Physio-chemical hydrodynamic mechanism underlying the formation of thin adsorbed boundary films

Abstract

Abstract.Formation of low shear strength surface-adhered thin films mitigates excessive friction in mixed or boundary regimes of lubrication. Tribo-films are formed as a consequence of molecular chemical reaction with the surfaces. The process is best viewed in the context of a lubricant-surface system. Therefore, it is usually surmised that the adsorption of lubricant molecular species to the contact surfaces would be underlying to the formation of ultra-thin lubricant films.The paper considers contact of smooth surfaces at close separation. This may be regarded as the contact of a pair of asperity summits, whose dimensions, however small, are far larger than the size of fluid molecules within the conjunction. In such diminishing separations the constraining effect of relatively smooth solid barriers causes oscillatory solvation of fluid molecules. This effect accounts for the conjunctional load capacity but does not contribute to mitigating friction, except when molecular adsorption is taken into account with long chain molecules which tend to inhibit solvation. The paper presents an analytical predictive model based on the Ornstein-Zernike method with Percus-Yevick approximation of a narrow interaction potential between conjunctional composition. The predictions confirm the above stated physical facts in a fundamental manner.

Combined numerical and experimental investigation of the micro-hydrodynamics of chevron-based textured patterns influencing conjunctional friction of sliding contacts

“…7,8 Therefore, unlike the idealised dry friction, wet rough contacting surface topography can actually aid lubrication and reduce friction. The realisation of this point has gradually led to the introduction of engineered textured features on sliding surfaces.…”

In-cycle and life-time friction transience in piston ring–liner conjunction under mixed regime of lubrication

“…Nevertheless, the use of this method has resulted in better prediction of in situ conditions, if accurate measurements of surface topography and shear strength characteristics of coatings can be made. Therefore, in the more detailed and advanced recent analyses friction is viewed as a lubricant-surface system response (Erdemir [16], Chong et al [17]). …”

Frictional characteristics of molecular length ultra-thin boundary adsorbed films

“…They include the works reported by Matsuoka and Kato [10], Al-Samieh and Rahnejat [11,12,13] and Chong et al [14] for the study of lightly loaded conjunctions with diminutively thin films, entrained through by hydrodynamic viscous action. To describe solvation, Chong et al [15,16] also adopted the use of Ornstein-Zernike (OZ) equation as expounded by Mitchel et al [17], Henderson and Lozada-Cassou [18] and Attard and Parker [19].…”