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We introduce a parameter-free structural indicator to classify local environments of water molecules in stable and supercooled liquid states, which reveals a clear two-peak distribution of local properties. The majority of molecules are tetrahedrally coordinated (T molecules), via low-energy hydrogen bonds. The minority component, whose relative concentration decreases with a decrease in the temperature at constant pressure, is characterized by prevalently three-coordinated molecules, giving rise to a distorted local network around them (D molecules). The inter-conversion between T and D molecules explains the increasing specific heat at constant pressure on cooling. The local structure around a T molecule resembles the one found experimentally in low-density amorphous ice (a network structure mostly composed by T molecules), while the local structure around a D molecule is reminiscent of the structural properties of high-density amorphous ice (a network structure composed by a mixture of T and D molecules). [ABSTRACT FROM AUTHOR]

We study the effect of heavy impurities on the dynamics of supercooled liquids. In a supercooled liquid, when we make a small fraction of particles heavier, they exhibit slower dynamics than the original particles and also make the overall system slower. If one looks at the overlap correlation function to quantify dynamics in the system, it has different behaviors for the heavy and the light particles. In particular, at the relaxation time of the overall system, the degree of relaxation achieved by the heavier particles is lesser, on average, than that achieved by the lighter particles. This difference in relaxation, however, goes down drastically as a crossover temperature, T0, is crossed. Below this crossover temperature, particles in the system have similar relaxation times irrespective of their masses. This crossover temperature depends on the fraction of the heavy particles and their masses. Next, we isolate the effect of mass heterogeneity on the dynamics of supercooled liquids and find that its effect increases monotonically with temperature. We also see that the development of dynamical heterogeneity with decreasing temperature is less dramatic for the system with impurities than for the pure system. Finally, the introduction of heavy impurities can be seen as a way of reducing the kinetic fragility of a supercooled liquid. [ABSTRACT FROM AUTHOR]

Kinetic rate factors of crystallization have a direct effect on formation and growth of an ordered solid phase in supercooled liquids and glasses. Using the crystallizing Lennard-Jones liquid as an example, in the present work, we perform a direct quantitative estimation of values of the key crystallization kinetic rate factors—the rate g+ of particle attachments to a crystalline nucleus and the rate g− of particle detachments from a nucleus. We propose a numerical approach, according to which a statistical treatment of the results of molecular dynamics simulations was performed without using any model functions and/or fitting parameters. This approach allows one to accurately estimate the critical nucleus size nc. We find that for the growing nuclei, whose sizes are larger than the critical size nc, the dependence of these kinetic rate factors on the nucleus size n follows a power law. In the case of the subnucleation regime, when the nuclei are smaller than nc, the n-dependence of the quantity g+ is strongly determined by the inherent microscopic properties of a system, and this dependence cannot be described in the framework of any universal law (for example, a power law). It has been established that the dependence of the growth rate of a crystalline nucleus on its size goes into the stationary regime at the size n > 3nc particles. [ABSTRACT FROM AUTHOR]

We study the evolution of enthalpic changes across the glass transition of model sodium silicate glasses (Na2O)x(SiO2)100−x, focusing on the detection of a flexible-rigid transition and a possible reversibility window in relationship with dynamic properties. We show that the hysteresis resulting from enthalpic relaxation during a numerical cooling–heating cycle is minimized for 12% ≤ x ≤ 20% Na2O, which echoes with the experimental observation. The key result is the identification of the physical features driving this anomalous behavior. The intermediate-flexible boundary is associated with a dynamic onset with increasing depolymerization that enhances the growing atomic motion with a reduced internal stress, whereas the intermediate-stressed rigid boundary exhibits a substantial increase in the temperature at which the relaxation is maximum. These results suggest an essentially dynamic origin for the intermediate phase observed in network glass-forming liquids. [ABSTRACT FROM AUTHOR]

Crystallization processes of amorphous germanium–tin (GeSn) under low-energy electron-beam irradiation were examined using transmission electron microscopy (TEM). Freestanding amorphous GeSn thin films were irradiated with a 100 keV electron beam at room temperature. The amorphous GeSn was athermally crystallized by electron-beam irradiation, when the electron flux exceeded the critical value. Heterogeneous structures consisting of nano- and micro-crystallites were formed after crystallization of amorphous GeSn with ∼24 at. % Sn in the as-sputtered amorphous state. In situ TEM observations of structural changes under electron-beam irradiation revealed that random nucleation and growth of nanocrystallites occur at the early stage of crystallization, followed by rapid formation of micro-grains surrounding the nanocrystals. It has been suggested that the growth of micro-grains progresses via supercooled liquid Sn at the amorphous/crystalline interface. The resultant GeSn grains with a size of a few micrometers contained ∼15 at. % Sn, much larger than the solubility limit of Sn in Ge (∼1 at. % Sn). [ABSTRACT FROM AUTHOR]

We present an information-theoretic approach inspired by distributional clustering to assess the structural heterogeneity of particulate systems. Our method identifies communities of particles that share a similar local structure by harvesting the information hidden in the spatial variation of two- or three-body static correlations. This corresponds to an unsupervised machine learning approach that infers communities solely from the particle positions and their species. We apply this method to three models of supercooled liquids and find that it detects subtle forms of local order, as demonstrated by a comparison with the statistics of Voronoi cells. Finally, we analyze the time-dependent correlation between structural communities and particle mobility and show that our method captures relevant information about glassy dynamics. [ABSTRACT FROM AUTHOR]

Many measurements have indicated that thin polymer films in their glass state exhibit a mobile interfacial layer that grows in thickness upon heating, while some measurements indicate the opposite trend. Moreover, simulations and limited measurements on glass-forming liquids at temperatures above the glass transition temperature Tg exhibit a growing interfacial mobility scale ξ upon cooling. To better understand these seemingly contradictory trends, we perform molecular dynamics simulations over a temperature regime for which our simulated polymer film enters a non-equilibrium glassy state and find that the relaxation time τα within the film interior, relative to the polymer–air interfacial layer, exhibits a maximum near the computational Tg. Correspondingly, we also observe that the interfacial mobility length scale exhibits a maximum near Tg, explaining the apparent reversal in the temperature dependence of this scale between the glass and liquid states. We show that the non-monotonic variation of ξ and the relative interfacial mobility to the film interior arise qualitatively from a non-monotonic variation of the gradient of the effective activation free energy of the film; we then obtain a quantitative description of this phenomenon by introducing a phenomenological model that describes the relaxation time layer-by-layer in the film for a temperature range both above and below Tg of the film as a whole. This analysis reveals that the non-monotonic trend in the relative interfacial mobility and ξ both arise primarily from the distinctive temperature dependence of relaxation in the interfacial layer, which apparently remains in local equilibrium over the whole temperature range investigated. [ABSTRACT FROM AUTHOR]

We study experimentally the temperature evolution of the thickness of the interfacial layer, Lint(T), between bulk matrices and the surface of nanoparticles in nanocomposites through broadband dielectric spectroscopy. Analyses revealed a power-law dependence between the logarithm of structural relaxation time in the interfacial layer, τint(T), and the Lint(T): ln τ i n t (T) / τ 0 ∝ L i n t β (T) / T , with τ0 ∼ 10−12 s, and β index ∼0.67 at high temperatures and ∼1.7 at temperatures close to the glass transition temperature. In addition, our analysis revealed that the Lint(T) is comparable to the length scale of dynamic heterogeneity estimated from previous nonlinear dielectric measurements and the four-point NMR [ξNMR(T)], with Lint(T) ∼ ξNMR(T). These observations may suggest a direct correlation between the Lint(T) and the size of the cooperatively rearranging regions and have strong implications for understanding the dynamic heterogeneity and cooperativity in supercool liquids and their role in interfacial dynamics. [ABSTRACT FROM AUTHOR]

In this communication, the Adam–Gibbs model connecting molecular dynamics with configurational entropy is tested for the first time for ionic liquids. For this purpose, we investigate simultaneously the shear viscosity η and configurational entropy Sc of an aprotic ionic liquid: 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm TFSI). Comparing the Sc data obtained by the combination of Vogel–Fulcher–Tammann and Adam–Gibbs equations to the Sc points determined directly from the calorimetric experiment, good agreement is found in the entire supercooled liquid region. These results indicate the validity of the Adam–Gibbs model in materials with electrostatic interactions being dominated. These important findings not only generalize the applications of the Adam–Gibbs theory but also provide an opportunity to gain insight into the relationship between thermodynamics and molecular dynamics in ionic liquids. [ABSTRACT FROM AUTHOR]

There is strong interest in understanding the behavior of water in its supercooled state. While many of the qualitative trends of water dynamical properties in the supercooled regime are well understood, the connections between the structure and dynamics of room temperature and supercooled water have not been fully elucidated. Here, we show that the reorientational time scales and diffusion coefficients of supercooled water can be predicted from simulations of room temperature liquid water. Specifically, the derivatives of these dynamical time scales with respect to inverse temperature are directly calculated using the fluctuation theory applied to dynamics. These derivatives are used to predict the time scales and activation energies in the supercooled regime based on the temperature dependence in one of two forms: that based on the stability limit conjecture or assuming an equilibrium associated with a liquid–liquid phase transition. The results indicate that the retarded dynamics of supercooled water originate from structures and mechanisms that are present in the liquid under ambient conditions. [ABSTRACT FROM AUTHOR]

We propose a microscopic theory for the decoupling of self-diffusion and structural relaxation in glass-forming liquids within the Elastically Collective Nonlinear Langevin Equation (ECNLE) activated dynamics framework. Our central hypothesis is that the heterogeneity relevant to this problem is static fluctuations of local density on the scale of 3–4 particle diameters and how this changes local packing correlations. These fluctuations modify the degree of dynamical cage expansion that mechanistically couples intracage large amplitude hopping and longer range collective elasticity in ECNLE theory. Decoupling only emerges in the deeply supercooled regime where the strongly temperature dependent elastic barrier becomes non-negligible relative to its noncooperative local analog. The theory makes predictions for various aspects of the decoupling phenomenon, including apparent fractional power law Stokes-Einstein behavior, that appear to be consistent with experiments and simulations on hard sphere fluids and molecular liquids. Of central importance is a microscopic connection between the barrier fluctuation variance and most probable barrier height. Sensible results are also obtained for the nonexponential stretching of a generic relaxation time correlation function and its temperature evolution. Nonuniversality can arise from the relative importance of the local and collective barriers (related to fragility) and the precise magnitude of the length scale that defines the transition from local cage to elastic physics. Comparison is made with a traplike model based on a Gaussian distribution of barriers. [ABSTRACT FROM AUTHOR]

The shadow energy, Es, is the conserved quantity in microcanonical ensemble (NVE) molecular dynamics simulations carried out with the position Verlet central-difference algorithm. A new methodology for calculating precise and accurate values of Es is presented. It is shown for the first time that Es rather than E is constant during structural changes occurring within a supercooled liquid. It is also explained how to prepare and conduct microsecond range bulk-phase NVE simulations with essentially zero energy drift without the need for thermostating. The drift is analyzed with block averaging and new drift functions of the shadow energy. With such minimal drift, extremely small and accurate standard errors in the mean for quantities like Es, E, and temperature, T, can be obtained. Values of the standard error for Es of ≈10−10 in molecule-based reduced units can be routinely achieved for simulations of 108 time steps. This corresponds to a simulation temperature drift of ≈10−6 K/μs, six orders of magnitude smaller than generally considered to be acceptable for protein simulations. We also show for the first time how these treatments can be extended with no loss of accuracy to polyatomic systems with both flexible degrees of freedom and arbitrary geometric constraints imposed via the SHAKE algorithm. As a bonus, estimates of simulation-average kinetic and total energies from high order velocity expressions can be obtained to a good approximation from 2nd order velocities and the average mean square force (for polyatomics, this refers to per site, including any constraint forces). [ABSTRACT FROM AUTHOR]

Heterogeneous ice nucleation is thought to be the primary pathway for the formation of ice in mixed-phase clouds, with the number of active ice-nucleating particles (INPs) increasing rapidly with decreasing temperature. Here, molecular-dynamics simulations of heterogeneous ice nucleation demonstrate that the ice nucleation rate is also sensitive to pressure and that negative pressure within supercooled water shifts freezing temperatures to higher temperatures. Negative pressure, or tension, occurs naturally in water capillary bridges and pores and can also result from water agitation. Capillary bridge simulations presented in this study confirm that negative Laplace pressure within the water increases heterogeneous-freezing temperatures. The increase in freezing temperatures with negative pressure is approximately linear within the atmospherically relevant range of 1 to - 1000 atm. An equation describing the slope depends on the latent heat of freezing and the molar volume difference between liquid water and ice. Results indicate that negative pressures of - 500 atm, which correspond to nanometer-scale water surface curvatures, lead to a roughly 4 K increase in heterogeneous-freezing temperatures. In mixed-phase clouds, this would result in an increase of approximately 1 order of magnitude in active INP concentrations. The findings presented here indicate that any process leading to negative pressure in supercooled water may play a role in ice formation, consistent with experimental evidence of enhanced ice nucleation due to surface geometry or mechanical agitation of water droplets. This points towards the potential for dynamic processes such as contact nucleation and droplet collision or breakup to increase ice nucleation rates through pressure perturbations. [ABSTRACT FROM AUTHOR]

Fragility is a fundamental property of glass-forming liquids. Here, we evaluated the liquid fragility and structural and dynamic heterogeneity of glassy solids for four model binary alloys. The most fragile alloy exhibited the maximum dynamic heterogeneity in the mechanical unfreezing process. The local atomic order contributed to structural and dynamic heterogeneities in the glassy solid. We observed that atomic displacement significantly correlated with degrees of clustering of local atomic orders. The clustering produced during the glass-forming quenching process enhanced structural and dynamic heterogeneities, especially in fragile glass alloys. Therefore, this alloy system exhibited correlations among liquid fragility, dynamic heterogeneity in liquid alloys, and dynamic and structural heterogeneities in glassy solids. We discussed the underlying physics of the correlation based on a theoretical model for fragility. These structural and dynamic analyses also provided deeper insights into the features of structural heterogeneity in glassy solids. The alloy with the most fragility exhibited the largest difference in atomic mobility between the densely and loosely packed local atomic orders, implying the greatest heterogeneity in the degree of packing density. Unveiling correlations in glassy alloy liquid fragility: Researchers reveal correlations among liquid fragility, dynamic heterogeneity in liquid and glassy solids, and structural heterogeneity in glassy solids using molecular dynamics simulations on binary Cu-Zr alloy models. The study shows that the development of local order in supercooled liquid induces structural heterogeneity in glass solids, affecting fragility. Fragile alloys have a large fraction of densely packed regions and a small fraction of loosely packed regions, with a significant difference in the degree between densely and loosely packed states. This study highlights the connection between liquid fragility and structural heterogeneity in metallic glasses, providing valuable insights for future research and applications. We evaluated the liquid fragility and structural and dynamic heterogeneity of glassy solids. The most fragile alloy exhibited the maximum dynamic heterogeneity in the mechanical unfreezing process. We observed that atomic displacement significantly correlated with degrees of clustering of local atomic orders. The clustering produced during the glass-forming quenching process enhanced structural and dynamic heterogeneities. Therefore, there are correlations among liquid fragility, dynamic heterogeneity in liquid alloys, and dynamic and structural heterogeneities in glassy solids. In addition, the alloy with the most fragility exhibited the largest difference in atomic mobility between the densely and loosely packed local atomic orders. [ABSTRACT FROM AUTHOR]

The western United States region, an economic and agricultural powerhouse, is highly dependent on winter snowpack from the mountain west. Coupled with increasing water and renewable electricity demands, the predictability and viability of snowpack resources in a changing climate are becoming increasingly important. In Idaho, specifically, up to 75% of the state's electricity production comes from hydropower, which is dependent on the timing and volume of spring snowmelt. While we know that 1 April snowpack is declining from SNOTEL observations and is expected to continue to decline as indicated by GCM predictions, our ability to understand the variability of snowfall accumulation and distribution at the regional level is less robust. In this paper, we analyze snowfall events using 0.9-km-resolution WRF simulations to understand the variability of snowfall accumulation and distribution in the mountains of Idaho between 1 October 2016 and 31 April 2017. Various characteristics of snowfall events throughout the season are evaluated, including the spatial coverage, event durations, and snowfall rates, along with the relationship between cloud microphysical variables—particularly liquid and ice water content—on snowfall amounts. Our findings suggest that efficient snowfall conditions—for example, higher levels of elevated supercooled liquid water—can exist throughout the winter season but are more impactful when surface temperatures are near or below freezing. Inefficient snowfall events are common, exceeding 50% of the total snowfall events for the year, with some of those occurring in peak winter. For such events, glaciogenic cloud seeding could make a significant impact on snowpack development and viability in the region. Significance Statement: The purpose and significance of this study is to better understand the variability of snowfall event accumulation and distribution in the Payette Mountains region of Idaho as it relates to the local topography, the drivers of snowfall events, the cloud microphysical properties, and what constitutes an efficient or inefficient snowfall event (i.e., its ability to convert atmospheric liquid water into snowfall). As part of this process, we identify how many snowfall events in a season are inefficient to determine the number of snowfall events in a season that are candidates for enhancement by glaciogenic cloud seeding. [ABSTRACT FROM AUTHOR]

The temperature and chemical dependence of the melt viscosity are ubiquitous in the model development of the volcanic dynamics, as well as in the glass production and design. We focussed on the yet-explored relationship between the bulk and shear moduli ratio and boson peak with the melt fragility of their parental glasses. Here, we explored the extension of the observed trend by testing the conventional binary system Na2O-SiO2, thus providing new evidence supporting the link between the flow of melts and supercooled liquids and the vibrational dynamics of their parental glasses. This was accomplished by integrating new low-frequency Raman measurements and integrating data from the literature on Brillouin light scattering and viscometry. This approach allows us to feed the MYEGA equation with reliable input parameters to quantitatively predict the viscosity of the Na2O-SiO2 system from the liquid up to the glass transition. [ABSTRACT FROM AUTHOR]

The shear thinning observed in viscometers, which has been so successful in establishing the effects of shear-dependent viscosity on film thickness, should be used for evaluation of shear-thinning models because we have confidence in their accuracy. The field of EHL (elastohydrodynamic lubrication) may be the only one in science in which a model for shear-dependent viscosity would be evaluated by means other than viscometer measurements. One of the oils used by Johnson and Tevaarwerk [[4]] to generate traction curves was Shell Turbo 33, a mineral oil with a low inflection pressure at the experimental temperatures, so that the slower-than-exponential piezoviscous response did not appear [[5]]. For nearly a century, viscometer measurements at EHL pressures [[2]] have indicated that the pressure response, which is slower than exponential, is restricted to the lowest pressures and becomes faster than exponential or at least exponential above an inflection pressure. [Extracted from the article]

This study evaluates high latitude stratiform mixed‐phase clouds (SMPC) in the atmosphere model of the Energy Exascale Earth System Model version 2 (EAMv2) by utilizing one‐year‐long ground‐based remote sensing measurements from the Atmospheric Radiation and Measurement (ARM) program. A nudging approach is applied to model simulations for a constrained comparison with the ARM observations. Observed and modeled SMPCs are sampled and collocated to address the difference in data resolution, so that we can consistently evaluate their macrophysical properties at the North Slope of Alaska (NSA) site in the Arctic and the McMurdo (AWR) site in the Antarctic. We found that EAMv2 overestimates SMPC frequency of occurrence at both sites. However, the model captures the observed larger cloud frequency of occurrence at the NSA site. For collocated SMPCs, the annual statistics of observed cloud macrophysics are generally reproduced at the NSA site, while at the AWR site, there are larger biases. Compared to the AWR site, the lower cloud top and cloud base and the warmer cloud top temperature observed at NSA are well simulated. On the other hand, simulated cloud phase is substantially biased. The model largely overestimates liquid water path, and the ice water path is underestimated at NSA, but at AWR, the liquid water path is frequently underestimated due to the dominance of snow in Antarctic SMPCs. As a result, the observed hemispheric difference in cloud phase partitioning is misrepresented in EAMv2. This study implies that additional model development is needed for high latitude mixed‐phase clouds. Plain Language Summary: Stratiform mixed‐phase clouds (SMPCs) contain both liquid droplets and ice crystals at temperatures between −40° and 0°C. These clouds are ubiquitous at high latitudes and can largely impact global climate change. This study evaluates how well the SMPCs are simulated in the newly released second version of the Energy Exascale Earth System Model atmosphere model (EAMv2) by comparing simulated cloud properties to ground‐based observations. Observed cloud properties are obtained at two high latitude sites in the Arctic and Antarctic, respectively. The meteorological states in model simulations are constrained toward reality to allow a consistent comparison between the model and observations. We find that EAMv2 reasonably simulates the more frequent occurrences of SMPCs, the higher cloud top and cloud base, and the warmer cloud top temperature at the Arctic site than at the Antarctic site, consistent with the observations. However, the model overly simulates the SMPC occurrences at both sites compared to observations. Biases in simulated cloud boundaries are also found, particularly in the Antarctic. Moreover, the simulated cloud phase partitioning, the fraction of liquid‐phase water to ice‐phase water, is substantially biased. This study implies the requirement of additional model development for high latitude mixed‐phase clouds. Key Points: Stratiform mixed‐phase clouds sampled from the Energy Exascale Earth System Model version 2 nudged simulation are consistently evaluated with ground‐based remote sensing dataCloud boundary properties and their hemispheric difference are better simulated than the cloud phaseCloud phase is largely biased, with an opposite hemispheric difference feature in supercooled liquid fraction compared to observations [ABSTRACT FROM AUTHOR]

Vertically pointing Ka-band radar measurements are used to derive fall velocity--reflectivity factor (Vt = aZbe) relations for frozen hydrometeor populations of different habits during snowfall events observed at Oliktok Point, Alaska, and at the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC). Case study events range from snowfall with highly rimed particles observed during periods with large amounts of supercooled liquid water path (LWP > 320 g m-2) to unrimed snowflakes including instances when pristine planar crystals were the dominant frozen hydrometeor habit. The prefactor a and the exponent b in the observed Vt-Ze relations scaled to the sea level vary in the approximate ranges 0.5-1.4 and 0.03-0.13, respectively (reflectivities are in mm6 m-3 and velocities are in m s-1). The coefficient a values are the smallest for planar crystals (a ~ 0.5) and the largest (a > 1.2) for particles under severe riming conditions with high LWP. There is no clear distinction between b values for high and low LWP conditions. The range of the observed Vt-Ze relation coefficients is in general agreement with results of modeling using fall velocity--size (νt = aDβ) relations for individual particles found in literature for hydrometeors of different habits, though there is significant variability in aand bcoefficients from different studies even for a same particle habit. Correspondences among coefficients in the Vt-Ze relations for particle populations and in the individual particle νt = D relations are analyzed. These correspondences and the observed Vt-Ze relations can be used for evaluating different frozen hydrometeor fall velocity parameterizations in models. [ABSTRACT FROM AUTHOR]

In this work, we report the impacting and freezing dynamics when a hexadecane droplet impacts on a supercooled immiscible water pool. By utilizing the synchronized high-speed imaging and thermal imaging, three phases for the droplet dynamics have been identified: the jet phase, the flat phase, and the bowl phase. These different phases arise from the solidification process of the hexadecane droplet, and hence, depend on the degree of supercooling or water temperature. We further perform the scaling analysis for the phase transition, which agrees with the experimental observations remarkably. At a high Weber number, the transition between each phase is primarily determined by the supercooling temperature of the liquid pool. [ABSTRACT FROM AUTHOR]

Glassy and liquid state metal–organic frameworks (MOFs) are emerging type of materials subjected to intense research for their rich physical and chemical properties. In this report, we obtained the first glassy MOF that involves metal‐carboxylate cluster building units via multi‐stage structural transformations. This MOF is composed of linear [Mn3(COO)6] node and flexible pyridyl‐ethenylbenzoic linker. The crystalline MOF was first perturbed by vapor hydration and thermal dehydration to give an amorphous state, which can go through a glass transition at 505 K into a super‐cooled liquid. The super‐cooled liquid state is stable through a wide temperature range of 40 K and has the largest fragility index of 105, giving a broad processing window. Remarkably, the super‐cooled liquid can not only be quenched into glass, but also recrystallize into the initial MOF when heated to a higher temperature above 558 K. The mechanism of the multi‐stage structural transformations was studied by systematic characterizations of in situ X‐ray diffraction, calorimetry, rheological, spectroscopic and pair‐distribution function analysis. These multi‐stage transformations not only represent a rare example of high temperature coordinative recognition and self‐assembly, but also provide new MOF processing strategy through crystal‐amorphous‐liquid‐crystal transformations. [ABSTRACT FROM AUTHOR]

By controlling the properties of its medium, supercooled liquid Ga (SLGa) based stretchable remains stretchable at −22 °C, i.e., 52 °C below its thermodynamic melting point of Ga. Thus far, our oldest deposited SLGa circuit and film have remained liquids for 2 years at room temperature. The study investigates the crystallization of SLGa triggered by the surface energy of nucleation agents, temperature, circuit cross‐section, and mechanical impact. Based on these parameters, a method is presented to integrate electronic components with SLGa circuits without compromising its supercooling effect. Further, the large stiffness variation induced by phase transition is demonstrated in different applications. For the desired stiffness variation, the crystallization rate can be controlled by varying the temperature and cross‐section area. Finally, spray‐printing an ink of microscale SLGa microscale particles can conformally pattern Ga on a rough surface, e.g., to fabricate a stretchable array of SLGa microelectrodes. A smart patch with stretchable SLGa electrode arrays records human electrocardiogram signals in cold water and does not stain the skin after use. Its low and stable impedance in water will enable novel applications in wearable electronics. [ABSTRACT FROM AUTHOR]

This review is devoted to the theory of nucleation and growth of the ellipsoidal crystals in supercooled melts and supersaturated solutions. We first outline the theory of single crystal growth in such systems and derive the growth rate of ellipsoidal particle volume as a function of the liquid supercooling/supersaturation and current volume. Then we formulate the mathematical models for the growth of polydisperse ensembles of ellipsoidal crystals in supercooled single-component and binary melts and supersaturated solutions. Methods for solving these models are further discussed and their approximate analytical solutions are given. A behaviour of analytical solutions and their comparison with experimental data are demonstrated. This review also allows one to visualize the common features and differences in the analytical description of the evolution of crystal ensembles in supercooled melts (one-component and binary) and supersaturated solutions. [ABSTRACT FROM AUTHOR]

Over recent years, molecular simulations have provided invaluable insights into the microscopic processes governing the initial stages of crystal nucleation and growth. A key aspect that has been observed in many different systems is the formation of precursors in the supercooled liquid that precedes the emergence of crystalline nuclei. The structural and dynamical properties of these precursors determine to a large extent the nucleation probability as well as the formation of specific polymorphs. This novel microscopic view on nucleation mechanisms has further implications for our understanding of the nucleating ability and polymorph selectivity of nucleating agents, as these appear to be strongly linked to their ability in modifying structural and dynamical characteristics of the supercooled liquid, namely liquid heterogeneity. In this perspective, we highlight recent progress in exploring the connection between liquid heterogeneity and crystallization, including the effects of templates, and the potential impact for controlling crystallization processes. This article is part of a discussion meeting issue 'Supercomputing simulations of advanced materials'. [ABSTRACT FROM AUTHOR]

The use of depolarization lidar to measure atmospheric volume depolarization ratio (VDR) is a common technique to classify cloud phase (liquid or ice). Previous work using a machine learning framework, applied to peak properties derived from co-polarised attenuated backscatter data, has been demonstrated to effectively detect supercooled liquid water containing clouds (SLCC). However, the training data from Davis Station, Antarctica, includes no warm liquid water clouds (WLCC), potentially limiting the model's accuracy in regions where WLCC are present. In this work, we apply the Davis model to a 9-month Micro Pulse Lidar dataset collected in Christchurch, New Zealand, a location which includes WLCC. We then evaluate the results relative to a reference VDR cloud phase mask. We found that the Davis model performed relatively poorly at detecting SLCC with an accuracy of 0.62, often misclassifying WLCC as SLCC. We then trained a new model, using data from Christchurch, to perform SLCC detection on the same set of co-polarized attenuated backscatter peak properties. Our new model performed well, with accuracy scores as high as 0.89, highlighting the effectiveness of the machine learning technique when appropriate training data relevant to the location is used. [ABSTRACT FROM AUTHOR]

It was found recently that the liquid dynamics of several metals (Li, Zn, Ni, Fe, Tl, Pb) under pressure is characterized by transverse spectral functions containing an additional high-frequency peak. To rationalize the pressure dependence of the contributions from different propagating processes to transverse spectral functions in liquid metals, ab initio molecular dynamics simulations were performed for two typical liquid metals (Na and Al) in a wide range of pressures. The influence of density/pressure is investigated for Na by considering four pressures ranging from 15 to 147 GPa, while the temperature influence is considered for Al between 600 K in the deep supercooled liquid up to 1700 K well above the melting point at ambient pressure. Both temperature and density dependence of the spectra of collective excitations are analyzed with a focus on the appearance of a second high-frequency mode in the transverse spectra. A correspondence between spectra of transverse collective excitations and the peak positions of the Fourier-spectra of velocity autocorrelation functions (vibrational density of states) is found. [ABSTRACT FROM AUTHOR]

Are the results of aerosol invigoration studies that neglect entrainment valid for diluted deep convective clouds? We address this question by applying an entraining parcel model to soundings from tropical and midlatitude convective environments, wherein pollution is assumed to increase parcel condensate retention. Invigoration of 5%–10% and <2% is possible in undiluted tropical and midlatitude parcels respectively when freezing is rapid. This occurs because the positive buoyancy contribution from freezing is larger than the negative buoyancy contribution from condensate loading, leading to positive net condensate contribution to buoyancy. However, aerosol‐induced weakening is more likely when realistic entrainment rates occur because water losses from entrainment more substantially reduce the latent heating relative to the loading contribution. This leads to larger net negative buoyancy contribution from condensates in polluted than in clean entraining parcels. Our results demonstrate that accounting for entrainment is critical in conceptual models of aerosol indirect effects in deep convection. Plain Language Summary: Past theoretical studies of how pollution affects thunderstorms typically ignore the mixing of clouds with their surrounding environment. Some of these studies argue that pollution should make thunderstorms more vigorous. Here, we use a theoretical model to investigate how pollution and mixing affects the interplay within the region of a cloud where both supercooled liquid water and ice are present. Our results suggest that pollution becomes increasingly detrimental to storm updrafts as the rate of mixing of thunderstorm air with the storm's surroundings increases. Consequently, because mixing is common in thunderstorms (especially those occurring in the tropics), our results suggest that pollution should weaken (not strengthen) storm updrafts. Our results emphasize the importance of considering mixing when studying pollution effects on storm updrafts. Key Points: Deep convection is often diluted in nature, calling into question past studies on aerosol invigoration in undiluted convective cloudsEntrainment makes pollution more likely to weaken clouds relative to their clean counterpartsNegative buoyancy from condensate loading more than compensates for latent heat gains from freezing in diluted parcels [ABSTRACT FROM AUTHOR]

Rapid Arctic climate warming, amplified relative to lower latitude regions, has led to permafrost thaw and associated thermokarst processes. Recent work has shown permafrost is a rich source of ice nucleating particles (INPs) that can initiate ice formation in supercooled liquid clouds. Since the phase of Arctic clouds strongly affects the surface energy budget, especially over ice-laden surfaces, characterizing INP sources in this region is critical. For the first time, we provide a large- scale survey of potential INP sources in tundra terrain where thermokarst processes are active and relate to INPs in the air. Permafrost, seasonally thawed active layer, ice wedge, vegetation, water, and aerosol samples were collected near Utqiaġvik, Alaska in late summer and analyzed for their INP contents. Permafrost was confirmed as a rich source of INPs that was enhanced near the coast. The aerosol likely contained a mixture of known and unsurveyed INP types that were inferred as biological. Arctic water bodies were shown to be important links of sources to the atmosphere in thermokarst regions. Therefore, a positive relationship found with total organic carbon gives a mechanism for future parameterization as permafrost continues to thaw and drive regional landscape shifts. [ABSTRACT FROM AUTHOR]

Regional atmospheric models struggle to maintain supercooled liquid in mixed‐phase clouds during polar cold‐air outbreaks (CAOs). Previous studies focused on the parameterization of aerosol, microphysics and turbulence to understand the origin of this widespread model bias. This study investigates the role of macrophysics parameterizations (MacP) in the simulation of mixed‐phase clouds. Km‐scale simulations are performed for a large number of CAO cases over Norway, for which continuous ground observations were collected at one site over 6 months. We use a novel analysis that attributes the cloud‐radiative errors to deficiencies in specific cloud regimes. We show that the MacP matters for cloud‐radiative effects in CAOs, but that it is probably not the primary cause of the lack of liquid water in simulated mixed‐phase clouds. Of all the MacP sensitivities explored in this study, the prognostic representation of both liquid and ice shows most promise in increasing the liquid water path. A newly proposed hybrid MacP with prognostic frozen and diagnostic liquid cloud fraction reproduces some of the benefits of the prognostic scheme at reduced cost and complexity. The two‐moment microphysics scheme in this study produces too large precipitation particles. Reducing the snow deposition rate decreases the precipitation particle sizes and largely improves the liquid water path. Simulations are less sensitive to reduced riming rates. Plain Language Summary: Cloud droplets and ice crystals often coexist in polar clouds, even at temperatures well below the freezing level. These clouds play an important role in the climate system, since they reflect more sunlight back to space than completely frozen clouds. Therefore it is important that climate and weather forecasting models are thoroughly evaluated in their ability to produce these so‐called mixed‐phase clouds. This study compares simulations of polar clouds with detailed cloud observations over Norway. We confirm that simulations produce clouds that are nearly completely frozen, while observations clearly show both liquid and frozen clouds. We test sensitivities of the simulations to specific model components to assess potential avenues for model improvement. Of all the tests performed, the ones affecting the simulated snowflake sizes seem most promising in allowing both liquid and frozen cloud to coexist. Key Points: The role of cloud‐fraction parameterizations in mixed‐phase simulations during cold‐air outbreaks is investigatedCloud‐fraction parameterizations matter for cloud‐radiative effects, but have limited impact on the liquid water contentSimulations with reduced snow depositional growth improve liquid water path and precipitation size distributions [ABSTRACT FROM AUTHOR]

Dynamic room temperature phosphorescence (RTP) materials have potential applications in optoelectronics, which inevitably suffer from poor processability, flexibility or stretchability. Herein, we report a concise strategy to develop supercooled liquids (SCLs) with dynamic RTP behavior using terminal hydroxyl engineering. The terminal hydroxyls effectively hinder the nucleation process of molecules for the formation of stable SCLs after thermal annealing. Impressively, the SCLs show reversible RTP emission via alternant stimulation by UV light and heat. Photoactivated SCLs have phosphorescent efficiency of 8.50 % and a lifetime of 31.54 ms under ambient conditions. Regarding the dynamic RTP behavior and stretchability of SCLs, we demonstrate the applications in erasable data encryption and patterns on flexible substrates. This finding provides a design principle for obtaining SCLs with RTP and expands the potential applications of RTP materials in flexible optoelectronics. [ABSTRACT FROM AUTHOR]

As a result of examining the structure of Zr55Cu35Al10 alloy around the glass transition temperature (Tg) using the classical molecular dynamics simulations, it was proven that the atomic bonds in the interconnecting zones (i-zones) became loose with the small amount of energy absorption, and it became free volumes easily when the temperature approached Tg. Instead of i-zones, when clusters were largely separated by free volume networks, the solid amorphous structure was converted into supercooled liquid state, resulting in a sharp strength reduce and the great plasticity change from a limited plastic deformation to superplasticity. [ABSTRACT FROM AUTHOR]

As a result of examining the structure of Zr55Cu35Al10 alloy around the glass transition temperature (Tg) using the classical molecular dynamics simulations, it was proven that the atomic bonds in the interconnecting zones (i-zones) became loose with the small amount of energy absorption, and it became free volumes easily when the temperature approached Tg. Instead of i-zones, when clusters were largely separated by free volume networks, the solid amorphous structure was converted into supercooled liquid state, resulting in a sharp strength reduce and the great plasticity change from a limited plastic deformation to superplasticity. [ABSTRACT FROM AUTHOR]

As a result of examining the structure of Zr55Cu35Al10 alloy around the glass transition temperature (Tg) using the classical molecular dynamics simulations, it was proven that the atomic bonds in the interconnecting zones (i-zones) became loose with the small amount of energy absorption, and it became free volumes easily when the temperature approached Tg. Instead of i-zones, when clusters were largely separated by free volume networks, the solid amorphous structure was converted into supercooled liquid state, resulting in a sharp strength reduce and the great plasticity change from a limited plastic deformation to superplasticity. [ABSTRACT FROM AUTHOR]

As a result of examining the structure of Zr55Cu35Al10 alloy around the glass transition temperature (Tg) using the classical molecular dynamics simulations, it was proven that the atomic bonds in the interconnecting zones (i-zones) became loose with the small amount of energy absorption, and it became free volumes easily when the temperature approached Tg. Instead of i-zones, when clusters were largely separated by free volume networks, the solid amorphous structure was converted into supercooled liquid state, resulting in a sharp strength reduce and the great plasticity change from a limited plastic deformation to superplasticity. [ABSTRACT FROM AUTHOR]

Icephobic material is of great importance in power transportation, communication, aerospace, and so on. Bionic lotus superhydrophobic surfaces show good application prospects in anti‐icing by repelling impacting droplets. However, the boundary (criterion) between droplet bounce and deposition on superhydrophobic surface under cold freezing rain is unclear. Here, from the view of statistics, the boundary and internal heat transfer mechanism of the droplet bounce, pinning, and three kinds of deposition including icing at later, early retraction, and spread. are clarified Droplet viscosity increase reduces droplet contact with surface and inhibited splash at high We. Surfaces with temperature above −20.6 °C showed 100% droplet bounce after impact on We = 64.7, and the probability of water adhesion and ice nucleation decreases to ≈0%, resulting in completely anti‐icing. Droplet bounce transition mainly ascribe to the decrease retraction driven force caused by interface freezing and transition temperature increases approximately linearly from −25.9 to −21.1 °C within 21.6 < We < 75.5. Ice nuclei brought by condensation in humid environment (60–100 RH%) further cause droplet eccentric retraction and transition temperature increases to −6 to −10 °C. The fundamental understanding of droplet behaviors on supercooled superhydrophobic surface is beneficial for icephobic surfaces applications. [ABSTRACT FROM AUTHOR]

This article investigated the effect of shear strain on the nematic itraconazole (ITR) from both elastic and plastic deformation regions. The rheo-dielectric technique was used for this purpose. It has been demonstrated that shear strain can change the sample color, liquid crystal alignment as well as its dielectric and thermal properties. The observed modifications depend on the shear strain value. One can distinguish four regions regarding the slope of ITR stress–strain dependence and caused changes. Proper alignment changes (obtained after the shearing procedure) can additionally affect the further recrystallization of ITR to other than the initial, i.e., second polymorphic form. [Display omitted] [ABSTRACT FROM AUTHOR]

A chiral Schiff base platinum(II) complex 1 bearing polyethylene glycol (PEG) chains was synthesized. The complex was found to melt at 44 °C whereas its non‐substituted analogue 2 has a high melting point (>300 °C). Upon cooling after melting, the complex remained liquid at room temperature over 30 minutes and exhibited yellow phosphorescence. Circularly polarized phosphorescence (CPP) properties were examined and it was found that the absolute value of the luminescence dissymmetry factor (glum) increases significantly in the liquid state compared to the dilute solution state. Herein, we report the first example of CPP from solvent‐free supercooled liquids. [ABSTRACT FROM AUTHOR]

Upward lightning is rarer than downward lightning and requires tall (100+ m) structures to initiate. It may be either self‐initiated or triggered by other lightning discharges. While conventional lightning location systems (LLSs) detect most of the upward lightning flashes superimposed by pulses or return strokes, they miss a specific flash type that consists only of a continuous current. Globally, only few specially instrumented towers can record this flash type. The proliferation of wind turbines in combination with damages from upward lightning necessitates an improved understanding under which conditions self‐initiated upward lightning and the continuous‐current‐only subtype occur. This study uses a random forest machine learning model to find the larger‐scale meteorological conditions favoring the occurrence of the different phenomena. It combines ground truth lightning current measurements at the specially instrumented tower at Gaisberg mountain in Austria with variables from larger‐scale meteorological reanalysis data (ERA5). These variables reliably explain whether upward lightning is self‐initiated or triggered by other lightning discharges. The most important variable is the height of the −10°C isotherm above the tall structure: the closer it is, the higher is the probability of self‐initiated upward lightning. For the different flash types, this study finds a relationship to the larger‐scale electrification conditions and the LLS‐detected lightning situation in the vicinity. Lower amounts of supercooled liquid water, solid, and liquid differently sized particles and no LLS‐detected lightning events nearby favor the continuous‐current‐only subtype compared to the other subtypes, which preferentially occur with LLS‐detected lightning events within 3 km from the Gaisberg Tower. Plain Language Summary: Upward lightning (UL) is much rarer than downward lightning. It needs tall structures of 100+ m to initiate. However, UL has a much larger damage potential as it starts with a weak but long‐lasting current. Lightning data from a specially instrumented tower reveal that (a) a large proportion of UL is initiated by the tall structure itself and (b) a subtype of UL, which only has a long‐lasting current, cannot be detected by conventional lightning location system. Since so many tall wind turbines are built to generate electricity, correctly assessing the UL risk has become indispensable. Insights, which the networks cannot give, are gained using a large set of meteorological data and powerful machine learning models that combine it with the tower measurements. The most important variable for self‐initiated UL is the height at which −10°C are measured above the tower. The closer to the tower, the higher the chance that the tower itself triggers UL. The occurrence of the particular subtype of UL requires including larger‐scale electrification conditions and information on the prevailing lightning activity. No LLS‐detected lightning events or weak electrification conditions preferentially yield the long‐lasting current type. Key Points: The closer the thundercloud's main electrification region to the tower, the higher the probability that upward lightning is self‐initiatedContinuous‐current‐only flashes have network‐detected lightning nearby in only 37% of upward lightning events, the other types in 92%Larger‐scale meteorological conditions let a random forest model distinguish upward lightning flash types with an area under the receiver operating characteristic curve of 0.75 [ABSTRACT FROM AUTHOR]

In situ observations of the austenite grain growth and martensite transformations in developed NM500 wear-resistant steel were conducted via confocal laser scanning high-temperature microscopy. The results indicated that the size of the austenite grains increased with the quenching temperature (37.41 μm at 860 °C → 119.46 μm at 1160 °C) and austenite grains coarsened at ~3 min at a higher quenching temperature of 1160 °C. Furthermore, a large amount of finely dispersed (Fe, Cr, Mn)3C particles redissolved and broke apart at 1160 °C, resulting in many large and visible carbonitrides. The transformation kinetics of martensite were accelerated at a higher quenching temperature (13 s at 860 °C → 2.25 s at 1160 °C). In addition, selective prenucleation dominated, which divided untransformed austenite into several regions and resulted in larger-sized fresh martensite. Martensite can not only nucleate at the parent austenite grain boundaries, but also nucleate in the preformed lath martensite and twins. Moreover, the martensitic laths presented as parallel laths (0~2°) based on the preformed laths or were distributed in triangles, parallelograms, or hexagons with angles of 60° or 120°. [ABSTRACT FROM AUTHOR]

As a result, they found that accurate predictions were made by this NN system, the machine learning of which included the information provided by fast vibrational dynamics and was quantified by the local Debye-Waller factor. Based on the performed BDS, DSC, and refractometry measurements as well as earlier investigations, we proposed a plausible molecular mechanism of the obtained satisfactory physical stability of the amorphous composition, providing a promising outcome for pharmaceutical applications in this case. In the measurements, the Field-Cycling (FC) NMR technique was used as a versatile tool to determine the dynamic susceptibilities of glass-forming liquids over a broad frequency range [[6]]. Despite recent advances in the study of complex systems, which were recognized by the Nobel Prize in Physics in 2021, glass transition and the physicochemical phenomena that occur in the supercooled liquid and glassy states have remained shrouded, at least partially, in mystery for various material groups. [Extracted from the article]

A generally accepted understanding of the anomalous properties of water will only emerge if it becomes possible to systematically characterize water in the deeply supercooled regime, from where the anomalies appear to emanate. This has largely remained elusive because water crystallizes rapidly between 160 K and 232 K. Here, we present an experimental approach to rapidly prepare deeply supercooled water at a well-defined temperature and probe it with electron diffraction before crystallization occurs. We show that as water is cooled from room temperature to cryogenic temperature, its structure evolves smoothly, approaching that of amorphous ice just below 200 K. Our experiments narrow down the range of possible explanations for the origin of the water anomalies and open up new avenues for studying supercooled water. Supercooled water in so-called "no man's land" promises to reveal the origin of the water anomalies. Here, the authors use electron diffraction to provide the first characterization that spans this temperature range, which narrows down the array of possible explanations. [ABSTRACT FROM AUTHOR]

Upon approaching the glass transition, the relaxation of supercooled liquids is controlled by activated processes, which become dominant at temperatures below the so-called dynamical crossover predicted by Mode Coupling theory (MCT). Two of the main frameworks rationalising this behaviour are dynamic facilitation theory (DF) and the thermodynamic scenario which give equally good descriptions of the available data. Only particle-resolved data from liquids supercooled below the MCT crossover can reveal the microscopic mechanism of relaxation. By employing state-of-the-art GPU simulations and nano-particle resolved colloidal experiments, we identify the elementary units of relaxation in deeply supercooled liquids. Focusing on the excitations of DF and cooperatively rearranging regions (CRRs) implied by the thermodynamic scenario, we find that several predictions of both hold well below the MCT crossover: for the elementary excitations, their density follows a Boltzmann law, and their timescales converge at low temperatures. For CRRs, the decrease in bulk configurational entropy is accompanied by the increase of their fractal dimension. While the timescale of excitations remains microscopic, that of CRRs tracks a timescale associated with dynamic heterogeneity, t * ~ τ α 0.8 . This timescale separation of excitations and CRRs opens the possibility of accumulation of excitations giving rise to cooperative behaviour leading to CRRs. Experimental data of the transition of a supercooled liquid into glass is compatible with both dynamic and thermodynamic theories. Here the authors use experiments and MD simulations at very low temperatures to show that both theories are connected. [ABSTRACT FROM AUTHOR]

Understanding and controlling liquid–liquid phase separation in aluminosilicates is crucial for optimizing glass properties. However, the metastable nature of aluminosilicates' phase separation has made it difficult to study experimentally, and uncertainty persists regarding the compositional and temperature extents of the miscibility gap. Here, we present new experimental evidence that suggests a consolute temperature between 1440 and 1590°C and endmember compositions of 7 and 62 mol.% Al2O3 for the phase‐separated glasses. Using containerless melt processing, deeply supercooled liquids over the 0–60 mol.% Al2O3 range are probed with in situ small‐ and wide‐angle X‐ray scattering, which simultaneously reveals changes in nanoscale density heterogeneity and atomic structure. Correlations between phase separation and atomic coordination environments are compared for liquids and glasses. Pair distribution function analysis shows mean O–(Si + Al) coordination increases with Al2O3 content and decreases with temperature. [ABSTRACT FROM AUTHOR]

Recent works show that glass-forming liquids display Fickian non-Gaussian Diffusion, with non-Gaussian displacement distributions persisting even at very long times, when linearity in the mean square displacement (Fickianity) has already been attained. Such non-Gaussian deviations temporarily exhibit distinctive exponential tails, with a decay length λ growing in time as a power-law. We herein carefully examine data from four different glass-forming systems with isotropic interactions, both in two and three dimensions, namely, three numerical models of molecular liquids and one experimentally investigated colloidal suspension. Drawing on the identification of a proper time range for reliable exponential fits, we find that a scaling law λ (t) ∝ t α , with α ≃ 1 / 3 , holds for all considered systems, independently from dimensionality. We further show that, for each system, data at different temperatures/concentration can be collapsed onto a master-curve, identifying a characteristic time for the disappearance of exponential tails and the recovery of Gaussianity. We find that such characteristic time is always related through a power-law to the onset time of Fickianity. The present findings suggest that FnGD in glass-formers may be characterized by a "universal" evolution of the distribution tails, independent from system dimensionality, at least for liquids with isotropic potential. [ABSTRACT FROM AUTHOR]

A study of the vertical structure of postfrontal shallow clouds in the marine boundary layer over the Southern Ocean is presented. The central question of this two-part study regards cloud phase (liquid/ice) of precipitation, and the associated growth mechanisms. In this first part, data from the Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean (MARCUS) field campaign are analyzed, starting with a 75-h case with continuous sea surface-based thermal instability, modest surface heat fluxes, an open-cellular mesoscale organization, and very few ice nucleating particles (INPs). The clouds are mostly precipitating and shallow (tops mostly around 2 km above sea level), with weak up- and downdrafts, and with cloud-top temperatures generally around 2188 to 2108C. The case study is extended to three other periods of postfrontal shallow clouds in MARCUS. While abundant supercooled liquid water is commonly present, an experimental cloudphase algorithm classifies nearly two-thirds of clouds in the 08 to 258C layer as containing ice (cloud ice, snow, or mixed phase), implying that much of the precipitation grows through cold-cloud processes. The best predictors of ice presence are cloud-top temperature, cloud depth, and INP concentration. Measures of convective activity and turbulence are found to be poor indicators of ice presence in the studied environment. The water-phase distribution in this cloud regime is explored through numerical simulations in Part II. [ABSTRACT FROM AUTHOR]

Liquid water is the most intriguing liquid in nature, both because of its importance to every known form of life, and its numerous anomalous properties, largely magnified under supercooled conditions. Among the anomalous properties of water is the seeming divergence of the thermodynamic response functions and dynamic properties below the homogenous nucleation temperature (~ 232 K). Furthermore, water exhibits an increasingly decoupling of the viscosity and diffusion, upon cooling, resulting in the breakdown of the Stokes-Einstein relationship (SER). At high temperatures and pressures, however, water behaves more like a "simple" liquid. Nonetheless, experiments at 400 K and GPa pressures (Bove et al. (2011) Phys. Rev. Lett., 111:185,901) showed that although the diffusion decreases monotonically with the pressure, opposite to pressurized supercooled water, a decoupling of the viscosity and diffusion, larger than that found in supercooled water at normal pressure, is observed. Here, we studied the validity of SER and different pressure-dependent thermodynamic response functions, known to exhibit an abnormal behavior upon cooling, including the density, isothermal compressibility, and the thermal expansion coefficient along the 400 K isotherm up to 3 GPa through molecular dynamics simulations. Seven different water models were investigated. A monotonic increase of the density (~ 50%) and decrease of the isothermal compressibility (~ 90%) and thermal expansion (~ 65%) is found. Our results also show that compressed hot water has various resemblances to cool water at normal pressure, with pressure inducing the formation of a new second coordination sphere and a monotonic decrease of the diffusion and viscosity coefficients. Whereas all water models provide a good account of the viscosity, the magnitude of the violation of the SER at high pressures (> ~ 1 GPa) is significantly smaller than that found through experiments. Thus, violation of the SER in simulations is comparable to that observed for liquid supercooled water, indicating possible limitations of the water models to account for the local structure and self-diffusion of superheated water above ~ 1 GPa. [ABSTRACT FROM AUTHOR]

Solidification patterns during nonequilibrium crystallization are among the most important microstructures in the natural and technical realms. In this work, we investigate the crystal growth in deeply supercooled liquid using the classical density functional-based approaches. Our result shows that the complex amplitude expanded phase-field crystal (APFC) model containing the vacancy nonequilibrium effects proposed by us could naturally reproduce the growth front nucleation (GFN) and various nonequilibrium patterns, including the faceted growth, spherulite, symmetric and nonsymmetric dendrites among others, at the atom level. Moreover, an extraordinary microscopic columnar-to-equiaxed transition is uncovered, which is found to depend on the seed spacing and distribution. Such a phenomenon could be attributed to the combined effects of the long-wave and short-wave elastic interactions. Particularly, the columnar growth could also be predicted by an APFC model containing inertia effects, but the lattice defect type in the growing crystal is different due to the different types of short-wave interactions. Two stages are identified during the crystal growth under different undercooling, corresponding to diffusion-controlled growth and GFN-dominated growth, respectively. However, compared with the second stage, the first stage becomes too short to be noticed under the high undercooling. The distinct feature of the second stage is the dramatic increments of lattice defects, which explains the amorphous nucleation precursor in the supercooled liquid. The transition time between the two stages at different undercooling is investigated. Crystal growth of BCC structure further confirms our conclusions. [ABSTRACT FROM AUTHOR]

Secondary ice production (SIP) has an essential role in cloud and precipitation microphysics. In recent years, substantial insights were gained into SIP by combining experimental, modeling, and observational approaches. Remote sensing instruments, and among them meteorological radars, offer the possibility to study clouds and precipitation in extended areas over long time periods, and are highly valuable to understand the spatio-temporal structure of microphysical processes. Multi-modal Doppler spectra measured by vertically-pointing radars reveal the coexistence, within a radar resolution volume, of hydrometeor populations with distinct properties; as such, they can provide decisive insight into precipitation microphysics. This paper leverages polarimetric radar Doppler spectra as a tool to study the microphysical processes that took place during a snowfall event on 27 January 2021, in the Swiss Jura Mountains, during the ICE GENESIS campaign. A multi-layered cloud system was present, with ice particles sedimenting through a supercooled liquid water (SLW) layer in a seeder-feeder configuration. Building on a Doppler peak detection algorithm, we implement a peak labeling procedure to identify the particle type(s) that may be present within a radar resolution volume. With this approach, we can visualize spatio-temporal features in the radar time series that point to the occurrence of distinct mechanisms at different stages of the event. By focusing on three 30-minute phases of the case study, and by using the detailed information contained in the Doppler spectra, together with dual-frequency radar measurements, aircraft in-situ images, and simulated profiles of atmospheric variables, we narrow down the possible processes which can be responsible for the observed signatures. Depending on the availability of SLW and the droplet sizes, on the temperature range, and on the interaction between the liquid and ice particles, various SIP processes are identified as plausible, with distinct fingerprints in the radar Doppler spectra. A simple modeling approach suggests that the ice crystal number concentrations likely exceed typical concentrations of ice nucleating particles by one to four orders of magnitude. While a robust proof of occurrence of a given SIP mechanism cannot be easily established, the multi-sensor data provides various independent elements each supporting the proposed interpretations. [ABSTRACT FROM AUTHOR]

Understanding crystallization and its correlations with liquid dynamics is relevant for developing robust amorphous pharmaceutical solids. Herein, nimesulide, a classical anti-inflammatory agent, was used as a model system for studying the correlations between crystallization kinetics and molecular dynamics. Kinetic parts of crystal growth (ukin) of nimesulide exhibited a power law dependence upon the liquid viscosity (η) as ukin~η−0.61. Bulk molecular diffusivities (DBulk) of nimesulide were predicted by a force-level statistical–mechanical model from the α-relaxation times, which revealed the relationship as ukin~Dbulk0.65. Bulk crystal growth kinetics of nimesulide in deeply supercooled liquid exhibited a fragility-dependent decoupling from τα. The correlations between growth kinetics and α-relaxation times predicted by the Adam–Gibbs–Vogel equation in a glassy state were also explored, for both the freshly made and fully equilibrated glass. These findings are relevant for the in-depth understanding and prediction of the physical stability of amorphous pharmaceutical solids. [ABSTRACT FROM AUTHOR]

Slippery liquid-infused porous surfaces (SLIPS) have received growing attention as promising icephobic materials. In this study, SLIPS were prepared on aluminum alloys by combining anodization and infusion of common silicone oil. An SLIPS with low ice-adhesion strength (6 kPa) was obtained by optimizing the anodizing time parameters (10 min). In addition, the frosting process and freezing of water droplets on the as-prepared SLIPS at −10 °C were delayed for 2000 s and 4800 s, respectively. Simultaneously, the as-prepared SLIPS also exhibited excellent anti-icing performance in glaze ice, since the supercooled water drips/ice slipped from the surface. The ice weight of the as-prepared SLIPS was significantly lower than that of the bare aluminum surface and the anti-icing-fluid-coated aluminum surface, which was reduced by 38.2%–63.6% compared with the bare aluminum surface. The ice weight increased with decreased temperature and inclination angle. This work proposes a method suitable for large-area preparation of SLIPS that achieves excellent anti-icing performance and significantly reduces the weight of glaze ice. [ABSTRACT FROM AUTHOR]