Water Electrolytes Solutions in Extreme Conditions

This project is an ambitious program to explore the stable and metastable phases of common (LiCl, NaCl, KCl) electrolyte water solutions which are relevant for many fields in science, ranging from cryobiology to planetary science, in regions up to now inaccessible to current techniques. In particular, we propose to characterize water`s polyamorphous phases (Kohl, Loerting et al., Nature 2005) in dilute solutions at moderate pressure (kbar), and the recently discovered crystalline phases developed under high pressure (GPa=10kbar) in concentrated solutions (Klotz, Bove et al. Nature Material 2009). An important and innovative part of this project will be devoted to the development of new, complementary and unique methods to characterize the thermodynamic behavior, the microscopic structure, the proton diffusion, and the dielectric and conductivity properties of these systems. The goal of our project is twofold: -to characterize the thermodynamic and structural behavior of dilute solutions as well as their relaxation times, as a function of increasing dilution and pressure, in order to access the properties of undercooled and glassy water in the vicinity of the glass transition. We will enter this region, inaccessible to experiments (no men`s land), by the use of unique methods developed by our team, as hyperquenching (cooling rates fast enough to hinder ice nucleation) and pressure-induced amorphisation, and we will then shed light on one of the fundamental issues in condensed matter physics: the link between liquid-liquid transition and polyamorphism in water (Giovambattista, Loerting et al., Nature Scientific Reports 2012). - to search for the existence of crystalline ice forms highly loaded with ionic species of astrophysical relevance and to characterize their new exotic properties, like the expected superionicity, a novel spectacular state of matter predicted to appear in water under extreme conditions (Cavazzoni et al., Science 1999) where the proton delocalizes and the crystalline system shows a `liquid behaviour` concerning the proton diffusivity thus acting as a proton super-conductor. These challenging conditions will be accessible, in salty ices, to the novel experimental techniques and methodology we propose to develop. Various studies support the presence of high-pressure ice polymorphs in the interior of Galilean satellites such as Ganymede, Europa and Calisto, as well as Saturn`s Titan, and there is strong evidence of subsurface salty ice crusts in some of them. If ice forms highly loaded with salts exist in nature in significant quantity, with most likely exotic properties, such as the described superionicity, their characterization would be highly relevant for the understanding of icy bodies in the Universe

Water is ubiquitous, and yet its properties are far from being understood. It differs from other liquids in many ways more than 70 anomalous properties that make water outstanding are known today. These anomalous properties become especially pronounced in its supercooled state below 0C. One of the most fascinating, yet contested, anomalies is the possibility of supercooled liquid water to spontaneously separate into two distinct types of liquid water, a low-density liquid (LDL) and a high-density liquid (HDL). In aqueous solutions these anomalies may persist or be suppressed, depending on what the solute is and how much of it is dissolved in water. In the project Water Electrolytes Solutions in Extreme Conditions we have studied supercooled water, typically at temperatures below -100C, and investigated the properties of these liquids in bulk water and in the presence of a range of solutes, including salts (NaCl, LiCl), alcohols (glycerol), sugars (sucrose, trehalose), drugs (prilocaine, proteins) or gases (CO2). The influence of dopants and isotope substitution has been crucial to understand the structure and dynamics of supercooled solutions on the molecular level. Key findings include an understanding of the competition between liquid-like relaxation, ice nucleation and crystal growth in these solutions. This understanding has allowed us to study supercooled water at higher temperature than ever before without ice crystallization interfering. Based on that we were able to show that water may indeed appear as two liquids at cryo-conditions. These liquids are fundamentally different they do not only differ by 25% in terms of density, but also significantly in terms of their molecular dynamics, where HDL is characterized by faster molecular movements. Hence, HDL remains in the liquid state down to lower temperatures than LDL. Molecular movement then ceases, resulting in an arrest of the molecular structure, turning the liquid into a glassy state often called amorphous ice. The glass transition temperature of HDL was revealed in our work to be -157C, about 20 degrees lower than for LDL. Above the glass transition temperature molecular motion unfreezes again where we were able to show that the molecules not only start to rotate, but experience diffusion, making them able to cover long distances, as it is typical of liquids. We were able to demonstrate that HDL can persist up to pressures of 3000 bar, above which the diffusive motion can no longer take place because of ice crystallization being too rapid. Also the crystalline states formed under pressure turned out to be intriguing, and to differ from known ice phases. Most notably, the type of hydrogen-ordering differs and so we were able to discover a novel ice phase, called ice ß-XV, that has unprecedented properties. It is the first ice form that undergoes a transition from one hydrogen-ordered phase to another hydrogen-ordered phase.