UNIVERSITY OF BIRMINGHAM
Researchers at the Universities of Birmingham and Sapienza Università di Roma have discovered fresh evidence that water can change from one liquid to another, denser liquid.
This ‘phase transition’ in water was first suggested 30 years ago in a study by researchers from Boston University. However, since the transition has been predicted to occur under supercooled conditions, confirming its existence has been challenging. That’s because at this low temperature, water really doesn’t want to become a liquid, rather it wants to quickly become ice. Due to its hidden state, much is still unknown about this liquid-liquid phase transition, unlike the everyday examples of phase transitions in water between solid or vapor phase and liquid phase.
This new evidence, published year Natural Physics, represents a significant step forward in validation The idea of a liquid-liquid phase transition was first proposed in 1992. Francesco Sciortino, now a professor at Sapienza Università di Roma, was a member of the original research team at Boston University and also a co-author of this paper.
The team used computer simulations to help explain what features distinguish the two liquids at the microscopic level. They found that the arrangement of water molecules in the form of a high-density liquid is considered “structurally complex”, such as a triangular knot (think of the molecules arranged in such a way that they are like a cookie) or the Hopf link (think of two links in a steel chain). Therefore, the molecules in high-density liquids are said to be cumbersome.
In contrast, molecules in low-density liquids mainly form simple rings, and thus molecules in low-density liquids are no problem.
Andreas Neophytou, a PhD student at the University of Birmingham with Dr Dwaipayan Chakrabarti, is the lead author of the paper. “This insight has provided us with a whole new perspective on what is now a 30-year-old research problem, and will hopefully be just the beginning,” he said.
The researchers used a colloidal model of water in their simulation, and then two widely used water molecule models. Colloids are particles that can be a thousand times larger than a water molecule. Thanks to them relative Larger in size, and therefore slower in motion, the colloids used to observe and understand physical phenomena also occur at much smaller atomic and molecular length scales.
Dr Chakrabarti, co-author, said: “This colloidal water model provides a magnifying glass into the water molecule and allows us to unravel the secrets of water related to the story of two liquids. “
“In this work, we propose for the first time a view of liquid-liquid phase transitions based on the ideas of lattice entanglement,” said Professor Sciortino. I am sure that this work will inspire new theoretical models based on topological concepts. “
The team hopes that the model they have devised will pave the way for new experiments that validate the theory and extend the concept of ‘entangled’ liquids to other liquids such as silicon.
Pablo Debenedetti, professor of chemical and biological engineering at Princeton University in the US and a world-leading expert in this area of research, commented: “This beautiful computational work uncovers the basis the basic topology of the existence of different liquid phases in the same lattice-former. “In so doing, it essentially enriches and deepens our understanding of a phenomenon that abundant experimental and computational evidence increasingly shows is at the heart of our physics,” he added. the most important substance of a liquid: water.”
Christian Micheletti, professor at the International School of Advanced Studies in Trieste, Italy, whose current research interest is in understanding the effects of entanglement, particularly knots and connections, on static , kinetics and function of biofilm-forming substances, commented: “With this paper, Neophytou et al. has made a number of breakthroughs that will result across diverse scientific fields. First, their elegant and experimental colloidal model for water opens up entirely new prospects for large-scale studies of fluids. In addition, they present very solid evidence that phase transitions that can be elusive for traditional analysis of the local structure of liquids are instead readily obtained by tracking the kinks. and bonding in the interconnected network of fluids. The idea of finding such complexity in the somewhat abstract space of pathways running along transient molecular bonds is a very powerful one and I hope it will be widely applicable to research. complex molecular systems. “
Sciortino adds: “Water in turn reveals its secrets! How beautiful it would be if we could look inside a liquid and observe the dancing of water molecules, the way they flicker and how they exchange partners, restructuring the network of hydrogen bonds. The realization of the glue model for water that we propose can make this dream come true.”
The research is supported by the Royal Society through the International Exchange Award, which enables international collaboration between researchers in the UK and Italy, the EPSRC Center for Doctoral Training in Topological Design and Institute for Advanced Study at the University of Birmingham, and Italian Minister Istruzione Università Ricerca – Progetti di Rilevante Interestsse Nazionale.
Simulation / Computational Modeling
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ARTICLE PUBLICATION DATE
August 11, 2022