World first: New polymer moves itself under the influence of light

polymer

Scientists have developed a new material that can move itself forward under the influence of light. To this end, they clamp a strip of this polymer material in a rectangular frame. When illuminated it goes for a walk all on its own. This small device is the world"s first machine to convert light directly into walking, simply using one fixed light source.

The maximum speed is equivalent to that of a caterpillar, about half a centimeter per second. Researchers said, it can transport small items in hard-to-reach places or to keep the surface of solar cells clean. They placed grains of sand on the strip and these were removed by the wave movement. The mechanism is so powerful, the strip can transport even an object that is much bigger and heavier than the device.

reaction to light

The motion of the new material contracts one side in reaction to light, and the other one expands, causing it to bulge when illuminated. That deformation disappears instantaneously once the light is gone. Although the material looks transparent to the human eye, it fully absorbs the violet light the researchers used, thus creating a shadow behind it.

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Study lead researcher Dick Broer from Eindhoven University of Technology creates a continual undulating movement, using this "self-shadowing" effect. They attached a strip of the material in a frame shorter than the strip, causing it to bulge.

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The part of the strip that is in the light, starts to bulge downward, creating a "dent" in the strip. As a consequence, the next part of the strip comes in the light and starts to deform. This way the "dent" moves backwards, creating a continual undulating movement.

This sets the device in motion, walking away from the light. When the device is placed upside down, the wave travels in the opposite direction, causing it to walk towards the light.

The research team managed to reach this specific behavior of the material using LCD’s. The principle relies on the incorporation of a fast responding light-sensitive variant in a liquid crystalline polymer network. This response is translated to an instantaneous deformation of the strip when illuminated, and relaxation directly when light absent.

More information: [nature]