AlbertPacino
Skilled
Fabricated out of millions of carbon nanotubes, the minuscule brushes could even paint the inside of capillaries thinner than a human hair.
But besides being small, the nanotubes have other advantages over traditional bristles, says one of their creators Pulickel Ajayan at Rensselaer Polytechnic Institute in Troy, New York.
The materials typically used for making brush bristles include animal hairs, synthetic polymer fibres and metal wires. But each has its limitations. Metals corrode and weaken, hair is not very strong and synthetic fibres melt.
Carbon nanotubes, on the other hand, are 30 times stronger than steel, yet five times less dense. They are highly elastic, resistant to heat, have large surface areas and even conduct electricity. The latter property makes them highly suitable for the contact brushes used in electric motors, says Ajayan.
He and Anyuan Cao at Rensselaer, in collaboration with colleagues at the University of Hawaii in Honolulu, US, have designed brushes consisting of a silicon carbide fibre base on which the carbon nanotubes are grown in a single row of bristles like a toothbrush, or in groups of bristles more like a toilet brush. One end of the base is coated with gold, which acts like a “handle†and also inhibits nanotube growth at that end. The dimensions can be varied dramatically, says Ajayan, but typically the bundle of nanotubes is no smaller than a few micrometres in diameter.
The brushes could have a variety of applications. They have already been used to sweep particles measuring just 50 nanometres in diameter off a plain surface, and off another surface pitted with microscopic grooves. The researchers have also attached the gold handle of a three-pronged brush to the shaft of a small electric motor. This allowed them to rotate the bristles inside a 300-micrometre-wide capillary tube, cleaning contamination off its walls. Then, by coating the brush with a red dye, they were able to paint the inside of the cavity using the same approach.
The brushes’ ability to clean small particles appears to be extremely good, says Ajayan, although he is still not sure why. “Perhaps the cleaning occurs by electrostatic interactions, and since the surface area of the nanostructures is large, the cleaning is possibly more effective.†The aim now is to apply the brushes to more specific microelectronic and biomedical applications.
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