Supercooled and glassy water: Metastable liquid(s), amorphous solid(s), and a no-man's land

We review the recent research on supercooled and glassy water, focusing on the possible origins of its complex behavior. We stress the central role played by the strong directionality of the water-water interaction and by the competition between local energy, local entropy, and local density. In this context we discuss the phenomenon of polyamorphism (i.e., the existence of more than one disordered solid state), emphasizing both the role of the preparation protocols and the transformation between the different disordered ices. Finally, we present the ongoing debate on the possibility of linking polyamorphism with a liquid-liquid transition that could take place in the no-man's land, the temperature-pressure window in which homogeneous nucleation prevents the investigation of water in its metastable liquid form

Link between the diversity, heterogeneity and kinetic properties of amorphous ice structures

Based on neutron wide-angle diffraction and small-angle neutron scattering experiments, we show that there is a correlation between the preparational conditions of amorphous ice structures, their microscopic structural properties, the extent of heterogeneities on a mesoscopic spatial scale and the transformation kinetics. There are only two modifications that can be identified as homogeneous disordered structures, namely the very high-density vHDA and the low-density amorphous LDA ice. Structures showing an intermediate static structure factor with respect to vHDA and LDA are heterogeneous phases. This holds independently from their preparation procedure, i.e. either obtained by pressure amorphisation of ice I_h or by heating of vHDA. The degree of heterogeneity can be progressively suppressed when higher pressures and temperatures are applied for the sample preparation. In accordance with the suppressed heterogeneity the maximum of the static structure factor displays a pronounced narrowing of the first strong peak, shifting towards higher Q-numbers. Moreover, the less heterogeneous the obtained structures are the slower is the transformation kinetics from the high--density modifications into LDA. The well known high-density amorphous structure HDA does not constitute any particular state of the amorphous water network. It is formed due to the preparational procedure working in liquid nitrogen as thermal bath, i.e. at about 77 K

Pressure-induced transformations in LiCl–H2O at 77 K

A systematic study of the properties of high-density amorphous ice (HDA) in the presence of increasing amounts of salt is missing, especially because it is challenging to avoid ice crystallization upon cooling the pressurized liquid. In order to be able to study HDA also in the presence of small amounts of salt, we have investigated the transformation behaviour of quenched aqueous LiCl solutions (mole fraction x 1 GPa. The observed densification is consistent with the idea that a freeze concentrated LiCl solution of x = 0.14 (R = 6) segregates, which transforms to the glassy state upon cooling, and that the densification is only due to the Ih → HDA transition. Also the XRD patterns and DSC scans are almost unaffected by the presence of the segregated glassy LiCl solution. Upon heating at ambient pressure HDA experiences the polyamorphic transition to low-density amorphous ice (LDA) at ∼120 K, even at x ∼ 0.10. Based on the latent heat evolved in the transition we suggest that almost all water in the sample transforms to an LDA-like state, even the water in the vicinity of the ions. The glassy LiCl solution acts as a spectator that does not shift the transformation temperature significantly and experiences a glass-to-liquid transition at ∼140 K prior to the crystallization to cubic ice. By contrast, at x > 0.12 the phenomenology completely changes and is now dominated by the salt. Hexagonal ice no longer forms upon quenching the LiCl solution, but instead LDA forms. A broad pressure-induced transformation at >0.6 GPa can be attributed to the densification of LDA, the glassy LiCl solution and/or glassy hydrates.Fil: Ruiz, G. N.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Innsbruck; AustriaFil: Bove, L. E.. Universite Pierre et Marie Curie; Francia. Ecole Polytechnique Federale de Lausanne; SuizaFil: Corti, Horacio Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Loerting, T.. Universidad de Innsbruck; Austri

Structure of a new dense amorphous ice

The detailed structure of a new dense amorphous ice, VHDA, is determined by isotope substitution neutron diffraction. Its structure is characterized by a doubled occupancy of the stabilizing interstitial location that was found in high density amorphous ice, HDA. As would be expected for a thermally activated unlocking of the stabilizing "interstitial," the transition from VHDA to LDA (low-density amorphous ice) is very sharp. Although its higher density makes VHDA a better candidate than HDA for a physical manifestation of the second putative liquid phase of water, as for the HDA case, the VHDA to LDA transition also appears to be kinetically controlled

Calorimetric study of water's two glass transitions in the presence of LiCl

A DSC study of dilute glassy LiCl aqueous solutions in the water-dominated regime provides direct evidence of a glass-to-liquid transition in expanded high density amorphous (eHDA)-type solutions. Similarly, low density amorphous ice (LDA) exhibits a glass transition prior to crystallization to ice Ic. Both glass transition temperatures are independent of the salt concentration, whereas the magnitude of the heat capacity increase differs. By contrast to pure water, the glass transition endpoint for LDA can be accessed in LiCl aqueous solutions above 0.01 mole fraction. Furthermore, we also reveal the endpoint for HDA's glass transition, solving the question on the width of both glass transitions. This suggests that both equilibrated HDL and LDL can be accessed in dilute LiCl solutions, supporting the liquid-liquid transition scenario to understand water's anomalies.Fil: Ruiz, Guadalupe N.. Universidad de Innsbruck; Austria. Universidad Politécnica de Catalunya; EspañaFil: Amann Winkel, Katrin. AlbaNova University Center; Suecia. Universidad de Innsbruck; AustriaFil: Bove, Livia E.. Université Pierre et Marie Curie; FranciaFil: Corti, Horacio Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad de Buenos Aires; ArgentinaFil: Loerting, Thomas. Universidad de Innsbruck; Austri

Vibrational Features of Water at the Low-Density/High-Density Liquid Structural Transformations

A structural transformation in water upon compression was recently observed at the temperature $T=277$~K in the vicinity of the pressure $p \approx 2\;000$~Atm [R.M. Khusnutdinoff, A.V. Mokshin, J. Non-Cryst. Solids \textbf{357}, 1677 (2011)]. It was found that the transformations are related with the principal structural changes within the first two coordination shells as well as the deformation of the hydrogen-bond network. In this work we study in details the influence of these structural transformations on the vibrational molecular dynamics of water by means of molecular dynamics simulations on the basis of the model Amoeba potential ($T=290$~K, $p=1.0 \div 10\;000$~Atm). The equation of state and the isothermal compressibility are found for the considered ($p$,$T$)-range. The vibrational density of states extracted for $THz$-frequency range manifests the two distinct modes, where the high-frequency mode is independent on pressure whereas the low-frequency one has the strong, non-monotonic pressure-dependence and exhibits a step-like behavior at the pressure $p \approx 2000$~Atm. The extended analysis of the local structural and vibrational properties discovers that there is a strong correlation between the primary structural and vibrational aspects of the liquid-liquid structural transformation related with the molecular rearrangement within the range of the second coordination shell.Comment: Accepted to Physica A: Statistical Mechanics and its Application

Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water

Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature Tg. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of Tg(P) for LDA and HDA by performing computer simulations of two water models – one with a LLPT, and one without. In the absence of a LLPT, Tg(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different Tg(P) which are directly linked with the LLPT. Available experimental data for Tg(P) are only consistent with the scenario including a LLPT

Glass transition of LiCl aqueous solutions confined in mesoporous silica

The thermal transitions of confined LiCl aqueous solutions were studied by differential scanning calorimetry for solutions with salt concentrations with eutectic (R = 7) and subeutectic (R > 7) compositions (R = moles of water/moles of LiCl). The confinement media consist of mesoporous silica with pore diameters between 2 nm and 58 nm, with a small negative surface charge density. The vitrification of confined LiCl aqueous solutions was observed in all samples, expanding the vitrification region up to R = 15, and probably beyond for cooling rates of ≈1000 K/min. Ice crystallization was observed in some samples, except for those confined in the narrower pores. The onset and endpoint glass transition temperatures for the confined eutectic samples increase by 2 K and 5 K, respectively, for the smallest pore diameters (2 nm), which is equivalent to the effect of applying a pressure of up to 100 MPa to the bulk sample. This behavior is opposite of that reported for aqueous subeutectic NaCl solutions confined in silica glasses of similar sizes. We speculate that this is due to the fact that the mechanism of double confinement of the NaCl solution, between the pore wall and the precipitated ice, is not operative for LiCl solutions. Instead, the Li+ ions might force the hydration water in to a high-density state.Fil: Longinotti, María Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Fuentes Landete, Violeta. Universidad de Innsbruck; AustriaFil: Loerting, Thomas. Universidad de Innsbruck; AustriaFil: Corti, Horacio Roberto. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin