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Physics

Light makes polymer walk like a caterpillar

Bart van Overbeeke Film made of photosensitive liquid crystal moves when illuminatedBart van Overbeeke

A paper-clip-sized film made of a photosensitive liquid crystal moves whenever it is exposed to light. Guided by light, this film made of a special polymer stretches and contracts, and can travel over a surface in a movement that resembles the dragging movement of a worm. The film was created by experts in new materials at Eindhoven University of Technology in the Netherlands, and at Kent State University in the United States (Nature, June 29, 2017). The structure reaches a maximum speed of half a centimeter per second, more or less the pace of a moving caterpillar. The polymer film exhibits this motor behavior because one of its sides contracts immediately when it comes in contact with light, while the other expands. These opposing reactions make the film stretch when it is illuminated, creating an undulating movement. As soon as the polymer stops receiving light, the structure enters a resting state. According to the authors of the paper, a film made of this material responds so efficiently to the light stimulus that it could even be used to transport objects that are larger and heavier than itself. This photosensitive polymer may also be useful for developing self-cleaning surfaces that exploit these expansion/contraction movements to remove dirt from floors.

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