Can light drive a motor?
You can see above this plastic motor powered by light in action. "Azobenzene-containing liquid-crystalline elastomers (LCEs) and their composite materials have the potential to show three-dimensional movement by light irradiation. With the LCE laminated films, a first light-driven plastic motor has been developed, which can convert light energy directly into a continuous rotation without the aid of batteries, electric wires, or gears." (Credit: Angewandte Chemie)
This plastic motor is the brainchild of Tomiki Ikeda, Professor of Polymer Chemistry at the Tokyo Institute of Technology, and the members of his lab. Among his research projects, here is a link to the photomobile smart materials based on crosslinked azobenzene liquid-crystalline polymers which were used to build these plastic motors.
According to Pink Tentacle, a site focused on technology advances in Japan, "this first-of-a-kind motor converts light directly into mechanical energy, thanks to a belt made from a special elastomer whose molecular structure expands or contracts when illuminated, depending on the wavelength of light."
But how the idea of such a motor came from? "Ikeda began working on the light-activated motor in 2003, after discovering that a plastic compound containing azobenzene would contract when exposed to ultraviolet light and resume its original shape when exposed to visible light. Since then, in addition to working on improving the material’s shape-shifting properties, Ikeda’s team has been looking at ways to use the material in a motor that converts light directly into motion. To test whether the material could be used as a mechanical power source, the researchers coated a polyethylene film with the shape-shifting plastic to create a 0.08-millimeter thick belt, which they looped around a pair of wheels measuring 10 millimeters and 3 millimeters in diameter. Then, by shining ultraviolet light on the belt near the smaller wheel and visible light near the larger wheel, the belt snapped into action and began turning the wheels. The larger wheel recorded a top speed of 1 rpm."
In "Shape-Shifting Plastic Converts Light Directly to Mechanical Energy" (July 28, 2008), GoodCleanTech gives additional details about this 'belt.' "The belt is then wound around two wheels (with diameters measuring 10 mm and 3 mm) like a conveyor belt. To test if the plastic would be able to move the wheels, UV light was shone on the part of the belt near the smaller wheel, while the part near the larger wheel was bathed in visible light."
This research work has been published in a recent issue of the German chemistry journal Angewandte Chemie International Edition under the title "Photomobile Polymer Materials - Towards Light-Driven Plastic Motors" (Volume 47, Issue 27, Pages 4986-4988, June 23, 2008). You can see on the left the inside cover of this issue. Here is a link to the abstract. The two illustrations of this post have been picked from this issue. (Credit: Angewandte Chemie).
Now, let's look at a Nanowerk Spotlight, "Plastic motors driven by light only" (Michael Berger, June 20, 2008) for additional details. "'A motor device is one of the most useful energy conversion systems that can convert input energy directly into a continuous rotation' Dr. Tomiki Ikeda explains to Nanowerk. 'Although chemomechanical motors and light-switchable molecular machines that can move objects by light have been demonstrated, light-driven plastic motors converting light energy directly into a rotation have not yet been realized.'"
Finally, here is the conclusion of the Berger article. "Apart from the fact that photomobile materials don't require batteries, electric wires, or gears, another intriguing aspect of these polymers is that they can be controlled remotely just by manipulating the irradiation conditions. By controlling the area of irradiation, wavelength and the intensity of the light, one can drive a film or fiber made of these materials in a manner of choice, which enables them to be used as a wide range of photo actuators."
Sources: Pink Tentacle, Japan, July 23, 2008; and various websites
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