With out the power known as friction, automobiles would skid off the roadway, people could not stride down the sidewalk, and objects would tumble off your kitchen counter and onto the ground. Even so, how friction works at a molecular scale stays poorly understood.
Utilizing advanced modeling and pc simulations, a workforce led by a postdoctoral researcher on the Johns Hopkins Whiting Faculty of Engineering and Krieger Faculty of Arts and Sciences studied friction at each the molecular and macroscopic scale. The workforce’s research outcomes, which seem in DHW Nanonot solely make clear friction basically, however might additionally inform the design of improved prosthetic units and synthetic joints.
“Friction is puzzling as a result of it isn’t ruled by a single interplay, like attraction between expenses; it emerges from a mix of processes that may happen at totally different scales. In our work, we tried to hyperlink the nano and macro worlds for a specific characteristic of friction known as getting older, which is when one strong rests on one other for a very long time with out sliding, the power wanted to slip them aside will increase. We wished to search out out why,” mentioned Lucas Frérot, now a postdoctoral researcher at Albert-Ludwigs- Universität’s Institute for Mikrosystemtechnik.
Analysis workforce members on the Laboratoire de Tribologie et Dynamique des Systèmes at École Centrale de Lyon in France had beforehand performed experiments that gave a really detailed image of the friction response of surfaces coated with fatty acids, an environmentally pleasant household of lubricants, however these alone couldn’t clarify the phenomenon behind getting older. Utilizing measurements of floor roughness and the properties of the single-molecule-thick layer of fatty acid molecules, the workforce at Johns Hopkins was in a position to reproduce the getting older course of in a molecular simulation.
“Our simulation allowed us to strive issues unimaginable in experiments, comparable to what would occur if the surfaces involved had been mathematically flat,” mentioned workforce member Jaafar El-Awady, professor of mechanical engineering on the Whiting Faculty.
They discovered that the principle explanation for getting older was floor roughness. The truth is, the fashions with out roughness didn’t age in any respect, in response to Frérot.
“This was stunning as a result of the floor roughness measured by the workforce in Lyon was extraordinarily small; the very best mountain and the deepest valley of the floor could be separated by concerning the size of 1 fatty acid molecule,” Frérot mentioned.
The workforce concluded that even such a small quantity of roughness is sufficient to forestall the molecules from making contact over the entire floor, leaving the molecules on the sides of contact spots free to maneuver. Over time, extra molecules are available contact, leading to getting older.
Though the mechanism found is just not the one one that may clarify why frictional methods age, the workforce believes it may be utilized to a variety of methods the place chain-like molecules such because the fatty acids they studied type a protecting layer on a floor.
“That is the case in organic methods like joints, and if we perceive these methods higher, we will design higher and extra sturdy prostheses. In a extra basic sense, understanding the physics behind friction is necessary within the design of sustainable methods. Some research estimate that about 23% of the world’s power consumption is misplaced to friction,” Frérot mentioned.
Analysis workforce members notice that the design of the simulations used on this research had been initially envisioned by Mark O. Robbins, a professor within the Johns Hopkins Division of Physics and Astronomy, who died in 2020.
“Lucas and I then continued to push on the simulations with our collaborators to realize their targets efficiently, and to dedicate it to Mark’s reminiscence,” El-Awady mentioned.