16 February 2011

Cosmic ice crystals reveal nanotech bonus

By
Cosmos Online
A discovery of 'ice lava' crystals with unusual expansion properties from volcanoes on Saturn and Neptune's moons has given scientists new insight into how nanotechnology may develop, and could inspire new meta-materials.
Enceladus ice

This image shows geyser-like eruptions of ice particles and water vapor shooting out from the south pole of Saturn's moon, Enceladus. The structure of the crystals have now revealed some very unusual properties. Credit: NASA/JPL/Space Science Institute

ASHLAND: A discovery of ‘ice lava’ crystals with unusual expansion properties from volcanoes on Saturn and Neptune’s moons has given scientists new insight into how nanotechnology may develop, and could inspire new meta-materials.

According to the researchers, the finding could lead to the development of new materials that can retain their structure in fluctuating temperatures, as the crystals made from methanol monohydrate posses the rare ability to shrink when heated and expand when compressed.

“What we’re interested in here is the arrangement of structural units in methanol monohydrate which cause [the crystals] to exhibit the weird elastic properties we observed,” said Dominic Fortes, a planetary geologist at University College London.

Expanding and compressing in all directions

Fortes made the discovery, published in Science, while studying icy moons such as Neptune’s Triton, and observed the crystals using neutron scattering – a technique that allows the structure and dynamics of materials to be examined under different conditions at atomic or molecular levels.

Made from methanol monohydrate – a one to one mix of water and methanol and a key ingredient in outer solar system ice – the crystals revealed to the researchers that when heated at room pressure, they expand in one direction while shrinking in the other two. When heated under an even pressure, the crystals expanded in two directions, while compressing in the third.

This unexpected expansion (elongating and thinning) under uniform pressure is known as negative linear compressibility (NLC). NLC materials are extremely rare with only around 15 known examples, and what causes this property is still relatively unknown.

Understanding the ice bridge

“In methanol monohydrate what we have is basically an ice bridge,” said Fortes. “At its heart, a bridge is a structure capable of distributing forces in such a way that one can move heavy loads over an open space.”

But, said Fortes, even an ice bridge – which in the outer Solar System, at temperatures of -200 degrees C, is as strong as granite – would be useless here on Earth, as the bridge would melt.

“We need to understand the aspects of its architecture which are useful to us, and build [the] bridge out of stuff that’ll do a useful job.”

Building artificial muscles and deep sea objects

According to Fortes, this research will help scientists who want to identify meta-materials (stuff with counter-intuitive elastic or optical properties) to carry out micromechanical tasks in unusual environments, such as deep under the ocean, where the pressure becomes increasingly high.

Biologists are also interested in this kind of material, said Fortes. “Rather than compression, they want to put them under tension and have them shrink in a certain way.” This phenomenon, called stretch densification, is something researchers want to employ in artificial muscles.

“It was certainly unexpected,” said Fortes. “As a planetary geologist, my focus is understanding the mechanisms behind volcanic eruptions in the outer solar system. If my results open doors for more applied science back on Earth, that’s a bonus.”

Predictable shape-shifters handy in nanotech

Such a finding is of significant interest to scientists in developing nanotechnology because the predictable expansion of such crystals, along with their shape-shifting properties, makes them viable tools for nano-switches, or other microscopic, pressure-controlled valves.

Richard Wagner, director at the Institut Laue Langevin in Paris, agrees, “Future applications of NLC materials in nanotechnology, which are based on a precise knowledge of the structure and dynamics in those materials, may be seen in the development of nano/micro pressure sensors and nano-mechanical devices such as nano-switches.”

“The present discovery of the NLC effect on methanol crystals certainly will help to gain that understanding,” Wagner added.

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