Revealing water’s secrets

Revealing water’s secrets

4:21 PM, 2nd August 2011
Revealing water’s secrets
Researchers Yang Zhang and Sow-Hsin Chen.

 

CAMBRIDGE, US: An MIT doctoral student and a team of researchers have carried out new experiments supporting a controversial theory about water’s behaviour that could help explain some of its mysteries.

Their findings, recently published in the Proceedings of the National Academy of Sciences, could have important implications for fields ranging from biology to construction, the researchers said, because the behaviour of water affects so many important processes.

Water is “Probably the most weird substance on earth,” said Yang Zhang, lead author of the PNAS paper, which was based on his doctoral thesis research. “It behaves very differently from other materials,” he said, with scores of anomalous characteristics. The work was done in collaboration with Zhang’s doctoral supervisor, Sow-Hsin Chen, professor in MIT’s Department of Nuclear Science and Engineering, and six other co-authors.

All materials undergo phase transitions between the basic states of matter, wherein, a material’s properties can change significantly and suddenly. A theory proposed about two decades ago explained some of water’s odd behaviour by suggesting that a similar transition may take place between two different liquid states.

The new research, which probed water’s molecular structure under a wide range of pressures and temperatures, provided some evidence for the existence of this liquid-liquid transition.

Evidence for this posited transition has been difficult to obtain because it occurs only at temperatures and pressures at which water normally could not exist in liquid form. One key trick is the use of tiny tubes of silica. The tight confinement made it possible to maintain water in liquid form far below its normal freezing point.

With the water molecules in this state, Zhang, was able to probe their density at the National Institute of Standards and Technology and he gradually varied the pressure and temperature. “Supercooled water that remains liquid below the normal freezing point is relatively easy to produce. Water can also be “superheated” in a microwave oven to well above the boiling point, flashing to a boil all at once only when it is disturbed in some way,” said Zhang.

Because water is key to so many aspects of people’s lives, these phenomena could have important consequences. For example, Chen believes the fact that living organisms apparently cannot be revived after being subjected to temperatures below about minus 45 C is explained by water’s transition to a lower-density state that prevents proteins from functioning. This density difference could also affect construction. If the theory is correct, this critical temperature could set a fundamental limitation for both organisms and concrete buildings.

“The building blocks of our bodies and the building blocks of our society,” said Zhang, “Both have a lower limit of temperature that is based on the properties of water.” But by understanding those limits, he said, it might be possible to alter the water - for example, by dissolving certain chemicals in it - to change the transition points and lower that limit.

(C) Massachusetts Institute of Technology News

 

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