This Little Device Can Convert Light Into Motion

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walking polymer
A timelapse image of the walking polymeric device. Credit: Bart van Overbeeke

Yes, you read that absolutely right!

Scientists at Einthoven University of Technology, in collaboration with Kent State University, have developed a new polymer that displays an undulating (smooth, wave-like) motion when influenced by light. A strip of this polymeric material is clamped to a rectangular frame. On being illuminated, it “walks” on its own. This seemingly small device is the world’s first machine to convert light into motion. You can observe this for yourself in the video below:

Walking Polymer: How It Works

When one end of the polymer is exposed to light, it contracts, and the other end expands, causing it to form a bulge/wave. This deformation disappears once the illumination is removed. Although the material appears transparent, it absorbs the violet light (shown in the video) and creates a shadow behind itself. The team at Einthoven University of Technology, led by Professor Dr. Dick Broer, was able to create a continuous undulating motion using this ‘self-shadowing’ effect.

Continuous Undulating Movement

To produce the motion shown in the video, the team took a strip of the polymer, a little larger in size than the frame taken; so that once clamped, the material would already have a protruding bulge or wave. When one end of the device is illuminated with concentrated (LED) light, this end begins to bulge downward, creating a ‘dent’, hence causing the other end of the strip to be exposed to light, which then further bulges downward, while the former end regains its position upward due to the absence of light. This way the ‘dent’ and the ‘bulge’ create a continuous undulating movement, owing to which, the polymer ‘walks’. This way the device walks away from the source of light. To make it walk towards the light source, all that has to be done is for the device to be placed upside down.

Principle

To reach this particular behavior of the material, the team worked with liquid crystals. The basic underlying principle was to introduce a fast-responding, light-sensitive variant in a liquid-crystalline polymer network. This polymer was devised in a way that upon illumination, it would instantaneously deform, and upon the removal of illumination, it would immediately relax into its former state.

Applications

The maximum speed of the undulating movement recorded so far is equivalent to that of a caterpillar; at most, about half a centimeter per second. The team placed grains of sand on the polymer strip and observed that those were removed by the undulating motion. Also, the team informs that the strip can carry and transport objects that are bigger and heavier than the entire device itself, that too, uphill.

The team of researchers is of the opinion that it can be used to transport small items in places that are otherwise hard to reach or to keep the surface of solar cells clean.

Sources:

Eindhoven University of Technology
Nature

 

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