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A new technique has been devised by scientists to examine supercooled water using electron diffraction.


Illustration of the experimental approach. aAnd B Engineering sample illustration. The gold lattice supports a gold film covered with a few layers of graphene. A 176-nm-thick layer of solid, amorphous water (sample temperature 101 K) is deposited, and then locally heated with a microsecond-shaped laser pulse to prepare no-man’s-land water. c The diffraction pattern of the supercooled liquid is captured with an intense 6 µs electron pulse. credit: Nature Communications (2023). DOI: 10.1038/s41467-023-38520-7

Researchers at EPFL have found a way to study water in “no man’s land,” a subzero temperature range where water crystallizes rapidly. Historically, the inability to reach “no-man’s-land” kept scientists from teasing out the anomalous nature of the waters, but a breakthrough method can now change that.

Water is one of the most important and widespread compounds on Earth. Covering more than 70% of the planet’s surface, it has shaped its composition and geology, regulates its climate and weather patterns, and is the basis of all life as we know it.

But water is also strange. It displays a number of abnormal characteristics, of which more than seventy have been identified by scientists–to date. Many theories attempt to explain these anomalies, but verifying them experimentally is difficult. One reason is that this would require studying water between 160 K and 232 K (-113 °C to -41 °C), an infamous temperature range known as “no man’s land” where water crystallizes so quickly that it has been impossible for scientists to study Its characteristics.

But why would anyone want to cool water to such low temperatures? Because when water is cooled below its freezing point, it becomes “supercooled” with unique and wonderful properties; For example, under certain conditions, it can remain in liquid form but can freeze instantly when disturbed or exposed to certain substances. Supercold water is obtained by taking liquid water and cooling it below its freezing point while using tricks to prevent it from crystallizing or at least slow down this process. However, even with these tricks, crystallization in “no man’s land” is still very fast.

“The experience of systematically investigating the structure of water across the so-called ‘no-man’s land’ has remained elusive for decades,” says Professor Ulrich Lorenz of the School of Basic Sciences at EPFL. Now, scientists led by Lorenz have found a way to do just that. The team developed a method for rapidly preparing supercooled water at a well-defined temperature and electron diffraction probes for it before it crystallized.

“We still don’t fully understand why water is an anomalous liquid, even though this topic has been hotly debated for more than forty years,” says Lorenz. “The answer seems to lie in ‘no man’s land.’ But because of the rapid crystallization, no measurement has been possible over the full temperature range. We’re doing this for the first time. It brings us closer to solving this long-standing mystery.”

The scientists conducted the experiments using a specialized time-resolved electron microscope that they custom built in their lab. Prepare supercooled water at a well-defined temperature and probe it immediately before crystallization occurs. To do this, they cooled a layer of graphene to 101 K and applied a thin layer of amorphous ice. They then melted the film locally with a microsecond laser pulse to get the water in the “no-man’s land,” and captured the diffraction pattern with an intense, high-brightness electron pulse.

The researchers found that when water is cooled from room temperature to very cold temperatures, its structure evolves smoothly. At temperatures just below 200 K (about -73 °C), the structure of water begins to look like that of amorphous ice—a form of ice where water molecules are in disorder—in contrast to the ordered, crystalline ice we usually know. .

“The fact that the structure evolves so smoothly allows us to narrow the range of possible explanations for the origin of the water anomalies,” says Lorenz. “Our findings and the method we have developed bring us closer to solving the mysteries of water. It is hard to escape the fascination of this ubiquitous, seemingly simple liquid that has not yet given up all its secrets.”

Publication of the research in the journal Nature Communications.

more information:
Konstantin R Kruger et al., Electron diffraction of supercooled water in no man’s land, Nature Communications (2023). DOI: 10.1038/s41467-023-38520-7

Provided by Ecole Polytechnique Federale de Lausanne

the quote: Researchers develop method to probe supercooled water using electron diffraction (2023, May 30) Retrieved May 30, 2023 from https://phys.org/news/2023-05-method-probe-supercooled-electron-diffraction.html

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