Shortened By the Light

Stretching it. The new material resembles this material, which shrinks when heated.

It's not such a stretch to think of uses for a new rubbery material. Shine ultraviolet light on the substance and it shrinks; leave it in the dark and it grows. The novel material might lead the way to optical switches in future computers, as well as other exotic uses.

Getting a substance to shrink or grow is nothing new; if you heat an iron rod, for instance, it will expand. Scientists have also exposed chunks of solid matter to electric fields to change their size and succeeded with several other stimuli, but they never were able to get matter to grow or shrink very much in response to light--until now.

Heino Finkelmann of the Albert Ludwigs University in Freiburg and his colleagues in Germany and the United Kingdom have created a rubbery substance that has a lot of rodlike molecules pointing in the same direction. As they describe in the 2 July issue of Physical Review Letters, the molecules reshuffle their bonds when exposed to ultraviolet light so that they are bent, rather than straight. The bent molecules ruin the nice, ordered state where all the molecules point the same way; soon, the molecules point in different directions, causing the substance to shrink by about a quarter of its length and thicken as well. "You observe a huge effect that cannot be seen for any other material," says Finkelmann, who adds that they have created yet another substance that shrinks by 75%. When left in the dark, both substances grow back to their original size.

"This is great stuff," says Peter Palffy-Muhoray of Kent State University in Ohio, who believes that such substances might be useful in building optical switches, changeable lenses, and little light-operated transducers. "There's going to be a lot of activity in this area--and I think this is an important first paper."

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