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“A New Picture of Water and Possible Consequences"

Date:

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Time:

Thursday, 16 Sept 2021

Video-Recording for any system with MP4-support

- Video.mp4 (ca. 228 Mb)

15:15 – 16:05

Abstract:

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.

Speaker today: Lars Pettersson (Stockholm University)