Korean Team Unveils the "Mystery of Water" for the First Time in the World... Discovers "Critical Point" at Minus 60 Degrees [Reading Science]

POSTECH Research Team Observes World's First Liquid-Liquid Critical Point
Published in Science: Experimental Resolution to Decades-Long Debate

The "mystery of water," which humanity had been unable to solve for decades, has been experimentally elucidated for the first time thanks to a decade of dedication by a Korean research team. Experts note that the existing theories explaining the properties of water may now need to be revised.

Photo. Pixabay

The Ministry of Science and ICT announced that the research team led by Professor Kyunghwan Kim at Pohang University of Science and Technology, in collaboration with Stockholm University, has observed the "liquid-liquid critical point" of water for the first time in the world. The research results were published in the international journal Science on March 27 (Korean time).

Schematic diagram of experimental evidence for the existence of a liquid-liquid critical point observed using an X-ray free-electron laser. Below the critical point, water separates into two states, and above it, it mixes into one, experimentally proving the existence of the "liquid-liquid critical point" for the first time. Provided by Professor Kyunghwan Kim of Pohang University of Science and Technology

Water exhibits unique properties that set it apart from other liquids—for example, it becomes densest at 4°C and then becomes lighter as it cools further. To explain this, the hypothesis that "two distinct liquid states exist" was proposed. However, for decades, this could not be verified experimentally because water freezes rapidly at extremely low temperatures.

The research team overcame this challenge by creating water that does not freeze even at -70°C and by employing an X-ray free-electron laser to observe its molecular structure at ultrafast speeds. As a result, they identified for the first time the "critical point" near -60°C, where the boundary between the two liquid states disappears.

Carrying Out Experiments Amid COVID-19: "Breaking Through the Impossible"

This achievement is significant as it provides experimental conclusions to a long-standing academic debate. It strengthens the explanation that the unique properties of water arise from the competition between the two liquid states.

The research process was far from easy. Water at extremely low temperatures freezes within one ten-thousandth of a second, making observation extremely difficult, and it was impossible to approach the critical point using conventional methods. The research team overcame these limitations by introducing a new technique that used two types of infrared lasers simultaneously.

Research team photo. From left, Kyunghwan Kim, Professor at Pohang University of Science and Technology (corresponding author), Seonju Yoo, doctoral candidate (first author). Provided by the Ministry of Science and ICT

In particular, the key experiment, which was the final hurdle in the nearly decade-long research, was conducted during the COVID-19 pandemic. Even though international collaborators had difficulty coming on-site, the team pressed on with the experiments under strict quarantine measures, ultimately achieving success.

Professor Kyunghwan Kim said, "This study has brought a conclusion to the long-standing debate over the 'liquid-liquid critical point,'" adding, "It will serve as a new starting point for understanding the role of water."

The government also emphasized the significance of this achievement as a result of investment in basic research. Gu Hyukchae, the 1st Vice Minister of Science and ICT, stated, "This is an example of how long-term and stable research support can lead to world-class achievements," and added, "We will continue to create an environment where researchers can fully focus on their work."

This content was produced with the assistance of AI translation services.