#supercooling

Although water can freeze below 0 degrees Celsius, it requires a little help--in the form of a nucleation site--to do so. Often temperatures must dip well below 0 degrees Celsius for droplets to become ice. But a new study shows that at least one fungus forms proteins that help the process along. (Image and research credit: R. Eufemio et al.; via Gizmodo; see also V. Tech)

A groundbreaking University of Hawai'i at Manoa study on the freezing of water droplets suspended in air sheds light on a key process in Earth's water cycle: the transformation of supercooled water into ice. Conducted using a novel cryogenically cooled ultrasonic levitation chamber, the research captures real-time molecular-level changes during the freezing process, mimicking conditions in the Earth's atmosphere. This innovative setup enables researchers to observe how water droplets transition to ice at subzero temperatures, providing valuable insights into cloud formation and precipitation. This research ties into the larger effort by UH Manoa researchers and their collaborators to address climate challenges through a $26 million project to develop sustainable refrigerant technologies.

To avoid freezing to death in cold conditions, some animals supercool. This is when the body fluids of the animal remain in a liquid state below their normal freezing point. However, to do this effectively, the animal must empty the body of components that may potentially form ice crystals such as food in the gut which would undo the process and freeze the animal.

From Earth Science Picture of the Day; May 25, 2018:

Ice Blades in a Small Frozen Pool Photographer: Kathy Arbuckle; Summary Authors: Kathy Arbuckle, Jim Foster

The photo above showing curious blades of ice was taken on a chilly late March morning in eastern Washington State. The temperature registered 27 F (-3 C). It was cold enough to freeze the shallow pool of rainwater that had accumulated in one of the ends of a large (about 24 in or 60 cm diameter) plastic spool. Each blade grew jutting upward at the same angle as it emerged from the icy pool. The largest formation pictured here measures approximately 4.5 inches in height (11.5 cm)

It's likely that clear skies allowed temperatures to drop quickly during the overnight hours, permitting fast freezing (supercooling) of the little pool. Since water typically freezes first along the edges of an enclosed container, the volume of water in the center of the pool, where the blades emerged, tends to be slightly raised and is last to freeze. Expanding ice beneath the surface of the water forces the remaining liquid water out through the hole near the center, forming a hollow protrusion. Bizarre shapes, including needles, spikes and sails can result. The small size of the pool, the confined space, differential freezing rates all play a role in determining whether or not protrusions will occur and the shape they'll take. In addition, because of the preferred growth of ice in crystalline planes, the protrusions often are at similar angles (often 60 degrees) to the ice-covered surface.

If you have a frost-free freezer perhaps on occasion you've noticed sharp spikes form on ice cubes. Photo taken on March 23, 2018, at 6:50 a.m.

Photo Details: Camera: NIKON COOLPIX P90; Software: Microsoft Windows Photo Viewer 6.1; Exposure Time: 0.012s (1/81); Aperture: ƒ/4.5; ISO equivalent: 160; Focal Length (35mm): 129.

Eastern Washington Coordinates: 47.66538, -118.94897

Related Links

Ice Sail in Pothole

More About Ice Spikes

Student Links

Freezing Point Explanation

Ice is a Mineral

Earth Observatory

Supercooling

Though pure materials have set freezing temperatures, conditions need to be right for solidification to actually occur. If conditions are right, liquids can be cooled below the freezing point of the substance and remain a liquid - this is known as supercooling. Supercooled liquids are by nature unstable and the right stimuli can lead to rapid solidification. Supercooling can be found naturally in some types of clouds and is often demonstrated with water; under the right conditions, with pure water (impurities act as nucleation sites for solidification) you can open your freezer to find a still liquid bottle of water. Supercooling is also sometimes known as undercooling.