The new evidence represents a significant step forward in confirming the idea of a liquid-liquid phase transition first proposed in 1992.
Characterization of the liquid-liquid phase transition in colloidal (top) and molecular water (bottom) by identifying links and knots. LDL – low-density liquid; HDL – high-density liquid. Image credit: Neophytou et al., doi: 10.1038/s41567-022-01698-6.
“In this work, we propose, for the first time, a view of the liquid-liquid phase transition based on network entanglement ideas,” said Professor Francesco Sciortino, a researcher in the Dipartimento di Fisica at Sapienza Università di Roma.
“I am sure this work will inspire novel theoretical modeling based on topological concepts.”
In the study, Professor Sciortino and colleagues 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 or a Hopf link. The molecules in the high-density liquid are thus said to be entangled.
In contrast, the molecules in the low-density liquid mostly form simple rings, and hence the molecules in the low-density liquid are unentangled.
“This insight has provided us with a completely fresh take on what is now a 30-year old research problem, and will hopefully be just the beginning,” said Andreas Neophytou, a Ph.D. student in the School of Chemistry at the University of Birmingham.
The researchers used a colloidal model of water in their simulation, and then two widely used molecular models of water.
Colloids are particles that can be a thousand times larger than a single water molecule.
By virtue of their relatively bigger size, and hence slower movements, colloids are used to observe and understand physical phenomena that also occur at the much smaller atomic and molecular length scales.
“This colloidal model of water provides a magnifying glass into molecular water, and enables us to unravel the secrets of water concerning the tale of two liquids,” said Dr. Dwaipayan Chakrabarti, a researcher in the School of Chemistry at the University of Birmingham.
The authors expect that their model will pave the way for new experiments that will validate the theory and extend the concept of ‘entangled’ liquids to other liquids such as silicon.
“Water, one after the other, reveals its secrets,” Professor Sciortino said.
“Dream how beautiful it would be if we could look inside the liquid and observe the dancing of the water molecules, the way they flicker, and the way they exchange partners, restructuring the hydrogen bond network.”
“The realization of the colloidal model for water we propose can make this dream come true.”
The study was published in the journal Nature Physics.
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A. Neophytou et al. Topological nature of the liquid-liquid phase transition in tetrahedral liquids. Nat. Phys, published online August 11, 2022; doi: 10.1038/s41567-022-01698-6
