Light-Driven Pulleys Turn Plastic Motor

Tomiki Ikeda at the Tokyo Institute of Technology and colleagues have developed the first plastic motor powered only by light (Angew. Chem. Int. Ed. 2008, 47, 4986). The researchers used an organic-dye-based material to convert light energy directly into mechanical work without the aid of batteries or electric wires. To test whether the material could turn a homemade, millimeter-sized two-wheel pulley system, the researchers made a polyethylene belt and coated it with the material, which is a cross-linked liquid-crystalline elastomer that contains photochromic azobenzene dyes. The material reversibly expands or contracts when illuminated, depending on the wavelength of the light. Simultaneously applying ultraviolet and visible light to different points on the belt changed the belt's shape and rotated the pulley wheels; shutting off the light stopped the motion. Other photochromic polymers can bend or expand, but they can't undergo that type of continuous, complex three-dimensional movement, the researchers note. Ikeda suggests that the material could be used at various dimensions, ranging from nanoscale motors to the plastic wheels of a passenger car.