Optical nanomotor goes solid state
All previous versions of light-driven motors, say the researchers, have resided in a solution of some sort, which held back their potential for most real-world applications.
“Life started in the water and eventually moved on land,” says Yuebing Zheng, an associate professor in the Walker Department of Mechanical Engineering. “We’ve made these micro nanomotors that have always lived in solution work on land, in a solid state.”
The new motor is less than 100 nanometers wide, and it can rotate on a solid substrate under light illumination. It can serve as a fuel-free and gear-free engine to convert light into mechanical energy for various solid-state micro-/nano-electro-mechanical systems.
These motors, say the researchers, could be used to power a variety of things. For example, the spinning motion could pick up dust and other particles, making it useful for air quality measurement; or the motors could be used to propel drug delivery devices in the human body; and they could power tiny drones for surveillance and measurements, as well as other mini-vehicles.
Bringing these nanomotors on land and out of water, so to speak, say the researchers, avoids Brownian Motion, one of the biggest hurdles holding back implementation of these devices. It happens when water molecules push the motors off their spin. The smaller the motor, the stronger this motion becomes. Removing the solution from the equation side steps this problem entirely.
Nanomotors are part of a large and growing field of miniature power sources and serve as a middle ground in scale between molecular machines at the smaller end and micro-engines at the larger end. The field is of immense interest, say the researchers, but at this point, scientists are still trying to figure out the fundamental science to make these tiny motors more viable through increased efficiency.
Such tiny motors are of special interest because they mimic some of the most important biological structures. In nature, these motors drive the division of cells and help them move. They combine to help organisms move.
“Nanomotors help us to precisely control the nanoworld and make up new things we want for our real world.” says Jingang Li, a PhD graduate from Zheng’s group and the lead author of a study on the research.
By taking these motors out of the solution and putting them onto chips, they have the potential to replace batteries in some instances, using only light to generate mechanical motion and power devices. The researchers achieved this breakthrough using a novel design: a thin layer of phase change material on the substrate. The thin film can undergo a local and reversible change from the solid to a quasi-liquid phase when exposed to light. This phase change can reduce the friction force of the nanomotors and drives the rotation.
This was the researchers’ first demonstration of the motors using nanoparticles. Going forward, say the researchers, they will continue to improve their creation, working on enhancing performance, by making them more stable and controllable, which leads to converting light to mechanical energy at higher rates.
For more, see “Opto-Thermocapillary Nanomotors on Solid Substrates.”
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