Probing the weirdest substance on earth

Water has some unusual properties – many of which scientists still don’t understand – and a team from MIT have been probing how water behaves in confined spaces. A controversial theory proposed 20 years ago suggests that water can exist in two different liquid states in which the arrangement of water molecules changes so that the two states have very different densities.

Now, the team from MIT’s department of nuclear science and engineering have been probing water’s molecular structure under a wide range of pressures and temperatures at which it would not exist in liquid form.

“Water is probably the most weird substance on Earth,” said Yang Zhang, who carried out the research as part of his doctoral thesis. “It behaves very differently from other materials, with scores of anomalous characteristics.”

Zhang tightly confined water in tiny tubes of silica where it became supercooled and unable to crystallise. He used a neutron beam from a reactor at the National Institute of Standards and Technology and gradually varied the pressure from normal sea-level atmospheric pressure to about 3,000 times that amount. The temperature varied over a range of 170?C.

Check out a video of Zheng demonstrating supercooled water under LabNews Recommends at www.youtube.com/labnews.

He found a difference in water’s density by approaching the expected transition temperature – where the water would change state – from opposite directions, as predicted by the theory.

The work – published in the Proceedings of the National Academy of Sciences – could have important implications in biology and manufacturing. Below -45°C, the researchers believe living organisms like plants may be unrevivable because the water has changed to a lower-density state that prevents proteins from functioning. Water held in concrete on roads and in buildings that is subject to similar temperatures could also crack.“The building blocks of our bodies and the building blocks of our society both have a lower limit of temperature that is based on the properties of water,” Zhang said. “But by understanding these limits, it might be possible to alter water to change the transition points and lower that limit.”