Mission creep: illumination influences undulating movement of material

A polymer has been developed that moves forward like a caterpillar when exposed to light.

Bart van OverbeekeTU Eindhoven researcher Anne Hélène Gélébart showing the walking device.

A material that can creep across and climb up surfaces and into otherwise inaccessible places has been created.

A strip of the polymer material is clamped in a rectangular frame the size of a paperclip and, when illuminated by a single light source, ‘walks’ all by itself.

Maximum speed is about half a centimetre per second and researchers think it can be used to transport small items into places difficult to access in any other way, or to keep the surface of solar cells clean.

In an experiment, grains of sand were placed on the strip and were then removed by the undulating movement. The powerful mechanism can transport a much larger and heavier object uphill.

Scientists at Eindhoven University of Technology and Kent State University, who developed the new material, revealed that the motion of the polymer is caused by the contraction of one side of the material reacting to light while the other one expands, causing it to bulge when hit by violet light.

The motion was achieved by attaching a strip of the material to a frame that was shorter than it was, causing it to bulge in the middle.

When light was shone on it, it bulged downwards forming a ‘dent’ in the strip. The next part of the strip then came into the light and reacted in the same way, creating the undulating movement.

When the device was placed upside down, the wave moved in the opposite direction, causing it to ‘walk’ towards the light.

Scientists developed the material using ‘liquid crystals’ (such as in LCDs) as a base. The principle relying on the incorporation of a fast responding light-sensitive variant in a liquid crystalline polymer network.

The research findings were published in the journal Nature.