Chainmail is a 1,300-year-old Celtic invention that became an armory staple and was used well into the Middle Ages. Now, in a 21st century take on this age-old protective technology, scientists from Northwestern University have successfully created a chainmail-like 2D nanomaterial with exceptional flexibility and strength.
Unlike the metal adornments that accompanied warriors on the battlefield, this piece of “chainmail” is actually mechanically interlocked polymers linked together at an unprecedented density—100 trillion mechanical bonds per square centimeter. Incredibly, even though this is the highest density ever achieved, the material seems to be scalable and could drastically increase the effectiveness of ballistic material. The details of this new polymer chainmail were published in the journal Science earlier this week.
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“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,” William Dichtel, a co-author of the study from Northwestern, said in a press statement. “If you pull it, it can dissipate the applied force in multiple directions. And if you want to rip it apart, you would have to break it in many, many different places. We are continuing to explore its properties and will probably be studying it for years.”
This new material is the result of decades of pioneering work, kickstarted when British chemist Fraser Stoddart discovered and introduced the idea of mechanical bonds in the 1980s (he won a Nobel Prize for the idea in 2016). Stoddart, who died last month at the age of 82, discovered a way to form molecules mechanically instead of chemically, and essentially created the building blocks of nanomachines. The authors dedicated their new paper to Stoddart.
“Molecules don’t just thread themselves through each other on their own, so Fraser developed ingenious ways to template interlocked structures,” Dichtel, who worked with Stoddart, said in a press statement. “But even these methods have stopped short of being practical enough to use in big molecules like polymers.”
To create this chainmail wonder, the researchers started with X-shaped monomers and arranged them in a specific crystalline structure. After reacting these crystals with another molecule, bonds formed between the molecules. Finally, more monomers were woven between the gaps of these bonded molecules to form a rigid-yet-flexible material.
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Of course, it was one thing to create the bonds. It was another to actually study them. Ditchel told Interesting Engineering that it took a diverse team of synthetic chemists, electron microscopists, and polymer engineers to figure out how to actually study the new material, saying the collaboration was “perhaps the most challenging aspect” of developing the material.
Researchers at Duke University then added the ‘chainmail’ to a material known as Ultem, which is in the same family as Kevlar. With a composite material made of 97 percent Ultem and only 2.5 percent of the new molecular chainmail, the Ultem gained a dramatic increase in toughness and strength.
One of the most limiting factors of material discoveries is the inability to produce them at scale. That said, the researchers note that they actually made nearly one pound of the stuff, and that the process should be scalable.
“We have a lot more analysis to do,” Dichtel said in a press statement, “but we can tell that it improves the strength of these composite materials. Almost every property we have measured has been exceptional in some way.”
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.