The results were reported in the August 19 issue of Science by Dr. Ray H. Baughman, Robert A. Welch Professor of Chemistry and director of the UTD NanoTech Institute and a collaborator, Dr. Ken Atkinson from CSIRO.
Starting from chemically grown, self-assembled structures in which nanotubes are aligned like trees in a forest, the sheets are produced at up to seven meters per minute by the coordinated rotation of a trillion nanotubes per minute for every centimetre of sheet width. By comparison, the production rate for commercial wool spinning is 20 metres per minute.
Unlike previous sheet fabrication methods using dispersions of nanotubes in liquids, which are quite slow, the fast dry-state process developed by the UTD-CSIRO team can use ultra-long nanotubes.
Strength normalized to weight is important for many applications, especially in space and aerospace, and this property of the nanotube sheets already exceeds that of the strongest steel sheets and the Mylar and Kapton sheets used for ultralight air vehicles and proposed for solar sails for space applications, according to the researchers.
The nanotube sheets can be made so thin that a square kilometre of solar sail would weigh only 30 kilograms. While sheets normally have much lower strength than fibres or yarns, the strength of the nanotube sheets in the nanotube alignment direction already approaches the highest reported values for polymer-free nanotube yarns.
The nanotube sheets combine high transparency with high electronic conductivity, are highly flexible and provide giant gravimetric surface areas, which has enabled the team to demonstrate their use as electrodes for bright organic light emitting diodes for displays and as solar cells for light harvesting.
Since the nanotube sheets strongly absorb microwave radiation, which causes localized heating, the scientists were able to use a kitchen microwave oven to weld together plexiglas plates to make a window. Neither the electrical conductivity of the nanotube sheets nor their transparency was affected by the welding process — which suggests a novel way to imbed these sheets as transparent heating elements and antennas for car windows.
The nanotube sheets generate surprisingly low electronic noise and have an exceptionally low dependence of electronic conductivity on temperature. That suggests their possible application as high-quality sensors – which is a very active area of nanotube research.