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SMART THREADS: The development of fabrics infused with carbon nanotubes and other nanoscale substances could someday make smart clothing a reality. View a slide show containing images of nanotube-coated threads Image: Image courtesy of University of Michigan
A soldier is badly wounded on the battlefield in Afghanistan or Iraq by a roadside explosive. As he lies beside his vehicle, unable to reach his radio to contact his unit on his location and condition, blood from the wound seeps into his shirt. Luckily, its fibers are coated with cylindrical, nanosize carbon molecules that contain antibodies able to detect the presence of albumin, a protein common in blood. The shirt senses that its wearer is bleeding and sends a signal through the shirt's carbon nanotubes (1,000 times more conductive than copper) that activates an emergency radio-frequency beacon on the soldier's belt. This distress call is picked up by a nearby patrol that rushes to the aid of their wounded comrade.
This may be the stuff of science fiction, but ongoing development of fabrics coated with carbon nanotubes and other nanoscale substances could someday make such smart clothing a reality, says Nicholas Kotov, an engineering professor at the University of Michigan at Ann Arbor. Kotov and several colleagues have taken the first step of creating carbon nanotube–coated cotton fibers woven into a swatch of fabric a few square inches in size, they report this week in the American Chemical Society journal, Nano Letters.
View a slide show containing images of nanotube-coated threads
Earlier versions of such fabrics were made by weaving metallic strands in with the cloth. The problem was that such duds are not only uncomfortable to wear but the metals in them corroded over time, Kotov says. By coating cotton fibers with carbon nanotubes, which do not corrode, the researchers created highly conductive, yet relatively soft strands of yarn that will not corrode.
The process involved dipping the cotton strands first in Nafion polymer (a chemical first discovered at DuPont in the late 1960s), then in a black solution containing single-walled carbon nanotubes and polystyrene sulfonate (PSS) (a type of polymer sometimes that can be used as a dye improving agent for cotton) and letting them dry. The Nafion polymer preps the strand so that the carbon nanotubes will adhere to it, whereas the PSS solution keeps the nanotubes from clumping together, which they have a tendency to do, Kotov says. The process, which takes only a few minutes, is repeated until the cotton strands are saturated.
"Once we saw that the strands have conductivity, we decided to incorporate some smart functionality," Kotov says. This involved adding antibodies to the spaces within and between the carbon nanotubes. "When the fabric is exposed to blood, antibodies are [released from] the carbon nanotubes and the conductivity is greatly increased."
Kotov acknowledges that blood is a bit of an extreme example. He envisions carbon nanotube–infused fabric containing a variety of antibodies that would respond to different medical conditions and act as biomonitoring and telemedicine sensors. The next step is to produce a larger patch of fabric and figure out how to integrate it with a communication device, such as a shortwave radio or cell phone.
It is too early to tell whether such smart fabrics could be thrown in the wash, would need to be sent to the dry cleaner or could be washed at all. "I'm not sure if the fabric would lose conductivity over time," Kotov admits.
Perhaps the greatest challenge will be taking advantage of carbon nanotubes' strength and conductivity when combined to make larger materials. It is a problem that Kotov reported success with recently when he and his colleagues found a way to convey the strength of the nanomaterials to larger materials by transferring stress between nanosheets and a nanoscale polymer resembling white glue [see Scientific American.com's "Making Plastic as Strong as Steel"]. The result resembles a brick wall in which clay nanosheet "bricks" are held together by water-soluble polyvinyl alcohol "mortar" to create a sheet of plastic that, according to Kotov, is as strong as steel.