Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water

Abstract

Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature Tg. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of Tg(P) for LDA and HDA by performing computer simulations of two water models – one with a LLPT, and one without. In the absence of a LLPT, Tg(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different Tg(P) which are directly linked with the LLPT. Available experimental data for Tg(P) are only consistent with the scenario including a LLPT.

Pressure-induced transformations in computer simulations of glassy water

“…However, at accessible quench and compression rates, the SPC/E model fails to reproduce the qualitative glass diagram found in experiments and the ST2 model, as discussed in Ref. 50.…”

“…26, 29, 32-34, and 64, its behavior in the glass domain has not been well explored. 26,50,53 Paradoxically, most experimental work has been performed in the glass domain, since experiments around the expected LLPT temperatures have not been possible due to rapid crystallization. Hence, the present work fills a gap between ST2 model simulations and experiments, and provides a logical test for the LLPT hypothesis.…”

“…Additionally, examining ensembles of independent compression runs in SPC/E shows that the LDA-HDA transformation occurs always at nearly the same pressure, 50 rather than the run-torun variation we see in ST2. This supports the notion that the transformation in ST2 has an underlying phase transition as its origin, while in SPC/E the transformation is rapid, but continuous.…”

“…26,50,53 As in previous works, we prepare these glassy states by following analogous procedures used in experiments in the preparation of LDA and HDA. However, due to the comparatively short time scales accessible to simulation, cooling and compression/decompression rates used are significantly faster than those used in experiments.…”

“…Even for the case of the ST2 model, which is the first model found to exhibit liquid polymorphism, the corresponding glass behavior is relatively unexplored. 26,53 In this work we use the ST2 model -not because it may or may not quantitatively reproduce the properties of water -but rather because it has been demonstrated to qualitatively reproduce the behavior of the glass transition temperature of water as function of pressure, 50 which appears to be associated with a LLPT.…”