Boundary lubrication by adsorption film

Abstract

A complete understanding of the mechanism of boundary lubrication is a goal that scientists have been striving to achieve over the past century. Although this complicated process has been far from fully revealed, a general picture and its influencing factors have been elucidated, not only at the macroscopic scale but also at the nanoscale, which is sufficiently clear to provide effective instructions for a lubrication design in engineering and even to efficiently control the boundary lubrication properties. Herein, we provide a review on the main advances, especially the breakthroughs in uncovering the mysterious but useful process of boundary lubrication by adsorption film. Despite the existence of an enormous amount of knowledge, albeit unsystematic, acquired in this area, in the present review, an effort was made to clarify the mainline of leading perspectives and methodologies in revealing the fundamental problems inherent to boundary lubrication. The main content of this review includes the formation of boundary film, the effects of boundary film on the adhesion and friction of rough surfaces, the behavior of adsorption film in boundary lubrication, boundary lubrication at the nanoscale, and the active control of boundary lubrication, generally sequenced based on the real history of our understanding of this process over the past century, incorporated by related modern concepts and prospects.

Quantification/mechanism of interfacial interaction modulated by electric potential in aqueous salt solution

“…It is helpful to reduce the friction between interfaces by maintaining a flat potential energy surface [11,12]. When a liquid medium is introduced between two solid surfaces, it works as a lubricant to reduce the friction force according to the hydrodynamic effect and/or adsorbed boundary film [13][14][15][16][17][18]. Water-based lubricants have been widely studied owing to their low viscosity and environmentally friendly properties [19][20][21].…”

Investigation of calcium phosphate (CaP) tribofilms from commercial automatic transmission fluids (ATFs) and their correlation with antishudder performance

“…For instance, when the dependence of the kinetic friction coefficient on the relative velocity (μ-v curve) is negative, steady sliding at the equilibrium point becomes unstable, and the instability generates shudder [2]. Stick-slip is another type of shudder that results from the discontinuity between static and kinetic friction; stick-slip can arise when the static friction is higher than the dynamic friction [3,4]. The tendencies of a wet clutch to experience both stick-slip and shudder are usually characterized by the μ-v curve.…”

Molecular behaviors in thin film lubrication—Part three: Superlubricity attained by polar and nonpolar molecules

“…For a thick film, the contact surfaces are separated completely by a fluid layer, which makes the ordered layers less important and leads to a lubrication regime that shows EHL behavior [4,5]. When the thickness of a film is decreased to a few nanometers, the fluid layer and ordered layers are destroyed, only the adsorbed layers (or tribochemical layers) function between the contact surfaces, and BL [6] is established there. Clearly, a transition regime is expected between EHL and BL, where the fluid layer, ordered layers, and adsorbed layers (or tribochemical layers) coexist and function to reduce the friction.…”