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There's a Great Future in Carbon Nanotubes

By Rachel Swaby

How scientists treat nanotubes like woven textiles to maximize their strength and potential.

Ever since the idea was first floated by a Russian rocket scientist in the late 1800s, somebody somewhere has been thinking about how fantastically awesome it would be to build an elevator to space. Sure, we need to work out a lot of issues before we can anchor into geostationary orbit, but materials are arguably the trickiest. Although we rely on steel for our tallest structures, the iron and carbon alloy is simply too heavy and too rigid to stretch 62,000 miles into the sky. (You could imagine a strong wind turning the construction site into a mega expensive toppling Jenga tower.) In order to effectively reach for the stars—in theory, anyways—we’d need to deploy a material that’s both incredibly light and shockingly strong. That’s where carbon nanotubes come in.

Carbon nanotubes are exactly what they sound like: really really tiny tubes made of carbon atoms. The carbon atoms are the same ones that show up in our bodies and in graphite, but the way they are bonded together makes them act differently. Each tube boasts an impressive skill set, thanks to the carbon atoms’ repeating chicken wire pattern. That structure makes individual tubes super strong—50 times stronger pound-per-pound than steel wire—and their conductive nature means they could have applications in electronics, materials science, and optics.

When they were first discovered in 1991, it was clear carbon nanotubes were special, but one tube isn’t much use to us on its own (and doesn’t get us much closer to our space elevator dreams). In order to get the most out of the tubes, a lot of them—like many trillions of them—need to work together. Simply aligning them, though, doesn’t do their individual strengths justice because the connections between can be weak. But in 2003, Ray Baughman at the University of Texas at Dallas had a breakthrough. He and his team twist spun nanotube threads together, which increased their collective strength a thousand fold. “It’s like the spinning technology long practiced for wool,” explains Baughman. “We’ve downsized an ancient technology to the nanoscale.”

Here’s where modern technology meets old-school textiles.

In order to make one pound of the stuff, four billion miles of nanotubes would have to be spun together.

The carbon nanotube yarn Baughman and others produce is extremely fine; in order to make one pound of the stuff, four billion miles of nanotubes would have to be spun together. Suffice it to say, the innovations weaved from super strong thread tend to be quite small. But even with a diminutive footprint, these yarns have impressive capabilities.

By spraying or printing a superconducting powder on the threads while being twisted, for instance, Baughman can create a pair of separated yarn battery electrodes about the size of a human hair that could be woven into high tech clothing to store energy.

And most recently, Baughman’s team has created artificial muscles by adding wax to the threads and twisting them to the point that they coil. The coiling process is similar to what rubber bands go through on a rubber band airplane: “As I rotate the propeller, it twists the rubber band,” explains Baughman. “If you keep on rotating the propeller, the twist turns to coiling.” This coiling amplifies the yarn’s ability to expand and contract by a factor of 10. This is the stuff that Peter Parker dreams about.

The yarn will perform a back and forth action—the lift—on its own when subjected to super high temperatures. But wax helps the yarn perform in temperatures much much less extreme, as it can be easily persuaded to melt. When researchers send a current through the yarn, the wax turns to liquid, and the yarn contracts. Turn the current off, and the wax solidifies again, which causes the yarn to expand. “It’s very strange,” admits Baughman, who relates reaction to what happens in a finger trap toy. In order to extract your fingers from the tube, you need to push the two sides together. This action at once increases the toy’s volume while also causing the material to contract in length.

These tiny weight lifters can haul a load 200 times heavier than a human muscle of the same size.

These tiny weight lifters can haul a load 200 times heavier than a human muscle of the same size, and they have a quicker contraction rate, too. The yarn’s back and forth feat is accomplished in less time than it takes to blink an eye.

Right now Baughman’s mini actuators are best suited for small tasks, as the hair-thin muscles are only capable of lifting a 50 gram weight. Even still, Baughman could see them being commercialized within the next two years in miniscule robots, pumps for so-called laboratories on a chip, or little muscles capable of performing tasks in catheters.

Farther into the future, once researchers nail faster production and can operate many yarm muscles in parallel, these yarns could, in theory, even help with the housework by opening and closing living room blinds as the temperature fluctuates throughout the day. They could also be sewn into clothes for firefighters that change porosity upon entering a burning building, and then again when leaving it. Or the yarns could be incorporated into exoskeletons for future soldiers, giving them superhuman abilities.

But before we’re able to make carbon nanotube clothing, researchers are going to have to figure out how to scale up from 1cm by 1cm swatches—and then determine how best to weave them together. Just like carbon fiber, which tailors its pattern to a specific use, “Weave will be very important,” says Baughman. “We’re only starting to look at weave structures.”

Whatever it takes to elevate us to space.