Creating thermoset polymers — materials used in coatings, adhesives, and castings — often involves heating up the bulk material in a large oven, which is not energy efficient.
However, researchers at the University of Chicago Pritzker School of Molecular Engineering have developed a new technique that is much more energy-efficient and precise. Using a laser to heat up the material simultaneously at multiple points, the process creates “fronts,” or waves, throughout the material. The fronts polymerize the material as they travel, then meet and form seams to create specific patterns.
The technique could ultimately be used to create composite-like patterned materials that have different features at different points, like polymers that are stretchy at one part but break easily at another.
“People have been trying to find a way to make polymers using less energy,” said Prof. Aaron Esser-Kahn, who co-led the research. “We thought that instead of making a material all at one time, we could start from these points and have the reactions intersect in different ways. It’s closer to the way that biology creates materials.”
The results were published in ACS Applied Materials & Interfaces.
Creating simultaneous fronts with a laser
The technique resulted from a collaboration between Esser-Kahn, whose research spans vaccine development and materials science; Asst. Prof. Allison Squires, whose research focuses on sensing, imaging, and manipulating nanoscale processes; and Justin Jureller, the technical director of UChicago’s Materials Research Science and Engineering Center.
In discussions with joint graduate student Andrés Cook, the team wondered if they might advance the state of the art of this laser technique, called frontal polymerization. Previously, research teams have used one laser to show that creating a front to polymerize a material is possible. But no one had demonstrated that it could be done simultaneously at more than two points.
“If you have a sufficiently high-powered laser, you can steer it to several different points on the material fast enough that it looks simultaneous to the human eye and to the material,” Squires said. “You create a pattern of heat that flows from those points.” When the polymerizing fronts meet, they create a seamed pattern.
The team tried a few different laser setups before they added carbon black (pure carbon particles) to the material, which allowed it to heat up faster. Using the technique, the team was able to create multiple fronts that polymerized the material simultaneously. They then refined the process to create more and more complex patterns, including lattices and honeycombs.
But perhaps more surprisingly, they found that they could create a fairly simple mathematical framework that determined how the patterns would form based on where the laser points originate.
“Whatever pattern you want to make, you can solve for that,” Esser-Kahn said. “We expected it to be complex and hard to predict, but it turns out that it is simple mathematics, which should make it much more useful for people.”