The application of ionic liquids (ILs) as lubricants, surface modifiers, solvents for colloidal materials or as electrolytes in energy devices (production or storage) rely on their utilization on confined spaces such as narrow pores or thin films.[1-2] Such geometries can have dramatic effects on the morphological characteristics of the IL and bulk properties such as viscosity, density or conductivity could not be valid for a confined liquid.[3-4]
In this work it was employed Molecular Dynamics (MD) simulations to study the structure of the ionic liquid N,N-decylmethylpyrrolidinium bis[(trifluoromethane)sulfonyl]imide, [C10C1Pyrr][Ntf2], confined between two negatively charged muscovite-2M mica surfaces. The MD results for one, two and three IL nanoconfined bilayers revealed that at the mica-IL interface the Ntf2 anions reside between the pyrrolidinium cation headgroups, suggesting the formation of a very thin electrical double-layer structure. Regarding on the nonpolar domain, the pyrrolidinium decyl chains were mainly parallel to the surface normal and the chains belonging to the half-layer of cations oriented towards one of the mica surfaces are interdigitaded with the alkyl chains coming from the half-layer oriented to the second mica wall, crossing around the C8 carbon. The inclusion of small quantities of water did not induce appreciable changes on the structure of the IL bilayer. However, the normal load on z direction exhibited a small but consistent increase as the water content on these systems increased, indicating that the hydration of the ionic liquid induces an expansion of the nanoconfined bilayer.
References
[1] Smith, A. M.; Lovelock, K. R. J.; Perkin S. Faraday Discuss. 2013, 167, 279–292.
[2] Smith, A. M.; Parkes, M. A.; Perkin, S. J. Phys. Chem. Lett. 2014, 5, 4032–4037.
[3] Shimizu, K.; Tariq, M.; Freitas, A. A.; Canongia Lopes, J. N. J. Braz. Chem. Soc. 2016, 27, 349–362.
[4] Shimizu, K.; Pensado, A.; Malfreyt, P.; Pádua, A. A. H. ; Canongia Lopes, J. N. Faraday Discuss. 2012, 154, 155–169.
Acknowledgements
The authors thank FCT/MEC (Portugal) for financial support through grants SFRH/BPD/94291/2013 (K. S.) and SFRH/BPD/94299/2013 (A. A. F.) and through UID/QUI/00100/2013.
