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

Tuesday, January 21st, 2025

For decades, chemists have known how to interlock individual molecular rings, or small groups of them, but a reliable way to interlock large groups of these rings into strings and sheets had so far eluded them:

Researchers led by William Dichtel, a chemist at Northwestern University, have now done just that. They started by coaxing myriad copies of X-shaped molecules to settle into a crystal, so that they lined up in two interpenetrating sheets: In one direction the tips of each molecular X nearly touched those adjacent to it, like XXXXXXX. The same pattern repeated in a perpendicular direction, creating an interlocking fishnet. But these links were held together by weak hydrogen bonds, which meant the meshed material could easily come apart. So, Dichtel and his colleagues added a silicon-based compound that inserted itself at the tips of each pair of Xs, strengthening these attachment points with tougher, more durable covalent bonds and producing a polymer composed of interlocking rings, each of which serves as “mechanical” bond further strengthening the material.

The result, Dichtel and his colleagues report, is strong sheets of interlocking rings. “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,” he says. “If you pull it, it can dissipate the applied force in multiple directions. And if you want to rip it apart, you have to break it in many, many different places.”

When a team of collaborators led by Matthew Becker at Duke University wove just 2.5% of this new material into Ultem—a material made of high-strength fibers in the same family as Kevlar, the resulting fabric’s stiffness increased by nearly 50%. It’s still early days, but “almost every property we have measured has been exceptional in some way,” Dichtel says.

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