Transition In Supercooled Water Research Articles

Kinetics and Mechanisms of Pressure-Induced Ice Amorphization and Polyamorphic Transitions in a Machine-Learned Coarse-Grained Water Model.

Water glasses have attracted considerable attention due to their potential connection to a liquid-liquid transition in supercooled water. Here we use molecular simulations to investigate the formation and phase behavior of water glasses using the machine-learned bond-order parameter (ML-BOP) water model. We produce glasses through hyperquenching of water, pressure-induced amorphization (PIA) of ice, and pressure-induced polyamorphic transformations. We find that PIA of polycrystalline ice occurs at a lower pressure than that of monocrystalline ice and through a different mechanism. The temperature dependence of the amorphization pressure of polycrystalline ice for ML-BOP agrees with that in experiments. We also find that ML-BOP accurately reproduces the density, coordination number, and structural features of low-density (LDA), high-density (HDA), and very high-density (VHDA) amorphous water glasses. ML-BOP accurately reproduces the experimental radial distribution function of LDA but overpredicts the minimum between the first two shells in high-density glasses. We examine the kinetics and mechanism of the transformation between low-density and high-density glasses and find that the sharp nature of these transitions in ML-BOP is similar to that in experiments and all-atom water models with a liquid-liquid transition. Transitions between ML-BOP glasses occur through a spinodal-like mechanism, similar to ice crystallization from LDA. Both glass-to-glass and glass-to-ice transformations have Avrami-Kolmogorov kinetics with exponent n = 1.5 ± 0.2 in experiments and simulations. Importantly, ML-BOP reproduces the competition between crystallization and HDA→LDA transition above the glass transition temperature Tg, and separation of their time scales below Tg, observed also in experiments. These findings demonstrate the ability of ML-BOP to accurately reproduce water properties across various regimes, making it a promising model for addressing the competition between polyamorphic transitions and crystallization in water and solutions.

Correlated Fluctuations of Structural Indicators Close to the Liquid-Liquid Transition in Supercooled Water.

Multiple numerical studies have unambiguously shown the existence of a liquid-liquid critical point in supercooled states for different numerical models of water, and various structural indicators have been put forward to describe the transformation associated with this phase transition. Here we analyze numerical simulations of near-critical supercooled water to compare the behavior of several of such indicators with critical density fluctuations. We show that close to the critical point most indicators are strongly correlated to density, and some of them even display identical distributions of fluctuations. These indicators probe the exact same free energy landscape, therefore providing a thermodynamic description of critical supercooled water which is identical to that provided by the density order parameter. This implies that close to the critical point, there is a tight coupling between many, only apparently distinct, structural degrees of freedom.

Predictions for the properties of water below its homogeneous crystallization temperature revisited

Properties of liquid water supercooled below its melting point have been thoroughly investigated. Experiments on bulk water become increasingly difficult as the temperature is lowered, and eventually impossible when the delay before ice nucleation becomes too short, around 230 K at ambient pressure. At low temperatures, amorphous ices and their glass transition may be studied only below the temperature of crystallization during heating, around 150 K. The temperature range from around 150 to 230 K at ambient pressure thus appears as a no man's land where the properties of bulk water are not accessible. Following Austen Angell's footsteps, I provide here physically acceptable predictions for thermodynamic properties (heat capacity, entropy) of liquid water down to its glass transition, and use the Adam-Gibbs approach to predict its dynamic properties (shear viscosity, self-diffusion coefficient, rotational correlation time). • The Adam-Gibbs relation between entropy and dynamic properties is applied to water. • The entropy of supercooled water is described with a modified two-state model. • We predict viscosity, diffusion, and rotational time down to the glass transition. • The results are consistent with a fragile-to-strong transition in supercooled water.

Comment to “Dynamics of supercooled confined water measured by deep inelastic neutron scattering”

We comment on the findings of “Dynamics of supercooled confined water measured by deep inelastic neutron scattering”, by V. De Michele, G. Romanelli, and A. Cupane [Front. Phys. 13, 138205 (2018)]. We show that the current sensitivity of the deep inelastic neutron scattering (DINS) method, cannot detect with confidence small differences in the proton kinetic energy, Ke(H), involved in a liquid-liquid transition in supercooled water confined in nanoporous silica. We also critisize the calculation of Ke(H) carried out in Front. Phys. 13, 138205 (2018).

Surface tension of supercooled water nanodroplets from computer simulations.

We estimate the liquid-vapor surface tension from simulations of TIP4P/2005 water nanodroplets of size N = 100 to 2880 molecules over a temperature T range of 180 K-300 K. We compute the planar surface tension γp, the curvature-dependent surface tension γs, and the Tolman length δ, via two approaches, one based on the pressure tensor (the "mechanical route") and the other on the Laplace pressure (the "thermodynamic route"). We find that these two routes give different results for γp, γs, and δ although in all cases, we find that δ ≥ 0 and is independent of T. Nonetheless, the T dependence of γp is consistent between the two routes and with that of Vega and de Miguel [J. Chem. Phys. 126, 154707 (2007)] down to the crossing of the Widom line at 230 K for ambient pressure. Below 230 K, γp rises more rapidly on cooling than predicted from behavior for T ≥ 300 K. We show that the increase in γp at low T is correlated with the emergence of a well-structured random tetrahedral network in our nanodroplet cores and thus that the surface tension can be used as a probe to detect behavior associated with the proposed liquid-liquid phase transition in supercooled water.

The stability-limit conjecture revisited.

The stability-limit conjecture (SLC) proposes that the liquid spinodal of water returns to positive pressure in the supercooled region and that the apparent divergence of water's thermodynamic response functions as temperature decreases are explained by the approach to this re-entrant spinodal. Subsequently, it has been argued that the predictions of the SLC are inconsistent with general thermodynamic principles. Here, we reconsider the thermodynamic viability of the SLC by examining a model equation of state for water which was first studied to clarify the relationship of the SLC to the proposed liquid-liquid phase transition in supercooled water. By demonstrating that a binodal may terminate on a spinodal at a point that is not a critical point, we show that the SLC is thermodynamically permissible in a system that has both a liquid-gas and a liquid-liquid phase transition. We also describe and clarify other unusual thermodynamic behavior that may arise in such a system, particularly that associated with the so-called "critical-point-free" scenario for a liquid-liquid phase transition, which may apply to the case of liquid Si.

Water Is a Cagey Liquid.

Liquid water is considered poorly understood. How are water's physical properties encoded in its molecular structure? We introduce a statistical mechanical model (CageWater) of water's hydrogen-bonding (HB) and Lennard-Jones (LJ) interactions. It predicts the energetic and volumetric and anomalous properties accurately. Yet, because the model is analytical, it is essentially instantaneous to compute. This model advances our understanding beyond current molecular simulations and experiments. Water has long been regarded as a "2-density liquid": a dense LJ liquid and a looser HB one. Instead, we find here a different antagonism underlying water structure-property relations: HBs in water-water pairs drive density, while HBs in cooperative cages drive openness. The balance shifts strongly with temperature and pressure. This model interprets the molecular structures underlying the liquid-liquid phase transition in supercooled water. It may have value in geophysics, biomolecular modeling, and engineering of materials for water purification and green chemistry.

Origin of the emergent fragile-to-strong transition in supercooled water

Liquids can be broadly classified into two categories, fragile and strong ones, depending on how their dynamical properties change with temperature. The dynamics of a strong liquid obey the Arrhenius law, whereas the fragile one displays a super-Arrhenius law, with a much steeper slowing down upon cooling. Recently, however, it was discovered that many materials such as water, oxides, and metals do not obey this simple classification, apparently exhibiting a fragile-to-strong transition far above [Formula: see text] Such a transition is particularly well known for water, and it is now regarded as one of water's most important anomalies. This phenomenon has been attributed to either an unusual glass transition behavior or the crossing of a Widom line emanating from a liquid-liquid critical point. Here by computer simulations of two popular water models and through analyses of experimental data, we show that the emergent fragile-to-strong transition is actually a crossover between two Arrhenius regimes with different activation energies, which can be naturally explained by a two-state description of the dynamics. Our finding provides insight into the fragile-to-strong transition observed in a wide class of materials.

CDW and Similarity of the Mott Insulator-to-Metal Transition in Cuprates with the Gas-to-Liquid-Liquid Transition in Supercooled Water

New advances in X-ray diffraction, extended X-ray absorption fine structure (EXAFS), and X-ray absorption near edge structure (XANES) using synchrotron radiation have now provided compelling evidence for a short-range charge density wave phase (CDW) called striped phase in the CuO2 plane of all cuprate high-temperature superconductors. The CDW is associated with a bond order wave (BOW) and an orbital density wave (ODW) forming nanoscale puddles which coexist with superconducting puddles below T c . The electronic CDW crystalline phase occurs around the hole doping 0.125 between the Mott charge transfer insulator and the 2D metal. The Van der Waals (VdW) theoretical model for a liquid of anisotropic extended objects proposed for supercooled water is used to describe the following: (a) the underdoped regime as a first spinodal regime of a “slightly doped charge transfer Mott insulator puddles coexisting with the striped polaronic CDW puddles;nd (b) the optimum doping regime as a second spinodal regime where striped polaronic CDW puddles coexist with the normal 2D metal puddles. This complex phase separation with three competing phases depends on the strength of the anisotropic electron-phonon interaction that favours the formation striped polaronic CDW phase.

Liquid–liquid transition in supercooled water suggested by microsecond simulations

The putative liquid-liquid phase transition in supercooled water has been used to explain many anomalous behaviors of water. However, no direct experimental verification of such a phase transition has been accomplished, and theoretical studies from different simulations contradict each other. We investigated the putative liquid-liquid phase transition using the Water potential from Adaptive Force Matching for Ice and Liquid (WAIL). The simulation reveals a first-order phase transition in the supercooled regime with the critical point at ~207 K and 50 MPa. Normal water is high-density liquid (HDL). Low-density liquid (LDL) emerges at lower temperatures. The LDL phase has a density only slightly larger than that of the ice-Ih and shows more long-range order than HDL. However, the transformation from LDL to HDL is spontaneous across the first-order phase transition line, suggesting the LDL configuration is not poorly formed nanocrystalline ice. It has been demonstrated in the past that the WAIL potential provides reliable predictions of water properties such as melting temperature and temperature of maximum density. Compared with other simple water potentials, WAIL is not biased by fitting to experimental properties, and simulation with this potential reflects the prediction of a high-quality first-principle potential energy surface.

Phase Transition of Nanoconfined Water in Clay: Positron Annihilation, Nuclear Magnetic Resonance, and Dielectric Relaxation Studies

The structural and dynamical features associated with the phase behavior of water confined in clay nanopores (2D confined water) are studied using positron annihilation spectroscopy, nuclear magnetic resonance, and dielectric relaxation spectroscopy techniques. We report the experimental evidence of a new phase transition (above the bulk freezing point of water) in nanoconfined water, in addition to a low-temperature transition in supercooled water. The study reveals it to be a structural rearrangement of water molecules associated with modification of hydrogen-bonded network. Evidence also suggests the dynamical arrest/immobilization of water layer near the clay platelet surface (bound water molecules) to be associated with this transition. This transition is a manifestation of the role of surface interaction on the phase behavior of confined liquids.

The putative liquid-liquid transition is a liquid-solid transition in atomistic models of water

We use numerical simulation to examine the possibility of a reversible liquid-liquid transition in supercooled water and related systems. In particular, for two atomistic models of water, we have computed free energies as functions of multiple order parameters, where one is density and another distinguishes crystal from liquid. For a range of temperatures and pressures, separate free energy basins for liquid and crystal are found, conditions of phase coexistence between these phases are demonstrated, and time scales for equilibration are determined. We find that at no range of temperatures and pressures is there more than a single liquid basin, even at conditions where amorphous behavior is unstable with respect to the crystal. We find a similar result for a related model of silicon. This result excludes the possibility of the proposed liquid-liquid critical point for the models we have studied. Further, we argue that behaviors others have attributed to a liquid-liquid transition in water and related systems are in fact reflections of transitions between liquid and crystal.

Liquid-liquid transition in supercooled water investigated by interaction with LiCl and Xe

The hypothesis that supercooled water consists of two distinct liquid phases has been explored on the basis of their ability to hydrate nonpolar (Xe) and electrolytic (LiCl) species. Xe incorporated in the bulk of amorphous solid water survives in the deeply supercooled regime above the glass-transition temperature of 136 K and is finally dehydrated at 165 K, whereas LiCl dissolves only in the liquid phase appearing above 165 K. The second liquid phase connects with normal water as inferred from high (poor) solubility of LiCl (Xe). This result also suggests that decoupling of translational diffusion and viscosity in the deeply supercooled regime is caused by domain structures of the two liquid phases formed during a possible liquid-liquid transition.

Theoretical Studies on the Structure and Dynamics of Water, Ice, and Clathrate Hydrate

Abstract We have investigated various anomalous properties of water such as the divergent character of the thermodynamic functions and liquid–liquid transition in supercooled water, the phase behaviors of water and new ices in nanoscale confinement, the thermodynamic stability of clathrate hydrates over a wide range of pressure, and anomalous thermodynamic and structural properties of ices. These are studied by some theoretical calculations and Monte Carlo/molecular dynamics computer simulations. It is demonstrated that the potential energy surface and the connectivity of supercooled water are keys to understand why liquid–liquid transition can take place in deeply supercooled water. A tetrahedral coordination of water is preserved even in extreme confinements, forming tubule ice and bilayer crystalline (or amorphous) ice, although the heavy stress makes the bond angles and lengths different from the ideal values. Thermodynamic stability of clathrate hydrates, including double occupancy, is more accurately predicted by considering the host–guest coupling and other factors. The negative thermal expansivity and the change in slope of the Debye–Waller factor of ice are explained with a simple model of water.

A Simple Statistical Mechanical Model of Water

We introduce a statistical mechanical model for the physical properties of water. Each water molecule is a two-dimensional disk with three radial hydrogen-bonding arms. Energetic interactions are based on water triplets, a central water molecule interacting with two neighbors via hydrogen bonds, van der Waals attractions, and steric repulsions. Interactions with more distant molecules are treated in a mean-field way. Each molecular triplet can be in one of three energy levels: cage-like hydrogen-bonded structures, denser nonbonded structures, and expanded structures with no near-neighbor interactions. The model predicts water's thermodynamic anomalies, including maxima in density, minima in isothermal compressibility and heat capacity, and expansion upon freezing at low pressure. It predicts the main features of water's phase diagram, including multiple crystalline phases and the proposed liquid−liquid transition in supercooled water. Also, it captures qualitatively the fragile-to-strong transition in the liquid's temperature-dependent relaxation processes. This model is intended to give simple insights into the microscopic origins of water's distinctive physical properties.

Curvature effect on the physical boundary of metastable states in liquids

The physical boundary of metastable states, the kinetic spinodal, is introduced as a locus where the lifetime of metastable state becomes shorter than a relaxation time to local equilibrium. The theory does not contain any adjustable parameters. If the surface tension is known, the kinetic spinodal is completely determined by the equation of state only. The curvature effect on the surface tension and nucleation barrier is considered and a general, curvature-corrected, equation for the kinetic spinodal is developed. The theory was tested against experimental data for the homogeneous nucleation limit of superheated, stretched, and supercooled water. In all cases, good agreement between theoretical predictions and experimental data was achieved. We find that in water, the Tolman length is negative and the curvature effect increases the surface tension and the nucleation barrier. The glass transition in supercooled water is also discussed. The high-temperature limit for glassy states is introduced as a second root of the kinetic equation in supercooled fluids.

A New Interpretation of Anomalous Properties of Water Based on Stillinger's Postulate

An attempt has been made to interpret the anomalous properties of supercooled water in a unified way by using Stillinger's postulate that the formation of bulky clathrate-like local structures is the main cause of the anomalous thermodynamic and transport properties exhibited by liquid water at low temperatures. Comparison of the thermodynamic properties of liquid water, tellurium, and sulfur suggests the existence of a λ-like Cp transition in supercooled water below TH (but above TK). It is inferred that the diverging trends of various anomalous properties with lowering temperature are preserved up to high pressures (<200 MPa) due to premature ice crystallization which conceals the expected extrema (e.g., a λ-like Cp transition) of thermodynamic properties from observation.

Thermodynamic determination of fragility in liquids and a fragile-to-strong liquid transition in water

If crystallization can be avoided when a liquid is cooled, it will typically form a glass. Near the glass transition temperature the viscosity increases continuously but rapidly with cooling. As the glass forms, the molecular relaxation time increases with an Arrhenius-like (simple activated) form in some liquids, but shows highly non-Arrhenius behaviour in others. The former are said to be ‘strong’ liquids, and the latter ‘fragile’1,2. Here we show that the fragility of a liquid can be determined from purely thermodynamic data (as opposed to measurements of kinetics) near and below the melting point. We find that for most liquids the fragilities estimated this way are consistent with those obtained by previous methods and by a new method (ref. 3 and K.I., C.A.A. and C.T.M., unpublished data) at temperatures near the glass transition. But water is an exception. The thermodynamic method indicates that near its melting point it is the most fragile of all liquids studied, whereas the kinetic approach indicates that near the glass transition it is the least fragile. We propose that this discrepancy can be explained by a fragile-to-strong transition in supercooled water near 228 K, corresponding to a change in the liquid's structure at this point.

水に二状態が存在する！？

Water has two amorphous solid states at low temperatures: the low-density and high-density amorphous ices. These two amorphous solids may be related to liquid water at high temperatures. We review experiments and simulations on liquid and amorphous solid water, and discuss the possibility of the existence of a liquid-liquid phase transition in supercooled water.