The effect of surface nano-corrugation on the squeeze-out of molecular thin hydrocarbon films between curved surfaces with long range elasticity

Abstract

Document VersionThe effect of surface nano-corrugation on the squeeze-out of molecular thin hydrocarbon films between curved surfaces with long range elasticity. The properties of linear alkane lubricants confined between two approaching solids are investigated by a model that accounts for the roughness, curvature and elastic properties of the solid surfaces. We consider linear alkanes of different chain lengths from C3H8 to C16H34, confined between corrugated solid walls. The pressure necessary to squeeze out the lubricant increases rapidly with the alkane chain length, but is always much lower than in the case of smooth surfaces. The longest alkanes form domains of ordered chains and the squeeze-out appear to nucleate in the more disordered regions between these domains. The short alkanes stay fluid-like during the entire squeeze out process which result in a very small squeeze-out pressure which is almost constant during the squeeze-out of the last monolayer of the fluid. In all cases we observe lubricant trapped in the valley of the surface roughness, which cannot be removed independent of the magnitude of the squeezing pressures.

Molecular Dynamics Simulation Study of Mechanical Effects of Lubrication on a Nanoscale Contact Process

“…An interesting finding is the squeeze-out of the lubricant from the contact zone which has been observed both in simulations in which the lubricant was only a thin adsorbed fluid layer [39,20], as well as in previous works from our group in which the indenter was immersed in the lubricant [37,38]. In some studies, the solids were modeled by only a few atom layers [39,20]. Cross-interactions resulting from the simultaneous presence of the bulk fluid phase and the bulk substrate have to the best of our knowledge only been investigated by Rentsch et al [36] and in previous studies of our group [37,38].…”

“…For an introduction into lubricated contact processes in general, we refer to the literature [14][15][16][17]. The influence of different variables on lubricated contact processes has been studied on the atomistic scale: chain length of the lubricant molecules [18,19], surface roughness [20], adsorbates [21][22][23][24][25][26][27][28][29][30], and surface chemistry [31]. There have also been attempts to link atomistic simulation with experiments in that field [32][33][34][35].…”

“…In most of these studies, lubrication was only considered by including adsorbed layers of fluid molecules on the substrate in the simulation, while studies in which the contact is truly immersed in a liquid are rare [36][37][38]. An interesting finding is the squeeze-out of the lubricant from the contact zone which has been observed both in simulations in which the lubricant was only a thin adsorbed fluid layer [39,20], as well as in previous works from our group in which the indenter was immersed in the lubricant [37,38]. In some studies, the solids were modeled by only a few atom layers [39,20].…”

Recent highlights in nanoscale and mesoscale friction

“…Different anions play a complex role depending on the surface potential, and related to the steric constraints they pose in relation to their partner cations. Steric effects in boundary lubrications were also investigated in the context of confined molecular fluids that were not electrically charged [ 122 – 125 ].…”

The Influence of Lubrication and the Solid–Fluid Interaction on Thermodynamic Properties in a Nanoscopic Scratching Process

“…Also, shear flow friction simulations where two solid bodies are separated by a fluid have been extensively investigated in the literature, for example, refs 29−45. Lubricated scratching processes where two solid bodies are in direct contact under the influence of a fluid, on the other hand, have not been investigated as systematically. Results on the influence of the chain length of the lubricant molecules, 46,47 the surface roughness, 48,49 adsorbates, 6,50−58 the squeeze-out of lubricant molecules, 9,48,59 and the surface chemistry 60,61 have been reported in the literature. In most of these studies, lubrication was only considered by single adsorbed layers of fluid molecules on the substrate surface in the simulation, while studies in which the contact is truly immersed in a liquid are still rare.…”