Formation of ultra-thin bi-molecular boundary adsorbed films

Chong, William Woei Fong; Teodorescu, Mircea; Rahnejat, Homer

doi:10.1088/0022-3727/45/11/115303

Cited by 9 publications

(9 citation statements)

References 42 publications

(75 reference statements)

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“…The latter; packing fraction, acknowledges the state of the fluidic medium, with progressively lower dispositions corresponding to vapour or gaseous media. Chong et al [23] extended their mono-molecular model to bi-molecular mixture, with the spherical additive molecules possessing adsorption energy to stick to the bounding surfaces. The model is based on the solution of Ornstein and Zernike [24] (OZ) integral equation, with an infinitely narrow attractive well potential represented by the Percus and Yevick [25] (PY) approximation.…”

Section: Introductionmentioning

confidence: 99%

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

2012

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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.

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Section: Introductionmentioning

confidence: 99%

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

2012

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“…A total packing fraction of Ã tot is assumed for a fluidic volume, constrained within nominally smooth solid boundaries. Therefore, for the fluid mixture, the 54 ) Process activation energy, Q y 1.33 Â 10 À20 J Pressure activation volume, y 1.93 Â 10 À13 m 3 /m 2 Shear activation volume, Ã y 1.21 Â 10 À12 m 3 /m 2 (values used in Chong et al 40,41 ) packing fraction for the long chain and hard spherical molecules becomes…”

Section: Resultsmentioning

confidence: 99%

“…A total packing fraction of Ã tot is assumed for a fluidic volume, constrained within nominally smooth solid boundaries. Therefore, for the fluid mixture, the 40,41 ) packing fraction for the long chain and hard spherical molecules becomes…”

Section: Resultsmentioning

confidence: 99%

Nanoscale elastoplastic adhesion of wet asperities

Chong

Teodorescu

Rahnejat

2013

Proceedings of the Institution of Mechanical Engineers, Part J:

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Accurate prediction of friction is crucial for design and efficient operation of many devices, comprising various contacts. In practice, contacting surfaces are rough and often wet. There are several mechanisms, which contribute to friction, including viscous shear of a coherent fluid film, as well as that of a thin adsorbed layer of boundary active molecular species. Additionally, adhesion and elastoplastic deformation of asperities on counterface surfaces may occur. Traditional friction models are based on statistical representation of surface topography as well as description of boundary shear films based on the theoretical lubricant film Eyring shear stress. The study reports a more realistic friction model than the traditional ones, which do not take into account the wet nature of the asperities. The fluid-surface interaction is a main contribution of the article, not hitherto reported in literature. It is shown that ignoring the effect of surface wetness can lead to the over-estimation of boundary friction and under-estimation of contact load-carrying capacity.

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“…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].…”

Section: Introductionmentioning

confidence: 99%

Frictional characteristics of molecular length ultra-thin boundary adsorbed films

Chong

Reddyhoff

et al. 2015

Meccanica

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The paper presents measurements of friction of any ultra-thin film entrained into the contact of a pair of very smooth specimen subjected to entrainment in a converging micro-wedge of a special-purpose micro-tribometer. An ultra-thin film is expected to form at the boundary solids through adsorption of boundary active molecules. Fluids with linear and branched molecules are used in the investigation. It is found that the frictional characteristics of these films can be adequately described through use of Eyring thermal activation energy and a potential energy barrier to sustain conjunctional sliding motion. The combined experimental measurement and the simple activation energy approach shows that the thin molecular adsorbed films act like hydroLangmuir-Blodgett layers, the formation and frictional characteristics of which are affected by the competing mechanisms of adsorption, forced molecular re-ordering and discrete-fashion drainage through the contact by the solvation effect. This process is a complex function of the contact sliding velocity as well as a defined Eyring activation density (packing density of the molecules within the conjunction). It is shown that the contribution of solvation to friction is in the form of energy expended to eject layers of lubricant out of the contact, which unlike the case of micro-scale hydrodynamic films, is not a function of the sliding velocity.

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Formation of ultra-thin bi-molecular boundary adsorbed films

Cited by 9 publications

References 42 publications

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

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

Nanoscale elastoplastic adhesion of wet asperities

Frictional characteristics of molecular length ultra-thin boundary adsorbed films

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