Spinning Nanomotor

Tiny motors take a big step forward: First solid-state optical nanomotor

Spinning engines. Photo credit: The University of Texas at Austin

Motors are omnipresent in our everyday life – from cars to washing machines, even if we hardly notice them. A futuristic field of science is working to develop tiny motors that could power a network of nanomachines and replace some of the power sources we currently use in electronic devices.

Researchers from the Cockrell School of Engineering at the University of Texas at Austin have developed the first-ever solid-state optical nanomotor. All previous iterations of these light-powered engines rely on some sort of solution that limited their potential for most real-world applications. This new research was recently published in the journal ACS nano.

“Life began in the water and eventually moved to land,” said Yuebing Zheng, associate professor in the Walker Department of Mechanical Engineering. “We made these micro-nanomotors that have always lived in solution, in a solid state on land.”

Scientists envision powering a variety of things with these engines. They could be useful for measuring air quality as the rotating movement could pick up dust and other particles. They could drive drug delivery devices into the human body. And they could also power tiny drones for surveillance and measurements, as well as other mini vehicles.

The tiny new motor is less than 100 nanometers wide (for reference: a sheet of paper is about 100,000 nanometers thick) and can rotate on a solid substrate when exposed to light. As a fuelless and gearless engine, it can convert light into mechanical energy for various solid-state micro/nano-electromechanical systems.

One of the biggest hurdles in implementing these devices is Brownian Motion, which is avoided by bringing these nanomotors on land and out of the water, so to speak. Brownian motion occurs when water molecules force these tiny motors out of rotation. The smaller the motor, the stronger this movement is. Removing the solution from the side equation completely solves this problem.

Nanomotors are part of a large and growing field of miniature power sources. They serve as a middle ground between molecular machines on the smaller end and micromotors on the larger end.

The area is of immense interest, but at this point researchers are still trying to figure out the basic science to make these tiny engines more viable through increased efficiency.

The reason scientists are so excited about developing these tiny motors is because they mimic some of the most important biological structures. In nature, these motors drive cells to divide and help them move. They combine to help organisms move.

“Nanomotors help us to precisely control the nanoworld and invent new things that we want in our real world,” said Jingang Li, a graduate student in Zheng’s group and lead author of the study.

By taking these motors out of solution and placing them on chips, they have the potential to replace batteries in some cases, using only light to create mechanical motion and power devices.

This breakthrough comes from a novel design: a thin layer of phase change material on the substrate. When exposed to light, the thin film can locally and reversibly change from the solid to a quasi-liquid phase. This phase change can reduce the frictional force of the nanomotors and drives the rotation.

This was the team’s first demonstration of motors using nanoparticles. In the future, researchers will continue to improve their creation and work on increasing its performance by making it more stable and controllable, resulting in light being converted into mechanical energy at higher rates.

Reference: “Opto-Thermocapillary Nanomotors on Solid Substrates” by Jingang Li, Pavana Siddhartha Kollipara, Ya Liu, Kan Yao, Yaoran Liu, and Yuebing Zheng, May 20, 2022, ACS nano.
DOI: 10.1021/acsnano.1c09800

Other team members are: from mechanical engineering Pavana Siddhartha Kollipara and Kan Yao; Yaoran Liu from the Department of Electrical and Computer Engineering and Ya Liu from Xi’an Jiaotong University in China. The research was funded by grants from the National Institutes of Health and the National Science Foundation.

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