Multiple different particles self-assemble in multiple phases

Self-assembling synthetic materials come together when tiny, uniform building blocks interact and form a structure. In nature, however, materials like proteins with varying sizes and shapes can self-assemble, allowing for complex architectures that can handle multiple tasks.

Engineers at the University of Illinois at Urbana-Champaign have now taken a closer look at how nonuniform synthetic particles assemble and were surprised to find that it happens in multiples phases. This opens the door for new reconfigurable materials for use in technologies such as solar cells and catalysis. The engineers report their findings in a paper in Nature Communications.

"Traditional self-assembly can be thought of like a grocery store stacking apples for a display in the produce section," explained Qian Chen, a professor of materials science and engineering and lead author of the paper. "They would need to work with similarly sized and shaped apples – or particles in the case of self-assembly – to make the structure sturdy."

In this new study, Chen's group observed the behavior of microscale silver plates of varying sizes and nanoscale thicknesses in liquids. Because the particles used to self-assemble materials are so small, they behave like atoms and molecules. This means classical chemistry and physics theories can be used to understand their behavior, the researchers said.

The nonuniform particles repel and attract according to the laws of nature in plain, deionized water. But when the researchers added salt to the water, the changing electrostatic forces triggered a multistep assembly process. The nonuniform particles begin to assemble to form columns of stacked silver plates and then further assemble into increasingly complex, ordered, three-dimensional, hexagonal lattices.

"We can actually witness the particles assemble in this hierarchy using a light microscope," said Binbin Luo, a materials science and engineering graduate student, and co-author of the paper. "This way, we can track particle motions one by one and study the assembly dynamics in real time."

"The findings of this study may allow for the development of reconfigurable self-assembly materials," said Ahyoung Kim, a materials science and engineering graduate student, and another co-author of the paper. "These materials can change from one type of solid crystal to another type with different properties for a variety of applications."

"Another benefit of this finding is that it can be generalized to other types of systems," Chen said. "If you have another type of nanoparticle, be it magnetic or semiconducting, this hierarchal assembly principal still applies, allowing for even more types of reconfigurable materials."

This story is adapted from material from the University of Illinois at Urbana-Champaign, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.