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Frictional characteristics of molecular length ultra-thin boundary adsorbed films

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journal contribution
posted on 2017-09-01, 13:11 authored by I.S.Y. Ku, W.W.F. Chong, T. Reddyhoff, Homer Rahnejat
© 2015, Springer Science+Business Media Dordrecht. 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 hydro Langmuir–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.

Funding

The authors acknowledge sponsorship provided by the EPSRC through Grant Numbers EP/D04099X and EP/L001624/1 (covering experimental work) along with the EPSRC ENCYCLOPAEDIC program grant (covering theoretical work).

History

School

  • Mechanical, Electrical and Manufacturing Engineering

Published in

Meccanica

Volume

50

Issue

7

Pages

1915 - 1922

Citation

KU, I.S.Y. ...et al., 2015. Frictional characteristics of molecular length ultra-thin boundary adsorbed films. Meccanica, 50(7), pp. 1915-1922.

Publisher

© Springer

Version

  • AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

2015

Notes

The final publication is available at Springer via http://dx.doi.org/10.1007/s11012-015-0186-0

ISSN

0025-6455

eISSN

1572-9648

Language

  • en

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