A Korean research team has proven for the first time in the world the hypothesis of water's "liquid-liquid critical point," a long-standing puzzle in the scientific community.
The Ministry of Science and ICT (MSIT) announced on the 27th that a research team led by Professor Kim Kyung-hwan at Pohang University of Science and Technology (POSTECH) observed water's "liquid-liquid critical point" for the first time through a joint experiment with Professor Anders Nilsson's team in the Department of Physics at Stockholm University in Sweden.
Ordinary liquids become heavier as their temperature drops until just before freezing, but water becomes heaviest at 4 degrees Celsius and then actually becomes lighter as it cools further. This unique characteristic is why only the surface of rivers and lakes freezes in winter while liquid water is maintained below, allowing life to survive underneath.
However, the fundamental reason why water behaves differently from other liquids had remained a long-standing question in the scientific community.
One proposed answer to this question is the "liquid-liquid critical point" hypothesis. The hypothesis assumes that water coexists in two liquid phases — "high-density water" and "low-density water" — and that when a specific temperature (the critical point) is reached, the distinction disappears and becomes the water we see in everyday life.
The scientific community expected this critical point to exist in the ultra-low temperature range between minus 40 and minus 70 degrees Celsius. However, because water freezes extremely rapidly the moment it drops below minus 40 degrees Celsius, no case had ever successfully proven the existence of the critical point.
