Fancy
Pants - One scientist has used nanotechnology to invent fabric
that actually repels spills. (12/3/02)
Clothes
That Change Color - A new thread might make retail returns
things of the past. You’ll be able to change the colors
of your clothes to suit yourself, whenever you please. (11/19/02)
In the spring, you're very likely to get caught in a downpour with no umbrella.
What if you could instantly transform your coat into a raincoat whenever you
need one?
As this ScienCentral News video reports, scientists say this kind of quick
change could happen. They've just made the very first switchable surface.
Switchback Science
At Massachusetts Institute of Technology’s Institute
for Soldier Nanotechnology chemical engineer Robert
Langer has specialized in research where engineering meets medicine. Like
other nanotechnologists, who work with materials at the molecular level, he
is keenly interested in manipulating the properties of materials. For example,
he has developed a shape-shifting plastic: If it’s bent or squashed
into a different form, it reverts to its original shape when it’s heated.
Langer’s plastic could be made into surgical thread—for stitches that
tighten themselves and then melt
away during healing.
Langer’s success in reversing shape led one researcher in his lab, Joerg
Lahann, to wonder, “Couldn’t we switch surfaces, too?” Langer
immediately recognized the enormous potential of Lahann’s idea: switchable
surfaces could mean not only new kinds of useful materials, but also components
for sensors or drug delivery systems. A surface that switched colors also
could be made into a combat uniform that camouflages a soldier as the surrounding
terrain changes.
The MIT team set out to make a surface that would toggle between attracting
water and repelling it. But between Lahann’s inspiration and the first
smart surface lay several challenges. The researchers began by making incredibly
thin layers of gold and silicon—each only about a millionth of the width
of a dime. On top, they evenly spaced rows of specially designed molecules,
shaped like miniscule hairbrush bristles. Langer compares this new surface
to “corn stalks in a field, all evenly spaced.” The top of each
molecule was designed to attract water, while the stem repelled it. When a
weak electric current passed through the layers, the researchers thought,
the molecules would bend over, switching to waterproof. When the current was
changed, the molecules would straighten up, reverting to water-attracting.
But there had to be just enough space between molecules to allow each one enough
room to bend. Normally, bristle-like molecules pack together too tightly on
a surface for Langer and Lahann’s purposes. So the team created mushroom-like
tops that fill space between the molecules on the gold surface, separating
them. Just below each mushroom head, the scientists built in a chemical breaking
point. When they broke off the mushroom heads, the remaining bristles had
enough room to bend down and straighten up again repeatedly.
Langer says that the team has toggled the surface back and forth up to eight
times. He is confident that the new surface will be the basis of materials
that can reverse properties indefinitely. Now he and his colleagues plan to
move on to more complex surfaces that could switch several properties at once.
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