Topological nature of the liquid-liquid phase transition in tetrahedral liquids

The first-order phase transition between two tetrahedral networks of different density-introduced as a hypothesis to account for the anomalous behaviour of certain thermodynamic properties of deeply supercooled water-has received strong support from a growing body of work in recent years. Here we show that this liquid-liquid phase transition in tetrahedral networks can be described as a transition between an unentangled, low-density liquid and an entangled, high-density liquid, the latter containing an ensemble of topologically complex motifs. We first reveal this distinction in a rationally designed colloidal analogue of water. 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, to demonstrate that there is also a clear topological distinction between its two supercooled liquid networks, thereby establishing the generality of this observation, which might have far-reaching implications for understanding liquid-liquid phase transitions in tetrahedral liquids. Supercooled water undergoes a liquid-liquid phase transition. The authors show that the two phases have distinct hydrogen-bond networks, differing in their degree of entanglement, and thus the transition can be described by the topological changes of the network.

Automated summary

This article demonstrates through experiments that the liquid-liquid phase transition in tetrahedral networks can be described as a transition between an unentangled, low-density liquid and an entangled, high-density liquid, with a clear topological distinction between the two phases.