Tribology of the lubricant quantized sliding state

Abstract

In the framework of Langevin dynamics, we demonstrate clear evidence of the peculiar quantized sliding state, previously found in a simple one-dimensional boundary lubricated model [A. Vanossi et al., Phys. Rev. Lett. 97, 056101 (2006)], for a substantially less idealized two-dimensional description of a confined multilayer solid lubricant under shear. This dynamical state, marked by a nontrivial "quantized" ratio of the averaged lubricant center-of-mass velocity to the externally imposed sliding speed, is recovered, and shown to be robust against the effects of thermal fluctuations, quenched disorder in the confining substrates, and over a wide range of loading forces. The lubricant softness, setting the width of the propagating solitonic structures, is found to play a major role in promoting in-registry commensurate regions beneficial to this quantized sliding. By evaluating the force instantaneously exerted on the top plate, we find that this quantized sliding represents a dynamical "pinned" state, characterized by significantly low values of the kinetic friction. While the quantized sliding occurs due to solitons being driven gently, the transition to ordinary unpinned sliding regimes can involve lubricant melting due to large shear-induced Joule heating, for example at large speed.

Static and dynamic friction in sliding colloidal monolayers

“…A second line is to include non-periodic complications to the corrugation potential, including the quasicrystal geometry such as that recently realized [35] and beyond that, random, or pseudo-random corrugations to be realized in the future. A third line involves the investigation of the lubricant speed quantization phenomena, characterized so far only theoretically [36,37,38,39].…”

Fundamentals of Friction and Wear on the Nanoscale

“…This dynamical regime, is shown to be robust against the effects of thermal fluctuations, quenched disorder in the confining substrates, and over a broad range of loading forces. By evaluating its tribological properties in terms of averaged kinetic friction F k exerted on the top slider, this lubricant quantized sliding has been found [127] to be characterized by significantly low values of F k , see Fig. 10.10.…”

Subharmonic Shapiro steps of sliding colloidal monolayers in optical lattices

“…[40,41,42,43,44,45,46,47,48,49,50,51]. The results of sliding simulation for w = 1/14, corresponding to ρ = 14/15, are shown in Fig.…”

“…(11) was discovered and studied in the context of the sliding of mismatched crystalline systems in mutual contact, and reported in the study of two sliding surfaces with an atomically thin solid lubricant layer in between [40,41,42,43,44,45,46,47,48,49,50,51]. There, the ratio ρ was that of the lattice spacing of a "bottom" slider to that of the lubricant layer, w was the mean velocity at which the lubricant moved over the bottom slider, in units of the externally imposed speed of the "top" slider.…”