A joint Korean-American team has identified new materials that directly convert ultraviolet light into motion without the need for electronics or other traditional methods.
The group includes Jeong Jae Wie, assistant professor of polymer science and engineering at Inha University in South Korea and M. Ravi Shankar, professor of industrial engineering at the University of Pittsburgh in Pennsylvania. Their experiments were conducted at the Air Force Research Laboratory (AFRL) in Ohio under the direction of Timothy White.
Shankar said earlier research had proposed the use of ambient energy resources such as magnetic fields, acoustics, heat and other temperature variations to avoid adding structures to induce locomotion. However, he says light is more appealing because of its speed, temporal control and the ability to effectively target the mechanical response.
The material they focussed on was monolithic polymer films prepared from a form of liquid crystalline polymer.
“The ability for these flexible polymers to move when exposed to light opens up a new ground game in the quest for soft robots,” he 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.”
Dr Shankar said a robot or similar device isn’t effective unless you can tightly control its motions, however, thanks to the team at AFRL, they were able to demonstrate directional control, as well as climbing motions
According to Jeong Jae Wie, the 'photomotility' of these specific polymers is the result of their spontaneous formation into spirals when exposed to UV light. Controlling the exposure enables a corresponding 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,” Dr 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 team was able to make the polymers climb a glass slide at a 15-degree angle. While the flat polymer strips are small – approximately 15mm long and 1.25mm wide – they can move at several millimeters per second propelled by light. And the movement can be perpetual, as long as the material remains illuminated.
[The helical polymer moves whan UV light is shone on it. Photo: University of Pittsburgh]