Shine a light and watch them shrink

17 Jun 2002

European researchers have developed a material that could herald a new wave of light-responsive micromachines.

By adding photosensitive molecules to an elastomer, researchers at the University of Freiburg, Germany, and UK-based Cambridge University have created a material that contracts when exposed to ultraviolet light, and expands again when the light is removed.

The recent development from Heino Finkelmann and colleagues hinges on molecular rods that bend when they adsorb light. The researchers stretched a nematic elastomer and added these rods to the elastomer's extended side-bonds or cross-links.

On shining an ultraviolet light at the elastomer network, the researchers were surprised to see the material contract by up to 24%, and then revert back to its original shape when the light was removed. "Solids that optically and reversibly change their dimensions by 20% were previously unknown," said Finkelmann.

Further investigations convinced Finkelmann and colleagues that the rods were responsible for their elastomer's "shape-shifting", and they now plan to scale-up this behavior to match the huge shape changes that are seen in thermally treated elastomers. "These photostrains are comparable to thermal effects," said Finkelmann. "Ultimately we can expect nematic elastomers to generate optical strains of up to the 400% [limit] that has been achieved thermally."

If the researchers reach this goal, they anticipate that photosensitive elastomers will hold interesting possibilities as actuators and other devices that generate mechanical work.