Pressure-annealed high-density amorphous ice made from vitrified water droplets: A systematic calorimetry study on water’s second glass transition

Abstract

In previous work, water's second glass transition was investigated based on an amorphous sample made from crystalline ice (Amann-Winkel et al., Proc. Natl. Acad. Sci. U.S.A. 110 (44) 17720-17725). In the present work, we investigate water's second glass transition based on the genuine glassy state of high-density water as prepared from micron-sized liquid water droplets, avoiding crystallinity at all stages. All the calorimetric features of water's second glass transition observed in the previous work are also observed here on the genuine glassy samples. This suggests that the glass transition indeed thermodynamically links amorphous ices continuously with deeply supercooled water. We proceed to extend the earlier study by investigating the effect of preparation history on the calorimetric glass transition temperature. The best samples prepared here feature both a lower glass transition temperature Tg,2 and a higher polyamorphic transition temperature Tons, thereby extending the range of thermal stability in which the deeply supercooled liquid can be observed by about 4 K. Just before the polyamorphic transition, we observe a spike-like increase of heat capacity that we interpret in terms of nucleation of low-density water. Without this spike, the width of water's second glass transition is 15 K, and the Δcp amounts to 3{plus minus}1 J K-1 mol-1, making the case for HDL being a strong liquid. We suggest that samples annealed at 1.9 GPa to 175 K and decompressed at 140 K to {greater than or equal to}0.10 GPa are free from such nuclei and represent the most ideal HDA glasses.

Glass Polymorphism in Hyperquenched Aqueous LiCl Solutions

“…The second increase at ∼135 K, also called a spike , was recently suggested by us to be caused by the nucleation barrier that must be overcome before the growth of low-density water occurs within HDL. 14 After the spike, the growth of bulk low-density water releases the energy at the origin of the polyamorphic transition. This is indicated by the massive exotherm that extends beyond the zoom level of the y -axis in Figure 6 .…”

“…The hyperquenched solutions (0–5.8 mol %; R = ∞–16.2) and a CS (12.2 mol %, R = 7.2, quenched in a container cooled with liquid nitrogen), were densified as described in a previous publication. 14 For each batch, ∼200−400 mg of hyperquenched solution was removed from the cryo-plate and placed into an indium container fitted to the 8 mm bore of the piston–cylinder setup. The compression cell remained immersed in liquid nitrogen during the transfer process.…”

“… 12 This includes strong experimental proof that LDA and HDA are truly glassy states, which turn into ultraviscous liquids upon heating. 13 , 14 …”

“…In the present study, we explore a novel pathway of preparing high-density glasses: the pressurization of hyperquenched aqueous LiCl solution, a method that we developed for pure water in a recent study. 14 This method allows studying LiCl-HDA even at the lowest molar fractions and without the need of an emulsifying agent. Specifically, we hyperquenched solutions between 0.5 and 5.8 mol % ( R = 199–16.2) of LiCl and compressed them isothermally to yield high-density glasses.…”

“…Dilatometric curves were recorded during compression. After high-pressure annealing, 14 the samples were quenched and recovered at ambient pressure, at which ex situ X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements were performed. In the following sections, we thoroughly discuss the phase behavior of the polyamorphs, including their glass-to-liquid transitions.…”