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A method that reduces friction between two surfaces to almost zero on macroscopic scales has been demonstrated by US researchers. The phenomenon, which was discovered accidentally, works by combining nanodiamonds with sheets of graphene, which curl around the nanodiamonds to form ‘nanoscrolls’ that lubricate the two surfaces. As friction wastes so much energy in all sorts of mechanical devices this discovery has huge potential to save both energy and money.
On the macroscale, friction is the result of microscopic imperfections in surfaces, but atomic-scale friction concerns the attractive forces between individual atoms. This opens up the phenomenon of structural lubricity, where the difference in atomic spacing between two surfaces makes it impossible for multiple atoms in one surface to get close to atoms in the other, leading to extraordinarily low friction. However,scaling this up has proven difficult, as macroscopic surfaces are not perfect single crystals with constant lattice separations, but instead are dotted with deformations and grain boundaries that can stick.
Martin Dienwiebel of Karlsruhe Institute of Technology in Germany is impressed. ‘It’s stunning that they observe these kinds of low frictional forces with a system of graphene and diamond, so it’s very interesting and important,’ he says. ‘I would have been a little concerned about this idea that the graphene patches are being rolled around the diamonds, but when you look at the transmission electron micrographs, that’s convincing.’
At present the technique only works in dry, inert conditions, as the oxygen in water droplets can bond to graphene and stop nanoscrolls forming. The researchers are now working on ways to overcome this problem, but Sumant says that, even now, the technique could be useful for many applications, such as space technology or electronic systems where the environment can be controlled. ‘If the benefits are so huge,’ he says, ‘you can imagine putting a container around something and filling it with nitrogen or argon.’