New Evidence that Water Separates Into Two Different Liquids at Low Temperatures
Arthur T Knackerbracket has processed the following story:
A new kind of "phase transition" in water was first proposed 30 years ago in a study by researchers from Boston University. Because the transition has been predicted to occur at supercooled conditions, however, confirming its existence has been a challenge. That's because at these low temperatures, water really does not want to be a liquid, instead it wants to rapidly become ice. Because of its hidden status, much is still unknown about this liquid-liquid phase transition, unlike the everyday examples of phase transitions in water between a solid or vapor phase and a liquid phase.
This new evidence, published in Nature Physics, represents a significant step forward in confirming the idea of a liquid-liquid phase transition first proposed in 1992. Francesco Sciortino, now a professor at Sapienza Universita di Roma, was a member of the original research team at Boston University and is also a co-author of this paper.
The team has used computer simulations to help explain what features distinguish the two liquids at the microscopic level. They found that the water molecules in the high-density liquid form arrangements that are considered to be "topologically complex," such as a trefoil knot (think of the molecules arranged in such a way that they resemble a pretzel) or a Hopf link (think of two links in a steel chain). The molecules in the high-density liquid are thus said to be entangled.
[...] "First, their elegant and experimentally amenable colloidal model for water opens entirely new perspectives for large-scale studies of liquids. Beyond this, they give very strong evidence that phase transitions that may be elusive to traditional analysis of the local structure of liquids are instead readily picked up by tracking the knots and links in the bond network of the liquid.
More information:
Andreas Neophytou, Dwaipayan Chakrabarti, Francesco Sciortino. Topological nature of the liquid-liquid phase transition in tetrahedral liquids, Nature Physics (2022). DOI: 10.1038/s41567-022-01698-6 Journal information: Nature Physics
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