Self-assembling carbon nanotubes may revolutionise modern engineering research.

Byline: ANI

Washington, January 14 (ANI): American scientists have developed an inexpensive process to make carbon nanotubes self-assemble in neat rows, and thereby moved a step closer to meeting the challenge of organising the atomic-scale rods in certain arrangements so as to advance electronic and material technologies.

The research team, comprising experts from the National Institute of Standards and Technology (NIST) and Rice University, say that a wide range of emerging electronic and materials technologies take advantage of the unique physical, optical and electrical properties of carbon nanotubes.

However, most of them - such as nanoscale conductors or "nanowires" - are dependent upon the ability to efficiently line the nanotubes up in some organized arrangement.

While there are a variety of mechanical approaches to orienting carbon nanotubes on a surface, th eresearchers say that a more elegant and attractive solution would be to get them to do it themselves.

The NIST researchers studying better ways to sort and purify carbon nanotubes to prepare standard samples of the material were using a bile acid to coat the nanotubes to prevent clumping.

"Bile acids are biological surfactants, and like most surfactants they have a part that likes water and a part that doesn't. This is a slightly complex surfactant because instead of having a head and a tail, the usual geometry, it has two faces, one that likes water and one that doesn't," says NIST research chemist Erik Hobbie.

Mixed in water, such hydrophobic/hydrophilic molecules normally want to group together in hollow spheres with their hydrophobic "tails" sheltered on the inside, according to Hobbie, but the two-faced geometry of this bile acid makes it form hollow rod shapes instead. Conveniently, the hollow rods can house the rod-shaped nanotubes.

The researcher says that over the course of about a day, the bile acid shells cause the nanotubes to begin lining up, end to end, in long strands, and then the strands begin to join together in twisted filaments, like a length of twisted copper wire.

Hobbie cautions that the discovery is a long way from a perfect solution for ordering nanotubes, and a lot of development remains to be done.

He says that the removal of the bile acid shells after the nanotubes are in their ordered positions has proven difficult, and since the surfactant is toxic to living cells, most biomedical applications are precluded unless it is removed.

He, however, insists that it is an easy and extremely inexpensive technique to study optical properties of carbon nanotubes.

"It gives a recipe for how to create ordered, aligned arrangements of individual carbon nanotubes. You don't need to use any external magnetic or electrical fields, and you don't need to dry the tubes out in a polymer and heat it up and stretch it. You can get fairly significant regions of very nice alignment just spontaneously through this self assembly," he says. (ANI)

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