Lift
to the Heavens (12.24.02) - Could an incredibly tiny, uniquely strong
structure make a space elevator?
Nano
Designer (1.16.03) - Silicon chips have made everything electronic smaller,
faster, and cheaper. Now scientists are working to make circuits so small,
we won’t see them at all.
What if you could wear lightweight armor that kept you warm – and let
you phone home? Nanotechnologists have come up with a super strong, flexible
fiber that can conduct heat and electricity. It could be made into a modern
version of chain mail, the heavy metal mesh worn by medieval knights. If woven
from the new fiber, modern chain mail could be light as a cotton shirt, but
bulletproof.
Molecular Chain Mail
Over hundreds of millions of years of evolution, many animals, plants, and
natural materials have developed extraordinary properties. Spider silk, for
example, is five times tougher than steel. (Toughness is defined as the measure
of the energy needed to break a fiber.) Some nanotechnologists would like
to make synthetic
yarn with the same toughness as spider silk.
At the NanoTech
Institute at the University
of Texas at Dallas, a research team headed by Institute director Ray
H. Baughman has spun a new lightweight fiber that the scientists say is
the toughest known. Their new fiber is four times tougher than spider silk,
and 17 times tougher than Kevlar,
now used to make bulletproof vests. The team’s key ingredient is tiny
carbon
nanotubes, miniscule rolled-up sheets of carbon atoms that can be found
naturally in soot.
Since carbon nanotubes were discovered in 1991, their enormous promise has
intrigued nanotechnologists. Carbon nanotubes are light and flexible, but
enormously strong. They also can conduct heat and electricity. Many researchers
want to make them into much larger materials with the same useful properties.
But because individual carbon nanotubes are very short, they are difficult
to align properly into an unbroken yarn, and if they are combined with plastics
or other binding materials, they tend to lump together.
Strings of the nanotube fiber.
The new fiber, says chemist John
Ferraris, a member of the research team, is “probably one of the
first realizations of taking something that has phenomenal properties at the
nanoscale, and actually converting it into something that has size that you
can do something with.” To make carbon-nanotube fibers, some researchers
have tried pulling
out threads from bundles of the nanotubes, like drawing silk thread from
a cocoon. But the Texas scientists turned to spinning, a method of working
with carbon nanotubes originally
developed in France.
The Texas group combines carbon nanotubes with water and a plastic. Materials
scientist Alan Dalton says the method works because the particular plastic
has “an affinity for water and it likes carbon nanotubes. When we assemble
the fibers, the polymer latches on to the surface of the nanotubes and forms
a gel.” Then the researchers spin the gel—70 times faster than their
French counterparts did—to produce long, continuous fibers.
The fiber woven into a fabric. image: Univ. of Texas at Dallas
Ferraris explains that this approach allows the researchers
to tailor the fibers by adjusting the ratio of carbon nanotubes to plastic,
or changing the plastic slightly. The result is fibers with “a wide
range of properties that we can actually maximize. We can maximize strength,
or toughness, or electrical conductivity or charge-storage capacity”
without sacrificing the fiber’s other properties. Ferraris foresees
the fiber, which is easy to weave and sew, being woven into “a multifunctional
fabric” that could protect wearers as well as provide warmth and telecommunications.
He predicts that antennae and batteries, sensors and electronic connections
could be wired into a lightweight
military uniform. As so often happens with military wear, the fiber also
could be made into fashionable street wear.
At present, however, the major obstacle is the steep price of carbon nanotubes—as
high as $15,000 an ounce.
The new fiber won’t be widely available until prices drop considerably—and
that isn’t likely for another five to ten years.
Dalton, Ferraris, Baughman, and other UTD team members’ work has appeared
in Nature, June
12, 2003. Their research is funded by the Defense Advanced Research Projects
Agency (DARPA).
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