Cinching nanotubes into tough fibers.

Heralded as the strongest known structures, carbon nanotubes have caught the attention and imagination of scientists around the world. Resembling teeny sheets of chicken wire rolled into tubes, the nanoscale structures could produce tougher and lighter-weight materials for, say, space applications or automotive parts.

However, making macroscopic materials out of structures that are a billionth of a meter wide remains a challenge. Taking a step toward that goal, researchers now have devised a trick for making larger-scale fibers out of carbon nanotubes without compromising too much of the material's inherent strength.

To make fibers up to tens of microns across, scientists must align hundreds of the nanotubes into bundles. However, because the nanotubes slip and slide along each other, these fibers are weak.

To prevent the sliding, Laszlo Forro of the Swiss Federal Institute of Technology in Lausanne and his colleagues irradiated bundles of nanotubes with high-energy electrons. The new treatment forged cross-links between neighboring nanotubes. The strength of the resulting bundles was 30 times that of fibers made without the irradiation step. The Swiss team hopes its strategy will pave the way for ultrastrong materials created out of ropes made of carbon nanotubes.

The researchers report their findings in the March issue of Nature Materials.--A. G.