Aug 23, 2022 09:00:00

Features that distinguish between the two states that exist in ultra-low temperature water ``amorphous ice'' below 0 degrees are revealed

Water is known to be a substance that turns into gaseous water vapor at 100 degrees and transitions to solid ice at 0 degrees. In fact, various conditions have been confirmed. A new research team at the University of Birmingham in the UK and the University of Rome La Sapienza in Italy has clarified the features that distinguish the two states of amorphous ice using computer simulations.

Topological nature of the liquid–liquid phase transition in tetrahedral liquids | Nature Physics
https://www.nature.com/articles/s41567-022-01698-6

New evidence shows water separates into two different liquids at low temperatures - University of Birmingham
https://www.birmingham.ac.uk/news/2022/new-evidence-shows-water-separates-into-two-different-liquids-at-low-temperatures

Amorphous ice is a non-crystalline substance made by rapidly freezing liquid water or evaporating water vapor onto a substrate, and a 2017 study confirmed that it is a liquid rather than a solid. Amorphous ice is rarely seen on Earth, but it is said to form relatively easily in outer space , where ultra-low temperature regions exist.

Since there are two types of amorphous ice, high-density amorphous ice (HDA) and low-density amorphous ice (LDA), there are two types of water in the ultra-low temperature state. However, since supercooled amorphous ice immediately undergoes a phase transition to ice, the details are not known.

Therefore, a research team led by Associate Professor Dwaipayan Chakrabarti at the University of Birmingham conducted research using computer simulations to investigate the characteristics that distinguish the two states of amorphous ice at the microscopic level.

In the simulation, the research team used a model of water in a colloidal state in which molecules are dispersed in a medium as extremely fine particles, and two widely used models of water molecules. Due to their relatively large size, colloids move slowly and are often used to study physical phenomena that occur at much smaller atomic and molecular scales.

As a result of simulation-based research, water molecules in high-density amorphous ice are topologically shaped into pretzel-like trefoil knots (clover knots) and Hopf links , in which two rings form a chain. It was found that they form a complex arrangement and are intertwined. On the other hand, the research team reports that most of the low-density amorphous ice forms simple rings and is not entangled.

``This insight has given us a completely fresh perspective on what has been a 30-year research agenda,'' said Dr. Dwaipayan Chakrabarti, lead author of the paper. Pablo Debenedetti, a professor of chemical engineering at Princeton University in the United States, who was not involved in the research, said, ``This beautiful computer study shows the underlying topology in which different liquid phases exist in the same network of substances. It has made clear,' he said.