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How Ice Melts: Longstanding Mystery Solved Robert Roy Britt
Senior Writer  LiveScience.com  Thu Jun 30, 4:02 PM ET

Until now, scientists could not explain why ice cubes in your drink melt.
They've known the basics, but the details remained elusive.

A breakthrough new study, announced today, supports a leading theory that
melting starts when the fundamental structure of matter begins to crack.

Melting is considered a basic phenomena in physics. An understanding of how
it works is crucial to gaining a firm grasp on the physical world.

"Yet major details about the mechanisms that drive the melting of an ice
cube are missing," said Arjun Yodh of the University of
Pennsylvania. "Superficially, the principle is straightforward. As a solid
heats up, molecules within the ice acquire more energy and jiggle around
more, driving the transition from a solid to a liquid. This is true in
part, but reality is richer and more complex."

The problem is that the earliest phase of melting has never been seen.
Scientists can't see the atoms involved because they are so small and
because they are hidden in the structure of solid material.

So Yodh's team made some big atoms. Specifically, they made see-through
crystals that are like small beads and are visible in an optical microscope.

"The spheres swell or collapse significantly with small changes in
temperature, and they exhibit other useful properties that allow them to
behave like enormous versions of atoms for the purpose of our experiment,"
said Ahmed Alsayed, a University of Pennsylvania doctoral student and lead
author of a paper on the results in the July 1 issue of the journal
Science.

A premelting occurs in spots where atoms within solid crystals are not
perfectly aligned, and they begin to move. The changes are seen in pictures
taken as the material was heated. The imperfections are much like the
differences seen in wood grain, the scientists said.

"These motions then spread into the more ordered parts of the crystal,"
Alsayed said. "We could see that the amount of premelting depended on the
type of crystal defect and on the distance from the defect."

Nature could inspire technology as the process is investigated further.

"The existence of premelting inside solid materials implies that liquids
exist within crystals before their melting temperature is reached," Yodh
said. "Understanding this effect will provide insight for the design of
strong materials that are more or less impervious to temperature changes
and could also apply to our theories of how natural materials, such as
water, evolve in our environment."

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