Tuning friction to develop 'nanomachines'

Using their technique, the researchers were able to directly observe individual atoms at the interface of two surfaces and manipulate their arrangement, tuning the amount of friction between the surfaces, MIT said.

By changing the spacing of atoms on one surface, they observed a point at which friction disappears.

’Superlubricity’

Friction - a seemingly ubiquitous force between two sliding surfaces - works against the motion of tyres on the road, when we put pen to paper and against the flow of proteins through the bloodstream, for example.

“What is new in our system is, for the first time on the atomic scale, we can see this transition from friction to superlubricity

MIT professor of physics Vladan Vuletic

However, in special circumstances, friction essentially vanishes - a phenomenon known as “superlubricity,” in which surfaces simply slide over each other without resistance.

By effectively tuning friction, the MIT physicists said it would be possible to develop tiny robots - or nanomachines - that are built from components the size of single molecules.

According to Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, at the nanoscale, friction may exact a greater force - for instance, creating wear and tear on tiny motors much faster than occurs at larger scales.

“There’s a big effort to understand friction and control it, because it’s one of the limiting factors for nanomachines, but there has been relatively little progress in actually controlling friction at any scale,” Vuletic said.

“What is new in our system is, for the first time on the atomic scale, we can see this transition from friction to superlubricity.”

’Adjusting friction’

To simulate friction at the nanoscale, the MIT team engineered two surfaces to be placed in contact: an optical lattice, and an ion crystal.

In general, the researchers found that when atoms in the ion crystal were regularly spaced, at intervals that matched the spacing of the optical lattice, the two surfaces experienced maximum friction.

“What we can do is adjust at will the distance between the atoms to either be matched to the optical lattice for maximum friction, or mismatched for no friction,” Vuletic said.

MIT graduate student Dorian Gangloff, who helped develop the technique, said it may be useful not only for creating nanomachines, but also for controlling proteins, molecules, and other biological components.

“In the biological domain, there are various molecules and atoms in contact with one another, sliding along like biomolecular motors, as a result of friction or lack of friction,” Gangloff said.

“So this intuition for how to arrange atoms so as to minimise or maximise friction could be applied.”