Anomalies Of Supercooled Water Research Articles

Absence of the liquid-liquid phase transition in aqueous ionic liquids.

The anomalies of supercooled water may be explained by an underlying liquid-liquid phase transition (LLPT) between high- and low-density states. Recently, its observation at 185 K was inferred using solutions containing aqueous ionic liquids at a solute mole fraction of x=0.156 [Woutersen et al., Science 359, 1127 (2018)10.1126/science.aao7049]. We employ x-ray diffraction, calorimetry, and dilatometry on these hydrazinium trifluoroacetate solutions at x=0.00-0.40 to show that the transition at 185 K is not related to a genuine LLPT of water. Continuous densification upon compression, continuous changes of halo position, and absence of thermal signatures for a high- to low-density transition rule out the possibility of an LLPT for x≥0.13. The data show that employing sophisticated solutions adds a layer of complexity that hampers extrapolation of the LLPT concept from one- to two-component systems. The possibility of an LLPT can only be probed for pure water or sufficiently dilute aqueous solutions.

Anomalies in Supercooled Water at ∼230 K Arise from a 1D Polymer to 2D Network Topological Transformation.

Puzzling anomalous properties of water are drastically enhanced in the supercooled region. However, the nature of these anomalies is not known. We report here molecular dynamics simulations using the RexPoN force field from 298 to 200 K along the 1 atm density curve. At 298 K, there are 2.1 strong hydrogen bonds (SHBs), leading to a dynamic branched one-dimensional (1D) polymer. Water remains 1D down to 240 K, but at and below 230 K, the number of SHBs becomes 3.0, leading to a two-dimensional (2D) network that persists to 200 K. We propose that this 1D-to-2D topological transition accounts for the anomalous properties of supercooled water. Near 230 K, the power spectra show dramatic increases in the angular vibrational frequency modes, while the diffusivity decreases dramatically, both arising from the 1D-to-2D transformation. This transition is not first order because free energy changes uniformly but fluctuations in the entropy near 230 K suggest a possible second-order transition.

Statistical mechanics of high-density bond percolation

High-density (HD) percolation describes the percolation of specific κ-clusters, which are the compact sets of sites each connected to κ nearest filled sites at least. It takes place in the classical patterns of independently distributed sites or bonds in which the ordinary percolation transition also exists. Hence, the study of series of κ-type HD percolations amounts to the description of classical clusters' structure for which κ-clusters constitute κ-cores nested one into another. Such data are needed for description of a number of physical, biological, and information properties of complex systems on random lattices, graphs, and networks. They range from magnetic properties of semiconductor alloys to anomalies in supercooled water and clustering in biological and social networks. Here we present the statistical mechanics approach to study HD bond percolation on an arbitrary graph. It is shown that the generating function for κ-clusters' size distribution can be obtained from the partition function of the specific q-state Potts-Ising model in the q→1 limit. Using this approach we find exact κ-clusters' size distributions for the Bethe lattice and Erdos-Renyi graph. The application of the method to Euclidean lattices is also discussed.

String-like propagation of the 5-coordinated defect state in supercooled water: molecular origin of dynamic and thermodynamic anomalies

We find that at low temperature water, large amplitude (~60°) rotational jumps propagate like a string, with the length of propagation increasing with lowering temperature. The strings are formed by mobile 5-coordinated water molecules which move like a Glarum defect (J. Chem. Phys., 1960, 33, 1371), causing water molecules on the path to change from 4-coordinated to 5-coordinated and again back to 4-coordinated water, and in the process cause the tagged water molecule to jump, by following essentially the Laage-Hynes mechanism (Science, 2006, 311, 832-835). The effects on relaxation of the propagating defect causing large amplitude jumps are manifested most dramatically in the mean square displacement (MSD) and also in the rotational time correlation function of the O-H bond of the molecule that is visited by the defect (transient transition to the 5-coordinated state). The MSD and the decay of rotational time correlation function, both remain quenched in the absence of any visit by the defect, as postulated by Glarum long time ago. We establish a direct connection between these propagating events and the known thermodynamic and dynamic anomalies in supercooled water. These strings are found largely in the regions that surround the relatively rigid domains of 4-coordinated water molecules. The propagating strings give rise to a noticeable dynamical heterogeneity, quantified here by a sharp rise in the peak of the four-point density response function, χ(4)(t). This dynamics heterogeneity is also responsible for the breakdown of the Stokes-Einstein relation.

Relation between structural and dynamical anomalies in supercooled water

We step toward the elucidation of the relation between the structural and dynamic anomalies in supercooled water. We present the results of molecular dynamics simulations of the extended simple point charge (SPC/E) model of water for the translational and rotational diffusion and for the number of neighbors and hydrogen bonds. We find that the product of diffusion coefficient and relaxation time is nearly constant. The coupling between the two mobilities is explained in the framework of the structural anomalies.

Anomalous Contact-Ion Pairing in the Glassy States of “Dilute” Aqueous Lithium and Sodium Perchlorate Solution

Aqueous D2O solutions of lithium (0.5, 1, and 3 M) and sodium (1 and 3 M) perchlorate have been studied by FT-IR spectroscopy in their glassy states at 80 K, and their IR spectra compared with those of 1.0 M D2O solutions recorded from 300 to 235 K. Evidence for strongly increasing contact-ion pairing in going from ambient temperature to the glassy state is based on the development of a second band in the ν1 band region centered at high frequency of the band from “free” perchlorate and complete loss of degeneracy in the ν3 and ν4 band region. On the basis of curve resolution of the ν1 band region, increasing contact-ion pairing is much more pronounced for sodium than for lithium perchlorate. The spectral features of contact-ion paired perchlorate are consistent with at most C2v symmetry with bidentate binding. Anomalous increase in contact-ion pairing on hyperquenching into the glassy state is attributed to water's density maximum and the anomalies of supercooled water and “dilute” aqueous solutions. Spectral features of ion-pairing are weakly observable already at 300 K in the ν1 and ν3 band region and become more pronounced on cooling to 235 K. Significance of the results is discussed with respect to (i) differences in local geometry of contact-ion pairs in aprotic donor solvents, (ii) vapor-deposited alkali metal perchlorates isolated in a water matrix, (iii) thermodynamic continuity of states between vapor-deposited amorphous water, hyperquenched glassy water and normal supercooled water, and (iv) cryofixation of polyelectrolyte-type biomolecules such as nucleic acid sodium salts.

Phase Diagram for Supercooled Water.

Molecular dynamics simulations have been carried out at constant pressure and temperature to examine phase behaviors of supercooled water. The anomalies of supercooled water in thermodynamic response functions at atmospheric pressure, the phase transition between low and high density liquids and a fragile-strong transition are accounted for by reconciling an idea introducing a second critical point separating two liquid states with a conjecture that low temperature state is a different phase from normal water.

Phase behaviors of supercooled water: Reconciling a critical point of amorphous ices with spinodal instability

The anomalies of supercooled water in thermodynamic response functions at atmospheric pressure, the phase transition between low and high density amorphous ices (LDA and HDA), and a predicted fragile–strong transition are accounted for in a unified manner by reconciling an idea due to Stanley and co-workers introducing a second critical point separating LDA and HDA ices with a conjecture proposed by Speedy that LDA is a different phase from a normal water, called water II. The reconciliation is made on the basis of results from extensive molecular dynamics simulations at constant pressure and temperature. It is found that there exist large gaps around temperature 213 K in thermodynamic, structural, and dynamic properties at atmospheric pressure, suggesting liquid–liquid phase transition. This transition is identified with an extension of the experimentally observed LDA–HDA transition in high pressure to atmospheric pressure. Thus, we propose a new phase diagram where the locus of the second critical point is moved into negative pressure region. With this simple modification, it becomes possible to account for the divergence of the thermodynamic response functions at atmospheric pressure in terms of the critical point and the spinodal-like instability of HDA. The unstable HDA undergoes a transition to LDA phase in lower temperature. The transition is also observed in high pressure region such as 200 MPa while it disappears at negative pressure, −200 MPa. This reinforces our proposed phase diagram in which there is no continuous path from a supercooled state to LDA at atmospheric pressure. It is argued that the HDA–LDA transition is accompanied by a fragile–strong transition. A possible mechanism of avoiding crystallization of aqueous solutions is also discussed in terms of a difference in hydrogen bond number distribution between LDA and HDA.

Pressure Dependence of the OH‐Stretch Raman Spectra of Supercooled Water

AbstractRaman spectra of the OH‐stretching region of liquid H2O and 10% H in D2O have been obtained between −50 and + 100°C at pressures up to 240 MPa, extending into the deeply supercooled region. Application of pressure made it possible to study liquid water at temperatures 20 K lower than reported so far.The low‐frequency shoulder of the H2O‐spectra grows rapidly with falling temperature. The relative intensity of the collective band increases monotonically to the lowest temperatures studied.Supercooled water shows a number of thermodynamic and transport anomalies, which become apparent from the unusual p‐, T‐dependence of the compressibility and the molecular mobility in the pressure range between 0 and 200 MPa. The Raman spectra, however, do not change significanctly in this pressure region. At the lowest temperatures they are practically independent of pressure.This finding suggests that the intensity of the collective Raman band originates from short range correlations of the OH‐bond vibrations, that are not identical to the more extended density fluctuations responsible for the well known anomalies of supercooled water.

The Random Graph Model of Hydrogen Bond Network

Abstract A new lattice model of liquid water is developed. The hydrogen bond network is represented by the Ising variables with the method similar to the one used in combinatorial problems in random graph. Thermodynamic properties of the model are studies with the mean-field approximation. Phase diagram, density maximum, and anomalies of supercooled water are discussed. Dynamical properties are also investigated by using the coupled-map-dynamics method. Energy fluctuation is shown to have 1/f like long time correlation. The network structural rearrangement takes place collectively in localized regions.

Lifetime of the bond network and gel-like anomalies in supercooled water.

We analyze the distribution of bond lifetimes in simulations of liquid water using a novel bond definition. We find that the characteristic lifetimes of the bonds and of the ``gel'' network itself both increase strongly when temperature is decreased\char21{}and even appear to diverge at a temperature well below the freezing temperature\char21{}thereby providing an appealing physical picture of the anomalous behavior of water in the supercooled region.