In a significant advancement toward creating smart coatings that can dynamically change their properties, researchers from the University of Michigan (U-M) and Indiana University (IU) have successfully manipulated nanoparticles to reconfigure themselves on command. This breakthrough paves the way for developing materials and coatings capable of transitioning between different optical, mechanical, and electronic states.

The collaborative study utilized an electron microscope combined with a specialized sample holder containing microscopic channels and sophisticated computer simulations. This setup allowed scientists to observe, in real-time, how nanoscale building blocks reorganize into various structures when prompted by external stimuli.

“One of my favorite examples of this phenomenon in nature is chameleons,” said Tobias Dwyer, a doctoral student in chemical engineering at U-M 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.”

Real-Time Imaging Technique Unveils Assembly Behavior

The researchers employed an advanced imaging technique that provides unprecedented insight into how nanoparticles respond to environmental changes. The IU team began by suspending nanoparticles—materials smaller than the average bacterial cell—in minuscule liquid channels within a microfluidic flow cell. This device enabled the introduction of various fluids into the cell while observing the mixture under an electron microscope.

The precise control of electrostatic forces within the microscope created just enough repulsion to separate the nanoparticles slightly, allowing them to form ordered structures despite their natural tendency to clump together. The gold nanoparticles, shaped like cubes, demonstrated the ability to arrange themselves either neatly aligned or in more chaotic configurations depending on the properties of the surrounding liquid. By flushing different liquids through the flow cell, researchers could prompt the nanoblocks to switch between these arrangements, effectively steering them into specific structures.

Potential Applications and Future Directions

This experiment serves as a proof of concept for controlling nanoparticle configurations by simply altering their environment. Such control is crucial for developing smart materials that can adapt their properties on demand for various applications, including responsive coatings and advanced electronic devices.

“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,” explained Xingchen Ye, IU associate professor of chemistry who developed the experimental technique and lead corresponding author of the study. “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.”

While an electron microscope was essential for activating and observing the particles in this study, the researchers noted that practical morphable materials could be triggered by more accessible stimuli such as changes in light and pH levels. To apply this technique across various types of nanoparticles, scientists need a comprehensive understanding of how to adjust environmental conditions and microscope settings effectively.

Computational Insights Support Experimental Findings

The U-M team conducted extensive computer simulations to identify the forces responsible for particle interactions and assembly. These simulations provide a foundational understanding necessary for predicting and controlling the behavior of different nanoparticle shapes and materials in future experiments.

“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 in chemical engineering and co-first author of the study. He developed the computer simulations alongside 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,” added Glotzer, who also holds titles as the John Werner Cahn Distinguished University Professor and Stuart W. Churchill Collegiate Professor of Chemical Engineering.

Conclusion

This research marks a significant step toward the development of adaptive materials that can alter their properties on demand, with wide-ranging implications across various industries, including electronics, optics, and biotechnology. The ability to control nanoparticle assembly in real-time opens new avenues for designing smart systems inspired by natural phenomena, such as the color-changing skin of chameleons, leading to innovative solutions in material science and engineering.

By Impact Lab