Bring out the small guns

Calculations show that carbon nanotubes collapse progressively along their length when squeezed at one end, and could thereby eject a molecular 'bullet'

Credit: © 2008 APS

Carbon nanotubes are typically included in devices to conduct electrons, give structural support or store energy in vibration; all of which they do very well. Now, Tienchong Chang of Shanghai University has proposed a use for carbon nanotubes that is novel in two ways: the nanotube provides energy to a system, and it does so by collapsing¹.

Elastic forces keep a standard carbon nanotube cylindrical in shape. These forces can be overcome, however, by van der Waals interactions, which can cause the nanotube to collapse. Chang shows that when one end of a nanotube is squeezed, the resulting collapse propagates along the tube length, much as a single falling domino causes an entire row to fall. As a result, the difference in potential energy between the collapsed and uncollapsed states becomes available for use.

But how might this energy be used? Chang proposes placing a C₆₀ 'bullet' into the tube to make a nano gun. He calculates the bullet’s acceleration could be a staggering 0.5 x 10¹⁵ m s^-2, causing it to reach a muzzle velocity of 1 km s^-1 in 2 picoseconds. By comparison, the acceleration and muzzle velocity of an AK-47 bullet is about 10⁶ m s^-2 and 0.7 km s^-1, respectively. There is a use, then, even for a nanotube's destruction.