Structural effects in nanotribology of nanoscale films of ionic liquids confined between metallic surfaces

Silvia Di Lecce, Alexei A. Kornyshev, Michael Urbakh, Fernando Bresme*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Room Temperature Ionic Liquids (RTILs) attract significant interest in nanotribology. However, their microscopic lubrication mechanism is still under debate. Here, using non-equilibrium molecular dynamics simulations, we investigate the lubrication performance of ultra-Thin (<2 nm) films of [C2MIM]+ [NTf2]- confined between plane-parallel neutral surfaces of Au(111) or Au(100). We find that films consisting of tri-layers or bilayers, form ordered structures with a flat orientation of the imidazolium rings with respect to the gold surface plane. Tri-layers are unstable against loads >0.5 GPa, while bi-layers sustain pressures in the 1-2 GPa range. The compression of these films results in monolayers that can sustain loads of several GPa without significant loss in their lubrication performance. Surprisingly, in such ultra-Thin films the imidazolium rings show higher orientational in-plane disorder, with and the rings adopting a tilted orientation with respect to the gold surface. The friction force and friction coefficient of the monolayers depends strongly on the structure of the gold plates, with the friction coefficient being four times higher for monolayers confined between Au(100) surfaces than for more compact Au(111) surfaces. We show that the general behaviour described here is independent of whether the metallic surfaces are modelled as polarizable or non-polarizable surfaces and speculate on the nature of this unexpected conclusion.

Original languageEnglish
Pages (from-to)22174-22183
Number of pages10
JournalPhysical Chemistry Chemical Physics
Volume23
Issue number38
DOIs
StatePublished - 14 Oct 2021

Funding

FundersFunder number
Imperial College High Performance Computing Service
Engineering and Physical Sciences Research CouncilEP/P020194/1, EP/T022213/1
Leverhulme TrustRPG-2016-223
Israel Science Foundation1141/18

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