Researchers gain control over internal structure of self-assembled composite materials

Researchers at the University of Illinois (UI) and the University of Michigan (UM) have developed a templating technique that instills greater order and gives rise to new 3D structures in a special class of materials called eutectics to form new, high-performance materials.

In the process, the researchers built templates with tiny posts arranged in hexagonal shapes to control the re-solidification of a melt containing silver chloride and potassium chloride, a eutectic material that naturally forms layers as it cools, according to a news release posted on UI's website on Wednesday.

"If not controlled, the only microstructures this system will form are layers," said Katsuyo Thornton, a professor of materials science and engineering at UM. "We can vary the cooling rate to make the layers thicker or thinner, but the pattern stays the same. By adding a template that the liquid solidifies around, we hoped new patterns would emerge."

The researchers found that as the silver and potassium chloride melt starts to solidify around the hexagonal-shaped templates, the posts get in the way of the layer formation and produce a composite with an array of different square, triangular and honeycomb-shaped microstructures instead, the specifics of structure depending on the distance between the posts on the template.

"The repeating nature of these templates and newly formed structures reduces the chances for defects to form," said Paul Braun, a professor of materials science and engineering and director of the Materials Research Lab at UI. "So, not only did we form exciting new microstructures, but we also reduced the number of defects in the resulting composite material."

The researchers will explore how the new microstructures influence the physical properties of a wide range of eutectic materials.

"The materials we used in our experiments are transparent, so the first direction to head in might be to explore optical materials, and there is a lot of potential in the area of photonic crystals," Braun said. "We're still a long way from real application, but the possibilities are abundant."

The findings of the collaborative study have been published in the journal Nature.