Sunday, December 1st, 2013
A recently published research paper from the University of Pittsburgh’s Swanson School of Engineering and the Air Force Research Laboratory at Wright-Patterson Air Force Base describes plastics that can “snap” when triggered by light. The light energy is converted into mechanical action with no need for traditional machine components such as switches and power sources.
“I like to compare this action to that of a Venus Fly Trap,” says M. Ravi Shankar, associate professor of engineering at Pitt, whose research focuses on innovative nanomaterials. “The underlying mechanism that allows the Venus Fly Trap to capture prey is slow. But because its internal structure is coupled to use elastic instability, a snapping action occurs, and this delivers the power to shut the trap quickly.
Shankar, collaborating with Timothy J. White of the Air Force Research Laboratory and Matthew Smith, assistant professor of engineering at Hope College (Holland, MI), focused on the elastic instability of azobenzene-functionalized polymers (both amorphous polyamides and liquid crystal polymers) prepared by the Air Force lab, which showed unprecedented actuation rates and output powers. With light from a hand-held laser pointer, the polymers generated high amounts of power that converted the light into mechanical work without any other power source.
“As we look to real-world applications, you could activate a switch simply by shining light on it,” Shankar said. “For example, you could develop soft machines such as stents or other biomedical devices that can be more adaptive and easily controlled. In a more complex mechanism, we could imagine a light-driven robotic or morphing structure, or micro-vehicles that would be more compact because you eliminate the need for an on-board power system. The work potential is built into the polymer itself and is triggered with light.”
Scientists have known for years about a class of photo-responsive polymers that would react to light with no other power source. Problem was, their movement was very slow. The research team shaped the polymer into a geometry resembling a hummingbird’s beak or the trap of a Venus Fly Trap plant. When irradiated with light, the polymer initially deforms slowly, but when it reaches a critical state, it snaps. Shankar told KurzweilAI they generated actuation in millisecond time-scales and power approaching kilowatts per cubic meter at radiation intensities far less than 100 milliwatts per square centimeter and potentially over long distances.
Shankar, White and Smith published their findings in the Proceedings of the National Academy of Sciences in early November. Shankar’s research was enabled through an eight-week Air Force Office of Scientific Research Summer Faculty Fellowship.