[M-IS14] Interface- and nano-phenomena on crystal growth and dissolution

[MIS14-P09] Spinodal Decomposition-like Dynamics of Unknown Water at Ice V-Water Interface

*Hiromasa Niinomi¹, Tomoya Yamazaki², Hiroki Nada³, Tetsuya Hama⁴, Akira Kouchi², Tomoya Oshikiri^1,5, Masaru Nakagawa¹, Yuki Kimura² (1.Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2.Institute of Low Temperature Science, Hokkaido University, 3.Tottori Univresity, 4.Tokyo University, 5.Research Institute for Electronic Science, Hokkaido University)

Keywords:water, spinodal decomposition, high-pressure ices, non-equilibrium interface

Water is such abundant on the Earth that its properties govern various phenomena in nature. Thus, it is significant to understand the origin of the mysterious properties of water unlike other normal liquids, which is often missed due to its commonness, such as non-linear dependence of thermodynamic response function on temperature. It is, therefore, indisputable that the elucidation of the origin of the property of water is highly desirable not only for Earth science but also for a broad range of scientific fields. However, the origin of the mysterious properties of water remains unclear. A key to understand the origin is experimental confirmation of macroscopic liquid-liquid phase separation (LLPS) of water into the two kinds of waters with different local structures, which is predicted to occur near the condition of thermodynamic singularity under low temperature and high pressure [1,2]. However, the experimental confirmation of LLPS in water is considered to be difficult because the predicted liquid-liquid critical point (LLCP) lies in an experimentally inaccessible ‘no-man’s land’, where deep supercooling of liquid water required to reach the LLCP is obstructed by fast crystallization kinetics beyond experimentally accessible timescales [3]. Amid this situation, we have previously reported that in-situ optical microscopy revealed the existence of two kinds of, low- and high-density at least, unknown waters macroscopically separated from the surrounding bulk water at the interfaces between water and ice Ih or high-pressure ices (ices III and VI) grown or melted in water on (de)pressurization by sapphire anvil cell under experimentally accessible conditions [4,5].
In this presentation, we show, by in-situ optical microscopy, that high-density unknown water at water-ice V interface can appear through spinodal decomposition-like dynamics which possibly follows those predicted by model H [6], a common model to describe the dynamics of spinodal decomposition of a binary liquid mixture. This means the spinodal-like generation dynamics of unknown water can be described by the existing theories of LLPS. Our discovery should provide insights on the mysterious links between the unique thermodynamic properties of water and liquid polymorphism in a single component liquid.

[1] P. H. Poole et al., Nature 1992, 360, 324-328.
[2] D. A. Fuentevilla et al., Phys. Rev. Lett. 2006, 97, 195702.
[3] K. H. Kim et al., Science 2017, 358, 1589-1593.
[4] H. Niinomi et al., J. Phys. Chem. Lett. 2020, 11, 6779-6784.
[5] H. Niinomi et al., J. Phys. Chem. Lett. 2022, 13, 4251-4256.
[6] P. C. Hohenberg et al., Rev. Mod. Phys. 1977, 49, 435-479.