UNIVERSITY OF BIRMINGHAM
Fresh evidence that water can change from one form of liquid into another, denser liquid, has been uncovered by researchers at the University of Birmingham and Sapienza Università di Roma.
This ‘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 about everyday examples of phase transitions in water between a solid or vapour 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 Università 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.
In contrast, the molecules in the low-density liquid mostly form simple rings, and hence the molecules in the low-density liquid are unentangled.
Andreas Neophytou, a PhD student at the University of Birmingham with Dr Dwaipayan Chakrabarti, is lead author on the paper. He says: “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.”
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.
Dr Chakrabarti, a co-author, says: “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.”
Professor Sciortino says: “In this work, we propose, for the first time, a view of the liquid-liquid phase transition based on network entanglement ideas. I am sure this work will inspire novel theoretical modelling based on topological concepts.”
The team expect that the model they have devised 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.
Pablo Debenedetti, a professor of chemical and biological engineering at Princeton University in the US and a world-leading expert in this area of research, remarks: “This beautiful computational work uncovers the topological basis underlying the existence of different liquid phases in the same network-forming substance.” He adds: “In so doing, it substantially enriches and deepens our understanding of a phenomenon that abundant experimental and computational evidence increasingly suggests is central to the physics of that most important of liquids: water.”
Christian Micheletti, a professor at International School for Advanced Studies in Trieste, Italy, whose current research interest lies in understanding the impact of entanglement, especially knots and links, on the static, kinetics and functionality of biopolymers, remarks: “With this single paper, Neophytou et al. made several breakthroughs that will be consequential across diverse scientific areas. 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. The idea of searching for such intricacies in the somewhat abstract space of pathways running along transient molecular bonds is a very powerful one, and I expect it will be widely adopted to study complex molecular systems.”
Sciortino adds: “Water, one after the other, reveals its secrets! 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 realisation of the colloidal model for water we propose can make this dream come true.”
The research was supported by the Royal Society via International Exchanges Award, which enabled the international collaboration between the researchers in the UK and Italy, the EPSRC Centre for Doctoral Training in Topological Design and the Institute of Advanced Studies at the University of Birmingham, and the Italian Ministero Istruzione Università Ricerca – Progetti di Rilevante Interesse Nazionale.
JOURNAL
Nature Physics
DOI
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE PUBLICATION DATE
11-Aug-2022
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I was told over 60yrs ago that water was liquid far below its freezing point in very fine clays. I thought it was because the fine clays impeded the joining of the molecular ends into a solid lattice. This was probably an engineering discovery that perhaps didn’t get published.
Here is a medical research study by engineers that found a way to maintain liquid water well below freezing.
https://www.techexplorist.com/new-method-keeps-liquid-from-freezing-very-low-temperatures/16095/
Methinks physicists today with little new science to add may be trolling the internet for stuff to “discover”. Google water below freezing in fine clays” for a whole bunch of these. There is even one about subsurface water on Mars. Seems the phenomenon is rather commonplace. Interesting to see if the paper has a big bibliography!
Supercooled water that requires to be pure with no impurites has been well known for decades. It remains well below freezing point of water but requires a trigger to suddenly change it to ice.
There is a phase separation process known as coacervation. Dilute solutions of oppositely charged colloids can separate into two phases, one colloid rich and the other colloid depleted. If you think of a colloid as mid way between a solution and a solid you can get the idea. This is not just a laboratory curiosity, it is the basis of a microencapsulation process used industrially to encapsulate oil emulsions in batches of several thousand gallons at a time.
I’m not saying this two phase water claim is true, just mentioning the colloid system. It is possible that there is a pre-frozen state when water molecules have aggregated into colloidal size particles. Aggregates of these aggregates could probably be centrifuged into a separate “denser” phase with the upper layer composed of normal free water molecules.
They are probably getting excited about what the rest of us call slush.
“METHOD OF RESEARCH: Computational simulation/modeling”
I.e. they played video games and here are the results.
Not science. Not close.
Ice Nine! We’re all going to die.
Classical reference explained:
“Cat’s Cradle” by Kurt Vonnegut
RTWT | Spoilers
I added the links. Herr Rotter was clever to add the picture above. But, the book was written in 1963, and I do not know if it is much read anymore.
If they wanted funding to pursue this further, they should have know they needed to link it with global warming. No climate change, no $$$.
Sounds like they are using the same computer models as the Global Warming XXXXX XXXXXXX Climate Change XXXXX XXXXXX Climate Disruption people.
I have a little familiarity with molecular dynamics. The models are heavily parameterized. Small changes in the parameters governing electrostatic interactions between water molecules (Lennard-Jones potentials) can strongly influence the simulated behavior of water molecules.
In 2016, my colleagues and I published the first experimental determination of the solvation structure of chloride, bromide, and iodide ions in water.
In doing so, we falsified an asymmetric molecular dynamics solvation model that had become very popular and cutting edge. It was wrong.
All-in-all, I take MD simulations with a grain of salt. At best, they may give one an idea of where to look. But experimental work tells the tale.
Such model work, absent experiment, is hardly more than philosophy. The computer graphics are very pretty and are made to look convincing; especially the videos. But the simulations are speculative, not indicative.
The problem is that the pertinent interactions are below the energy resolution limits of the theoretical mechanics. The physical theory (quantum mechanics) will need serious serious and detailed improvement before it can command belief at the level of solution interactions.
Looking at your abstract (the link needs to be edited to work), you may have stumbled onto an effect of cluster theory. Solubility may be controlled by spaces between clusters and it’s not surprising that this might be missed in an MD experiment, as a single cluster might consist of dozens to hundreds of water molecules. In our noble gas paper (definitely non polar and symmetrical), we found that fog had ice-like solubility, with enhanced He solubility (like ice), Ne solubility nearly the same as liquid water (like ice) and depleted concentrations of Ar, Kr and Xe (like ice, with Xe the most depleted). He and Ne can be accommodated within ice structures, but the three heavies cannot. Now a “crushed” or “entangled” high density cluster should not be able to handle having any noble gas atoms within the cluster. So most solubility must occur in spaces between clusters and for Ar, Kr and Xe, ALL solubility must occur between clusters. It’s just a guess at this point, but it’s a 10 to 20 sigma result that can’t be explained by a traditional theory of liquids.
Thanks for the comment, Chris. One could do an XAS experiment — at the Ar edge, for example — and use MXAN to derive an empirical model of the solvation environment.
Maurizio Benfatto is the MXAN expert and may be interested in the project.
If you’re interested, feel free to contact him and mention my name. Maurizio is a great guy and a brilliant condensed matter physicist.
All three halides had discrete local solvation structures. Chloride was unique and was particularly challenging.
Figure 11 shows the test of the MD-predicted solvation structure of chloride.
I’ll have to look at your paper to understand your description. 🙂
I’m retired now, so unfortunately I can’t do any experimental work. I was hoping to learn how to do some MD simulations, but the crypto-currency guys made high powered graphics cards too expensive!
Found it: Anomalous Noble Gas Solubility in Liquid Cloud Water: Possible Implications for Noble Gas Temperatures and Cloud Physics
Only this morning i read of the book “How Superstition Won and Science Lost. Popularising science & health in the United States.” by John Burnham… Has anyone any thoughts or advice, as it’s quite pricey for a pensioner ?
The “Higgs boson” or Higgs particle is an elementary particle in the Standard Model.
Oh, did I just use the term “model”? OK, don’t think of that.
Proposed in 1964, after a 40 year search, a subatomic particle with the expected properties was discovered in 2012by experiments at the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland.
So a number of interactions can take place by attraction between electrons in outer orbitals of this v-shaped molecule as it changes from water to ice. So minor we’ve hardly noticed even though water is the most studied fluid ever. Nobody is going to care about the pretty knot pics in this waste-of-research funds grant application.
It’s interesting that you’re not interested in the answer to the question of why ice floats (very anomalous), or that the bottom of the ocean and most northern lakes are all at nearly the same temperature, or details of steam thermodynamics, or details of water surface tension, etc., etc. The list of anomalous features of the most important and probably least understood liquid on the planet are nearly endless.
I missed something. The article never says at what temperature this unusual type of water happens.
How do use a computer model to show effects of cooling unless you program it to do those effects?
It happens at all temperatures when water is in liquid form. It seems that liquid water always has this “Janus” personality.
The article says “… occur at supercooled conditions…”. It just isn’t specific.
Ahh, but the hypothesis that they are addressing needs these two types of liquid water structures also must occur at normal liquid water temperatures. However, most attempts to verify this via methods like X-ray diffraction have used super-cooled water because the effects are more easy to document at those temperatures..
I was looking for something solid to have them hang their hats on, and there is nothing in this article worth reporting at a high quality place such as this.