UT researchers create tiny, light-driven motor

Koshik Mahapatra, News Reporter

UT researchers created the first ever solid-state optical nanomotor, which has the potential to power tiny drones and other devices directly from a beam of light.

Nanomotors are miniature versions of the motors used to power automobiles and deliver electricity in our everyday lives, researcher Pavana Siddhartha Kollipara said. But while traditional motors use energy from chemical reactions or electricity, optical nanomotors are powered by light, Kollipara said. 

“Instead of just using internal combustion engines or batteries to power the motors, you essentially use chemical methods or lasers to drive these nanomotors,” said Kollipara, a mechanical engineering graduate student. “And when you say ‘optically-driven nanomotors,’ what it means (is) you’re using lasers as a driving source and you are using the nanoparticle as a motor.”

Some nanomotors exist in the natural world by converting chemical energy in the body into mechanical energy to move molecules in a certain way, said Jingang Li, a materials science and engineering researcher and co-author of the research. Li said other scientists have created nanomotors in laboratory settings, but they have limited use in practical applications because they are liquid-state nanomotors, or motors held by a liquid base.

“If you put the particle with some small objects on the (solid) surface and you want to speed it up — you want to rotate the particles — it’s going to be hard because there will be friction between the object and the surface,” Li said. “So people normally do it in a liquid environment, that is, put the objects in water (where) the friction force is much smaller.”

Li said nanomotors in a liquid environment have two main limitations. First, extremely small motors are affected strongly by something called Brownian motion, a “rocking” effect where small objects in water will move randomly by water molecules bouncing off them. In addition, liquid-state nanomotors cannot be used in devices where other parts, like hard drives, need to operate without water. 

“If we could directly put the nanomotor on a solid substrate, it’s gonna be very hard to move, because there will exist (a) very strong friction force,” Li said. “So we insert … a thin material layer between the nanomotor and the solid surface. (Then), we can just manipulate the nanomotor as easily as it is in water, but actually, it is in the solid surface.”

After optimizing the nanomotor for speed and stability, Li said the researchers are interested in exploring practical applications of solid-state optical nanomotors, such as for air quality and ambient environment testing or to power tiny drones by light only.

“For nano-scale motors, the Brownian motion will be too strong for us to precisely control the motion of the nanomotor. That’s going to be the fundamental challenge of this (liquid) motor,” Li said. “Our motivation here is to create (a) nanomotor first to avoid Brownian motion by moving from the liquid state to the solid surface, and, second, to make it possible to operate for those different kinds of functions in our daily life.”