Illinois, Michigan researchers show progress in pinwheel structure study

Researchers at the University of Illinois and the University of Michigan have discovered a self-assembled pinwheel structure that could have a variety of useful applications. 

Using pyramid-shaped nanoparticles, the team discovered a new material with a key quality called chirality, a kind of twist found throughout nature, according to a news release. 

“It is amazing to observe how tight the relationship between chirality and practicality is,” said Nicholas Kotov, the Irving Langmuir Professor of Chemical Sciences and Engineering at Michigan, in the release. “As soon as the particle layer becomes chiral, it acquires new useful properties.”

Chirality is used to reliably engineer complex and dynamic systems, including all living organisms. Researchers have been attempting to recreate these twisted structures on the nanoscale, but this has proven challenging until now, the release said. 

The researchers used graph theory to predict that complex structures could emerge when the arrangements of pyramid-shaped particles were chiral. They found that as soon as the particle layer became chiral, it acquired new useful properties.

The team created the structures out of gold nanoparticles, which self-assembled while floating in a tiny droplet of a water-based solution that sat on top of a silicon wafer. As the fluid dried, the pyramids self-assembled onto the flat surface. When the particles had no electric charge, they formed a honeycomb pattern that wasn't chiral. 

However, electric charges made the tiny pyramids turn a little with respect to one another, twisting the honeycomb into a repeating pinwheel structure. The resulting lattice was large enough to be seen with the naked eye, according to the release. 

The dynamic reconfiguration of the pinwheel lattice could be useful for a range of applications, including machine vision, armor, chemical and biological sensing, and more. 

The team will explore how to achieve lattices that twist in only one direction and then translate these chiral assemblies into a range of applications, the release noted. The Office of Naval Research supported this research through a Multidisciplinary University Research Initiative (MURI).