Photomechanical 'snap' effects in polymers are triggered by light from laser pointer

Pittsburgh, PA--Researchers at the University of Pittsburgh are investigating photomechanical polymers that "snap" when triggered by light, thereby converting light energy into mechanical work (potentially eliminating the need for traditional machine components such as switches and power sources, they say).¹ The devices are bistable arches that have actuation rates of up to 102 mm/s under intensities of much less than 100 mW/cm².

"I like to compare this action to that of a Venus flytrap," says M. Ravi Shankar, lead author of the study. "The underlying mechanism that allows the Venus flytrap 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."

The research was performed by Shankar in collaboration with Timothy White of the Air Force Research Laboratory at Wright-Patterson Air Force Base and Matthew Smith, assistant professor of engineering at Hope College (Holland, MA).

Snap!
Focusing on this elastic instability, Shankar examined polymeric materials, prepared by researchers at the Air Force Research Laboratory, which demonstrated unprecedented actuation rates and output powers. With light from a hand-held laser pointer, the polymers generate high amounts of power to convert the light into mechanical work without any onboard power source or wiring. Specific functions could be preprogrammed into the material so that the device would function once exposed to a light source and controlled by changing the character of the light.

Because the snap-through of the device is symmetrical, the actuation can be bidirectional and reversible.

REFERENCE:

1. M. Ravi Shankar et al., PNAS early edition (2013); doi: 10.1073/pnas.1313195110