At some point in your elementary school (in first grade, if you’re a little more…experienced), you learned that the freezing point of water is 0ºC. If you haven’t learned, you haven’t Trouble, because it may be a time of need to forget Same. That’s because a new study brings up a much smaller margin than that.
By creating ice from tiny droplets the size of a few hundred molecules, researchers have been able to lower the freezing point of water more than ever before.
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And how important is it to know how and why water turns into ice? This information is essential for understanding a wide range of natural processes, according to scientists. For example, climate fluctuations, cloud dynamics and the water cycle are all affected by the freezing of water.
Animals living in cold conditions also need to know and use this knowledge. For example, wood frogs survive the winter on land by freezing their bodies. It allows them to exit hibernation Faster than species that winter under water without freezing.
However, ice crystals can break down cell membranes, so animals using this technique need to find a way to prevent ice from building up in their cells and tissues. A better understanding of how water freezes is not only important for domesticated animals, but it could lead to greater awareness of these extreme species by humans.
Is water freezing point relative?
While the rule of thumb is that water freezes at 0 °C, it can actually sometimes remain liquid at colder temperatures. Until now it was believed that this interval stops at minus 38ºC. That is, any temperature lower than this and the water freezes.
Now, in a recent study published in the journal nature communicationResearchers succeeded in keeping water droplets inside liquid state Up to an impressive minus 44 degrees Celsius.
They started with droplets of 150 nanometers, barely larger than a virus particle as small as 2 nanometers, a cluster of just 275 molecules of water. This variation in droplet sizes helped researchers explore the role of size in turning water into ice.
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“We cover all these bands so that we can understand under what conditions ice will form – what temperature, what size droplets,” co-author Hadi Ghasemi, a professor of mechanical engineering at the University of Houston, told the website Live Science. , “And most importantly, we found that if the water droplets were covered with some soft material, freezing temperatures could be suppressed to much lower temperatures.”
As a soft material, octane was used, an oil that wraps each drop inside the nanoscale pores of an anodized aluminum oxide membrane. This elicited droplets with a rounded shape and greater pressure, which scientists believe is necessary to prevent ice formation at these low temperatures.
The smaller the drop of water, the lower the temperature
Since it is nearly impossible to observe the freezing process at these small scales, the researchers used measurements of electrical conduction – since ice is more conductive than water – and emitted light in the infrared spectrum to capture the precise moment and temperature. In which the drops change. Water to ice
They found that the droplet should be as cold as ice to form – and for droplets 10 nanometers or smaller, the rate of ice formation dropped dramatically. In the tiny droplets they measured, ice did not form until the water reached 44 degrees Celsius below zero.
Does this mean that the microscopic droplets inside clouds and biological cells can be colder than we thought? “As a scientist, I would say we don’t know yet,” Ghasemi said. “But this discovery could mean big things for man-made materials such as stopping ice in aviation and power systems.”
If water takes longer to freeze on soft surfaces, engineers can incorporate a mix of soft and hard materials into their designs to prevent ice build-up on those surfaces. “There are many ways to use this knowledge to design surfaces to prevent ice from forming,” Ghasemi said. “Once we have that fundamental understanding, the next step is engineering these surfaces based on soft materials.”
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