Abstract
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.
Highlights
It has been argued that HDA and low density amorphous ice (LDA) could be solid proxies of distinct liquid states in the deeply supercooled regime, namely high-density supercooled liquid (HDL) and low-density liquid (LDL), respectively.[15]
In a previous study on pressure-induced amorphization and polyamorphism in LiCl aqueous solutions,[44] we showed that Unannealed HDA (uHDA) is formed by compression to 1.6 GPa at 77 K in the sub-eutectic concentration range, or water-dominated regime, as a result of the amorphization of segregated water.[45]
We focused our attention on the unannealed state of HDA, which does not show a glass transition at 1 bar, either in pure water or salty samples
Summary
One key open question regarding both glass transitions is the question about their endpoints, i.e., the temperatures above which the liquids can be regarded as equilibrated as opposed to approaching equilibrium. Angell and coworkers pioneered the study of liquid–liquid immiscibility and polyamorphism using LiCl aqueous solutions, which vitrify upon cooling, avoiding crystallization.[28,29,30] Yoshimura and Kanno performed detailed Raman spectroscopy studies on LiCl aqueous solutions and suggested the existence of a transition from the relaxed amorphous phase to the supercooled liquid at high pressures and low temperatures.[31] These studies were impeded by the non-glass forming tendency of dilute aqueous solutions through vitrification of the liquid. This process was carried out under liquid nitrogen so that weighing the samples was not possible and their mass had to be calculated
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