Scientists have captured the specific conditions under which two distinct liquid forms of supercooled water become indistinguishable.
Pohang – An international team led by Stockholm University’s Anders Nilsson, working with collaborators in South Korea, produced data that map how the liquids converge at the critical point, according to Science News. The work provides experimental confirmation of a phenomenon that had remained theoretical. The results were published in the latest issue of the journal Science.
The critical point was observed at about 210 kelvins (around -63 degrees Celsius) and about 1,000 times the pressure of Earth’s atmosphere at sea level.
Liquid at -70 degrees
The research builds on an idea that water can exist as two liquids: a high-density arrangement with tightly packed molecules and a more open, low-density arrangement. The research suggests water’s unusual properties arise from how the ratio of these two local structures shifts with temperature.
That duality could explain why water reaches its maximum density at 4 degrees Celsius and becomes less dense as it cools further. Related peculiarities include water’s unusually high boiling point for such a small molecule and the fact that ice is less dense than liquid water, according to Spektrum der Wissenschaft.
Earlier milestones by the Korean team showed that water can remain unfrozen below -45 degrees. In the latest experiments, the researchers created an extremely small amount of liquid water at -70 degrees Celsius. They tracked molecular movements at intervals of one ten-trillionth of a second.
“Through a decade of research, we have strengthened the hypothesis that water at room temperature exists in a state where the boundary between high- and low-density liquids has vanished, and its unique properties arise from the changing ratio of these two states with temperature,” said researcher Kim Kyung-hwan.