Department Dosch – Science in Press

New Scientist, vol 182, issue 2443, page 14
17 April 2004

A THIN layer of water is what allows glaciers to slide and ice skaters to glide. But it may not be water as we know it. An investigation of the lubricating liquid that forms when ice comes into contact with a solid shows that the water is super-dense.

While 1 cubic centimetre of normal water has a mass of 1 gram, the same volume of the newly discovered phase would be 17 per cent heavier. Its density is "unbelievable", says Helmut Dosch of the Max Planck Institute for Metals Research in Stuttgart, Germany, head of the research group that carried out the work.

To simulate what happens where a glacier meets bedrock or a skater's blade comes in contact with the rink, the researchers placed a small block of ice onto a polished piece of silicon dioxide. The sample was then cooled and bombarded with a beam of high-energy X-rays, which bounce off regions where the density changes. By analysing the reflected X-rays, the team was not only able to deduce that a thin liquid layer formed at the ice-silicon dioxide junction, but also estimate its density, Dosch reports in a paper to appear in Physical Review Letters.

The liquid layer was present even when the temperature was -17 °C. Dosch believes that the liquid layer forms because water molecules in the ice try to bond with the surface of the silicon dioxide rather than with each other, causing the ice to break up.

This interfacial melting has been observed before, says John Wettlaufer, a geophysicist at Yale University, but this is the first time anyone has been able to study the structure of the liquid. Understanding the implications for glaciers and skaters - where friction also plays a role in melting - will require many more experiments.

So far, little is known about this new, super-dense water. How exactly are its molecules arranged? Will impurities dissolve in it? Is it viscous? These are the questions to answer next, Dosch says.

Jenny Hogan