Polymer ribbons make waves in response to light

Abstract

Researchers have developed a polymer ribbon that adopts continuous mechanical wavelike motions when illuminated with a fixed source of ultraviolet light. The wave motion can eject tiny objects, such as sand particles, from the film surface and transport a larger object, such as a rod, along the length of the film. The waves move toward light with the ribbon in one orientation and away from light when it is reversed. And the film can “walk” when attached to a lightweight frame. Dirk J. Broer of Eindhoven University of Technology and coworkers devised the new material (Nature 2017, DOI: 10.1038/nature22987). A possible application is self-cleaning solar cells that remove sand and dust particles that accumulate on their surfaces. The film, a liquid-crystal network, contains a light-sensitive azobenzene dye that isomerizes from trans to cis conformation in response to UV light, shrinking the material, and relaxes quickly back to the trans isomer