AAAI, are observed in our simulations with the lateral pressure in the range of 1.0 GPa ≤ Pzz ≤ 6.0 GPa. TL-ABAI exhibits a square lattice in every layer, and the three layers exhibit the ABA stacking pattern; i.e., the oxygen atoms in the two outer layers are in registry. This new trilayer ice structure can also be viewed as a bilayer clathrate hydrate with water molecules in the middle layer serving as the guest molecules. With increasing lateral pressure, typically, the solid-to-liquid-to-solid phase transition occurs, during which the structural transformation from triangular to square-like in the ice layer is a...

The detection of nanobubbles on surfaces is well established (e.g., AFM and optical microscopy methods), but currently no methods exist for the direct detection of bulk nanobubbles. Here, cryo-electron microscopy (cryo-EM) has been employed to observe bubbles in aqueous solutions for the first time. Nitrogen bubbles generated by a chemical reaction were observed in amorphous ice trapped between two carbon films. The cryo-EM images of bubbles showed the same features as predicted by theory. The fact that no bubbles were observed near an air–water interface suggests that bubbles may diffuse to the nearby air–water interface and escape. The estimate of the bubble diffusion coefficient is about 30–250 μm2/s.

International audience; The surfaces of many objects in the Solar System comprise substantial quantities of water ice sometimes mixed with minerals and/or organic molecules. The sublimation of the ice changes the structural and optical properties of these objects. We present laboratory data on the evolution of the structure and the visible and near-infrared spectral reflectance of icy surface analogues of cometary ices, made of water ice, complex organic matter (tholins) and silicates, as they undergo sublimation under low temperature (

Surface melting of ice crystals forms quasi-liquid layers (QLLs) on ice surfaces, and affects a wide variety of natural phenomena. Since QLLs enhance various chemical reactions in ice clouds, the formation of QLLs by atmospheric gases has been studied intensively. However, such studies were performed using spectroscopy techniques, which have low spatial resolution. Here we show the first direct visualization of QLLs on ice basal faces in the presence of hydrogen chloride (HCl) gas (model atmospheric gas) by advanced optical microscopy, which can visualize individual 0.37 nm-thick elementary steps on ice crystal surfaces. We found that the HCl gas induced the appearances of QLLs with a droplet shape in the temperature range from −15.0 to −1.5 °C, where no QLL appears in the absence of HCl gas. This result indicates that HCl gas adsorbed on ice crystal surfaces probably changed the surface structure of ice crystals and then induced the subsequent melting of ice surfaces. We also observed the movement, shape...

In spite of the resurgence in ice nucleation research a comparatively small number of studies deal with the phenomenon of pre-activation in heterogeneous ice nucleation. Fifty years ago, it was shown that various mineral dust and volcanic ash particles can be pre-activated to become nuclei for ice crystal formation even at temperatures as high as 270–271 K. Pre-activation was achieved under ice-subsaturated conditions without any preceding macroscopic ice growth by just temporarily cooling the particles to temperatures below 228 K. A two-step mechanism involving capillary condensation of supercooled water and subsequent homogeneous freezing was proposed to account for the particles' enhanced ice nucleation ability at high temperatures. This work reinvestigates the efficiency of the proposed pre-activation mechanism in temperature-cycling experiments performed in a large cloud chamber with suspended particles. We find the efficiency to be highest for the clay mineral illite as well as for highly porous materials like zeolite and diatomaceous earth, whereas most aerosols generated from desert dust surface samples did not reveal a measurable pre-activation ability. The pre-activation efficiency is linked to particle pores in a certain size range. As estimated by model calculations, only pores with diameters between about 5 and 8 nm contribute to pre-activation under ice-subsaturated conditions. This range is set by a combination of requirements from the negative Kelvin effect for condensation and a critical size of ice embryos for ice nucleation and melting. In contrast to the early study, pre-activation is only observed for temperatures below 260 K. Above that threshold, the particles' improved ice nucleation ability disappears due to the melting of ice in the pores.

Complex living systems such as mammalian cells can be arrested in a solid phase by ultrarapid cooling. This allows for precise observation of cellular structures as well as cryopreservation of cells. The state of water, the main constituent of biological samples, is crucial for the success of cryogenic applications. Water exhibits many different solid states. If it is cooled extremely rapidly, liquid water turns into amorphous ice, also called vitreous water, a glassy and amorphous solid. For cryo-preservation, the vitrification of cells is believed to be mandatory for cell survival after freezing. Intracellular ice crystallization is assumed to be lethal, but experimental data on the state of water during cryopreservation are lacking. To better understand the water conditions in cells subjected to freezing protocols, we chose to directly analyze their subcellular water states by cryo-electron microscopy and tomography, cryoelectron diffraction, and x-ray diffraction both in the cryofixed state and after warming to different temperatures. By correlating the survival rates of cells with their respective water states during cryopreservation, we found that survival is less dependent on ice-crystal formation than expected. Using high-resolution cryo-imaging, we were able to directly show that cells tolerate crystallization of extra- and intracellular water. However, if warming is too slow, many small ice crystals will recrystallize into fewer but bigger crystals, which is lethal. The applied cryoprotective agents determine which crystal size is tolerable. This suggests that cryoprotectants can act by inhibiting crystallization or recrystallization, but they also increase the tolerance toward ice-crystal growth.

One of the characteristic properties of ice slurry is the buoyancy of ice particles, which leads to ice separation in unmixed ice slurries and the necessity to agitate storage vessels if ice slurry is to be extracted. Based on this, an investigation into the density modification of ice particles has been undertaken. Additional particles with higher density than ice should act as ice forming nuclei during ice generation, for which suitable particles have been determined and tested. It was possible to show that not all added particles act as ice forming nuclei in the role of a cell nucleus. Furthermore, it can be assumed that various particles agglomerate on the surface of ice particles; hence the density of ice particles increased more than expected due to the incorporation of several particles in each ice particle. These modified ice particles may sediment to the bottom of the container due to the high density of the numerous heavy foreign particles.

Water ice is the most abundant solid in the Universe. Understanding the formation, structure and multiplicity of physicochemical roles for water ice in the cold, dense interstellar environments in which it is predominantly observed is a crucial quest for astrochemistry as these are regions active in star and planet formation. Intuitively, we would expect the mobility of water molecules deposited or synthesised on dust grain surfaces at temperatures below 50 K to be very limited. This work delves into the thermally-activated mobility of H2O molecules on model interstellar grain surfaces. The energy required to initiate this process is studied by reflection-absorption infrared spectroscopy of small quantities of water on amorphous silica and highly oriented pyrolytic graphite surfaces as the surface is annealed. Strongly non-Arrhenius behaviour is observed with an activation energy of 2 kJ mol-1 on the silica surface below 25 K and 0 kJ mol-1 on both surfaces between 25 and 100 K. The astrophysical implication of these results is that on timescales shorter than that estimated for the formation of a complete monolayer of water ice on a grain, aggregation of water ice will result in a non-uniform coating of water, hence leaving bare grain surface exposed. Other molecules can thus be formed or adsorbed on this bare surface.

We have investigated the effects of compression and quantization on atomic distribution in ice Ic and in its compressed states at 77 K and 10 K, using the path integral molecular dynamics (PIMD) simulations over wide range of volume. It has been found that the high density amorphous ice (HDA) is attained by compression but volume range to retain ice structure is wider at 10 K than 77 K. We have discovered that quantum dispersion of atoms in ice Ic at 10 K induces non-zero probability that hydrogen-bonded H2O molecular molecules are oriented nonlinearly in the crystal structure, which was believed to contain exclusively linear orientation of hydrogen-bonded molecular pairs in this ice. It has been found that for HDA there is each non-zero probability of orientational disorder of hydrogen-bonded H2O pairs, of such uniform distribution of H atoms as observed in supercritical fluids in general, and of H atoms located at the O-O midpoint. The present PIMD simulations have revealed that these observed anomalous characteristics of atomic distribution in HDA are caused by both quantization of atoms and compression of the system.

Crystallization of ice from deeply supercooled water and amorphous ices - a process of fundamental importance in the atmosphere, interstellar space, and cryobiology - results in stacking disordered ices with a wide range of metastabilities with respect to hexagonal ice. The structural origin of this high variability, however, has not yet been elucidated. Here we use molecular dynamics simulations with the mW water model to characterize the structure of ice freshly grown from supercooled water at temperatures from 210 to 270 K, the thermodynamics of stacking faults, line defects, and interfaces, and to elucidate the interplay between kinetics and thermodynamics in determining the structure of ice. In agreement with experiments, the ice grown in the simulations is stacking disordered with a random distribution of cubic and hexagonal layers, and a cubicity that decreases with growth temperature. The former implies that the cubicity of ice is determined by processes at the ice/liquid interface, without memory of the structure of buried ice layers. The latter indicates that the probability of building a cubic layer at the interface decreases upon approaching the melting point of ice, which we attribute to a more efficient structural equilibration of ice at the liquid interface as the driving force for growth wanes. The free energy cost for creating a pair of cubic layers in ice is 8.0 J mol(-1) in experiments, and 9.7 ± 1.9 J mol(-1) for the mW water model. This not only validates the simulations, but also indicates that dispersion in cubicity is not sufficient to explain the large energetic variability of stacking disordered ices. We compute the free energy cost of stacking disorder, line defects, and interfaces in ice and conclude that a characterization of the density of these defects is required to predict the degree of metastability and vapor pressure of atmospheric ices.

Water, when constrained between two graphene sheets and under ultrahigh pressure, can manifest dramatic differences from its bulk counterparts such as the van der Waals pressure induced water-to-ice transformation, known as the metastability limit of two-dimensional (2D) liquid. Here, we present result of a new crystalline structure of bilayer ice with the AB-stacking order, observed from molecular dynamics simulations of constrained water. This AB-stacked bilayer ice (BL-ABI) is transformed from the puckered monolayer square-like ice (pMSI) under higher lateral pressure in the graphene nanocapillary at ambient temperature. BL-ABI is a proton-ordered ice with square-like pattern. The transition from pMSI to BL-ABI is through crystal-to-amorphous-to-crystal pathway with notable hysteresis-loop in the potential energy during the compression/decompression process, reflecting the compression/tensile limit of the 2D monolayer/bilayer ice. In a superheating process, the BL-ABI transforms into the AB-stacked bilayer amorphous ice with the square-like pattern.

To investigate the structure of interface between forsterite glass and amorphous H2O ice, we performed molecular dynamics calculations. The result shows that a low-density layer for both forsterite and ice exists in the interface. Furthermore, the decomposition of water molecules was observed in the interface, although the decomposition rate decreases as the temperature decreases. The decomposition mechanisms of H2O are important to understand not only to the origin of water on terrestrial planets but also to the chemical evolution processes of various molecules in interstellar molecular clouds.

Water Phases Theoretical simulations suggest that deeply supercooled water undergoes a transition between high- and low-density forms, but this transition is difficult to study experimentally because it occurs under conditions in which ice crystallization is extremely rapid. Kim et al. combined x-ray lasers for rapid structure determination with infrared femtosecond pulses for rapid heating of amorphous ice layers formed at about 200 kelvin. The heating process created high-density liquid water at increased pressures. As the layer expanded and decompressed, low-density liquid domains appeared and grew on time scales between 20 nanoseconds and 3 microseconds, which was much faster than competing ice crystallization. Science , this issue p. [978][1] [1]: /lookup/doi/10.1126/science.abb9385

In an effort to understand the effects of H2O activity on zeolite formation, we have synthesized LTA zeolite using a combination of freezing processes and varying drying temperatures. Sodium aluminate and sodium silicate were used to form LTA zeolite, according to the IZA (International Zeolite Association) protocol. The synthesis steps were modified by adding the precursor frozen process by a rapid liquid nitrogen (&minus, 196 &deg, C) treatment or slow conventional freezer treatment (&minus, 20 &deg, C). The samples were subsequently sonicated and then dried at 80 &deg, C or 40 &deg, C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed on the samples immediately after the drying process as well as after 2 weeks and 1 month of aging the solid products. The results indicated that LTA zeolite does not form. The silica-alumina precursor after both freezing processes and after being dried at 80 &deg, C showed the presence of sodalite displaying stable behavior over time. Both sets of samples dried at 40 &deg, C and did not show the presence of zeolite immediately after the drying process. However, after 2 weeks, the liquid nitrogen&ndash, frozen precursor was characterized by the presence of EMT whereas zeolites never formed in the &minus, C samples. These results suggest that freezing processes differently control the H2O activity during the drying and aging processes in the solid state. Thus, although the precursor chemical composition is the same, the type of zeolite formed is different.

Previous studies have shown that the Lorentz–Lorenz relationship, or molar refractivity/specific refractivity effective medium approximation, enables a reasonable prediction of the refractive index of amorphous water ice, given the refractive index of crystalline water ice. In the current study, we show that the Bruggeman effective medium approximation provides an even closer match to measurements of the refractive index of several amorphous materials, given the refractive index of their crystalline phase. We show that the Bruggeman effective medium approximation provides a good match to measurements of the refractive index of amorphous ice as well. Thus, assuming that the volume fraction of the scattering centers is a constant for a given amorphous material (with respect to a given range of wavelengths) seems to be a more robust assumption than assuming that the molar mass and molar refractivity or specific refractivity are preserved in going from the crystalline state to the amorphous state of the same material. Our results have implications for astrophysics applications, as well as for the optics of non-crystalline materials in general.

The 2D-Raman-THz response in all possible time-orderings (Raman-THz-THz, THz-Raman-THz, and THz-THz-Raman) of amorphous water ice is calculated in two ways: from atomistic molecular dynamics simulations and with the help of a Feynman diagram model, the latter of which power-expands the potential energy surface and the dipole and polarizability surfaces up to leading order. Comparing both results allows one to dissect the 2D-Raman-THz response into contributions from mechanical anharmonicity, as well as electrical dipole and polarizability anharmonicities. Mechanical anharmonicity dominates the 2D-Raman-THz response of the hydrogen-bond stretching and hydrogen-bond bending bands of water, and dipole anharmonicity dominates that of the librational band, while the contribution of polarizability anharmonicity is comparably weak. A distinct echo of the hydrogen-bond stretching band is observed for the THz-Raman-THz pulse sequence, again dominated by mechanical anharmonicity. A peculiar mechanism is discussed, which is based on the coupling between the many normal modes within the hydrogen-bond stretching band and which will inevitably generate such an echo for an amorphous structure.

Differential dynamic microscopy is performed in diamond anvil cells to measure the viscosity of water along the 24 ° C isotherm to high pressure by the determination of the tracer diffusion coefficient of monodisperse silica spheres of known diameter and the application of the Stokes–Einstein–Sutherland equation. This technique allows liquid samples to be compressed to greater pressure prior to freezing than with other viscometry methods. The highest-pressure measurement was made at 1.67 GPa, considerably deeper into the supercompressed regime than previously reported. The effect of the isotopic composition is investigated with samples of normal water, heavy water, and partially deuterated water. When data below 0.25 GPa are excluded, a free volume model fits the observed viscosities well, yielding a theoretical glass transition density close to that observed in very-high-density amorphous ice. The improved fit above 0.25 GPa coincides with the loss of other anomalous behaviors in liquid water caused by hydrogen bonding and represents a transition to properties closer to those of a simple liquid.

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.

Solar system objects with perihelia beyond the orbit of Jupiter ($q >$ 5 AU) are too cold for water ice to generate an appreciable coma via sublimation. Despite this, numerous high perihelion objects (HPOs) including many comets and recently escaped Kuiper belt objects (``Centaurs'') are observed to be active out at least to the orbit of Saturn ($q \sim$ 10 AU). Peak equilibrium temperatures at 10 AU ($\sim$125 K), while far too low to sublimate water ice, are sufficient to sublimate super-volatiles such as CO and CO$_2$ ice. Temperatures at 10 AU are also high enough to trigger the rapid crystallization of exposed amorphous ice, thus constituting another possible driver of distant activity. While supervolatile ices can sublimate strongly (as $r_H^{-2}$) to at least Kuiper belt (30 AU) distances, crystallization is an exponential function of temperature that cannot be sustained much beyond $\sim$10 AU. The heliocentric dependence of the activity thus suggests an observational test. If activity in high perihelion objects is triggered by crystallization, then no examples of activity should be found with perihelia $q >>$ 10 AU. If, on the other hand, activity is due to free sublimation of exposed supervolatile ices, or another cause, then distant activity might be detected. We obtained sensitive, high resolution Hubble Space Telescope observations of HPOs to search for activity beyond the crystallization zone. No examples of activity were detected in 53 objects with $q >$ 15 AU, consistent with the crystallization trigger hypothesis. However, sensitivity limits are such that we cannot reject the alternative hypothesis that mass loss is driven by the sublimation of supervolatile ices. We also searched for binary companions in our sample, finding none and setting an empirical 3$��$ limit to the binary fraction of $, 30 pages, 11 figures, 4 tables. Accepted by AJ

Amorphous ice has long been invoked as a means for trapping extreme volatiles into solids, explaining the abundances of these species in comets and planetary atmospheres. Experiments have shown that such trapping is possible and have been used to estimate the abundances of each species in primitive ices after they formed. However, these experiments have been carried out at deposition rates which exceed those expected in a molecular cloud or solar nebula by many orders of magnitude. Here we develop a numerical model which reproduces the experimental results and apply it to those conditions expected in molecular clouds and protoplanetary disks. We find that two regimes of ice trapping exist: `burial trapping' where the ratio of trapped species to water in the ice reflects that same ratio in the gas and `equilibrium trapping' where the ratio in the ice depends only on the partial pressure of the trapped species in the gas. The boundary between these two regimes is set by both the temperature and rate of ice deposition. Such effects must be accounted for when determining the source of trapped volatiles during planet formation., 13 pages, 6 figures

The thermal properties of airless icy surfaces are providing a wealth of information on their regolith structure after eons of space weathering. Numerous observations of the thermal cycles of Jupiter and Saturn icy satellites or Centaurs and TNOs have been acquired in the latest decades thanks to the Galileo and Cassini missions and to the Spitzer and Herschel telescopes. These observations and the latest developments on thermophysical modeling which have been achieved to link the thermal inertia to the regolith structure are reviewed here. Measured thermal inertias of these surfaces covered with water ice are very low, roughly between about 1 and 100 J/m2/K/s1/2. Often interpreted as due to unconsolidated or highly porous regoliths, these low values may result from a composition of amorphous ice or from the roughness of grains defacing contacts in a regolith of normal compaction. Taken together, thermal inertias appear to increase with probed depth and to decrease with heliocentric distance. This latter effect can be easily reproduced if heat transfer is dominated by radiation in pores, despite low temperatures, because the conduction through grains is limited, either due to the presence of amorphous ice or because of the roughness of grains.

In situ Raman and Brillouin light scattering techniques were used to study thermally induced high-density amorphous (HDA) to low-density amorphous (LDA) transition in silica glass densified in hot compression (up to 8 GPa at 1100 °C). Hot-compressed silica samples are shown to retain structural and mechanical stability through 600 °C or greater, with reduced sensitivity in elastic response to temperature as compared with pristine silica glass. Given sufficient thermal energy to overcome the energy barrier, the compacted structure of the HDA silica reverts back to the LDA state. The onset temperature for the HDA to LDA transition depends on the degree of densification during hot compression, commencing at lower temperatures for samples with higher density, but all finishing within a temperature range of 250-300 °C. Our studies show that the HDA to LDA transition at high temperatures in hot-compressed samples is different from the gradual changes starting from room temperature in cold-compressed silica glass, indicating greater structural homogeneity achieved by hot compression. Furthermore, the structure and properties of hot-compressed silica glass change continuously during the thermally induced HDA to LDA transition, in contrast to the abrupt and first-order-like polyamorphic transitions in amorphous ice. Different HDA to LDA transition mechanisms in amorphous silica and amorphous ice are explained by their different energy landscapes.

International audience; The origin of cometary volatiles remains a major open question in planetary science. Comets may have either agglomerated from crystalline ices condensed in the protosolar nebula (PSN) or from amorphous ice originating from the molecular cloud and interstellar medium. Here, based on the recent argon, krypton, and xenon measurements performed by the ROSINA mass spectrometer on board the European Space Agency's Rosetta spacecraft in the coma of 67P/Churyumov-Gerasimenko, we show that these noble gas relative abundances can be explained if the comet's building blocks formed from a mixture of gas and H 2 O grains resulting from the annealing of pristine amorphous ice (i.e., originating from the presolar cloud) in the PSN. In this scenario, the different volatiles released during the amorphous-to-crystalline ice phase transition would have been subsequently trapped at lower temperatures in stoichiometric hydrate or clathrate hydrate forms by the crystalline water ice generated by the transition. Once crystalline water was completely consumed by clathration in the ∼25-80 K temperature range, the volatile species remaining in the gas phase would have formed pure condensates at lower temperatures. The formation of clathrates hydrates and pure condensates to explain the noble gas relative abundances is consistent with a proposed interstellar origin of molecular oxygen detected in 67P/Churyumov-Gerasimenko, and with the measured molecular nitrogen depletion in comets.

We combine 1H, 2H, and 7Li NMR methods to investigate the dynamics of water molecules and lithium ions in LiCl aqueous solutions over wide ranges of time and length scales down to their glass transitions. Structural relaxation times τ and self-diffusion coefficients D reveal that water and lithium dynamics are faster for lower salt content at ambient temperatures, while the differences vanish upon cooling when fractional freezing leads to similar salt concentrations in the remaining liquid phases. Relaxation times and diffusion coefficients of water molecules agree with those of lithium ions in the weakly supercooled regime, indicating that the dynamics are strongly coupled. Furthermore, non-Arrhenius temperature dependence is found and the Stokes-Einstein relation is obeyed in this temperature range. However, we observe various decoupling phenomena for the motion of the constituents and for dynamics on different length scales in the deeply supercooled regime. Most notably, the rotational motion of the water molecules does not follow the glassy slowdown of the studied salt solutions below ∼145 K, but it rather resembles that in nanoscopic confinement, molecular solutions, and high-density amorphous ice at low temperatures. This common low-temperature water dynamics is characterized by large-angle reorientation and Arrhenius temperature dependence.

We employ classical molecular dynamics simulations to investigate the molecular-level structure of water during the isothermal compression of hexagonal ice ($\mathrm{I}h$) and low-density amorphous (LDA) ice at low temperatures. In both cases, the system transforms to high-density amorphous ice (HDA) via a first-order-like phase transition. We employ a sensitive local order metric (LOM) [F. Martelli et al., Phys. Rev. B 97, 064105 (2018)] that can discriminate among different crystalline and noncrystalline ice structures and is based on the positions of the oxygen atoms in the first- and/or second-hydration shell. Our results confirm that LDA and HDA are indeed amorphous, i.e., they lack polydispersed ice domains. Interestingly, HDA contains a small number of domains that are reminiscent of the unit cell of ice IV, although the hydrogen-bond network (HBN) of these domains differs from the HBN of ice IV. The presence of ice-IV-like domains provides some support to the hypothesis that HDA could be the result of a detour on the HBN rearrangement along the $\mathrm{I}h$-to-ice-IV pressure-induced transformation. Both nonequilibrium LDA-to-HDA and $\mathrm{I}h$-to-HDA transformations are two-step processes where a small distortion of the HBN first occurs at low pressures and then, a sudden, extensive rearrangement of hydrogen bonds at the corresponding transformation pressure follows. Interestingly, the $\mathrm{I}h$-to-HDA and LDA-to-HDA transformations occur when LDA and $\mathrm{I}h$ have similar local order, as quantified by the site-averaged LOMs. Since $\mathrm{I}h$ has a perfect tetrahedral HBN while LDA does not, it follows that higher pressures are needed to transform $\mathrm{I}h$ into HDA than that for the conversion of LDA to HDA. In correspondence with both first-order-like phase transitions, the samples are composed of a large HDA cluster that percolates within the $\mathrm{I}h/\mathrm{LDA}$ samples. Our results shed light on the debated structural properties of amorphous ices and indicate that the kinetics of the $\mathrm{I}h$-to-HDA and LDA-to-HDA transformations require an in-depth inspection of the underlying HBN. Such investigation is currently ongoing.

Formation of molecular oxygen in and on amorphous ice in the interstellar medium requires oxygen diffusion to take place. Recent experiments suggest that this process involves quantum tunneling of the oxygen atoms at sufficiently low temperatures. Fit- ting experimental diffusion rates between 6 and 25 K to an expression that accounts for the roughness of the surface yields excellent agreement. The molecular dynamics of adsorbed oxygen is characterized by rapid intrasite dynamics followed by intersite transitions over distances of ∼ 10 ̊ A. Explicit simulations using a realistic free energy surface for oxygen diffusion on amorphous ice down to 10 K show that quantum tun- neling is not required for mobility of adsorbed oxygen. This is confirmed by comparing quantum and classical simulations using the same free energy surface. The ratio of diffusional and desorption energy E dif /E des = 275/1082 ≈ 0.3 is at the lower end of typically used values but still consistent with assumptions made in models for inter- stellar chemistry.

International audience; The adsorption of methylamine at the surface of amorphous ice is studied at various temperatures, ranging from 20 to 200 K, by grand canonical Monte Carlo simulations under conditions that are characteristic to the interstellar medium (ISM). The results are also compared with those obtained earlier on crystalline (Ih) ice. We found that methylamine has a strong ability of being adsorbed on amorphous ice, involving also multilayer adsorption. The decrease of the temperature leads to a substantial increase of this adsorption ability; thus, considerable adsorption is seen at 20–50 K even at bulk gas phase concentrations that are comparable with that of the ISM. Further, methylamine molecules can also be dissolved in the bulk amorphous ice phase. Both the adsorption capacity of amorphous ice and the strength of the adsorption on it are found to be clearly larger than those corresponding to crystalline (Ih) ice, due to the molecular scale roughness of the amorphous ice surface as well as to the lack of clear orientational preferences of the water molecules at this surface. Thus, the surface density of the saturated adsorption monolayer is estimated to be 12.6 ± 0.4 μmol/m2, 20% larger than the value of 10.35 μmol/m2, obtained earlier for Ih ice, and at low enough surface coverages the adsorbed methylamine molecules are found to easily form up to three hydrogen bonds with the surface water molecules. The estimated heat of adsorption at infinitely low surface coverage is calculated to be −69 ± 5 kJ/mol, being rather close to the estimated heat of solvation in the bulk amorphous ice phase of −74 ± 7 kJ/mol, indicating that there are at least a few positions at the surface where the adsorbed methylamine molecules experience a bulk-like local environment.

Water in Sephadex® (crosslinked dextran) gels is known to indicate different freezing behavior which is dependent on the density of the crosslinks, and water in a Sephadex® G25 gel remains partially unfrozen during cooling and crystallizes during rewarming. The mechanism of anomalous ice crystallization during rewarming is still unclear. The objective of this study is to observe the ice grains that form in Sephadex® beads and to comprehend their frozen state with a focus on the ice crystallization during rewarming. Sephadex® beads containing 50 wt % water were prepared and used for the measurements. The observation of the ice grains was carried out by using synchrotron radiation-sourced X-ray CT (computed tomography). XRD (X-ray diffraction) analysis was also conducted to investigate the frozen state. As a result, ice grains that were larger than ~1 μm were hardly observed after the slow cooling of Sephadex® beads, except in the G25 beads. However, at the occurrence of ice crystallization during rewarming, ice grains that were larger than 10 μm appeared in the G25 beads. Using XRD, it was found that small incomplete ice crystals were formed in G25 beads and the presence of glassy water was indicated in the gel. In conclusion, the size and distribution of ice grains that formed in Sephadex® beads were different depending on the density of the crosslinks.

Some two-dimensional liquid systems are theoretically predicted to have an anomalous phase transition due to unique intermolecular interactions, for example the first-order transition between two-dimensional high-density water and low-density amorphous ice. However, it has never been experimentally observed, to the best of our knowledge. Here we report an entropy-driven phase transition between a high-density liquid crystal and low-density crystalline solid, directly observed by scanning tunneling microscope in carbon monoxide adsorbed on Cu(111). Combined with first principle calculations, we find that repulsive dipole–dipole interactions between carbon monoxide molecules lead to unconventional thermodynamics. This finding of unconventional thermodynamics in two-dimensional carbon monoxide not only provides a platform to study the fundamental principles of anomalous phase transitions in two-dimensional liquids at the atomic scale, but may also help to design and develop more efficient copper-based catalysis., Intermolecular interactions have a crucial role in the adsorption of molecules on a surface, however their role in promoting phase transitions is less well known. Here, the authors report an abnormal phase transition between a high-density liquid crystal and low-density solid in the case of carbon monoxide on Cu(111), driven by intermolecular interactions and entropy.

13 pags., 18 figs., 2 tabs., Aims. This paper investigates how the far-IR water ice features can be used to infer properties of disks around T Tauri stars and the water ice thermal history. We explore the power of future observations with SOFIA/HIRMES and SPICA's proposed far-IR instrument SAFARI. Methods. A series of detailed radiative transfer disk models around a representative T Tauri star are used to investigate how the far-IR water ice features at 45 and 63 μm change with key disk properties: disk size, grain sizes, disk dust mass, dust settling, and ice thickness. In addition, a series of models is devised to calculate the water ice emission features from warmup, direct deposit, and cooldown scenarios of the water ice in disks. Results. Photodesorption from icy grains in disk surfaces weakens the mid-IR water ice features by factors of 4-5. The far-IR water ice emission features originate from small grains at the surface snow line in disks at distance of 10-100 au. Unless this reservoir is missing in disks (e.g., transitional disks with large cavities), the feature strength does not change. Grains larger than 10 μm do not contribute to the features. Grain settling (using turbulent description) affects the strength of the ice features by at most 15%. The strength of the ice feature scales with the disk dust mass and water ice fraction on the grains, but saturates for dust masses higher than 10 M and for ice mantles that increase the dust mass by more than 50%. The various thermal histories of water ice leave an imprint on the shape of the features (crystalline and/or amorphous) and on the peak strength and position of the 45 μm feature. SOFIA/HIRMES can only detect crystalline ice features that are much stronger than those simulated in our standard T Tauri disk model in deep exposures (1 h). SPICA/SAFARI can detect the typical ice features in our standard T Tauri disk model in short exposures (10 min). Conclusions. The sensitivity of SPICA/SAFARI will allow the detailed study of the 45 and 63 μm water ice feature in unbiased surveys of T Tauri stars in nearby star forming regions and an estimate of the mass of their ice reservoir. The water ice emission features carry an imprint of the thermal history of the ice, and thus can distinguish between various formation and transport scenarios. Amorphous ice at 45 μm that has a much broader and flatter peak could be detected in deep surveys if the underlying continuum can be well characterized and the baseline stability of SAFARI is better than a few percent., IK and MM acknowledge funding from the EU FP7-2011 under Grant Agreement no. 284405. LK is supported by a grant from the Netherlands Research School for Astronomy (NOVA).

Nucleation of ice by airborne particles is a process vital to weather and climate, yet our understanding of the mechanisms underlying this process is limited. Kaolinite is a clay that is a significant component of airborne particles and is an effective ice nucleus. Despite receiving considerable attention, the microscopic mechanism(s) by which kaolinite nucleates ice is not known. We report molecular dynamics simulations of heterogeneous ice nucleation by kaolinite (001) surfaces. Both the Al-surface and the Si-surface nucleate ice. For the Al-surface, reorientation of the surface hydroxyl groups is essential for ice nucleation. This flexibility allows the Al-surface to adopt a structure which is compatible with hexagonal ice, Ih, at the atomic level. On the rigid Si-surface, ice nucleates via an unusual structure that consists of an ordered arrangement of hexagonal and cubic ice layers, joined at their basal planes where the interfacial energy cost is low. This ice structure provides a good match to the atomistic structure of the Si-surface. This example is important and may have far-reaching implications because it demonstrates that potential ice nuclei need not be good atomic-level matches to particular planes of ice Ih or cubic ice, Ic. It suggests that surfaces can act as effective ice nuclei by matching one of the much larger set of planes that can be constructed by regular arrangements of hexagonal and cubic ice.

The goal of this project is to study the properties of H 2 O ice in the environment of the Saturn satellites and in particular to measure the relative amounts of crystalline and amorphous H 2 O ice in and around two craters on Rhea. The craters are remnants of cataclysmic events that, by raising the local temperature, melted the ice, which subsequently crystallized. Based on laboratory experiments it is expected that, when exposed to ion bombardment at the temperatures typical of the Saturn satellites, the crystalline structure of the ice will be broken, resulting in the disordered, amorphous phase. We therefore expect the ice in and around the craters to be partially crystalline and partially amorphous. We have designed a technique that estimates the relative amounts of crystalline and amorphous H 2 O ice based on measurements of the distortion of the 2-μm spectral absorption band. The technique is best suited for planetary surfaces that are predominantly icy, but works also for surfaces slightly contaminated with other ices and non-ice components. We apply the tool to two areas around the Inktomi and the Obatala craters. The first is a young impact crater on the leading hemisphere of Rhea, the second is an older one on the trailing hemisphere. For each crater we obtain maps of the fraction of crystalline ice, which were overlain onto Imaging Science Subsystem (ISS) images of the satellite searching for correlations between crystallinity and geography. For both craters the largest fractions of crystalline ice are in the center, as would be intuitively expected since the ‘ground zero’ areas should be most affected by the effects of the impact. The overall distribution of the crystalline ice fraction maps the shape of the crater and, in the case of Inktomi, of the rays. The Inktomi crater ranges between a maximum fraction of 67% crystalline ice to a minimum of 39%. The Obatala crater varies between a maximum of 51% and a minimum of 33%. Based on simplifying assumptions and the knowledge that crystalline ice exposed to ion bombardment transforms into amorphous at a known rate, we estimate the age of the Obatala crater to be ∼450 Ma.

Cubic ice Ic is metastable, yet can form by the freezing of supercooled water, vapour deposition at low temperatures and by depressurizing high-pressure forms of ice. Its structure differs from that of common hexagonal ice Ih in the order its molecular layers are stacked. This stacking order, however, typically has considerable disorder; that is, not purely cubic, but alternating in hexagonal and cubic layers. In time, stacking-disordered ice gradually decreases in cubicity (fraction having cubic structure), transforming to hexagonal ice. But, how does this disorder originate and how does it transform to hexagonal ice? Here we use numerical data on dislocations in hexagonal ice Ih to show that (1) stacking-disordered ice (or Ic) can be viewed as fine-grained polycrystalline ice with a high density of extended dislocations, each a widely extended stacking fault bounded by partial dislocations, and (2) the transformation from ice Ic to Ih is caused by the reaction and motion of these partial dislocations. M...

Recently, our earlier data which led us to conclude that deeply supercooled water displays a second glass transition (Amann-Winkel et al., 2013) was reinterpreted (Johari, 2015). In particular, the increase in heat capacity observed for high-density amorphous ice (HDA) samples at 116 K was reinterpreted to indicate sub- T g features of low-density amorphous ice's (LDA's) glass transition. We reply to the criticism in detail and report an experiment triggered by the comment on our work. This experiment unequivocally confirms our original interpretation of the observations and reinforces the case for water's second glass transition, its polyamorphism, and the observation of two distinct ultraviscous states of water differing by about 25% in density.

It is known that ambient pressure DSC scan of a glass formed by cooling a liquid under a high pressure shows a sub-Tg endotherm with a Cp peak, an exothermic minimum, and finally the true Tg-endotherm of the glass (A. Weitz, B. Wunderlich, J. Polym. Sci. Polym. Phys. 12 (1974) 2473). Amann-Winkel et al. (Proc. Natl. Acad. Sci. (U.S.) 110 (2013) 17720) reported that the ambient pressure DSC scan of eHDA, the expanded high density amorphous ice, cooled under a pressure of 0.07 GPa shows onset of a Cp endotherm at 116 K. Unaware of the studies of pressure-densified glasses, they regarded this onset as a second glass transition of water at 116 K involving translational mobility. We show that: (i) their eHDA at 0.07 GPa and 140 K was ultraviscous water of high density, and the ex situ DSC scans were obtained for the recovered glassy solid that formed on cooling this water under 0.07 GPa pressure to 90 K, (ii) decrease in the onset temperature of the 116 K endotherm they found on decreasing the cooling rate, and used as a typical signature of glass-transition, is not a signature of glass transition – and this rules out the possibility of this endotherm being a glass transition endotherm – nor are the methods claimed to be standard are standard or reliable methods, (iii) the DSC scans of the recovered glassy solid at ambient pressure are qualitatively similar to those found for pressure-densified glasses, and (iv) the experimental procedure and data analysis of the dielectric relaxation study is too inaccurate to reliably support the view that water has a second Tg. We conclude that the rise in Cp at 116 K is the sub-Tg endotherm of pressure-densified glassy water, i.e., water has only one Tg in the DSC scan at ambient pressure. We also describe other findings on pressure-densified glasses, and the possibility of their sub-Tg mobility affecting certain irreversible processes, and suggest experiments for investigating why a glass formed by cooling under high pressure has different properties at ambient pressure than a glass formed by cooling at ambient pressure.

Observation of theorized glass-to-liquid transitions between low-density amorphous (LDA) and high-density amorphous (HDA) water states had been stymied by rapid crystallization below the homogeneous water nucleation temperature (∼235 K at 0.1 MPa). We report optical and X-ray observations suggestive of glass-to-liquid transitions in these states. Crack healing, indicative of liquid, occurs when LDA ice transforms to cubic ice at 160 K, and when HDA ice transforms to the LDA state at temperatures as low as 120 K. X-ray diffraction study of the HDA to LDA transition clearly shows the characteristics of a first-order transition. Study of the glass-to-liquid transitions in nanoconfined aqueous solutions shows them to be independent of the solute concentrations, suggesting that they represent an intrinsic property of water. These findings support theories that LDA and HDA ice are thermodynamically distinct and that they are continuously connected to two different liquid states of water.

The experimental setup is made to study the heat and mass transfer properties of frozen ceramics. Measurements were carried out for two ceramic samples, one of which (sample A) contains an ice body about 5 cm 3 , and ice in the other (sample B) is a set of small grains with sizes of 1–100 μm. The hydroconductivity and thermo-osmosis coefficients of the sample A are several orders higher than the corresponding coefficients of the sample B. Barothermic effect is registered for only one sample namely the ceramics with the ice macro-inclusion. The thermal conductivity coefficient of the sample A is a non-monotonic function of temperature, in contrast to the sample B. Distinctive features of the sample A are associated with the regelation movement of ice in a porous medium under the influence of the temperature and water pressure gradients.

Changes in the ice nucleation characteristics of atmospherically relevant mineral dust particles caused by a coating of nitric acid are not well understood. Further, the atmospheric implications of dust coatings on ice-cloud properties under different assumptions of primary ice nucleation mechanisms are unknown. We investigated the ice nucleation ability of Arizona Test Dust, illite, K-feldspar, and quartz as a function of temperature (−25°C to −30°C) and relative humidity with respect to water (75% to 110%). The particles (bare or nitric acid coated) were size selected at 250 nm, and the fraction of particles nucleating ice at various temperature and saturation conditions was determined. All of the dust species nucleated ice at subsaturated conditions, although the coated particles (except quartz) showed a reduction in their ice nucleation ability relative to bare particles. However, at supersaturated conditions, bare and coated particles had nearly equivalent ice nucleation characteristics. The results of a single-column model showed that simulated ice crystal number concentrations are mostly dependent upon the coated particle fraction, primary ice nucleation mechanisms, and competition among ice nucleation mechanisms to nucleate ice. In general, coatings were observed to modify ice-cloud properties, and the complexity of ice-cloud and mixed-phase-cloud evolution when different primary ice nucleation mechanisms compete for fixed water vapor budgets was supported.