In a step towards developing smart coatings that can change color or other properties on the fly, researchers at the University of Michigan and Indiana University have successfully manipulated nanoparticles to reconfigure themselves.
According to a recent study, researchers can use an electron microscope, a small sample holder with microscopic channels, and computer simulations to observe how nanoscale building blocks can reorganize into various structures on command.
The approach could develop smart materials and coatings capable of transitioning between optical, mechanical, and electronic properties.
Imaging technique
“One of my favorite examples of this phenomenon in nature is in chameleons,” said Tobias Dwyer, U-M doctoral student in chemical engineering and co-first author of the study published in Nature Chemical Engineering.
“Chameleons change color by altering the spacing between nanocrystals in their skin. The dream is to design a dynamic and multifunctional system that can be as good as some of the examples that we see in biology.”
The imaging technique allows researchers to observe how nanoparticles respond to changes in their environment in real-time, providing unparalleled insight into their assembly behavior.
In the study, the Indiana team first suspended nanoparticles , a class of materials smaller than the average bacteria cell, in tiny liquid channels on a microfluidic flow cell.
This device enabled the researchers to introduce various fluids into the cell in real time while observing the mixture under their electron microscope.
The instrument provided just enough electrostatic repulsion to push the nanoparticles apart, allowing them to form ordered arrangements despite their natural attraction to each other.
Gold nanoparticles
The gold nanoparticles, shaped like cubes, were either neatly aligned or arranged more chaotically.
The material’s final arrangement depended on the liquid’s properties in which the blocks were suspended. Flushing new liquids into the flow cell caused the nanoblocks to switch between the two arrangements.
The experiment served as a proof of concept for steering nanoparticles into specific structures.
Nanoparticles are too small to be manipulated manually, but this approach could help engineers learn to reconfigure other nanoparticles by changing their environment.
“You might have been able to move the particles into new liquids before, but you wouldn’t have been able to watch how they respond to their new environment in real-time,” said Xingchen Ye, IU associate professor of chemistry who developed the experimental technique and is the study’s lead corresponding author.
“We can use this tool to image many types of nanoscale objects, like chains of molecules, viruses, lipids and composite particles. Pharmaceutical companies could use this technique to learn how viruses interact with cells in different conditions, which could impact drug development.”
Microscope usage
The researchers stated that an electron microscope is unnecessary to activate the particles in practical morphable materials. Changes in light and pH can also serve that purpose.
Researchers need to understand how to adjust the liquids and microscope settings to manipulate the particles in order to apply the technique to various types of nanoparticles.
The U-M team conducted computer simulations that identified the forces responsible for the particles interacting and coming together, laying the groundwork for future research.
“We think we now have a good enough understanding of all the physics at play to predict what would happen if we use particles of a different shape or material,” said Tim Moore, U-M assistant research scientist of chemical engineering and co-first author of the study.
He designed the computer simulations with Dwyer and Sharon Glotzer, the Anthony C. Lembke Department Chair of Chemical Engineering at U-M and the study’s corresponding author.
“The combination of experiments and simulations is exciting because we now have a platform to design, predict, make and observe in real time new, morphable materials together with our IU partners,” said Glotzer, who is also the John Werner Cahn Distinguished University Professor and Stuart W. Churchill Collegiate Professor of Chemical Engineering.
The National Science Foundation funds the research.
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