Nature Nanotech. http://doi.org/p5r (2013)

It's impossible to get rid of friction completely — but under certain conditions, friction between two solid surfaces can almost vanish. This phenomenon, known as superlubricity, has been observed at the nanoscale and microscale in high vacuum; but its existence at larger scales is questionable because of structural deformation. Rufan Zhang and colleagues, however, show that superlubricity can occur under normal conditions even in centimetre-long structures.

Zhang et al. placed double-walled carbon nanotubes — one nanotube inside another, like a sword in a sheath — on a silicon nanorod. Using the tip of a scanning electron microscope, they then pulled out the inner nanotube, with the nanorod acting as a force sensor. The whole process was monitored under an optical microscope using nanoparticles attached to the nanotubes as visible markers.

The authors registered friction between the nanotubes that was as low as 1 nN and independent of the pull length. The existence of superlubricity in these conditions is unexpected and the observations may improve our understanding of friction and micro-and macroscales.