Dwaipayan Chakrabarti（Univ. of Birmingham) Knotted Water
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 . 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 . 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 . We first reveal this distinction in a rationally designed
colloidal analogue of water , exploiting a hierarchical self-assembly strategy . 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 far-
reaching implications for understanding liquid–liquid phase transitions in tetrahedral liquids .
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