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Ionic liquid nanoconfined between metal oxide and DLC surfaces


In this study we aim to characterize the use as lubricant of ionic liquids in realistic tribological contacts by means of molecular dynamics simulations. First, the confinement between two iron oxide surfaces is simulated to investigate the behavior of a steel/steel contact. Various configurations of the surfaces were model to fully apprehend their influence on the contact performances. Next, oxide surfaces are replaced by classic DLC coatings to depict a wear-resistant contact. Lubrication capability of the system is explored and compared to previous results and similar works. The potential of ionic liquids as lubricants is now well established [1]. Either as oil or additive replacement, or in very thin films, they can exhibit lower friction than classical lubricants. Simultaneously, environmental constraints and progresses in manufacturing techniques push to reduce the lubricant quantity inside lubricated systems. As a consequence, lubrication regimes digress from full lubrication and lubricant film thickness can decrease down to a few nanometers. From those statements, investigations on the shearing behavior of ionic liquids under nanoconfinement become essential. Numerous experimental research groups highlighted the complex response of ionic liquids to nanoconfinement and shearing. On the one hand, the fluid dynamics is remarkably dependent on their layering capacity [2]. On the other hand, their interfacial behavior is correlated to both the ionic liquid type and to the surface nature involved in the contact [3]. At this scale, molecular dynamics (MD) simulations offer a relevant alternative to experimental studies. While experimental devices are limited to the measurement of a few physical quantities, a lot of information can be extracted from MD simulations. In this work, the model is first validated with macroscopic quantities, workable results from simulations go then far beyond simple structural observations as multiple quantitative analysis of the dynamics are also possible. The considered ionic liquid contains an imidazolium cation and a fluorinated anion (Fig. 1); its viscosity is representative of that of conventional lubricants and excellent lubrication capability of similar ionic liquids is pointed out by different studies [4, 5]. Firstly, some experimental trends are corroborated when confined between two metal oxide surfaces (Fig. 2); the influence of surface charges on both the interfacial behavior and on the film rheology is clearly evidenced by virtually modifying atomic charges and crystal orientation of the surfaces. Secondly, the same fluid is confined and sheared between two DLC surfaces which ones are known for their high resistance to abrasive wear; a comparison is performed with the previous case to evaluate the ionic liquid suitability to lubricate contacts with DLC surfaces. References [1]Zhou, F., Liang, Y., and Liu, W., “Ionic liquid lubricants: designed chemistry for engineering applications,” Chemical Society Reviews, The Royal Society of Chemistry, 38, 2009, 2590-2599 [2]Perkin, S., “Ionic liquids in confined geometries,” Physical Chemistry Chemical Physics, The Royal Society of Chemistry, 14, 2012, 5052-5062 [3]Somers, A. E.; Howlett, P. C.; MacFarlane, D. R. and Forsyth, M., “A Review of Ionic Liquid Lubricants,” Lubricants, 1, 1, 2013, 3-21 [4]Lopez Sanchez, F.; Otero, I.; Lopez, E. R. and Fernandez, J., “Tribological Properties of Two Bis(trifluoromethylsulfonyl)imide-Based Ionic Liquids on Steel-Steel Contact”, Tribology Transactions, 57, 4, 2014, 637-646 [5]Fernández, J.; Paredes, X.; Gaciño, F. M.; Comuñas, M. J. P. & Pensado, A. S., “Pressure-viscosity behaviour and film thickness in elastohydrodynamic regime of lubrication of ionic liquids and other base oils”, Lubrication Science, 26, 7-8, 2013, 449-462


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hal-01222561 , version 1 (30-10-2015)


  • HAL Id : hal-01222561 , version 1


Nicolas Voeltzel, Nicolas Fillot, Laurent Joly, Philippe Vergne. Ionic liquid nanoconfined between metal oxide and DLC surfaces. International Tribology Conference ITC2015, Japanese Society of Tribologists, Sep 2015, Tokyo, Japan. ⟨hal-01222561⟩
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