Physicists at MIT have developed an experimental technique to observe and manipulate individual atoms at the interface of two surfaces, tuning the amount friction until it disappears.
In a phenomenon, known as “superlubricity,” surfaces simply slide over each other without resistance.
Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, says the ability to tune friction would be helpful in developing nano machines – tiny robots with components the size of single molecules. He says that at the nanoscale, friction may exact a greater force – and therefore more wear and tear – 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, have published their results the journal Science.
The team simulated friction at the nanoscale by pacing two surfaces in contact – an optical lattice – generated using two laser beams traveling in opposite directions – and an ion crystal – essentially, a grid of charged atoms.
They pushed and pulled the ion crystal across the lattice, as well as to stretch and squeeze the ion crystal, much like an accordion, altering the spacing between its atoms.
They 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, much like two matching Lego bricks.
But they discovered that if the atom spacing is mismatched from that of the optical lattice, friction between the two surfaces vanishes. In this case, the crystal tends not to stick then suddenly slip, but to move fluidly across the optical lattice.
The scientists believe the technique may also be useful 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 says. “So this intuition for how to arrange atoms so as to minimize or maximize friction could be applied.”
Bill Condie is a science journalist based in Adelaide, Australia.