Imagine a person on the ground guiding an aerial drone that draws its power from a laser beam, eliminating the need to carry a bulky onboard battery.That is the vision of a group of scientists from the Hayward Research Group at the University of Colorado at Boulder.
In a new study, researchers from the Department of Chemical and Biological Engineering have developed a novel and resilient photomechanical material that can convert light energy into mechanical work without heat or electricity, opening up innovative possibilities for energy-efficient, wireless and remotely controlled systems. Its wide-ranging potential spans several industries, including robotics, aerospace and biomedical devices.”We cut out the middleman and take light energy and convert it directly into mechanical deformation,” said Professor Ryan Hayward.
Hayward and his team describe the new material in a report published on 27 July in Nature Materials.
The material consists of tiny organic crystals that start to bend and lift things when exposed to light. The research shows that these photomechanical materials offer a promising alternative to electrically wired actuators, with the potential to wirelessly control or power robots or vehicles. Improving the efficiency of directly converting light into work also offers the potential to avoid cumbersome thermal management systems and heavy electrical components.
The research contrasts with previous attempts using delicate crystalline solids that change shape through a photochemical reaction, but often crack when exposed to light and are difficult to process into useful actuators.”The exciting thing is that these new actuators are much better than the ones we had before. They respond quickly, last a long time and can lift heavy things.”
Hayward’s lab’s innovative approach involves using arrays of tiny organic crystals inside a polymer material that resembles a sponge because of its tiny holes. As the crystals grow within the micron-sized pores of the polymer, their durability and energy production when exposed to light are greatly enhanced. Their flexibility and ease of moulding make them highly versatile for a wide range of applications.
The orientation of the crystals allows them to perform tasks when exposed to light, such as bending or lifting objects. When the material changes shape with a load attached, it acts like a motor or actuator, moving the load. The crystals can move objects much larger than themselves. For example, as shown in the image above, the 0.02 mg strip of crystals successfully lifts a 20 mg nylon ball, lifting 1,000 times its own mass.
The CU Boulder researchers include lead author Wenwen Xu, a former postdoctoral researcher in Hayward’s group (now at Sichuan University-Pittsburgh Institute), and Hantao Zhou (now at Western Digital), one of Hayward’s graduate students; the work also involved collaborators at the University of California Riverside and Stanford University.
Looking ahead, the team wants to improve the control of the material’s movement. Currently, the material can only move from a flat to a curved state by bending and then unbending. They also aim to increase efficiency by maximising the amount of mechanical energy output relative to the light energy input.
“We still have a long way to go, particularly in terms of efficiency, before these materials can really compete with existing actuators,” says Hayward. “But this study is an important step in the right direction and gives us a roadmap for how we might get there in the coming years.”
