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Packing more punch into polymer devices

Liquid crystals and bioinspired engineering help create soft materials that quickly unleash energy

by Matt Davenport
February 27, 2017 | A version of this story appeared in Volume 95, Issue 9

Credit: Angew. Chem.
Watch as UV light drives this pair of periodic polymer strips to bend, twist, and ultimately burst.

There’s no shortage of soft robots or actuators able to move themselves and other cargo, but these malleable machines tend to work slowly, says Nathalie Katsonis of the University of Twente. Researchers led by Katsonis and Stephen P. Fletcher of the University of Oxford want speedier energy delivery and decided to turn to liquid crystal chemistry. The researchers began with a thin film of an elastomeric liquid crystal featuring light-sensitive azobenzene moieties. By shining ultraviolet and visible light onto specific portions of the liquid crystal, the team created alternating stripes in the film such that half contained a well-aligned polymer, while the remaining stripes were more disordered. Then the researchers cut the striped film into ribbons and stuck two together, back-to-back. When illuminated with another dose of UV light, the alternating polymer stripes expanded at different rates, creating a strain that built up in the paired ribbons. The ribbons bent, twisted, and ultimately split apart, rapidly releasing their pent-up energy in a manner similar to the bursting seed pods of orchids and other plants (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201611325). Katsonis believes this work and future efforts will help elucidate the molecular underpinnings of the complex, macroscopic motions seen in nature, but they could also help researchers make more powerful soft robots and microfluidic systems.

A scheme shows the basic construction and operation of a new device with programmed material properties, allowing it to build and then rapidly discharge mechanical energy.
Credit: Angew. Chem. Int. Ed.
By joining strips with periodic polymer properties, researchers created a device that strains itself until it bursts under UV light, causing the strips to curl.


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