What is supercooled cooking

Liquid water at minus 46 degrees

Water exhibits many anomalies that remain a mystery to researchers to this day. Least understood is the behavior of liquid water when it is cooled below nominal freezing point without freezing. Scientists have now succeeded in observing so-called supercooled water molecules at a temperature of minus 46 degrees Celsius. This temperature is in a range that has not yet been measured and is therefore called “no man's land”. They published their results in the journal "Nature".

Diagram for water at low temperatures

Usually water freezes at freezing point at 0 degrees Celsius. But if you use very pure water, in which there are no particles that can serve as nuclei for crystallization, it remains liquid even below freezing point. In no man's land - between minus 38 degrees Celsius and minus 115 degrees Celsius - supercooled water is only liquid for fractions of a second and then suddenly freezes to ice. What exactly is happening in this area is unclear, however. One of the many possible theories describes a phase transition: supercooled water changes from a high density to a low density state at a certain point.

To support or refute this theory, Jonas Sellberg from the SLAC accelerator laboratory and his colleagues used a special injector that shoots tiny water droplets into a vacuum chamber. In a vacuum, water evaporates from the surface of the droplet, and the evaporation cold cools the remaining droplets, similar to how the human body cools itself through sweating. The scientists shot ultrashort X-ray pulses at these droplets, which are only 50 femtoseconds (one femtosecond is one quadrillionth of a second) long. With these laser pulses, they were able to control the temperature and analyze the molecular structure.

In a range between minus 44 and 46 degrees Celsius, the researchers were able to observe how the structural order of the water molecules increased ever faster. These data support the theory of a phase transition in no man's land. However, the researchers hope to be able to reach significantly colder temperatures and thus better understand the behavior of water.