MD simulation of ionic liquids nanoconfined between oxide surfaces

Nicolas Voeltzel (1) , Nicolas Fillot (1) , Laurent Joly (2) , Philippe Vergne (1)

1 TMI - Tribologie et Mécanique des Interfaces
2 ILM - Institut Lumière Matière [Villeurbanne]

The potential of ionic liquids as lubricants is now well established [1]. Either to replace oils or additives, or to be used in very thin films, they can exhibit lower friction than classical lubricants. Simultaneously, environmental constraints and progress in manufacturing techniques push to reduce the lubricant quantity inside systems. As a consequence, lubrication regimes are becoming closer to the limit between full and mixed lubrication, where lubricant film thickness can decrease down to a few nanometers. From those statements, knowledge on the shearing behavior of ionic liquids under nanoconfinement is becoming more than ever 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 relatively unexplored alternative to experimental studies. While experimental devices are limited to the measurement of a few macroscopic quantities, numerous local informations can be extracted from MD simulations. In this work, the considered ionic liquid contains an imidazolium cation and a fluorinated anion; its viscosity is representative of that of conventional lubricants. The MD model is first validated by comparison of the transport properties inherent to the ionic liquid with experimental data. Then the confinement between two sliding metal oxide surfaces is simulated. Some global experimental observations are corroborated and the reduction of the film thickness from 5 nm down to a few ion layers reveals the strong connection between the ionic liquid structuration and the resulting friction. [1]Zhou, F., Liang, Y., and Liu, W., 2009, Chem. Soc. Rev.. [2]Perkin, S., 2012, Phys. Chem. Chem. Phys. [3]Somers, A. E., Howlett, P. C., MacFarlane, D. R., and Forsyth, M., 2013, Lubricants.

Mots clés: Nano lubrication; ionic liquids; molecular dynamic simulation

Domaines: Autre

Nicolas Voeltzel, Nicolas Fillot, Laurent Joly, Philippe Vergne. MD simulation of ionic liquids nanoconfined between oxide surfaces. "Lubricated Contact Cádiz" Conference, Rowena Crockett, Swiss Tribology, Switzerland, Apr 2015, Cadix, Spain. ⟨hal-01222494⟩