The motion of the new material is due to the fact that one side contracts 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.

The scientific team, led by TU/e professor Dick Broer (Functional Organic Materials and Devices, Department of Chemical Engineering and Chemistry), was able to create a continual undulating movement, using this ‘self-shadowing’ effect. They attached a strip of the material in a frame shorter than the strip itself, causing it to bulge. Then they shone a concentrated led light on it, from in front. 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 maximum speed is equivalent to that of a caterpillar, about half a centimeter per second. The researchers think it can be used to 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 undulating movement. The mechanism is so powerful that the strip can even transport an object that is much bigger and heavier than the device itself, uphill.

Source: TU/e Press Team