LSU Research Bites: Acoustic Vibrations Solve a Long-Standing Challenge in Nanoparticle Assembly

December 19, 2025

For decades, scientists have been trying to overcome a very specific challenge: arrange nanoparticles smaller than the eye can see into a perfectly ordered “sheet” of particles — one particle thick — over a large surface area.

Imagine arranging pool balls perfectly inside a diamond pool table rack. Now imagine instead of pool balls, you are trying to similarly arrange extremely tiny plastic particles into a single layer on a surface. The particles want to clump and stick, like tiny pieces of Styrofoam when you are trying to clean up after unboxing furniture.

But why is a monolayer of nanoparticles over a surface useful in the first place? Nanoparticles have special properties because they are so small. Divide one meter into one billion pieces; one of those pieces is a nanometer. 

Problem: A perfectly arranged, single layer of nanoparticles can improve biological and chemical sensors and solar cell coatings. Such layers have been very difficult to make… until now.
Solution: LSU researchers used a small underwater speaker (transducer) to generate surface ripples on water that could coax nanoparticles into a perfect monolayer. Low-frequency water surface waves were key.
Impact: This “acoustic annealing” process makes it quick and easy to create nanoparticle layers for various applications.

Nanoparticles, especially when arranged just so, interact in special ways with light, vibration, and other inputs, making them perfect for use in ultra-sensitive biological and chemical sensors, light-absorbing or light-reflecting coatings, and more.

But how do you manipulate such tiny particles into a perfectly ordered, single layer? Before you suggest using the world’s tiniest pool ball rack … well, maybe try shaking the rack a bit?!

Kevin McPeak, Gordon A. & Mary Cain Professor of chemical engineering at LSU, and colleagues experimented with using specialized underwater speakers, or “transducers,” to vibrate polystyrene nanoparticles on the water surface.

They found that resulting low-frequency waves (as when you drop a stone into a pond) were key to coaxing the particles into position, forming a high-quality monolayer. Put another way, the nanoparticles surfed the water waves right into position. This process is called “acoustic annealing.”

“Our study unambiguously demonstrates that low-frequency, e.g., sub-100 Hz, capillary waves are key to improving the long-range order of colloidal monolayers on an air–water interface,” McPeak said.

In the video at the link below, watch in real-time as vibrations and water waves help form a monolayer of plastic nanoparticles that diffract light to produce brilliant colors.

Read the paper: Capillary Wave-Assisted Colloidal Assembly

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