Glass–liquid transition of water at high pressure

Abstract

The knowledge of the existence of liquid water under extreme conditions and its concomitant properties are important in many fields of science. Glassy water has previously been prepared by hyperquenching micron-sized droplets of liquid water and vapor deposition on a cold substrate (ASW), and its transformation to an ultraviscous liquid form has been reported on heating. A densified amorphous solid form of water, high-density amorphous ice (HDA), has also been made by collapsing the structure of ice at pressures above 1 GPa and temperatures below approximately 140 K, but a corresponding liquid phase has not been detected. Here we report results of heat capacity C p and thermal conductivity, in situ, measurements, which are consistent with a reversible transition from annealed HDA to ultraviscous high-density liquid water at 1 GPa and 140 K. On heating of HDA, the C p increases abruptly by ð3.4 AE 0.2Þ J mol −1 K −1 before crystallization starts at ð153 AE 1Þ K. This is larger than the C p rise at the glass to liquid transition of annealed ASW at 1 atm, which suggests the existence of liquid water under these extreme conditions. glass transition | pressure-induced amorphization | relaxation U nlike most liquids that vitrify by normal supercooling, water vitrifies only by hyperquenching of its micron-size droplets, and its porous amorphous state is made by vapor deposition (1-3). Pure bulk water densified by high pressure also does not vitrify on normal cooling; instead it freezes to proton-disordered high-density ices. However, in 1984 Mishima et al. (4) discovered a path to obtain a high-density amorphous ice (HDA) by pressurization of hexagonal ice, ice Ih, to approximately 1.5 GPa at 77 K. This amorphous form is characterized by the absence of Bragg peaks, but it is heterogeneous on a mesoscopic length scale (5). On heating at high pressures above approximately 0.5 GPa (6), it relaxes, homogenizes, and densifies before crystallization, and the ultimately densified form has been referred to as very highdensity amorphous ice (vHDA) (7). There are thus a multiplicity of amorphous states with densities in between HDA and vHDA, which are produced by isothermal pressurization of ice Ih at temperatures below approximately 140 K, and these are here generically referred to as HDA.States of water at extreme pressure and temperature conditions are important for, for example, understanding of tectonics in large bodies of the outer solar system where ice is one of the rock-forming minerals (8), and for water's phase diagram and properties (9), but it is not known whether HDA transforms to glassy and liquid states on heating. This work reports a unique high-pressure, in situ, heat capacity C p study of HDA just below its crystallization point where a glass to liquid transition may occur. It is here shown that HDA exhibits a glass transition with a heat capacity rise larger than that for amorphous solid water and hyperquenched water at 1 atm, which suggests a thermodynamic path between the annealed state of HDA and liquid wa...

Water’s second glass transition

“…2), as eHDA has converted to LDA at the end of trace 3. The heat capacity change for LDA (Δc p,1 ∼ 1 JK -1 ·mol -1 ) (6, 27) at its T g,1 = 136 ± 2 K is much lower than the heat capacity increase for an HDA sample at 1 GPa and 140 K, which Andersson reported to be 3.2 JK -1 ·mol -1 (13). This value is similar to Δc p,2 as obtained here for HDA at ambient pressure.…”

“…1B. Conversely, this finding implies that LDA's ambient pressure glass transition (4-6) and the glass transitions observed at high pressures (12)(13)(14)(15) are distinct phenomena, despite the similarity of the associated T g s. The observation of two distinct glass transitions, T g,1 and T g,2 , at ambient pressure rules out the possibility of a single T g scenario sketched in Fig. 1A.…”

“…The main experimental finding of the present work is the observation of two distinct glass transitions at ambient pressure, an observation ruling out a connection of water's "old" ambientpressure glass transition at T g,1 ∼ 136 K with the recently reported high-pressure glass transitions of water (12)(13)(14)(15). That is, the single T g scenario in Fig.…”

“…Even though the question about the nature of this transition has not been settled ultimately, recent work interprets this signature to be consistent with a glass-toliquid transition and places deeply supercooled water into the category of "strong" liquids (8)(9)(10)(11). Lately, it has become clear that water's high-density phase exhibits a glass transition at pressures ≥0.1 GPa, which has also been interpreted in terms of a glass-to-liquid transition (12)(13)(14)(15). However, it has remained unclear in experiments whether or not the high-pressure glass transition connects to the ambient pressure glass transition or whether water shows two distinct glass transitions at a given pressure.…”

Pressure-induced transformations in computer simulations of glassy water

“…[12][13][14][15] Experiments show that the pressure at which the low-pressure ice transforms to HDA, P ice → HDA (T), increases with decreasing temperature. 16 P ice → HDA (T) is indicated in Fig.…”