Move over, Spider-Man

2003-06-11 15:15

Paris - Attempts to create a super-strong fibre by mimicking the chemicals found in spider silk may have all been in vain.

University of Texas scientists say they have outdone the spider and its lab-coat imitators by spinning a fibre made of carbon nanotubes - the microscopic tubes of carbon that have remarkable properties, being tough, light and inert yet able to conduct heat and electricity.

Ray Baughman and colleagues, writing in Thursday's issue of the British science weekly Nature, say they have experimentally made up to 100 metre lengths of fibre, at the rate of 70 centimetres per minute.

They placed single-walled nanotubes in a rotating bath of aqueous polyvinyl alcohol, yielding gelatinous fibres which were then coagulated, washed in an acetone bath, dried and then reeled up.

The result, a composite that comprises 60 percent carbon nanotubes, is seven times stronger than previous attempts to spin carbon-nanotube fibres and many times quicker to make, they say.

Weight for weight and diameter for diameter, it is five times stronger than steel.

It matches spider silk for tensile strength - the strength needed to distort a substance before it is irretrievably deformed - and absorbs more than three times as much energy as spider dragline silk before it breaks. It easily surpasses commercial rivals such as Kevlar and graphic fibre on every test.

The fibres are "tougher than any natural or synthetic fibre described so far," claim Baughman's spin doctors.

They have already spun the fibres into cloth, making supercapacitors - devices that store electricity.

"Promising electronic-textile applications for these fibres, which are easy to weave and sew, include distributed sensors, electronic interconnects, electromagnetic shields, antennas and batteries," they write.

In 2000, the first nanotube fibres were created by scientists from the Paul Pascal Research Centre at the University of Bordeaux, southwestern France.

The ribbons were created by dispersing raw nanotube soot into a surfactant, or detergent, solution.

That solution was then injected into a flowing steam of polymer solution which caused the nanotube material to recondense into a mesh. The flow of the solution aligned the mesh into ribbon-like fibres.

That process was painstaking, because the jelly-like fibres could only be coaxed from the coagulation bath at the rate of about one centimetre (0.4 of an inch) per minute.

Baughman says his achievement is to improve on this method by using nanotubes made from carbon monoxide, by using lithium dodecyl sulphate as a surfactant and by modifying the flow rates of the spinning and coagulation solutions so that the gel retains some of the polyvinyl alcohol.

That means the gel fibres are less fragile and less prone to breaking when they are reeled in.

Carbon nanotubes, discovered in 1991, are single molecules.

They are hollow, cylindrical, hexagonal tubes made of a web of carbon atoms, just a few nanometres (millionths of a millimetre) across - 10 000 times narrower than the human hair - and several thousand nanometres long.

They are conventionally created by vaporising graphite rods by electric arc in a chamber filled with a gas such as helium or hydrogen, and then allowed to cool slowly.

Other potential applications touted for nanotube fibres include artificial muscles, hydrogen storage and flat-screen TVs.

- AFX