In a significant advancement in materials science, researchers at Northwestern University have developed a new type of nanoscale material with potential applications in body armor and other fields requiring lightweight, flexible, and tough materials. The innovative material resembles the interlocking links of chainmail, offering exceptional strength and flexibility.
The research team, led by William Dichtel, published their findings in the journal Science. The study introduces the first two-dimensional (2D) mechanically interlocked polymer containing an unprecedented density of mechanical bonds — 100 trillion per square centimeter. This was achieved through a novel polymerization process that is both efficient and scalable.
“We made a completely new polymer structure,” said Dichtel. “It’s similar to chainmail in that it cannot easily rip because each of the mechanical bonds has a bit of freedom to slide around.”
Dichtel is affiliated with Northwestern's Weinberg College of Arts and Sciences, as well as the International Institute of Nanotechnology (IIN). Madison Bardot, a Ph.D. candidate in Dichtel’s lab and IIN Ryan Fellow, is credited as the study's first author.
To create this groundbreaking material, Dichtel’s team devised a new approach using X-shaped monomers arranged into highly ordered crystalline structures. These were then reacted with another molecule to form bonds within the crystal. The resulting crystals consist of layers of 2D interlocked polymer sheets.
“I give a lot of credit to Madison because she came up with this concept for forming the mechanically interlocked polymer,” Dichtel stated.
The research included collaboration with Cornell University for electron microscopy analysis led by Professor David Muller. Their work confirmed the polymer's high degree of crystallinity and flexibility.
The scalability of this material is noteworthy; Dichtel's team successfully produced half a kilogram and anticipates even larger quantities will be feasible for practical applications.
Further enhancing its appeal, researchers at Duke University incorporated small amounts of this new polymer into Ultem fibers—a robust material akin to Kevlar—significantly boosting its toughness.
“We have a lot more analysis to do," said Dichtel about future uses for their discovery, "but we can tell that it improves the strength of these composite materials.”
The paper honors Sir Fraser Stoddart from Northwestern University who pioneered concepts related to mechanical bonds and passed away last month. Stoddart received the Nobel Prize in Chemistry in 2016 for his contributions.
“Molecules don’t just thread themselves through each other on their own," explained Dichtel regarding Stoddart's influence on this work.
This study was primarily supported by DARPA and Northwestern’s IIN Ryan Fellows Program.