這是2005/8/26 science 的報導
Ice, Served Warm
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 蟐reeze?water molecules in a similar way. However,
simulations have calculated that that would take a huge electric field,
about 10^9 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 passed the tip
of a scanning tunneling microscope within a few angstroms of a thin film of
water. 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.
http://sciencenow.sciencemag.org/cgi/content/full/2005/826/2
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