A study published in Nature investigates how the structural evolution of supercooled water couples to its glass transition, an open problem in the physics of liquids and condensed matter. Supercooled water — liquid below its freezing temperature — exhibits thermal and dynamical anomalies that have puzzled the scientific community for decades, among them a possible liquid–liquid critical point and a divergence of viscosity upon cooling.

The glass transition marks the point at which the liquid loses its ability to flow and behaves as an amorphous solid without crystallizing. Understanding which structural changes accompany this transition in water is particularly difficult because the timescales involved skyrocket near the transition temperature, and experimental measurements are limited by the rapid crystallization of water at ambient pressure.

The work examines the relationship between the liquid's local structural order and its relaxation dynamics as it approaches the glass transition. The results show that the evolution of the atomic structure of supercooled water and the slowing of its dynamics are coupled in a non-trivial way, shedding light on the microscopic origin of water's anomalies and on the general mechanisms of the glass transition in tetrahedral liquids.

The relevance of the study goes beyond water: liquids that form glasses share universal features of dynamical slowdown, and water is the paradigmatic case because of its exceptional properties. Establishing precisely how local structure changes during cooling helps to discriminate between competing theoretical models of the glass transition and of the possible existence of two liquids in supercooled water. Future research will need to confirm these findings with independent measurements and explore their extension to other tetrahedral liquids.