Now That's Cool: Engineers Out to Thaw the Mysteries of Ice

August 7, 2008
Now That's Cool: Engineers Out to Thaw the Mysteries of Ice
(a) A TEM image of the artificial spin ice created by the Cumings group. (b) a close-up image of a small region of the artificial spin ice. Each link is only 500 nm in length. (c) A Lorentz TEM image of the same region as (b). Here the magnetic direction can be determined by the bright and dark lines in each link. Despite showing disordered configurations, each vertex obeys the ice rule. (Cumings research group, U-Md.)

( -- "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.

The Third Law of Thermodynamics is on the minds of John Cumings, assistant professor of materials science and engineering at the University of Maryland's A. James Clark School of Engineering, and his research group as they examine the crystal lattice structure of ice and seek to define exactly what happens when it freezes.

"Developing an accurate model of ice would help architects, civil engineers, and environmental engineers understand what happens to structures and systems exposed to freezing conditions," Cumings said. "It could also help us understand and better predict the movement of glaciers."

Understanding the freezing process is not as straightforward as it may seem. The team had to develop a type of pseudo-ice, rather than using real ice, in order to do it.

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 32º F/0º 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 Third Law of Thermodynamics states that as the temperature of a pure substance moves toward absolute zero (the mathematically lowest temperature possible) its entropy, or the disorderly behavior of its molecules, also approaches zero. The molecules should line up in an orderly fashion.

Ice seems to be the exception to that rule. While the oxygen atoms in ice freeze into an ordered crystalline structure, its hydrogen atoms do not.

"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."

Materials that violated the Third Law as originally written were found in the 1930s, mainly non-crystalline substances such as glasses and polymers. The Third Law was rewritten to say that all pure crystalline materials' entropy moves toward zero as their temperatures move toward absolute zero. Ice is crystalline—but it seems only its oxygen atoms obey the Law. Over extremely long periods of time and at extremely low temperatures, however, ice may fully order itself, but this is something scientists have yet to prove.

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 °F/-196 °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.

To overcome these problems, scientists have designed meta-materials, which attempt to mimic the behavior of ice, but are created out of completely different substances. A previous material, spin ice, was designed from rare earth elements and had a molecular structure resembling ice, with magnetic atoms (spins) representing the position of hydrogen atoms. However, it did not always behave like ice.

The Cumings group is refining a successor to spin ice called artificial spin ice, which was originally pioneered by researchers at Penn State. The newer meta-material takes the idea a step further.

"The original spin ice research went from one part of the periodic table to a more flexible one," said Cumings. "But artificial spin ice goes off the periodic table altogether."

Artificial spin ice is a collection of "pseudo-atoms" made of a nickel-iron alloy. Each pseudo-atom is a large-scale model made out of millions of atoms whose collective behavior mimics that of a single one.

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 1000 times smaller than the width of a human hair)—gives the researchers control over the material and freedom to explore how real atoms behave.

"It mimics the behavior of real ice but is completely designable with specific properties," Cumings said. "We can change the strength of the spin or reformulate the alloy to change the magnetic properties, which creates new bulk properties that we either couldn't get from normal materials, or couldn't control at the atomic level."

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.

"This is the first time the rules of ice behavior have ever been rigorously confirmed by directly counting pseudo hydrogen atoms," explained group member and postdoctoral research associate Todd Brintlinger. "We can track the position and movement of each pseudo atom in our model, see where defects occur in the lattice, and simulate what happens over much longer periods of time."

The ultimate impact of the research may go beyond civil engineering and the environment. "Although we're mimicking the behavior of ice," Cumings explained, "our meta-material is very similar to patterned hard-disk media. Magnetic 'bits' used in hard drives are usually placed at random, but memory density could be increased if they were in a tight, regular pattern instead.

"We've found that both hydrogen in ice and the pseudo-hydrogen in our artificial spin ice also behave as bits, can carry information, and interact with each other. Perhaps in the future, engineers will be inspired by this in their hard drive designs. The formal patterning and bit interactions may actually help to stabilize information, ultimately leading to drives with much higher capacities."

Provided by University of Maryland

Explore further: Stenciling with atoms in 2-D materials possible

Related Stories

Stenciling with atoms in 2-D materials possible

May 1, 2017

The possibilities for the new field of two-dimensional, one-atomic-layer-thick materials, including but not limited to graphene, appear almost limitless. In new research, Penn State material scientists report two discoveries ...

Entropy landscape sheds light on quantum mystery

May 12, 2017

By precisely measuring the entropy of a cerium copper gold alloy with baffling electronic properties cooled to nearly absolute zero, physicists in Germany and the United States have gleaned new evidence about the possible ...

Magnetic charge crystals imaged in artificial spin ice

August 28, 2013

A team of scientists has reported direct visualization of magnetic charge crystallization in an artificial spin ice material, a first in the study of a relatively new class of frustrated artificial magnetic materials-by-design ...

Magnetic monopoles in spin ice crystals

November 12, 2015

Today one of the major goals of physicists is to unify the forces of nature into a Grand Unified Theory that could portray a more elegant and comprehensive representation of the Universe. One step towards this big theory ...

New method developed for exploring frustrated systems

January 18, 2006

A new method for exploring the secrets of Mother Nature's frustrations has been developed by a team of physicists lead by Penn State University professors Peter Schiffer, Vincent Crespi, and Nitin Samarth. The research, which ...

Recommended for you

Water exists as two different liquids

June 26, 2017

We normally consider liquid water as disordered with the molecules rearranging on a short time scale around some average structure. Now, however, scientists at Stockholm University have discovered two phases of the liquid ...

Tiny magnetic tremors unlock exotic superconductivity

June 26, 2017

Deep within solids, individual electrons zip around on a nanoscale highway paved with atoms. For the most part, these electrons avoid one another, kept in separate lanes by their mutual repulsion. But vibrations in the atomic ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Aug 07, 2008
could the answer lie in the fact that the hydrogen atoms in a water molecule do not contain any neutrons? am i wrong in my assumption (i am not a chemist)?
not rated yet Aug 07, 2008
"The most common naturally occurring isotope of hydrogen, known as protium, has a single proton and no neutrons."

That is true, but why do you attribute the results to the lack of neutrons? Why wouldn't these protons snap into place?
not rated yet Aug 08, 2008
could the answer lie in the fact that the hydrogen atoms in a water molecule do not contain any neutrons?

maybe. in standard models, the presence of a neutron should not have any effect other than adding mass to the atom.

but, there has been more recent theories (mostly "fringe" theories, but some good ones) that neutrons exhibit a repulsion to other neutrons. Third law of thermodynamics may be counting on the (possible) necessity of neutrons to repel one another at cold temperatures in order to help arrange the atoms in a lattice.

here's two other physorg articles that talk about very recent discoveries about the interaction between atoms, that pretty much fly in the face of our traditional models.

not rated yet Aug 11, 2008
This is very interesting. Is it really the case though that the H atoms stop moving. What about zero point vibrations?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.