Nanotube Theory

Effect of Twisting on Nanotube Electronic Structure




Effect of twisting on the properties of a metallic armchair (6,6) nanotube. Three twisted configurations are shown. Twisting is found to transform the metallic nanotube to a semiconducting one with a band-gap that varies with the twist angle as shown.



Effect of Bending on Nanotube Electronic Structure




Variation of the local density of states (LDOS) along the length of a (6,6) nanotube as a function of the bending angle.


Source:www.research.ibm.com/nanoscience/index/index.html



Nanotubes proved safe

But for the authors of [1] their results indicate that if carbon nanotubes reach the lungs, they are much more toxic than carbon black and can be more toxic than quartz. These studies have to be read with some caution because a study by the National Institute for Occupational Safety and Health (NIOSH) showed that none or only a small fraction of the nanotubes present in the air can be inhaled [2].

[1]Pulmonary Toxicity of Single-Wall Carbon Nanotubes in Mice 7 and 90 Days after Intratracheal Instillation. Toxicol Sci 2003, 77:126-134.

[2]Exposure to Carbon Nanotube Material: Aerosol Release During the Handling of Unrefined Single Walled Carbon Nanotube Material. J Toxicol Environ Health 2004, 67:87-107.





It is also important to note that specific particle surface area is probably a better indication for maximum tolerated exposure level than total mass. Inhaled nano-fibres (diameter smaller than 100 nm) also can enter the alveoli and their clearing would, in addition, depend on the length of the specific fibre.

A recent study [1] has provided, for the first time, morphological data showing that inhaled polystyrene particles are transported into the pulmonary capillary space, presumably by transcytosis........ In inhalation experiments with rats, using 13Clabelled particles, they found that nano-sized particles (25 nm) were present in several organs 24 hours after exposure. The most extraordinary finding was the discovery of particles in the central nervous system (CNS). The authors examined this phenomenon further and found that particles, after being taken up by the nerve cells, can be transported via nerves (in this experiment via the olfactory nerves) at a speed of 2.5 mm per hour [2].


[1]Evidence that exogenous substances can be phagocytized by alveolar epithelial cells and transported into blood capillaries. Cell Tissue Res 2003, 311:47-51.

[2]Extrapulmonary translocation of ultrafine carbon particle following whole-body inhalation exposure of rats. J Toxicol Environ Health A 2002, 65:1531-1543.