Sudden switchover between the polyamorphic phase separation and the glass-to-liquid transition in glassy LiCl aqueous solutions

Abstract

Lithium chloride aqueous solutions (LiClaq solutions) below 10 mol.% are vitrified by cooling from room temperature to 77 K at 0.3 GPa. We examine the solvent state of the glassy sample and its transformation by heating at 1 atm using low-temperature differential scanning calorimetry and Raman spectroscopy. This experimental study suggests strongly that the solvent state of the glassy LiClaq solution closely relates to the state of high-density amorphous ice. Moreover, we reconfirm that the separation into the low-density amorphous ice and the glassy highly concentrated LiClaq solution occurs in the glassy dilute LiClaq solution at ∼130 K, not the glass-to-liquid transition which is commonly observed in the glassy LiClaq solution above ∼10 mol.%. In order to interpret the sudden switchover between the glass-to-liquid transition and the phase separation at ∼10 mol.%, we propose a state diagram of LiClaq solution which connects with a polyamorphic state diagram of pure water and discuss a possibility that the electric field induces a polyamorphic transition of water.

Liquid-liquid separation of aqueous solutions: A molecular dynamics study

“…54,55 The liquid-liquid coexistence conditions of pure water is represented by a line in the pressuretemperature plane, whereas the coexistence conditions of an aqueous solution should be a twodimensional region in the plane for a value of composition. 43,59,63 In this study, we perform MD simulations of an aqueous NaCl solution at various temperatures and pressures to determine the liquid-liquid coexistence region in the phase diagram. Such coexistence region has not been examined in the previous simulation studies.…”

“…This result is consistent with experimental results obtained for amorphous solids of aqueous LiCl solutions. [41][42][43][44] HDL and LDL can also be distinguished by their structural properties; HDL is less structured than LDL. 2,38,[79][80][81][82] We calculate the tetrahedrality parameter given by…”

Glass polymorphism and liquid–liquid phase transition in aqueous solutions: experiments and computer simulations

“…The appearance of HDA is also supported by the observation that cooling pure water at similar pressure (0.3 GPa) leads to HDA, not LDA. 113 Furthermore, Suzuki and Mishima 134 confirm the presence of HDA based on Raman and differential scanning calorimetry (DSC) on pressure-vitrified aqueous LiCl solutions with x o 0.10 recorded at ambient pressure.…”

“…3b details the non-equilibrium states reached by cooling a pressurized solution of x E 0.05 at various rates. The figure is based on several experimental studies [132][133][134][135][150][151][152] whereas numerical studies have not been done in this context. On first sight, it becomes clear that Fig.…”

“…By contrast, previous publications conclude that hydration water is forced into the HDA structure through the influence of ions even at ambient pressure. [134][135][136]156 These apparently conflicting interpretations might be reconciled in different ways: (i) the polyamorphic transition occurs in the FCS part of the sample yet does not result in LDA but an LDA-like state of increased density; (ii) the transition in the FCS is not polyamorphic but continuous, slowly releasing enthalpy upon heating; and/or (iii) the transition is associated with water molecules being expelled from the salty solution, leaving behind a glassy solution of x = 0.14 (LiClÁ6H 2 O) containing all the unfreezable water.…”