Nature-inspired patterns boost polymer toughness

Biological systems are renowned for their ability to create strong yet resilient structures. A sea sponge, for instance, grows in layers, forming unique patterns that integrate minerals with softer regions, creating an ideal balance of strength and flexibility.

“Nature has a way of turning brittle materials into tough ones through intricate patterning,” said Nancy Sottos, a researcher at the Beckman Institute for Advanced Science and Technology and head and Maybelle Leland Swanlund Endowed Chair in the Department of Materials Science and Engineering at the University of Illinois Urbana-Champaign. “Patterned materials often contain both stiff and soft regions, allowing them to withstand high strains without breaking while maintaining impressive strength.”

A study published today in Nature describes how Sottos and her colleagues used frontal polymerization, a process which uses heat to trigger a chemical reaction that forms polymers, to replicate nature’s approach.

In a 2021 study, Sottos and her colleagues established frontal polymerization as a reliable method to manufacture biologically inspired polymer materials. Now, their novel technique builds on this by allowing for the controlled formation of crystalline patterns in those materials, significantly enhancing toughness and durability.

“Nature captivates us with spontaneous patterns formed through dissipating processes, yet in the world of synthetic materials, we typically rely on precise, controlled methods to create structure,” said Beckman researcher Jeff Moore.

Moore, who is also the Stanley O. Ikenberry Research Professor and a professor emeritus of chemistry at Illinois, was pivotal in fine-tuning the chemical formulations that led to the discoveries highlighted in the paper.

“Our work demonstrates a new frontier—patterning materials without molds or milling, resulting in unique properties that arise from this added structure,” he said.

By using the morphogenic manufacturing technique, the group made slight changes in the chemical reactions to achieve a crystalline pattern.

“Efforts to determine the optimal reaction conditions took several weeks to pinpoint. However, ultimately observing the spin-mode dynamics that resulted in these extraordinary changes in the patterned microstructure and material properties was a particularly gratifying experience,” said lead author Justine Paul, a former Beckman Institute Graduate Fellow.

The result was a material that had regions of amorphous, or unstructured, elements, as well as crystalline solid areas. The contrast between rubbery and rock-solid materials can make a product especially resilient. Similarly, creating a new way to control the architecture of a polymer would not have been possible without interdisciplinary collaborations within the Beckman Institute.

Cecilia Leal, a professor of materials science and engineering, used X-ray scattering to reveal how polymer chains orient themselves in the patterned material. This technique highlighted the importance of deciphering holistic structure-property relationships from molecule to matter, she said.

Aerospace engineering professor Philippe Geubelle focused on the modeling of the manufacturing process, with emphasis on capturing the thermo-chemical instabilities that lead to the creation of unique heterogeneous materials.

“The close collaboration between experimentalists and modelers, and between researchers from mechanics, materials science and chemistry was instrumental to the success of this project,” Geubelle said.

Sottos, Moore, Leal and Geubelle are part of the Autonomous Materials Systems Working Group at the Beckman Institute.

“This achievement required the combined expertise of an interdisciplinary team, making the collaborative environment of the Beckman Institute the perfect setting for such a breakthrough,” Moore said.