Scientists Discover Why Water Behaves Unusually When Supercooled Using X-Ray Lasers

Researchers have made a breakthrough in understanding the strange behavior of water at extremely low temperatures using ultra-short x-ray laser pulses in Japan and South Korea. Their findings reveal that water fluctuates between two distinct liquid states, and these fluctuations peak at -44°C, providing insight into the unique properties of this essential liquid.

Water, essential for life on Earth, exhibits unusual behavior compared to other liquids. Unlike most substances that become denser as they cool, water reaches its maximum density at 4°C. When cooled below this temperature, it begins to expand again, defying expectations. This expansion continues even below the freezing point under certain conditions, contributing to water’s anomalous properties, including unusual patterns in compressibility, heat capacity, and viscosity.

Using x-ray lasers, the Stockholm University team observed water at previously impossible speeds, capturing how it fluctuates between two liquid states. “What was special was that we were able to X-ray unimaginably fast before the ice froze and could observe how it fluctuated between the two states,” said Professor Anders Nilsson, a lead researcher.

These fluctuations, which peak at -44°C, explain why water behaves so strangely when supercooled. The study also highlights differences between light water (H₂O) and heavy water (D₂O), showing that the unusual properties are more pronounced in the lighter isotope due to nuclear quantum effects.

The findings mark a significant milestone in water research, ending decades of debate over its anomalous properties first noted by Wolfgang Röntgen. “Researchers can now confirm that water has a critical point in the supercooled regime,” Nilsson added. The next step for scientists is to determine the precise pressure and temperature conditions of this critical point.

Postdoctoral researchers Kyung Hwan Kim and Harshad Pathak, along with PhD student Alexander Späh, expressed excitement over the discovery, emphasizing its importance for further studies in chemical physics and the behavior of liquids at extreme conditions.

This study not only sheds light on water’s unique characteristics but also opens doors for new research in physics, chemistry, and material sciences, offering fresh insights into a substance that has fascinated scientists for over a century.