title: On the question of whether lubricants fluidize in stick-slip friction.
abstract: Intermittent sliding (stick-slip motion) between solids is commonplace (e.g., squeaking hinges), even in the presence of lubricants, and is believed to occur by shear-induced fluidization of the lubricant film (slip), followed by its resolidification (stick). Using a surface force balance, we measure how the thickness of molecularly thin, model lubricant films (octamethylcyclotetrasiloxane) varies in stick-slip sliding between atomically smooth surfaces during the fleeting (ca. 20 ms) individual slip events. Shear fluidization of a film of five to six molecular layers during an individual slip event should result in film dilation of 0.4-0.5 nm, but our results show that, within our resolution of ca. 0.1 nm, slip of the surfaces is not correlated with any dilation of the intersurface gap. This reveals that, unlike what is commonly supposed, slip does not occur by such shear melting, and indicates that other mechanisms, such as intralayer slip within the lubricant film, or at its interface with the confining surfaces, may be the dominant dissipation modes.
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel;
authors.forename: Irit
authors.initials: I
authors.lastname: Rosenhek-Goldian
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel;
authors.forename: Nir
authors.initials: N
authors.lastname: Kampf
authors.affiliation: Department of Electrical Engineering - Systems, Tel-Aviv University, Tel-Aviv 69978, Israel.
authors.forename: Arie
authors.initials: A
authors.lastname: Yeredor
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel; jacob.klein@weizmann.ac.il.
authors.forename: Jacob
authors.initials: J
authors.lastname: Klein
mesh_terms: D017276:Friction; D054327:Lubricants / Q000737:chemistry*; D033081:Shear Strength
chemical_list: D054327:Lubricants
keywords: friction; lubricant yield; lubrication; nanotribology; stick–slip friction