Tiny Micromotor Powered by Light

EMMETT WARREN, NEWS EDITOR
emmett.warren@photonics.com

Researchers at the University of Warsaw’s Faculty of Physics collaborated with researchers from the Polish Academy of Science and Xi’an Jiaotong-Liverpool University to demonstrate a rotary micromotor powered with light using liquid crystal elastomer technology. The 5-mm-diameter ring, driven and controlled by a laser beam, can rotate and perform tasks by rotating another element installed on the same axis.

Liquid crystal elastomers (LCE) are a group of materials that enable construction of small, moving, or mobile devices. Research on these materials focuses on design of LCE shape and its malleability with laser illumination.

“We are mainly interested in demonstrating that things are possible,” lead author Piotr Wasylczyk said. “In the case of this project, we asked ourselves ‘Is it possible to use the photo-induced deformation in LCE (which we already have been studying for some time) to build a rotating motor in small scale?’”

Wasylczyk said that time will tell if the motor will prove useful in future applications, but because the device can be directly scaled down to submillimeter dimensions, he noted that it could be implemented in high magnetic fields where movement needs to be controlled remotely without electric currents.

“One should remember that such motors are very unlikely to match piezo- or magnet-based motors in terms of efficiency or speed. But some niche applications may emerge anyway,” Wasylczyk said.

Despite a speed of around one rotation per minute, the researchers said their motor allows them to look at the micromechanics of intelligent soft materials from different angles and had inspired further research into their potential applications.

“This micromotor presents a new approach of small-scale mechanics driving and opening up a new class of light-powered, friction-coupled actuators, mimicking how an inchworm moves,” co-author Chen Xuan said.

The team’s earlier projects had demonstrated small-scale mechanics in a caterpillar and snail, both millimeter-scale robots.

“The motor uses the same material and similar principle,” said Wasylczyk, who describes the new mechanism as a caterpillar eating its tail. “By scanning the laser beam, a traveling deformation is induced in the polymer film. In the motor we used a different method for orienting the molecules in the polymer and different geometry.”

The motor design was based on ring piezoelectric motors found in the autofocus mechanisms of cameras.

“Piezoelectricity couples electricity and mechanics,” Xuan said. “Piezoelectric ultrasonic motors of this type have a piezoelectric ring actuator in which a traveling mechanical flexural wave can be electrically generated, driving a rotor via friction.”

Wasylczyk said the motor design was inspired by his fascination with the piezo motor design used in Canon autofocus lenses early on in his photography endeavors.

“Now, working with photo-responsive polymer, it struck me that the same principle can be used with our deformable polymer films,” Wasylczyk said. “The LCE research is quite unique in that we have a list of ideas in the office on the whiteboard and we take them, one by one, and try them in the lab.”

But the idea had to actually wait a few years before the team had time to conduct the experiments. Wasylczyk said that some of the ideas ended up working, and some didn’t, but the waiting list is growing longer with group members pitching new ideas every day.

The research was published in ACS Applied Materials & Interfaces (www.doi.org/10.1021/acsami.9b20309).