学術講演会

主催：広島大学WPI-SKCM²

講師：Prof. Dwaipayan Chakrabarti (University of Birmingham)
講義題目：Knotted Water

日時：2023/2/16(木)
場所：Room 204, Venture Business Laboratory (in front of HiSOR)

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要旨：
Water, despite being the most important liquid for our existence, is rather weird – apparent through a host of anomalous thermodynamic properties that it exhibits [1,2]. The hypothesis of the presence of a first-order liquid–liquid phase transition line in the supercooled region of the pressure–temperature phase diagram, terminating at a liquid-liquid critical point, was introduced three decades ago to account for the thermodynamic anomalies of water [3]. The competition for crystallisation into ice from deeply supercooled water has posed a sever challenge to the experimental verification of this hypothesis over the past three decades [4]. Although a growing body of computational studies has supported this hypothesis in recent years [5,6], a clear microscopic picture that fundamentally distinguishes the two liquid networks of different densities has remained elusive. In this presentation, I will show that this liquid–liquid phase transition in tetrahedral networks can be described as a transition between an unentangled, low-density liquid (LDL) and an entangled, high-density liquid (HDL), the latter containing an ensemble of topologically complex motifs, including links and knots [7]. We first reveal this distinction in a rationally designed colloidal analogue of water [7], exploiting a hierarchical self-assembly strategy [8]. We show that this colloidal water model displays the well-known water thermodynamic anomalies as well as a liquid–liquid critical point. We then investigate water, employing two widely used molecular models [9,10], to demonstrate that there is also a clear topological distinction between its two supercooled liquid networks – the HDL comprising trefoil knots and theta curves in addition to links. Our results thus unravel a topological perspective on the tale of two liquids, which should have farreaching implications for understanding liquid–liquid phase transitions in tetrahedral liquids [7].

参考文献：
1. C. A. Angell, Ann. Rev. Phys. Chem. 34, 593 (1983).
2. P. G. Debenedetti, J. Phys. Condens. Matter 15, R1669 (2003).
3. P. H. Poole, F. Sciortino, U. Essmann and H. E. Stanley, Nature 360, 324 (1992).
4. K. H. Kim et al., Science 370, 978 (2020).
5. J. C. Palmer, P. H. Poole, F. Sciortino and P. G. Debenedetti, Chem. Rev. 118, 9129 (2018).
6. P. G. Debenedetti, F. Sciortino and G. H. Zerze, Science 369, 289 (2020).
7. A. Neophytou, D. Chakrabarti and F. Sciortino, Nat. Phys. 18, 1248 (2022).
8. D. Morphew, J. Shaw, C. Avins and D. Chakrabarti, ACS Nano 12, 2355 (2018).
9. J. L. F. Abascal and C. Vega, J. Chem. Phys. 123, 234505 (2005).
10. J. L. F. Abascal, E. Sanz, R. G. Fernández and C. Vega, J. Chem. Phys. 123, 234511 (2005).