A new picture of water and possible consequences

by Lars Pettersson (Stockholm University)

Thursday 16 Sept 2021, 15:15 → 17:15 Europe/Stockholm

I will discuss the phase diagram of water with particular focus on the metastable region where, at deeply supercooled conditions and elevated pressure, the transition between two liquid states has recently been observed [1]. These differ in density and are denoted high- and low-density liquid, HDL and LDL. Similar to the one-phase region beyond the liquid-gas critical point, a maximum in the isothermal compressibility has been observed indicating crossing the extension of the coexistence line into the one-phase region [2]. The compressibility depends on density fluctuations and the enhanced compressibility upon supercooling water, as well as water’s anomalous behavior at ambient conditions, would find a natural explanation in the proposed existence of a critical point hidden below the temperature of homogeneous ice nucleation [3].

Several experimental observations indicate a bimodal distribution of local structures in the liquid also at ambient conditions [4]. Dissolution of gases in water is further enhanced below 20 C which indicates that more open structures become available to accommodate, e.g., O2. We speculate that these are clathrate-like [5] and discuss possible consequences for aquatic life and challenges to develop simulation models that capture correctly the fluctuations and bimodality in experimental observables. 

[1] Kim et al., Science 370 (2020) 978. [2] Kim et al., Science 358 (2017) 1589. [3] Poole et al., Nature 360 (1992) 324. [4] Nilsson and Pettersson, Nature Commun. 6 (2015) 8998. [5] Camisasca et al., J. Chem. Phys. 151 (2019) 034508.

 https://stockholmuniversity.zoom.us/j/62663587311

 

http://video.albanova.se/arc2021_23.html