This animated image shows an azobenzene-functionalized liquid crystalline polymer moving when exposed to broadband ultraviolet-visible light. Image: Jeong Jae Wie, Inha University/AFRL.One of the impediments to developing miniaturized, ‘squishy’ robots is the need for an internal power source that overcomes the power-to-weight ratio for efficient movement. An international group of researchers from the University of Pittsburgh, the US Air Force Research Laboratory and Inha University in South Korea has now identified new materials that can directly convert ultraviolet (UV) light into motion without the need for electronics or other traditional methods. The research is described in a paper in Nature Communications.
The group includes M. Ravi Shankar, co-author and professor of industrial engineering at Pitt's Swanson School of Engineering; the lead author is Jeong Jae Wie, assistant professor of polymer science and engineering at Inha University. The experiments were conducted at the Air Force Research Laboratory (AFRL)'s Materials & Manufacturing Directorate at Wright-Patterson Air Force Base, Ohio, under the direction of Timothy White.
Other research groups have proposed using ambient energy sources such as magnetic fields, acoustics, heat and other temperature variations to avoid adding structures to induce locomotion. Shankar explains that light is more appealing than these other sources because of its speed, temporal control and ability to target the mechanical response effectively. For their light-responsive material, the group zeroed in on monolithic polymer films prepared from a form of liquid crystalline polymer.
"Our initial research indicated that these flexible polymers could be triggered to move by different forms of light," Shankar explained. "However, a robot or similar device isn't effective unless you can tightly control its motions. Thanks to the work of Dr White and his team at AFRL, we were able to demonstrate directional control, as well as climbing motions."
According to Wie, the ‘photomotility’ of these specific polymers is the result of their spontaneous formation into spirals when exposed to UV light. By controlling this exposure, the researchers can induce motion without the use of external power sources attached directly to the polymer itself.
"Complex robotic designs result in additional weight in the form of batteries, limb-like structures or wheels, which are incompatible with the notion of a soft or squishy robot," Wie said. "In our design, the material itself is the machine, without the need for any additional moving parts or mechanisms that would increase the weight and thereby limit motility and effectiveness."
In addition to simple forward movement, the researchers were able to make the polymers climb a glass slide placed at a 15° angle. Although the flat polymer strips are small – approximately 15mm long and 1.25mm wide – they can move at several millimeters per second when propelled by light. This movement persists for as long as the material remains illuminated.
"The ability for these flexible polymers to move when exposed to light opens up a new ground game in the quest for soft robots," Shankar said. "By eliminating the additional mass of batteries, moving parts and other cumbersome devices, we can potentially create a robot that would be beneficial where excess weight and size is a negative, such as in space exploration or other extreme environments."
This story is adapted from material from the University of Pittsburgh, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.