That’s the most remarkable thing about a new polymer material developed by scientists at Eindhoven University of Technology and Kent State University. The researchers clamped a strip of the material in a rectangular frame to create a device the size of a paperclip; when illuminated, it undulates – and propels itself forward.
The mechanism works because light causes one side of the material to contract and the other to expand, forming a bulge. When researchers shone a concentrated light-emitting diode (LED) light on it from the front, the illuminated part of the strip would bulge downward, creating a “dent.” The next part of the strip then deforms after coming into contact with the light. The “dent” progressively moves backwards, creating a continual undulating movement, and the device essentially walks away from the light. If placed upside down, the wave would travel in the opposite direction – causing the device to walk toward the light.
Liquid crystals, like those use in liquid crystal displays (LCDs), were employed to engineer the material. By incorporating a fast-responding, light-sensitive variant in a liquid crystalline polymer network, the response was translated to an instantaneous deformation of the strip when illuminated; the deformation disappears the instant the light is gone. Although the material appears transparent to the human eye, it fully absorbs the violet light the researchers used and creates a shadow behind itself.
As published in a recent edition of the journal Nature, the device is the world’s first machine to convert light directly into walking, simply using one fixed light source. Such a mechanism may be used to keep the surface of solar cells clean, or to transport small items in hard-to-reach places. It’s powerful enough to transport objects much bigger and heavier than itself, uphill. Maximum speed is about half a centimeter per second, about the speed of a caterpillar.