Lateral ordering in nanoscale ionic liquid films between charged surfaces enhances lubricity

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

Research output: Contribution to journalArticlepeer-review

Abstract

Electric fields modify the structural and dynamical properties of room temperature ionic liquids (RTILs) providing a physical principle to develop tunable lubrication devices. Using nonequilibrium molecular dynamics atomistic simulations, we investigate the impact of the composition of imidazolium RTILs on the in-plane ordering of ionic layers in nanogaps. We consider imidazolium cations and widely used anions featuring different molecular structures, spherical ([BF4]-), elongated surfactant-like ([C2SO4]-), and elongated with a more delocalized charge ([NTf2]-). The interplay of surface charge, surface polarity, and anion geometry enables the formation of crystal-like structures in [BF4]- and [NTf2]- nanofilms, while [C2SO4]- nanofilms form disordered layers. We study how the ordering of the ionic liquid lubricant in the nanogap affects friction. Counterintuitively, we find that the friction force decreases with the ability of the RTILs to form crystal-like structures in the confined region. The crystallization can be activated or inhibited by changing the polarity of the surface, providing a mechanism to tune friction with electric fields.

Original languageEnglish
Pages (from-to)13256-13267
Number of pages12
JournalACS Nano
Volume14
Issue number10
DOIs
StatePublished - 27 Oct 2020

Keywords

  • Electrotunable friction
  • Lubricants
  • Nanoconfinement
  • Nanotribology
  • Nonequilibrium simulations
  • Room-temperature ionic liquids

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