Human
height
( 1. 7 m)
Golf ball
diameter
( 4. 2 cm)
Dust mite
length
(250 µm)
Thickness
of a dime
( 1 mm)
Ragweed
pollen
granule
( 20 µm)
Nanoshell
(100 nm)
DNA width
( 2 nm)
Hydrogen
atom
diameter
(0.1 nm)
Small virus
(50 nm)
House;y
length
( 1 cm)
Red blood
cells
( 7 µm)
Carbon
nanotube
width
( 1. 3 nm)
Much smaller than a bread box speck of dust, grain of sand— whatever your reference for tiny, let it go. nanosized objects are much,
much smaller. A typical carbon nanotube is 1. 3 nanometers wide, and a 5-foot-7-inch man stands 1. 7 billion nanometers tall.
Letters in 2007, suggests that nanotubes
could be used to transmit information
the way optical fibers do. Yet three years
on, scientists still don’t completely
understand why the heat doesn’t travel
slower in the contorted tubes.
“It’s just completely against all
thinking that the thermal conductiv-
ity remains the same,” Strano says. “It’s
really unprecedented.”
Strano has also been investigating how
heat courses through a nanotube. In the
experiments where the flaming carbon
did not burn, the nanotubes reached
temperatures as high as 2,800 kelvins
(or 2,500º Celsius).
“Clearly science tells us that it
shouldn’t take long for carbon at a
thousand degrees kelvin to turn to car-
bon dioxide and water,” Strano says. “It
should completely burn up.”
A clue to the nanotubes’ durability may
lie in the exceptional speed of the heat
wave, he speculates. In the macroworld, if
you were to pour a line of gasoline on the
ground, lay a stick of the same length next
to it and light both at one end, the flame
would travel far faster through the liquid
fuel than through the stick of wood. But in
the lab experiments, the heat wave created
by igniting one end of the fuel-drenched
nanotube moved 10,000 times faster than
it did through the bulk fuel alone.
This superfast wave turns out to be
self-propagating, Strano says. As the fuel
burns, it releases heat, which goes into
the nanotube. The heat wave moves faster
than the flame and heat leaks back out
ahead of the burnt fuel. This ignites more
fuel, and the overall effect is of a heat
wave moving so quickly that, perhaps, the
oxidation reactions that would combust
the carbon can’t even get started.
Using carbon nanotubes, scientists have
created the darkest material ever made.
Its uneven surface (top) and the sparse-ness of the tubes (black in the colorized
image at bottom) may help make it dark.
20 μm
20 μm
Dark matter
While some researchers probe the
bright and fiery side of carbon nanotubes, others focus on the material’s
dark side. Grow millions of the tubes en
masse in a forest and they can become
black as a starless night. Working with
such a forest, physicist Shawn-Yu Lin of
the Rensselaer Polytechnic Institute in
Troy, N. Y., recently created the darkest
material ever made.
More than 99.95 percent of the light
striking the nanotube forest is absorbed,
Lin, Pulickel Ajayan, now at Rice University in Houston, and colleagues
reported in Nano Letters in 2008. This
darkest of materials literally holds a
Guinness World Record; the previous
record absorbed a mere 99.84 percent
of incoming light.
Plenty of researchers work with
nanotube forests, but they are typically densely planted, thick with trees.
Lin and his team took the sparse route,
growing a thin woodland rather than a
Grimm Brothers’ forest. Yet almost all
the light that enters this forest is never
seen again. (“Sparse” is relative, though.
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