Water, always important, always controversial, always fascinating, remains surprising. For a substance that is ubiquitous on Earth, three quarters of our planet is covered with it, researchers can still be surprised by some of its properties, according to Arizona State University chemist C. Austen Angell.
Angell, a Regents Professor in ASU’s School of Molecular Sciences, has spent a good portion of his distinguished career tracking down some of water’s more curious physical properties. In a new piece of research just published in Science (March 9), Angell and colleagues from the University of Amsterdam have, for the first time, observed one of the more intriguing properties predicted by water theoreticians – that, on sufficient super-cooling and under specific conditions it will suddenly change from one liquid to a different one. The new liquid is still water but now it is of lower density and with a different arrangement of the hydrogen bonded molecules with stronger bonding that makes it a more viscous liquid.
“It has nothing to do with ‘poly-water,'” Angell adds recalling a scientific fiasco of many decades ago. The new phenomenon is a liquid-liquid phase transition, and until now it had only been seen in computer simulations of water models.
The problem with observing this phenomenon directly in real water is that, shortly before the theory says it should happen, the real water suddenly crystallizes to ice. This has been called the “crystallization curtain” and it held up progress in understanding water physics and water in biology for decades.
“The domain between this crystallization temperature and the much lower temperature at which glassy water (formed by deposition of water molecules from the vapor) crystallizes during heating has been known as a ‘no-man’s land,'” Angell said. “We found a way to pull aside the ‘crystallization curtain’ just enough to see what happens behind – or more correctly, below – it,” Angell said.
