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To Create the World's Toughest Fiber, Just Add Slipknots

Quick: What does nü-metal have to do with materials science?

Quick: What does nü-metal have to do with materials science? Well, not much, but both can now chalk up big breakthroughs to slipknots.

Click to enlarge. Figures 1-5 show a strand being pulled to the breaking point,
while the graph shows Pugno's data for various numbers of coils.

That's thanks to an Italian researcher who found that he could vastly increase the toughness of a synthetic fiber by tying slipknots into a strand of said fiber. According to Nicola Pugno of the Università di Trento, whose findings are shared on the arXiv preprint server, as the strand is pulled apart, the friction added by the sliding knot dissipates force until the knot is yanked closed, at which point the strand will break. But during that sliding period, the strand—in this case, a fiber known as Endumax, which Pugno writes is the world's toughest—is able to withstand far more force than it would otherwise.

That's an important distinction, as Pugno's technique, which he calls the "Egg of Columbus," doesn't actually make the individual fiber any stronger. That makes sense, as the properties of the fiber itself haven't changed. But in terms of toughness—how much force it can withstand before breaking—Pugno writes that the fiber's threshold leapt from 44 J/g up to 1070 J/g. According to the Physics arXiv Blog, that's the highest ever recorded, all with what amounts to a clever trick.

But it doesn't stop there. Graphene nanotubes are currently the darling of the materials science world, and Pugno sets the upper limit for strength of knotted fibers made from nanotubes at a potential 105 J/g. Curiously, Pugno also writes that even spider silk, which has been optimized by hundreds of thousands of years of evolution, could also be improved—although evolution might do that for them.

"Thus, even this spider (or us, using its silk and our concept) could further improve the toughness of its silk by a factor of ~350%," Pugno writes. "During the next millions of years this percentage of hidden toughness will be probably further reduced by evolution and the same appearance of knots/sliders/current “egg of Columbus” cannot be excluded. We can do better in the next few years."

Regardless, it's a rather fascinating concept, even if presumably the toughness-boosting effect would only work once. (This could make for huge breakthroughs in bulletproof vests, for example.) The key to optimizing strength moving forward is figuring out how to make the knot's slipping point as close the fiber's breaking point as possible, in order to diffuse the maximum amount of force through friction. As the arXiv Blog notes, that means optimizing knot designs, which is apparently why Pugno hasn't published the work yet—he needs to patent his designs first.

@derektmead