Friction is everywhere. Between tires and the road, between pen and paper, between redOrbit and people who say the imminent release of Jurassic World isn’t pee-pants exciting.
Friction is useful, too. Think, y’ know, walking. But it is problematic in the field of nanorobotics. As we approach the day when robots can be built with components the size of single molecules, the fear is that at the nanoscale, as in nanomachines, friction may exact a greater force than occurs at larger scales, creating wear and tear on tiny motors much more quickly.
“You can think of wear as the act of shaving off layers of atoms as the surfaces come into contact, stick, and eventually ‘catastrophically’ slip under pressure from a shear force,” MIT graduate student Dorian Gangloff told redOrbit.
“At the macro-scale, material thicknesses are generally billions of atomic layers, but at the nano-scale, you may only have a handful of atomic layers available. This makes friction a large concern for the lifetime of nanoscale components.”
His colleague, Vladan Vuletic, Lester Wolfe Professor of Physics at MIT, explained it in a press release: “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.”
The magical, disappearing friction
Now, however, Gangloff, Vuletic, and fellow MIT physicist Alexei Bylinskii have developed an experimental technique to simulate friction at the nanoscale and to “tune” the amount of friction going on. If required, this could extend to a phenomenon, known as “superlubricity,” in which friction essentially vanishes and surfaces slide over each other without resistance.
The researchers were able to directly observe individual atoms at the interface of two surfaces – an optical lattice and an ion crystal (essentially, a grid of charged atoms) – and manipulate their arrangement, fine-tuning the amount of friction between the surfaces. By changing the spacing of atoms on one surface and matching or mismatching them with the other, they observed a point at which friction disappears.
“The way that we engineered friction in our system from very large to very small, by matching or mismatching the object structures, is something that nature could have used to enhance or decrease sliding; it is also a method that could be potentially be used when designing synthetic biological
processes,” Gangloff said.
The group’s technique could be useful not only for 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 told us. “So this intuition for how to arrange atoms so as to minimize or maximize friction could be applied.”
“What can be transferred onto real-world applications is most importantly the intuition and quantitative understanding that we gained by observing a vast reduction in the friction force between two objects simply by mismatching their structures.”
Moving forward with nanomachines
“The design of nano-mechanical components will rely on a detailed understanding of how objects the size of a few atoms will slide against one another,” Gangloff said. “We hope that our study of friction atom-by-atom will assist such an understanding and control of friction for these applications. The system we used to be able to study friction at the level of individual atoms is a model system allowing us to understand friction, and ultimately engineer real surfaces.”
He concluded that: “In recent years, many fields of science and engineering have gained an understanding of how to manipulate organic and inorganic materials at the nanometer scale. This convergence of effort can only lead us closer to the dream of nano-robotics, and, excitingly, perhaps to unexpected scientific directions!”
The MIT team’s findings are published in the journal, Science.