Version 1
: Received: 13 July 2018 / Approved: 16 July 2018 / Online: 16 July 2018 (08:56:03 CEST)
Version 2
: Received: 16 July 2018 / Approved: 17 July 2018 / Online: 17 July 2018 (08:22:00 CEST)
How to cite:
Han, M.; Espinosa-Marzal, R.M. Molecular Mechanisms Underlying Lubrication by Ionic Liquids: Activated Slip and Flow. Preprints2018, 2018070248. https://doi.org/10.20944/preprints201807.0248.v2
Han, M.; Espinosa-Marzal, R.M. Molecular Mechanisms Underlying Lubrication by Ionic Liquids: Activated Slip and Flow. Preprints 2018, 2018070248. https://doi.org/10.20944/preprints201807.0248.v2
Han, M.; Espinosa-Marzal, R.M. Molecular Mechanisms Underlying Lubrication by Ionic Liquids: Activated Slip and Flow. Preprints2018, 2018070248. https://doi.org/10.20944/preprints201807.0248.v2
APA Style
Han, M., & Espinosa-Marzal, R.M. (2018). Molecular Mechanisms Underlying Lubrication by Ionic Liquids: Activated Slip and Flow. Preprints. https://doi.org/10.20944/preprints201807.0248.v2
Chicago/Turabian Style
Han, M. and Rosa M. Espinosa-Marzal. 2018 "Molecular Mechanisms Underlying Lubrication by Ionic Liquids: Activated Slip and Flow" Preprints. https://doi.org/10.20944/preprints201807.0248.v2
Abstract
The present study provides molecular insight into the mechanisms underlying energy dissipation and lubrication of a smooth contact lubricated by an ionic liquid. We have performed normal and lateral force measurements with a surface forces apparatus and by colloidal probe atomic force microscopy on following model systems: 1-ethyl-3-methyl imidazolium bis-(trifluoro-methylsulfonyl)imide, in dry state and in equilibrium with ambient (humid) air; the surface was either bare mica or functionalized with a polymer brush. The velocity-dependence of the friction force reveals two different regimes of lubrication, boundary-film lubrication, with distinct characteristics for each model system, and fluid-film lubrication above a transition velocity V*. The underlying mechanisms of energy dissipation are evaluated with molecular models for stress-activated slip and flow, respectively. The stress-activated slip assumes that two boundary layers (composed of ions/water strongly adsorbed to the surface) slide pass each; the bond dynamics and the strength of the interaction at the slip plane dictate the change in friction -decreasing, increasing or remaining constant- with velocity in the boundary-film lubrication regime. Above a transition velocity V*, friction monotonically increases with velocity in the three model systems. Here, layers of ions slide past each (“flow”) under a shear stress and friction depends on a shear-activation volume that is significantly affected by confinement. The proposed friction model provides a molecular perspective of the lubrication of smooth contacts by ionic liquids and allows identifying the physical parameters that control friction.
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
