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The morphology and growth kinetics of ice single crystals in aqueous solutions of type III antifreeze protein (AFP-III) have been studied in detail over a range of AFP-III concentrations and supercoolings. In pure water, the shape of ice crystals changes from the circular disklike to planar dendritic with increasing supercooling. In AFP-III solutions, ice crystals in the form of faceted plates, irregular dendrites with polygonized tips, and needles appear with increasing supercooling and AFP-III concentration. The growth rate of ice crystals in the crystallographic a direction is 2 orders of magnitude higher than that in the c direction. AFP-III molecules cause the stoppage of the growth of the prismatic and basal faces at low supercoolings. When supercooling exceeds the critical value, AFP-III favors the acceleration of the growth in both a and c directions. The observed behavior of AFP-III is explained in terms of the Cabrera-Vermilyea pinning model and the specificity of the dissipation of latent heat from the growing crystals with different shapes. [ABSTRACT FROM AUTHOR]

Apart from not having crystallized, supercooled liquids can be considered as being properly equilibrated and thus can be described by a few thermodynamic control variables. In contrast, glasses and other amorphous solids can be arbitrarily far away from equilibrium and require a description of the history of the conditions under which they formed. In this paper we describe how the locality of interactions intrinsic to finite-dimensional systems affects the stability of amorphous solids far off equilibrium. Our analysis encompasses both structural glasses formed by cooling and colloidal assemblies formed by compression. A diagram outlining regions of marginal stability can be adduced which bears some resemblance to the quasi-equilibrium replica meanfield theory phase diagram of hard sphere glasses in high dimensions but is distinct from that construct in that the diagram describes not true phase transitions but kinetic transitions that depend on the preparation protocol. The diagram exhibits two distinct sectors. One sector corresponds to amorphous states with relatively open structures, the other to high density, more closely packed ones. The former transform rapidly owing to there being motions with no free energy barriers; these motions are string-like locally. In the dense region, amorphous systems age via compact activated reconfigurations. The two regimes correspond, in equilibrium, to the collisional or uniform liquid and the so-called landscape regime, respectively. These are separated by a spinodal line of dynamical crossovers. Owing to the rigidity of the surrounding matrix in the landscape, high-density part of the diagram, a sufficiently rapid pressure quench adds compressive energy which also leads to an instability toward string-like motions with near vanishing barriers. Conversely, a dilute collection of rigid particles, such as a colloidal suspension leads, when compressed, to a spatially heterogeneous structure with percolated mechanically stable regions. This jamming corresponds to the onset of activation when the spinodal line is traversed from the low density side. We argue that a stable glass made of sufficiently rigid particles can also be viewed as exhibiting sporadic and localized buckling instabilities that result in local jammed structures. The lines of instability we discuss resemble the Gardner transition of meanfield systems but, in contrast, do not result in true criticality owing to being short-circuited by activated events. The locally marginally stable modes of motion in amorphous solids correspond to secondary relaxation processes in structural glasses. Their relevance to the low temperature anomalies in glasses is also discussed. [ABSTRACT FROM AUTHOR]

The freezing of supercooled water films on different substrates was investigated using a high-speed camera coupled to an optical microscope, obtaining details of the freezing process not described in the literature before. We observed the two well known freezing stages (fast dendritic growth and slow freezing of the water liquid left after the dendritic growth), but we separated the process into different phenomena that were studied separately: two-dimensional dendrite growth on the substrate interface, vertical dendrite growth, formation and evolution of ice domains, trapping of air bubbles and freezing of the water film surface. We found all of these processes to be dependent on both the supercooling temperature and the substrate used. Ice dendrite (or ice front) growth during the first stage was found to be dependent on thermal properties of the substrate but could not be unequivocally related to them. Finally, for low supercooling, a direct relationship was observed between the morphology of the dendrites formed in the first stage, which depends on the substrate, and the roughness and the shape of the surface of the ice, when freezing of the film was completed. This opens the possibility of using surfaces and coatings to control ice morphology beyond anti-icing properties. [ABSTRACT FROM AUTHOR]

How are water's material properties encoded within the structure of the water molecule? This is pertinent to understanding Earth's living systems, its materials, its geochemistry and geophysics, and a broad spectrum of its industrial chemistry. Water has distinctive liquid and solid properties: It is highly cohesive. It has volumetric anomalies -- water's solid (ice) floats on its liquid; pressure can melt the solid rather than freezing the liquid; heating can shrink the liquid. It has more solid phases than other materials. Its supercooled liquid has divergent thermodynamic response functions. Its glassy state is neither fragile nor strong. Its component ions -- hydroxide and protons -- diffuse much faster than other ions. Aqueous solvation of ions or oils entails large entropies and heat capacities. We review how these properties are encoded within water's molecular structure and energies, as understood from theories, simulations, and experiments. Like simpler liquids, water molecules are nearly spherical and interact with each other through van der Waals forces. Unlike simpler liquids, water's orientation-dependent hydrogen bonding leads to open tetrahedral cage-like structuring that contributes to its remarkable volumetric and thermal properties. [ABSTRACT FROM AUTHOR]

2-Ethyl-1-hexanol monoalcohol is a well-known molecular glassformer, which for a long time attracts attention of researchers. As in all other monohydroxy alcohols, its dielectric relaxation reveals two distinct relaxation processes attributed to the structural relaxation and another more intense process, which gives rise to a low-frequency Debye-like relaxation. In this monoalcohol, the frequency separation between these two processes reaches an extremely high value of 3 orders of magnitude, which makes this substance a rather convenient object for studies of mechanisms (supposedly common to all monoalcohols) leading to vitrification of this type of liquids. In this work, we apply two experimental techniques, dielectric spectroscopy and ultrasonic measurements (in both longitudinal and transverse polarizations) at high pressure, to study interference between different relaxation mechanisms occurring in this liquid, which could shed light on both structural and dielectric relaxation processes observed in a supercooled liquid and a glass state. Application of high pressure in this case leads to the simplification of the frequency spectrum of dielectric relaxation, where only one asymmetric feature is observed. Nonetheless, the maximum attenuation of the longitudinal wave in ultrasonic experiments at high pressure is observed at temperatures ≈50 K above the corresponding temperature for the transverse wave. This might indicate different mechanisms of structural relaxation in shear and bulk elasticities in this liquid. [ABSTRACT FROM AUTHOR]

Crystallization kinetics of phase change materials (PCMs) at high temperatures is of key importance for the extreme speed of data writing and erasing. In this work, the crystallization behavior of one of the typical PCMs, GeTe, has been studied using ultrafast differential scanning calorimetry (DSC) at high heating rates up to 4 × 104 K s-1. A strong non-Arrhenius temperature-dependent viscosity has been observed. We considered two viscosity models for estimating the crystal growth kinetics coefficient ( U kin). The results showed that the MYEGA model was more suitable to describe the temperature-dependent viscosity and the crystal growth kinetics for supercooled liquid GeTe. The glass transition temperature ( T g) and fragility m were estimated to be 432.1 K and 130.7, respectively. The temperature-dependent crystal growth rates, which were extrapolated by the MYEGA model, were in line with the experimental results that were measured by in situ transmission electron microscopy at a given temperature. The crystal growth rate reached a maximum of 3.5 m s-1 at 790 K. These results based on ultrafast DSC with the MYEGA model offer a revelation for crystallization kinetics of supercooled liquid GeTe. [ABSTRACT FROM AUTHOR]

Uniform SiO2 microparticles containing controllable content of Na2SO4·10H2O against supercooling and phase separation are developed for efficient energy storage at mild temperatures. Na2SO4 solution with 3-aminopropyltriethoxysilane and silicone oil with tetraethylorthosilicate are emulsified into monodisperse water-in-oil (W/O) emulsions from microfluidics for template fabrication of the microparticles via hydrolysis and condensation. During the reaction process, Na2SO4 in the emulsion droplets crystallizes in the microparticles. Incorporation of sodium borate and sodium hexametaphosphate, combined with the confined distribution of Na2SO4·10H2O in the mesoporous microparticles, successfully avoids the phase separation of Na2SO4·10H2O and dramatically reduces its supercooling. This allows the microparticles to achieve repeatable energy storage/release property at mild temperatures for thermoregulation. Such a thermoregulating performance is demonstrated by incorporating the microparticles into a model house for repeatedly regulating its surface and inside temperatures. These microparticles show great potential for developing advanced materials for myriad fields such as energy, architecture, and healthcare. [ABSTRACT FROM AUTHOR]

The current interest in amorphous forms of active pharmaceutical ingredients stems from their increasing use in enabling formulations for the delivery of poorly water-soluble compounds. Because amorphous drugs are metastable and have a tendency to revert to crystalline forms, their crystallization behavior is an important topic. This study reports the observation of concomitant polymorphs of vemurafenib following crystallization from the supercooled liquid, and their subsequent phase transformations. The crystallization behavior of amorphous vemurafenib was evaluated between the glass transition temperature and melting temperature. Six characteristic crystal morphologies were observed. Based on X-ray diffraction and Raman spectroscopic studies, these morphologies were associated with four polymorphic forms, designated α, β, γ, and δ. The thermodynamic stability is α > β > γ or δ. Isothermal crystallization between 120 and 240 °C resulted in concomitant polymorphs with samples containing either 2 or 3 of the 4 polymorphs depending on the specific temperatures, with the α-form or β-form typically dominating. Crystallization at even higher temperature yielded only the α-form. A monotropic relationship was inferred between the α- and β-forms based on calorimetric data. β-to-α, γ-to-β, and δ-to-β phase transformations were observed using hot-stage polarized light microscopy, Raman microscopy, and powder X-ray diffraction. The discovery of three new concomitant polymorphs of vemurafenib following crystallization from the supercooled liquid of vemurafenib highlights the rich polymorphic landscape that can be accessed by evaluating crystallization in supercooled liquids, and underscores the complexity in evaluating the crystallization of amorphous drug forms. [ABSTRACT FROM AUTHOR]

The spherulitic crystal growth velocity in selenium supercooled liquid has been measured by infrared microscopy in isothermal conditions for rapidly heated samples of a-Se from temperatures well below Tg. These data are compared and analyzed along with previously published data obtained on samples quenched from a temperature well above the melting point. The spherulites grew linearly over a course of time that corresponds to crystal growth controlled by crystal-liquid interface kinetics. The crystal growth velocity data obtained for these two different thermal histories can be described by the normal growth model for moderate supercoolings (ΔT <60 K). The screw dislocation growth provides a better description for larger supercoolings (ΔT > 90 K) that is also consistent with morphological observations. However, the prediction based on this model still significantly deviates for intermediate supercoolings. It is shown that all experimental data in the whole temperature range (Tg < T < Tm) can be described by a combined approach including both these models, taking into account actual viscosity scaling of crystal growth η-1. The kinetic information captured in the DSC curve is analyzed, providing evidence that the non-isothermal crystallization process can be described by the Johnson-Mehl-Avrami model. Two distinct regions characterized by different values of apparent activation energy were found. The transition between these regions coincides with morphological changes of spherulitic crystals and other properties. These regions are characterized by distinct apparent activation energies whose values are consistent with those obtained from microscopic measurement of crystal growth velocity. [ABSTRACT FROM AUTHOR]

The homogeneous freezing of water is of fundamental importance to a number of fields, including that of cloud formation. However, there is considerable scatter in homogeneous nucleation rate coefficients reported in the literature. Using a cold stage droplet system designed to minimize uncertainties in temperature measurements, we examined the freezing of over 1500 pure water droplets with diameters between 4 and 24 μm. Under the assumption that nucleation occurs within the bulk of the droplet, nucleation rate coefficients fall within the spread of literature data and are in good agreement with a subset of more recent measurements. To quantify the relative importance of surface and volume nucleation in our experiments, where droplets are supported by a hydrophobic surface and surrounded by oil, comparison of droplets with different surface area to volume ratios was performed. From our experiments it is shown that in droplets larger than 6 μm diameter (between 234.6 and 236.5 K), nucleation in the interior is more important than nucleation at the surface. At smaller sizes we cannot rule out a significant contribution of surface nucleation, and in order to further constrain surface nucleation, experiments with smaller droplets are necessary. Nevertheless, in our experiments, it is dominantly volume nucleation controlling the observed nucleation rate. [ABSTRACT FROM AUTHOR]

In this article, we conduct a comprehensive molecular relaxation study of amorphous Quinidine above and below the glass-transition temperature (Tg) through broadband dielectric relaxation spectroscopy (BDS) experiments and theoretical density functional theory (DFT) calculations, as one major issue with the amorphous state of pharmaceuticals is life expectancy. These techniques enabled us to determine what kind of molecular motions are responsible, or not, for the devitrification of Quinidine. Parameters describing the complex molecular dynamics of amorphous Quinidine, such as Tg, the width of the α relaxation (βKWW), the temperature dependence of α-relaxation times (τα), the fragility index (m), and the apparent activation energy of secondary γ relaxation (Ea-γ), were characterized. Above Tg (> 60 °C), a medium degree of nonexponentiality (βKWW = 0.5) was evidenced. An intermediate value of the fragility index (m = 86) enabled us to consider Quinidine as a glass former of medium fragility. Below Tg (< 60 °C), one well-defined secondary γ relaxation, with an apparent activation energy of Ea-γ = 53.8 kJ/mol, was reported. From theoretical DFT calculations, we identified the most reactive part of Quinidine moieties through exploration of the potential energy surface. We evidenced that the clearly visible γ process has an intramolecular origin coming from the rotation of the CH(OH)C9H14N end group. An excess wing observed in amorphous Quinidine was found to be an unresolved Johari-Goldstein relaxation. These studies were supplemented by sub-Tg experimental evaluations of the life expectancy of amorphous Quinidine by X-ray powder diffraction and differential scanning calorimetry. We show that the difference between Tg and the onset temperature for crystallization, Tc, which is 30 K, is sufficiently large to avoid recrystallization of amorphous Quinidine during 16 months of storage under ambient conditions. [ABSTRACT FROM AUTHOR]

Water in confined geometries has obvious relevance in biology, geology, and other areas where the material properties are strongly dependent on the amount and behavior of water in these types of materials. Another reason to restrict the size of water domains by different types of geometrical confinements has been the possibility to study the structural and dynamical behavior of water in the deeply supercooled regime (e.g., 150-230 K at ambient pressure), where bulk water immediately crystallizes to ice. In this paper we give a short review of studies with this particular goal. However, from these studies it is also clear that the interpretations of the experimental data are far from evident. Therefore, we present three main interpretations to explain the experimental data, and we discuss their advantages and disadvantages. Unfortunately, none of the proposed scenarios is able to predict all the observations for supercooled and glassy bulk water, indicating that either the structural and dynamical alterations of confined water are too severe to make predictions for bulk water or the differences in how the studied water has been prepared (applied cooling rate, resulting density of the water, etc.) are too large for direct and quantitative comparisons. [ABSTRACT FROM AUTHOR]

This review article focuses on the most recent advances in X-ray and neutron scattering studies of water structure, from ambient temperature to the deeply supercooled and amorphous states, and of water diffusive and collective dynamics, in disparate thermodynamic conditions and environments. In particular, the ability to measure X-ray and neutron diffraction of water with unprecedented high accuracy in an extended range of momentum transfers has allowed the derivation of detailed O--O pair correlation functions. A panorama of the diffusive dynamics of water in a wide range of temperatures (from 400 K down to supercooled water) and pressures (from ambient up to multiple gigapascals) is presented. The recent results obtained by quasi-elastic neutron scattering under high pressure are compared with the existing data from nuclear magnetic resonance, dielectric and infrared measurements, and modeling. A detailed description of the vibrational dynamics of water as measured by inelastic neutron scattering is presented. The dependence of the water vibrational density of states on temperature and pressure, and in the presence of biological molecules, is discussed. Results about the collective dynamics of water and its dispersion curves as measured by coherent inelastic neutron scattering and inelastic X-ray scattering in different thermodynamic conditions are reported. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Water is the most abundant liquid on earth and also the substance with the largest number of anomalies in its properties. It is a prerequisite for life and as such a most important subject of current research in chemical physics and physical chemistry. In spite of its simplicity as a liquid, it has an enormously rich phase diagram where different types of ices, amorphous phases, and anomalies disclose a path that points to unique thermodynamics of its supercooled liquid state that still hides many unraveled secrets. In this review we describe the behavior of water in the regime from ambient conditions to the deeply supercooled region. The review describes simulations and experiments on this anomalous liquid. Several scenarios have been proposed to explain the anomalous properties that become strongly enhanced in the supercooled region. Among those, the second critical-point scenario has been investigated extensively, and at present most experimental evidence point to this scenario. Starting from very low temperatures, a coexistence line between a high-density amorphous phase and a low-density amorphous phase would continue in a coexistence line between a high-density and a low-density liquid phase terminating in a liquid-liquid critical point, LLCP. On approaching this LLCP from the one-phase region, a crossover in thermodynamics and dynamics can be found. This is discussed based on a picture of a temperature-dependent balance between a high-density liquid and a low-density liquid favored by, respectively, entropy and enthalpy, leading to a consistent picture of the thermodynamics of bulk water. Ice nucleation is also discussed, since this is what severely impedes experimental investigation of the vicinity of the proposed LLCP. Experimental investigation of stretched water, i.e., water at negative pressure, gives access to a different regime of the complex water diagram. Different ways to inhibit crystallization through confinement and aqueous solutions are discussed through results from experiments and simulations using the most sophisticated and advanced techniques. These findings represent tiles of a global picture that still needs to be completed. Some of the possible experimental lines of research that are essential to complete this picture are explored. [ABSTRACT FROM AUTHOR]

This work deals with the anti-icing behavior at subfreezing temperatures of CeO2/polyurethane nanocomposite coatings with and without a stearic acid treatment on aluminum alloy substrates. The samples ranged from superhydrophilic to superhydrophobic depending on surface morphology and surface functionalization. X-ray photoelectron spectroscopy was used to determine the surface composition. The anti-icing behavior was studied both by importing fog into a chamber with controlled atmosphere at subzero temperatures and by conducting experiments with drop impact velocities of 1.98, 2.8, 3.83, and 4.95 m/s. It was found that the ice-phobicity of the ceramic/polymer nanocomposite coating was dependent on the surface roughness and surface energy. Water drops were observed to completely rebound from the surface at subfreezing temperatures from superhydrophobic surfaces with small contact angle hysteresis regardless of the impact velocity, thus revealing the anti-icing capability of such surfaces. [ABSTRACT FROM AUTHOR]

Ultrastable glasses produced by vapor deposition exhibit properties consistent with glasses that have been aged for thousands of years or more. These materials' properties are believed to emerge from the presence of a mobile layer at the surface of supercooled liquids that allows access to lower-energy states. However, the precise mechanism by which this enhanced mobility is translated into ultrastable glass behavior remains incompletely understood. Here we show that enhanced densities and stabilities consistent with ultrastable glasses specifically can emerge as a result of a mismatch in the length scales of thermodynamic and dynamic gradients at the surfaces of equilibrium supercooled liquids. In particular, ultrastable glass properties can be understood within a three-layer model of the interface in which a "facilitated layer" intermediate between the surface and bulk exhibits bulk-like liquid-state density but suppressed Tg. This mismatch in length-scale has previously been correlated with the scale of cooperative rearrangements in the supercooled state, suggesting that ultrastable glasses may be a direct consequence of the cooperative nature of dynamics in equilibrium supercooled liquids. [ABSTRACT FROM AUTHOR]

Owing to the universal presence of intermolecular interactions, it has to be expected that at some well-defined lower temperature a liquid loses its dynamic properties like fluidity and self-diffusion. As a sequel to two earlier papers on the discovery of such an arrest temperature T0 for supercooled water at 243 K, where also the coexisting vapor pressure was found to become zero, in this paper a further study is undertaken of the behavior of a selection of other liquids. At first, two simple equations of state (van der Waals and virial) are shown in principle to predict a zero vapor pressure at a finite temperature. The interaction parameters B (second virial coefficient) and μJT (Joule-Thomson coefficient) of the vapor are found to become virtually infinite at a temperature T0,B, with a value equal or close to the T0 derived from the liquid properties. Just as earlier found for water, the latter is obtained by extrapolation of several available dynamic and equilibrium data, which should produce an intersection with the temperature axis at the same T0 value. With the exception of molten salts and liquid pure metals, this condition appears to be fulfilled quite accurately. Thus, the temperature of arrest is a general phenomenon for supercooled liquids. As an illustration, it is shown how the PVT diagram of carbon dioxide can be extended into the supercooled temperature region. It is argued that T0 is the temperature below which the Boltzmann energy, kT, is lower than the minimal energy needed for a molecule to break the interactions with its surrounding molecules. We propose to name this minimal energy, kT0, the multimolecular potential of the liquid object. The relationship of the liquid multimolecular potential with the pair potential, ε, of the molecular species is established for various examples and appears to be a proportionality with ε ≈ kT0. [ABSTRACT FROM AUTHOR]

In a polymeric material near its glass transition temperature, segmental dynamics of a given spatial region may differ considerably from that of neighboring regions without apparent structural origin, analogous to the supercooled liquid state of low molecular weight glass formers. Given that the supercooled liquid state is a (metastable) equilibrium state, spatial variations in dynamics are expected to average out in time, consistent with ergodicity of the system. By probing the rotations of fluorescent guest molecules, local segmental dynamics of polystyrene was scrutinized molecule by molecule. Two perylene dicarboximide dyes were investigated as potential reporters, and one of these was found to report a substantial proportion of the dynamic heterogeneity of the host polystyrene. Using this probe, we demonstrate that the polystyrene system is ergodic and characterize time scales over which molecules experience changes to their dynamics. We identify a characteristic time scale of exchange much longer than the structural relaxation of the host segmental dynamics, consistent with both previous studies on polystyrene and studies on small molecule glass formers. Moreover, we show that dynamic exchange spans a wide range of time scales from <150 to ~35000 times the segmental relaxation time of the polystyrene. [ABSTRACT FROM AUTHOR]

Via analysis of spatiotemporal arrangements of atoms based on their dynamics in supercooled liquid and glassy states of a 2D monatomic system with a double-well Lennard-Jones-Gauss (LJG) interaction potential, we find a new scenario of dynamical heterogeneity. Atoms with the same or very close mobility have a tendency to aggregate into clusters. The number of atoms with high mobility (and size of their clusters) increases with decreasing temperature passing over a maximum before decreasing down to zero. Position of the peak moves toward a lower temperature if mobility of atoms in clusters is lower together with an enhancement of height of the peak. In contrast, the number of atoms with very low mobility or solidlike atoms (and size of their clusters) has a tendency to increase with decreasing temperature and then it suddenly increases in the vicinity of the glass transition temperature leading to the formation of a glassy state. A sudden increase in the number of strongly correlated solidlike atoms in the vicinity of a glass transition temperature (Tg) may be an origin of a drastical increase in viscosity of the glass-forming systems approaching the glass transition. In fact, we find that the diffusion coefficient decays exponentially with a fraction of solidlike atoms exhibiting a sudden decrease in the vicinity of the glass transition region. [ABSTRACT FROM AUTHOR]

Glass-forming materials are employed in information storage technologies making use of the transition between a disordered (amorphous) and an ordered (crystalline) state. With increasing temperature, the crystal growth velocity of these phase-change materials becomes so fast that prior studies have not been able to resolve these crystallization dynamics. However, crystallization is the time-limiting factor in the write speed of phase-change memory devices. Here, for the first time, we quantify crystal growth velocities up to the melting point using the relaxation of photoexcited carriers as an ultrafast heating mechanism. During repetitive femtosecond optical excitation, each pulse enables dynamical evolution for tens of picoseconds before the intermediate atomic structure is frozen-in as the sample rapidly cools. We apply this technique to Ag4In3Sb67Te26 (AIST) and compare the dynamics of as-deposited and application-relevant melt-quenched glass. Both glasses retain their different kinetics even in the supercooled liquid state, thereby revealing differences in their kinetic fragilities. This approach enables the characterization of application-relevant properties of phase-change materials up to the melting temperature, which has not been possible before. [ABSTRACT FROM AUTHOR]

Polyamorphoustransitions in supercooled water, porous substances,solutions of polyols, and proteins are studied intensively. They accompanythe self-organization of hydrocarbons and surfactants. In this study,the methods of polyamorphous transition identification are proposed,and their dependence on hydrocarbons and surfactant concentrationand sizes is investigated. The place of polyamorphous transitionsin the general theory of phase separation is determined, and theirbistability, self-oscillations, hysteresis, fluctuations, cooperativeeffect, enthalpy, and entropy are described. Surface, volume, anddiffusion instabilities of polyamorphous transitions are analyzed.Technologies based on the properties of polyamorphous transitionsare proposed. [ABSTRACT FROM AUTHOR]

Measurementsof the surface tension of supercooled water down to−25 °C have been reported recently (Hrubý et al. J. Phys. Chem. Lett.2014, 5, 425–428). These experiments did not show any anomalous temperaturedependence of the surface tension of supercooled water reported bysome earlier measurements and molecular simulations. In the presentwork, this finding is confirmed using a counterpressure capillaryrise method (the counterpressuremethod) as wellas through the use of the classical capillary rise method (the heightmethod). In the counterpressuremethod,the liquid meniscus inside the vertical capillary tube was kept ata fixed position with an in-house developed helium distribution setup.A preset counterpressure was applied to the liquid meniscus when itstemperature changed from a reference temperature (30 °C) to thetemperature of interest. The magnitude of the counterpressure wasadjusted such that the meniscus remained at the same height, thuscompensating the change of the surface tension. One advantage of the counterpressuremethod over the heightmethod consists of avoiding theuncertainty due to a possible variation of the capillary diameteralong its length. A second advantage is that the equilibration timedue to the capillary flow of the highly viscous supercooled watercan be shortened. For both the counterpressuremethodand the heightmethod, the actualresults are relative values of surface tension with respect to thesurface tension of water at the reference temperature. The combinedrelative standard uncertainty of the relative surface tensions isless than or equal to 0.18%. The new data between −26 and +30°C lie close to the IAPWS correlation for the surface tensionof ordinary water extrapolated below 0.01 °C and do not exhibitany anomalous features. [ABSTRACT FROM AUTHOR]

Fragility is a measure of the departure from non-Arrhenius behavior for supercooled liquids and glasses, and various simple methods are available for its quantification. However, the obtained values usually do not agree with each other. One of the purposes of this study was to compare the fragility values obtained by different methodologies. Thermodynamic fragility (FT) is a simple concept that is evaluated from the heat capacity change at the glass transition temperature (Tg). Dynamic fragility is evaluated using three methodologies in this study: extrapolation of the configurational entropy (Sc) to the Kauzmann temperature (Tk) (FDC), ramp-rate dependence of Tg (FDTg), and that of the fictive temperature (Tf) (FDTf). FT and FDC of 19 pharmaceutical compounds were correlated, whereas FDTg and FDTf did not correlate with either of them. This result seems reasonable because both FT and FDC are calculated from thermodynamic parameters in the quasi-equilibrium state, but FDTg and FDTf are likely affected by kinetics as well. Another goal of this study was to find the correlation between the glass-forming ability (GFA) and fragility. FDTg was shown to correlate with GFA, presumably because both were determined on the balance of thermodynamic and kinetic factors. This correlation suggests that fragile glass has low GFA. Furthermore, the relevance of fragility to isothermal crystallization is discussed. Compounds with small FDTg and FDTf tended to exhibit pressure-controlled crystallization, for which better storage stability can be expected relative to temperature-controlled compounds. Fragility was shown to be a useful parameter practically as well as scientifically. [ABSTRACT FROM AUTHOR]

We generalize the force-level Elastically Collective Nonlinear Langevin Equation theory of supercooled molecular liquid dynamics to polymer melts based on mapping chains to disconnected and noninterpenetrating Kuhn-sized spheres. This allows first-principles, no adjustable parameter calculations to be performed for the temperature-dependent mean segmental relaxation time of chemically diverse van der Waals polymers over a wide range of molecular weights. Despite the simplicity of the mapping, the theory does a good job of a priori predicting the glass transition temperature (Tg), the dynamic fragility, and full temperature dependence of the α-relaxation time for some high molecular weight polymers and the chain length dependence of Tg as the consequence of the molecular weight dependence of backbone stiffness. The minimalist model does not capture the unusually low and high fragilities of certain long chain polymers which are not typical of van der Waals molecular liquids. This seems likely due to the simple coarse graining adopted which ignores longer range chain connectivity and nonuniversal factors on the sub-Kuhn length scale. Elasticity, not of an entropic single chain origin, emerges in deeply supercooled polymer liquids due to transient segmental localization and is studied at the microscopic stress-tensor level. Calculations of the frequency-dependent dynamic storage modulus close to Tg appear to be qualitatively consistent with recent measurements. [ABSTRACT FROM AUTHOR]

Electrofreezing is the electricallyinduced nucleation of ice fromsupercooled water. This work studies ice nucleation in electrowettedwater droplets, wherein there is no electric field inside the dropletresting on a dielectric layer. Instead, there is an interfacial electricfield and charge buildup at the solid–liquid interface. Thissituation is in contrast to most previous electrofreezing studies,which have used bare electrodes, involve current flow, and have avolumetric electric field inside the liquid. Infrared and high-speedvisualizations of static water droplets are used to analyze surfaceelectrofreezing. Ultrahigh electric fields of up to 80 V/μmare applied, which is one order of magnitude higher than in previousstudies. The results facilitate an in-depth understanding of variousmechanisms underlying electrofreezing. First, it is seen that interfacialelectric fields alone can significantly elevate freezing temperaturesby more than 15 °C, in the absence of current flow. Second, themagnitude of electrofreezing induced temperature elevation saturatesat high electric field strengths. Third, the polarity of the interfacialcharge does not significantly influence electrofreezing. Overall,it is seen that electrofreezing nucleation kinetics is primarily influencedby the three-phase boundary and not the solid–liquid interface.Through careful electrofreezing measurements on dielectric layerswith pinholes to allow current flow, the individual role of electricfields and electric currents on electrofreezing is isolated. It isseen that both the electric field and the electric current influenceelectrofreezing; however, the physical mechanisms are very different. [ABSTRACT FROM AUTHOR]

Wepresent a density functional theory approach to investigate the thermodynamicsof ice nucleation in supercooled water. Within the theoretical framework,the free-energy functional is constructed by the direct correlationfunction of oxygen–oxygen of the equilibrium water, and thefunction is derived from the reference interaction site model in considerationof the interactions of hydrogen–hydrogen, hydrogen–oxygen,and oxygen–oxygen. The equilibrium properties, including vapor–liquidand liquid–solid phase equilibria, local structure of hexagonalice crystal, and interfacial structure and tension of water–iceare calculated in advance to examine the basis for the theory. Thepredicted phase equilibria and the water–ice surface tensionare in good agreement with the experimental data. In particular, thecritical nucleus radius and free-energy barrier during ice nucleationare predicted. The critical radius is similar to the simulation value,suggesting that the current theoretical approach is suitable in describingthe thermodynamic properties of ice crystallization. [ABSTRACT FROM AUTHOR]

The diffusion of ferrocene methanolin supercooled glycerol–watermixtures has been measured over a wide viscosity range, which allowedanalyzing the composition dependence of the Stokes–Einsteinbreakdown (diffusion–viscosity decoupling). The observed decouplingexhibits a common behavior for all studied compositions (glycerolmass fractions between 0.7 and 0.9), determined by the reduced temperature(T/Tg) of the mixtures.This result differs from that reported previously for the diffusionof glycerol in its aqueous solutions, where the reduced temperaturefor the decoupling decreases with increasing water content. We concludethat the contradictory results are only apparent, and they can beexplained by the use of inconsistent extrapolated values of the viscosityof the glycerol–water mixtures in the supercooled region. [ABSTRACT FROM AUTHOR]

A contendingtechnology for nonvolatile memories of the next generationis based on a remarkable property of chalcogenide alloys known asphase change materials, namely their ability to undergo a fast andreversible transition between the amorphous and crystalline phasesupon heating. The fast crystallization has been ascribed to the persistenceof a high atomic mobility in the supercooled liquid phase, down totemperatures close to the glass transition. In this work we unravelthe atomistic, structural origin of this feature in the supercooledliquid state of GeTe, a prototypical phase change compound, by meansof molecular dynamic simulations. To this end, we employed an interatomicpotential based on a neural network framework, which allows simulatingthousands of atoms for tens of ns by keeping an accuracy close tothat of the underlying first-principles framework. Our findings demonstratethat the high atomic mobility is related to the presence of clustersof slow and fast moving atoms. The latter contain a large fractionof chains of homopolar Ge–Ge bonds, which at low temperatureshave a tendency to move by discontinuous cage-jump rearrangements.This structural fingerprint of dynamical heterogeneity provides anexplanation of the breakdown of the Stokes–Einstein relationin GeTe, which is the ultimate origin of the fast crystallizationof phase change materials exploited in the devices. [ABSTRACT FROM AUTHOR]

An electrical phenomenon consistingof two alternating voltagepeaks of up to 6 V amplitude was observed during the rapid dendriticfreezing phase of supercooled water droplets in the millimeter sizerange with supercoolings ΔTin the range of5 to 20 K. For correlation of the dendritic freezing front with theelectric potential, a fast recording oscilloscope was combined witha high-speed camera operating at up to 5000 frames per second. Thestrength of the effect is roughly proportional to the supercoolingand dendritic freezing speed. Furthermore, during the subsequent secondfreezing phase, which is much slower than the dendritic, a qualitativelydifferent electric potential evolution of similar magnitude has beenfound which resembles the well-investigated Workman–Reynoldsfreezing potential (WRFP). The experiments show clear evidence thatthe first rapid dendritic freezing stage significantly influencesdirection and amount of the electric potential during the second slowfreezing stage. Compared to the WRFP, which takes place for much smallersupercoolings of ΔT≪ 5 K, the evolutionof the presented dendritic freezing potential occurs about 104times faster, is about 10 times smaller in view of the maximumvoltage, and shows similar break off concentrations but remarkablydoes not vanish at low foreign ion concentrations. This phenomenonhas direct relevance to atmospheric freezing processes of the Earth,other planets, and satellites. [ABSTRACT FROM AUTHOR]

Monitoring single molecule probe rotations is an increasingly common approach to studying dynamics of complex systems, including supercooled liquids. Even with advances in fluorophore design and detector sensitivity, such measurements typically exhibit low signal to noise and signal to background ratios. Here, we simulated and analyzed orthogonally decomposed fluorescence signals of single molecules undergoing rotational diffusion in a manner that mimics experimentally collected data of probes in small molecule supercooled liquids. The effects of noise, background, and trajectory length were explicitly considered, as were the effects of data processing approaches that may limit the impact of noise and background on assessment of environmental dynamics. In many cases, data treatment that attempts to remove noise and background were found to be deleterious. However, for short trajectories below a critical signal to background threshold, a thresholding approach that successfully removed data points associated with noise and spared those associated with signal allowed for assessment of environmental dynamics that was as accurate and precise as would be achieved in the absence of noise. [ABSTRACT FROM AUTHOR]

Ultrastable thin film glasses transforminto supercooled liquidvia propagating fronts starting from the surface and/or interfaces.In this paper, we analyze the consequences of this mechanism in theinterpretation of specific heat curves of ultrastable glasses of indomethacinfor samples with varying thickness from 20 nm up to several microns.We demonstrate that ultrastable films above 20 nm have identical fictivetemperatures and that the apparent change of onset temperature inthe specific heat curves originates from the mechanism of transformationand the normalization procedure. An ad hoc surface normalization ofthe heat capacity yields curves which collapse into a single one irrespectiveof their thickness. Furthermore, we fit the surface-normalized specificheat curves with a heterogeneous transformation model to evaluatethe velocity of the growth front over a much wider temperature intervalthan previously reported. Our data expands previous values up to Tg+ 75 K, covering 12 orders of magnitude in relaxation times. The resultsare consistent with preceding experimental and theoretical studies.Interestingly, the mobility of the supercooled liquid in the regionbehind the transformation front remains constant throughout the thicknessof the layers. [ABSTRACT FROM AUTHOR]

Westudy the fragile-to-strong (F–S) transition of metallicglass-forming liquids (MGFLs) by measuring the thermal response duringannealing and dynamic heating of La55Al25Ni5Cu15glass ribbons fabricated at different coolingrates. We find that the glasses fabricated in the intermediate regimeof cooling rates (15–25 m/s) exhibit an anomalous crystallizationbehavior upon reheating as compared to the glasses formed at othercooling rates. This anomalous crystallization behavior implies theexistence of a thermodynamic F–S transition, could be usedas an alternative method for detecting the F–S transition inMGFLs, and sheds light on the structure origin of the F–S transition.This work also contributes to obtaining a general thermodynamic pictureof the F–S transition in supercooled liquids. [ABSTRACT FROM AUTHOR]

Moleculardynamics simulations and a stochastic method based onthe Fokker–Planck equation are used to explore the consequencesof inhomogeneous density profiles on the thermodynamic and dynamicproperties of the hard-sphere fluid and supercooled liquid water.Effects of the inhomogeneity length scale are systematically consideredvia the imposition of sinusoidal density profiles of various wavelengths.For long-wavelength density profiles, bulk-like relationships betweenlocal structure, thermodynamics, and diffusivity are observed as expected.However, for both systems, a crossover in behavior occurs as a functionof wavelength, with qualitatively different correlations between thelocal static and dynamic quantities emerging as density variationsapproach the scale of a particle diameter. Irrespective of the densityvariation wavelength, average diffusivities of hard-sphere fluidsin the inhomogeneous and homogeneous directions are coupled and approximatelycorrelate with the volume available for insertion of another particle.Unfortunately, a quantitatively reliable static predictor of position-dependentdynamics has yet to be identified for even the simplest of inhomogeneousfluids. [ABSTRACT FROM AUTHOR]

Wecompare dynamical heterogeneities in equilibrated supercooledliquids and in the nonequilibrium glassy state within the frameworkof the random first order transition theory. Fluctuating mobilitygeneration and transport in the glass are treated by numerically solvingstochastic continuum equations for mobility and fictive temperaturefields that arise from an extended mode coupling theory containingactivated events. Fluctuating spatiotemporal structures in aging andrejuvenating glasses lead to dynamical heterogeneity in glasses withcharacteristics distinct from those found in the equilibrium supercooledliquid. The non-Gaussian distribution of activation free energies,the stretching exponent β, and the growth of characteristiclengths are studied along with the four-point dynamical correlationfunction. Asymmetric thermodynamic responses upon heating and coolingare predicted to be the result of the heterogeneity and the out-of-equilibriumbehavior of glasses below Tg. Our numericalresults agree with experimental calorimetry. We numerically confirmthe prediction of Lubchenko and Wolynes in the glass that the dynamicalheterogeneity can lead to noticeably bimodal distributions of localfictive temperatures during some histories of preparation which explainsin a unified way recent experimental observations that have been interpretedas coming from there being two distinct equilibration mechanisms inglasses. [ABSTRACT FROM AUTHOR]

Aqueous solutions of LiCl have recentlyreceived much attentionin connection with the study of the anomalies of supercooled waterand its polyamorphism. From the point of view of computer simulation,there is need for a force field that can reproduce the structuraland dynamical properties of this solution, and more importantly itis also simple enough to use in large scale simulations of supercooledstates. We study by molecular dynamics the structure of the LiCl–watersolutions with the force field proposed by Joung and Cheatham (J. Phys. Chem. B2008, 112, 9020) appropriate for the water TIP4P-Ew model potential. We foundthat this force field does not reproduce the experimental ion pairingwhen the Lorentz–Berthelot (LB) rules are used. By incorporatingdeviations to the LB rules to obtain the crossed interactions betweenthe ions, it is possible to get agreement with experiment. We havestudied how the modification of the LB rule affects the structuraland thermodynamic properties of the solution at increasing concentrationof the solution from the low (around 2%) to medium (around 14%) concentrationregimes. We also tested the transferability of the Joung and Cheathamforce field to the water TIP4P/2005 model that works very well forsupercooled water. [ABSTRACT FROM AUTHOR]

Bimolecular collision rate constantsof a model solute are measuredin water at T= 259–303 K, a range encompassingboth normal and supercooled water. A stable, spherical nitroxide spinprobe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl, isstudied using electron paramagnetic resonance spectroscopy (EPR),taking advantage of the fact that the rotational correlation time,τR, the mean time between successive spin exchangeswithin a cage, τRE, and the long-time-averaged spinexchange rate constants, Kex, of the samesolute molecule may be measured independently. Thus, long- and short-timetranslational diffusion behavior may be inferred from Kexand τRE, respectively. In order tomeasure Kex, the effects of dipole–dipoleinteractions (DD) on the EPR spectra must be separated, yielding asa bonus the DD broadening rate constants that are related to the dephasingrate constant due to DD, Wdd. We findthat both Kexand Wddbehave hydrodynamically; that is to say they vary monotonicallywith T/η or η/T, respectively,where η is the shear viscosity, as predicted by the Stokes–Einsteinequation. The same is true of the self-diffusion of water. In contrast,τREdoes not follow hydrodynamic behavior, varyingrather as a linear function of the density reaching a maximum at 276± 2 K near where water displays a maximum density. [ABSTRACT FROM AUTHOR]

Phasechange materials are widely considered for application innonvolatile memories because of their ability to achieve phase transformationin the nanosecond time scale. However, the knowledge of fast crystallizationdynamics in these materials is limited because of the lack of fastand accurate temperature control methods. In this work, we have developedan experimental methodology that enables ultrafast characterizationof phase-change dynamics on a more technologically relevant melt-quenchedamorphous phase using practical device structures. We have extractedthe crystallization growth velocity (U) in a functionalcapped phase change memory (PCM) device over 8 orders of magnitude(10–10< U< 10–1m/s) spanning a wide temperature range (415 < T< 580 K). We also observed direct evidence of non-Arrhenius crystallizationbehavior in programmed PCM devices at very high heating rates (>108K/s), which reveals the extreme fragility of Ge2Sb2Te5in its supercooled liquid phase. Furthermore,these crystallization properties were studied as a function of deviceprogramming cycles, and the results show degradation in the cell retentionproperties due to elemental segregation. The above experiments areenabled by the use of an on-chip fast heater and thermometer calledas microthermal stage (MTS) integrated with a vertical phase changememory (PCM) cell. The temperature at the PCM layer can be controlledup to 600 K using MTS and with a thermal time constant of 800 ns,leading to heating rates ∼108K/s that are closeto the typical device operating conditions during PCM programming.The MTS allows us to independently control the electrical and thermalaspects of phase transformation (inseparable in a conventional PCMcell) and extract the temperature dependence of key material propertiesin real PCM devices. [ABSTRACT FROM AUTHOR]

N,N-R-Phenyl-7-amino-2,4-trifluoromethylquinolinederivatives (R = Me (1), Et (2), isopropyl(3), and Ph (4)) were prepared as a newtype of fluorophore responsive to external stimuli. 1, 2, 3, and 4were obtainedas single crystals including three crystal polymorphs (1α, 1β, and 1γ) of 1and two (2αand 2β) of 2. In 4, a phase transition from 4173and 490between 173 and 90 K was observed. The solid-state emissionshowed a red shift by 30–58 nm compared with the emission in n-hexane, and their emission properties depended on themolecular arrangements. The modes of molecular arrangements for 1α, 1β, and 1γwere a slipped parallel (SP), head-to-tail γ-type herringbone(HT-γ-HB), and head-to-head γ-type herringbone (HH-γ-HB);those for 2αand 2βwere HT-γ-HBand head-to-tail dimer (HT-dimer), and that for 3washead-to-tail columnar (HTC). 4173and 490were similar HT-γ-HB.The crystal-to-crystal transformations from 1γto 1βand from 2βto 2αwere observed by heating and grinding the crystal, respectively,with emittance changes. After melting, on cooling, all crystals formedsupercooled liquid (SCL) and then glass states. In the SCL state,molecules were amorphous and were quickly crystallized by a mechanicalstimulus such as scratching. By taking advantage of the differenceof emitting intensity between the SCL and the crystal states for 1, “writing” and “erasing” ofa letter with scratching and heating, respectively, were demonstrated. [ABSTRACT FROM AUTHOR]

Crystal–liquid interfacialfree energy is important to understandin crystal study, for example, nucleation, crystal growth, and vitrification.Here, we report the nanosized nucleus-supercooled liquid interfacialfree energy of early and late transition liquid metals using the electrostaticlevitation (ESL) technique and classical homogeneous nucleation theory(CNT). For the estimation of the interfacial free energy, we obtainedthermophysical parameters of the transition liquid metals (Ti, Fe,Ni, Zr, Nb, Rh, and Hf), such as hypercooling limit (ΔThyp), specific heat (Cp), total hemispherical emissivity (εT), and density (ρ). The estimated interfacial free energiesof Ti, Ni, and Zr agreed well with a previous report having similarhypercooling limit and fusion enthalpy, while Fe, Nb, Rh, and Hf showdifferent values from the report. This reflects the importance ofaccurate measurement of the two quantities. The obtained Turnbull’scoefficients (α) of the liquid metals is higher than 0.45. Theinterfacial free energy is discussed with configurationally differentlocal order of the crystal and the liquid. [ABSTRACT FROM AUTHOR]

Heterogeneousice growth exhibits a maximum in freezing rate arisingfrom the competition between kinetics and the thermodynamic drivingforce between the solid and liquid states. Here, we use moleculardynamics simulations to elucidate the atomistic details of this competition,focusing on water properties in the interfacial region along the secondaryprismatic direction. The crystal growth velocity is maximized whenthe efficiency of converting interfacial water molecules to ice, collectivelyknown as the attachment kinetics, is greatest. We find water moleculesthat contact the intermediate ice layer in concave regions along theatomistically roughened surface are more likely to freeze directly.An increased roughening of the solid surface at large undercoolingsconsequently plays an important limiting role in the rate of ice growth,as water molecules are unable to integrate into increasingly deepersurface pockets. These results provide insight into the molecularmechanisms for self-assembly of solid phases that are important inmany biological and atmospheric processes. [ABSTRACT FROM AUTHOR]

We study the temperature dependenceof the lifetime of geometricand geometric/energetic water hydrogen-bonds (H-bonds), down to supercooledwater, through molecular dynamics. The probability and lifetime ofH-bonds that break either by translational or librational motionsand those of energetic broken H-bonds, along with the effects of transientbroken H-bonds and transient H-bonds, are considered. We show thatthe fraction of transiently broken energetic H-bonds increases atlow temperatures and that this energetic breakdown is caused by oxygen–oxygenelectrostatic repulsions upon too small amplitude librations to disruptgeometric H-bonds. Hence, differences between geometric and energeticcontinuous H-bond lifetimes are associated with large H-bond energyfluctuations, in opposition to moderate geometric fluctuations, withincommon energetic and geometric H-bond definition thresholds. Exclusionof transient broken H-bonds and transient H-bonds leads to H-bonddefinition-independent mean lifetimes and activation energies, ∼11kJ/mol, consistent with the reactive flux method and experimentalscattering results. Further, we show that power law decay of specifictemporal H-bond lifetime probability distributions is associated withlibrational and translational motions that occur on the time scale(∼0.1 ps) of H-bond breaking /re-forming dynamics. While ouranalysis is diffusion-free, the effect of diffusion on H-bond probabilitydistributions where H-bonds are allowed to break and re-form, switchingacceptors in between, is shown to result in neither exponential norpower law decay, similar to the reactive flux correlation function. [ABSTRACT FROM AUTHOR]

Wecompute the temperature-dependent barrier for α-relaxationsin several liquids, without adjustable parameters, using experimentallydetermined elastic, structural, and calorimetric data. We employ therandom first order transition (RFOT) theory, in which relaxation occursvia activated reconfigurations between distinct, aperiodic minimaof the free energy. Two different approximations for the mismatchpenalty between the distinct aperiodic states are compared, one dueto Xia and Wolynes (Proc. Natl. Acad. Sci. U. S. A.2000,97, 2990), whichscales universally with temperature as for hard spheres, and one dueto Rabochiy and Lubchenko (J. Chem. Phys.2013, 138, 12A534), which employs measured elastic andstructural data for individual substances. The agreement between thepredictions and experiment is satisfactory, given the uncertaintyin the measured experimental inputs. The explicitly computed barriersare used to calculate the glass transition temperature for each substanceakinetic quantityfrom the static input data alone. The temperaturedependence of both the elastic and structural constants enters thetemperature dependence of the barrier over an extended range to adegree that varies from substance to substance. The lowering of theconfigurational entropy, however, seems to be the dominant contributorto the barrier increase near the laboratory glass transition, consistentwith previous experimental tests of the RFOT theory using the XW approximation.In addition, we compute the temperature dependence of the dynamicalcorrelation length, also without using adjustable parameters. Theseagree well with experimental estimates obtained using the Berthieret al. (Science2005, 310, 1797) procedure. Finally, we find the temperature dependence ofthe complexity of a rearranging region is consistent with the picturebased on the RFOT theory but is in conflict with the assumptions ofthe Adam–Gibbs and “shoving” scenarios for theviscous slowing down in supercooled liquids. [ABSTRACT FROM AUTHOR]

We investigate the mobility of supercooledliquid toluene, ethylbenzene,and benzene near their respective glass transition temperatures (Tg). The permeation rate of Ar, Kr, and Xe throughthe supercooled liquid created when initially amorphous overlayersare heated above their glass transition temperature is used to determinethe diffusivity. Amorphous benzene crystallizes at temperatures wellbelow its Tg, and as a result, the inertgas underlayer remains trapped until the onset of benzene desorption.In contrast, for toluene and ethylbenzene the onset of inert gas permeationis observed at temperatues near Tg. Theinert gas desorption peak temperature as a function of the heatingrate and overlayer thickness is used to quantify the diffusivity ofsupercooled liquid toluene and ethylbenzene from 115 to 135 K. Inthis temperature range, diffusivities are found to vary across 5 ordersof magnitude (∼10–14to 10–9cm2/s). The diffusivity data are compared to viscositymeasurements and reveal a breakdown in the Stokes–Einsteinrelationship at low temperatures. However, the data are well fit bythe fractional Stokes–Einstein equation with an exponent of0.66. Efforts to determine the diffusivity of a mixture of benzeneand ethylbenzene are detailed, and the effect of mixing these materialson benzene crystallization is explored using infrared spectroscopy. [ABSTRACT FROM AUTHOR]

In situ AC nanocalorimetry was usedto measure the reversing heatcapacity of vapor-deposited glasses of decahydronaphthalene (decalin).Glasses with low heat capacity and high kinetic stability, as comparedto the corresponding liquid-cooled glass, were prepared from cis-decalin and from several cis/trans-decalin mixtures. This is the first report of highlystable glass formation for molecular mixtures. The 50/50 cis/trans-decalin mixture is the highest fragilitymaterial reported to produce an ultrastable glass. The 50/50 mixtureexhibited high kinetic stability, with a ∼500 nm film depositedat 116 K (0.86 Tg) displaying a transformationtime equivalent to 104.4times the structural relaxationtime of the supercooled liquid at the annealing temperature. cis-Decalin and the decalin mixture formed stable glassesthat had heat capacities as much as 4.5% lower than the liquid-cooledglass. [ABSTRACT FROM AUTHOR]

We present a comprehensive first-principles Born−Oppenheimer molecular dynamics (BOMD) simulation study of halide anion solvation in a deeply supercooled water droplet (with diameter ∼1.8 nm). We show that larger halide anions Br− and I− show “outer-layer surface preference”, whereas F− exhibits bulk preference. Contrary to behavior of other halide anions, Cl− in the water droplet appears to exhibit no strong tendency of surface or bulk preference at either the supercooled or ambient condition, a phenomenon not previously reported in the literature. BOMD simulation indicates that fully hydrated complex of F− is mainly five-fold coordinated (showing square pyramid structure), whereas Cl−, Br− and I− hydrated complexes are either fiveor six-fold coordinated (showing sandwich-like structure). Among Cl−, Br−and I− anions, BOMD simulation indicates that I− exhibits the largest diffusion coefficient despite its largest size. However, computed resident time of the four halide ions suggests that Br− can approach from the interior to the surface of the water droplet at a much faster rate than I− and Cl−. [ABSTRACT FROM AUTHOR]

Thenucleation rate from classical nucleation theory is independentof sample size. In the past decades, several experimental and theoreticalstudies argued that the homogeneous nucleation rate of ice in supercooleddroplets increases when the drop size is decreased. In this paper,we investigate the nucleation of ice in nanoscale water films usingmolecular dynamics simulations. We found that the nucleation rateof ice actually decreases when the film thickness decreases in thenanoscale regime. A theoretical model is presented to interpret themechanism of nucleation rate decrease, which agrees well with thesimulation results. The model divides films into the near-surfaceand the middle regions that are characterized by relatively low andhigh nucleation rates, respectively. The middle region dominates thenucleation process of films, whereas its effect is continuously weakenedwhen increasing volume fraction of the near-surface region by decreasingthe film size, leading to a decrease of the total nucleation rate.The structural and thermodynamic analyses indicate that the high stressinduced by the surface layering slows down the diffusion and increasesthe nucleation barrier in the near-surface region, which is responsiblefor the low nucleation rate and eventually the decrease of the totalnucleation rate. [ABSTRACT FROM AUTHOR]

The return of a supercooled liquidto equilibrium usually beginswith a fast heating up of the sample which ends when the system reachesthe equilibrium freezing temperature. At this stage, the system isstill a microsegregated mixture of solid and liquid. Only later issolidification completed through the exchange of energy with the surroundings.Using the IAPWS-95 formulation, we investigate the adiabatic freezingof supercooled water in a closed and rigid vessel, i.e., under thermallyand mechanically isolated conditions, which captures the initial stageof the decay of metastable water to equilibrium. To improve realismfurther, we also account for a fixed amount of foreign gas in thevessel. Under the simplifying assumption that the system is at equilibriumimmediately after the nominal freezing temperature has been attained,we determineas a function of undercooling and gas mole numberthefinal temperature and pressure of the system, the fraction of iceat equilibrium, and the entropy increase. Assuming a nonzero energycost for the ice–water interface, we also show that, unlesssufficiently undercooled, perfectly isolated pure-water droplets cannotstart freezing in the bulk. [ABSTRACT FROM AUTHOR]

Wereport a crystal–liquid interfacial free energy of asupercooled liquid Fe, which is estimated from the classical homogeneousnucleation theory, using a containerless technique, electrostaticlevitation (ESL). Thermophysical properties on the supercooled andthe stable Fe liquids that are prerequisite for the estimation ofinterfacial free energy are measured by the ESL, for the first time.A hypercooling limit, which is one of the important parameters todetermine the interfacial free energy, is obtained with 357 °C.Specific heat (Cp) andtotal hemispherical emissivity (εT) are 45.1 ±3 J/mol·K and 0.314 at melting temperature, respectively. The Cpof the supercooled liquidFe shows weak temperature dependence, confirmed by a calculated coolingcurve. Densities of the stable, the supercooled liquid, and the crystalphases of Fe are successfully measured in a wide temperature rangefrom 650 to 1600 °C. Finally, the crystal–liquid interfacialfree energy of Fe is estimated with the measured thermophysical parameters.The value is about 0.22 ± 0.01 J/m2, which is consistentwith a molecular dynamic simulation result. [ABSTRACT FROM AUTHOR]

Recently, a second crystalline polymorph (Form II) ofracemic ibuprofenwas reported to be obtained by crystallization from the supercooledliquid state. The reported procedure involved a temperature schedulethat included the requirement to quench the sample to a temperature(168 K) significantly below the glass-transition temperature (228K) followed by annealing at a temperature (typically 258 K) abovethe glass-transition temperature. In the present work, we show (bydifferential scanning calorimetry and in situ, variable-temperaturepowder X-ray diffraction) that Form II of racemic ibuprofen can beprepared by crystallization from the supercooled liquid at temperaturesas high as 273 K, without the requirement for low-temperature quenchingand without the requirement for the material to pass below the glass-transitiontemperature. Our results lead to a new interpretation of the experimentalconditions for producing Form II of racemic ibuprofen and remove racemicibuprofen from the set of crystalline materials that are obtainedonly vialow-temperature quenching of a supercooledliquid. [ABSTRACT FROM AUTHOR]