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Ice, Served Warm

26 August 2005 (All day)
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Ice, ice baby. Forming ice crystals like these at room temperature might be tough, but scientists have managed it with a single drop of water.

Room-temperature ice sounds like a contradiction. But it might not be such a soggy invention. In a strong electric field, scientists report that warm water seems to immobilize in a distinctly icy fashion. Although it sounds unnatural, room-temperature ice might occur throughout the natural world--and even explain why the regular kind forms.

Water molecules are dipoles; most of their negatively charged electrons are clustered at one end of the molecule, leaving the other end positively charged. In liquid water, the charges are only loosely arranged But if an electric field is applied, the charges snap into formation, all pointing in the same direction. When water freezes from the cold, its molecules lock into a hexagonal shape. Theoretical physicists have predicted that a large enough electric field should ‘freeze' water molecules in a similar way. However, simulations have calculated that that would take a huge electric field, about 109 volts per meter, to overcome water's thermal energy--100 times more than it takes to unleash a lightning bolt.

The simulations were wrong. In the 19 August issue of Physical Review Letters, researchers from Seoul National University in Korea report this effect at fields 1000 times weaker than predicted. The group began by placing a water droplet on a gold surface and passed the tip of a scanning tunneling microscope within a few angstroms of the drop. Over such short distances, even small electric fields are very intense. The team applied a field of tens of millivolts over a few angstroms, which is equivalent to just 106 volts over a meter. So the team was shocked to see a thin layer of water form from the drop that appeared solid, despite an ambient temperature of 20 degrees Celsius.

"I found the paper very intriguing," says Harald Reichert, a physicist at the Max Planck Institute for Metal Research in Stuttgart, Germany. Although he cautions that the researchers do not know if the solid layer was structured like normal water ice, Reichert notes this may solve the mystery of how normal ice begins to freeze. If tiny ice nuclei are forming all the time in the tiny fields of crevices, they may be the seeds for regular ice crystals.

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