Researchers at Stockholm University utilized an ultrafast laser to investigate supercooled water before crystallization, revealing significant evidence of a long-predicted transition between two distinct liquid states. This included a marked increase in heat capacity and critical fluctuations.
Research indicates a rapid increase in heat capacity at 210 K, coinciding with density fluctuations in supercooled water. Image credit: POSTECH University.
Professor Anders Nilsson highlighted, “We captured X-ray images at unprecedented speeds prior to ice formation, allowing us to observe how the liquid-liquid transition fades, leading to the emergence of a new critical state.”
“For decades, various theories have attempted to explain these anomalous properties of water, one of which proposed the existence of a tipping point. We have now confirmed its presence,” he explained.
Using advanced X-ray laser technology, Professor Nilsson and his team identified a critical point in supercooled water at around 210 K (equivalent to -63 °C or -81 °F) under 1,000 atmospheres of pressure.
“Water stands out as it can exist in two liquid macroscopic phases, each with unique molecular bonding behaviors at low temperatures and high pressures,” the researchers noted.
“As temperature rises and pressure drops, these two liquid phases converge, presenting as a single indistinguishable phase.”
“This demonstrates a significant instability point, resulting in fluctuations across a broad temperature and pressure range, extending even to ambient conditions.”
“Water transitions between two liquid states, sometimes appearing as a mixture, leading to its distinctive properties,” they added.
“The state beyond the critical point is termed supercritical, with neighboring water remaining in that state.”
Another crucial discovery from this study is the slowdown in system dynamics upon reaching the critical point.
“Once you approach the tipping point, escaping becomes nearly impossible,” stated Dr. Robin Tybulski of Stockholm University.
Dr. Aigerim Karina, a postdoctoral researcher, remarked, “It’s fascinating that amorphous ice, extensively studied, serves as a gateway to this crisis zone. This inspires my future research and underscores the potential for discoveries in well-established fields like the study of water.”
Dr. Iason Andronis, a student, expressed, “Measuring water under such low-temperature conditions without freezing it is a dream realized.”
“Many have aspired to pinpoint this critical point, but we lacked the necessary technologies until the advent of the X-ray laser,” he added.
“It’s captivating to consider that water is the sole supercritical liquid under ambient conditions conducive to life, and without it, life as we know it wouldn’t exist,” explained Dr. Phibos Perakis from Stockholm University.
“Is this merely coincidental, or could we uncover essential insights in the future?”
Professor Nilsson mentioned, “The origins of water’s unusual properties have been debated for over a century, tracing back to Wolfgang Roentgen’s early investigations.”
“Researchers within the realm of water physics now align with a model suggesting the presence of a critical point in supercooled states.”
“Our next goal is to explore the implications of these findings for various physical, chemical, biological, geological, and climate-related processes, which poses a significant challenge for the years ahead.”
Findings have been published in a study dated March 26th in Science.
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Song Juyu et al. 2026. Experimental evidence of a liquid-liquid critical point in supercooled water. Science 391 (6792): 1387-1391; doi: 10.1126/science.aec0018
Source: www.sci.news
