OR: dried elements different from those in suspension: a case in point
(can you do this at home?)
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Science News Week of Aug. 11, 2007; Vol. 172, No. 6 , p. 94
Pliable carbon
Davide Castelvecchi
Researchers have made graphene paper. Graphene is the net of carbon
atoms, reminiscent of chicken wire, that forms graphite and carbon
nanotubes.
In graphite, electrostatic forces make graphene layers cling together
and form microscopic stacks, says Rodney Ruoff, a physical chemist at
Northwestern University in Evanston, Ill. Different stacks don't stick
together well, which is why pencil lead is soft. But a graphene layer
itself is one of the strongest materials in nature, Ruoff says.
Ruoff's team sought to take the layers apart and reassemble them in a
new way. The researchers oxidized graphite and shook it in water,
producing a suspension of graphene fragments up to 1 micron wide in
which about every other carbon atom was strongly bonded to an oxygen
atom.
After most of the water has been filtered out, the fragments stuck
together to create a new material in the form of a pliable sheet.
Remaining water molecules held graphene layers less than a nanometer
apart, the team reports in the July 26 Nature. "Water is playing the
role of a sort of molecular glue," Ruoff says.
The graphene paper is about as strong as aluminum foil, but Ruoff says
that replacing water with better molecular glues could lead to new,
superstrong materials.
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