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Posted: August 6, 2008

Now that's cool: Engineers out to thaw the mysteries of ice

(Nanowerk News) "Ye canna change the laws of physics!" Scotty warned Captain Kirk on Star Trek. But engineers and physicists at the University of Maryland may rewrite one of them.
Despite being one of the most abundant materials on Earth, water, particularly how it freezes, is not completely understood. Most people learn that as temperatures fall, water molecules move more slowly, and that at temperatures below 32 degrees F / 0 degrees C, they lock into position, creating a solid-ice. What's going on at a molecular level, says Cumings, is far more complicated and problematic. For one thing, it seems to be in conflict with a fundamental law of physics.
"The hydrogen atoms stop moving," Cumings explains, "but they just stop where they happen to lie, in different configurations throughout the crystal with no correlation between them, and no single one lowers the energy enough to take over and reduce the entropy to zero." So is the Third Law truly a law, or more of a guideline? "It's a big fundamental question," says Cumings. "If there's an exception, it's a rule of thumb."
Creating an accurate model of ice to study has been difficult. The study of ice's crystal lattice requires precise maintenance of temperatures below that of liquid nitrogen (-321 degrees F / -196 degrees C), and also a lot of time: no one knows how long it takes for ice to ultimately reach an ordered state-or if it does at all. Experiments have shown that if potassium hydroxide is added to water, it will crystallize in an ordered way-but researchers don't know why, and the addition shouldn't be necessary due to the Third Law's assertion that pure substances should be ordered as they freeze.
As with the original spin ice, magnetic fields are stand-ins for hydrogen atoms. Working at this "large" scale - each pseudo-atom is 100x30 nanometers in size (100 nanometers is 1,000 times smaller than the width of a human hair) - gives the researchers control over the material and freedom to explore how real atoms behave.
The team is also able to image the behavior of the pseudo hydrogen atoms using an electron microscope - such direct observation is not possible with the original spin ice or real ice.
Source: University of Maryland