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Friction simulated at nanoscale reaches zero

Posted: 03 Jul 2015 ?? ?Print Version ?Bookmark and Share

Keywords:MIT? friction? nanomachine? superlubricity?

A team of physicists at MIT has created an experimental technique to simulate friction at the nanoscale. Using their technique, the researchers are able to directly observe individual atoms at the interface of two surfaces and manipulate their arrangement, tuning the amount of friction between the surfaces. By changing the spacing of atoms on one surface, they observed a point at which friction disappears.

In tuning friction to the point where it disappears, technique could boost development of nanomachines. Friction is all around us, working against the motion of tires on pavement, the scrawl of a pen across paper, and even the flow of proteins through the bloodstream. Whenever two surfaces come in contact, there is friction, except in very special cases where friction essentially vanishes, a phenomenon, known as "superlubricity," in which surfaces simply slide over each other without resistance.

Technique tunes friction between two surfaces

A technique tunes friction between two surfaces, to the point where friction can vanish. MIT researchers developed a frictional interface at the atomic level. The blue corrugated surface represents an optical lattice; the red balls represent ions; the springs between them represent Coulomb forces between ions. By tuning the spacing of the ion crystal surface above to mismatch the bottom corrugated surface, friction disappears. The ions smoothly slide along the surface in a caterpillar-like motion. This discovery could aid in developing nanomachines, built from components the size of single molecules. Illustration: Christine Daniloff/MIT and Alexei Bylinkskii

Vladan Vuletic, the Lester Wolfe professor of physics at MIT, said the ability to tune friction would be helpful in developing nanomachines, tiny robots built from components the size of single molecules. Vuletic stated that 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 says. "What is new in our system is, for the first time on the atomic scale, we can see this transition from friction to superlubricity."

Vuletic, along with graduate students Alexei Bylinskii and Dorian Gangloff, publish their results today in the journal Science.

Melanie Gonick/MIT (with computer simulations from Alexei Bylinkskii)

Friction and force fields

The team simulated friction at the nanoscale by first engineering two surfaces to be placed in contact: an optical lattice, and an ion crystal.

The optical lattice was generated using two laser beams traveling in opposite directions, whose fields add up to form a sinusoidal periodic pattern in one dimension. This so-called optical lattice is similar to an egg carton, where each peak represents a maximum electric potential, while each trough represents a minimum. When atoms travel across such an electric field, they are drawn to places of minimum potential, in this case, the troughs.

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