Ice 0: Scientists discover unusual new form of ice

 

Concept art of water and ice close up

Japanese researchers have discovered 0-ice, a new type of ice that forms near the surface of water, that could redefine scientific understanding and influence technology and climate studies. (Artist’s concept). Credit: SciTechDaily.com

Japanese researchers have discovered a new form of ice called ice-0, which can promote the formation of ice crystals in supercooled water. Their study reveals that ice nucleation can occur near the surface of water droplets due to structures similar to ice-0, resolving a long-standing debate. These findings have important implications for various fields, including climate studies and food science, by improving our understanding of ice formation.

Ice is much more complex than most people realize. Science has identified more than 20 different varieties that form under various combinations of pressure and temperature. The type of ice we use to cool our drinks, called ice I, is one of the few forms found naturally on Earth. Recently, Japanese researchers discovered another type of ice: ice O, an unusual form of ice that can initiate the formation of ice crystals in supercooled water.

Ice formation near the surface of liquid water can begin from tiny crystalline precursors with a structure similar to a rare type of ice, known as ice 0. In a study recently published in Nature CommunicationsResearchers from the Social Cooperation Research Department “Freeze Protection Science” at the Institute of Industrial Science at the University of Tokyo have shown that these ice-like structures 0 can cause a water droplet to freeze near its surface rather than at its core. The discovery solves a long-standing puzzle and could help redefine our understanding of how ice forms.

Ice nucleation process

Ice crystallization, called ice nucleation, usually occurs heterogeneously, that is, on a solid surface. This is normally expected to occur at the surface of the water container, where the liquid meets the solid. However, this new research shows that ice crystallization can also occur just below the water surface, where it meets air. Here, ice nucleates around small precursors that have the same characteristic ring structure as ice 0.

“Simulations showed that a water droplet is more likely to crystallize near the free surface under isothermal conditions,” said Gang Sun, lead author of the study. “This resolves a long-standing debate about whether crystallization occurs more easily at the surface or inside.”

Rare form of ice at center of exciting new discovery about how water droplets freeze

Researchers at the Institute of Industrial Science at the University of Tokyo have discovered that ice begins to form near the water surface via structures similar to a recently discovered rare type of ice, helping us better understand how ice forms. Credit: Institute of Industrial Science at the University of Tokyo

Ice Precursors 0

The precursors of ice 0 have a structure very similar to that of supercooled water, which makes it easier for water molecules to crystallize from it, without having to form directly into the structure of ordinary ice. The tiny precursors of ice 0 form spontaneously, due to the negative pressure effects caused by the surface tension of water. Once crystallization begins from these precursors, structures similar to ice 0 quickly rearrange to form the more familiar ice I.

Lead author Hajime Tanaka highlights the broad implications of this study, noting that “the findings regarding the mechanism of water surface crystallization are expected to contribute significantly to various fields, including climate studies and food science, where water crystallization plays a critical role.”

A more detailed understanding of ice and how it forms could provide valuable insights into many fields of study. This work could be particularly important in meteorology, for example, where ice formation by ice-0 precursors can have a much more noticeable effect in small water droplets like those found in clouds. Understanding ice could also have benefits in technology, from food science to air conditioning.

Reference: “Surface-induced water crystallization caused by precursors formed in negative pressure regions” by Gang Sun and Hajime Tanaka, July 26, 2024, Nature Communications.

DOI: 10.1038/s41467-024-50188-1