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Lateral Ordering in Nanoscale Ionic Liquid Films between Charged Surfaces Enhances Lubricity
Silvia Di Lecce1, Alexei A Kornyshev1, Michael Urbakh2
1Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, W12 0BZ London, U.K.
ACS Nano
|October 15, 2020
Summary
Electric fields tune friction in ionic liquids by controlling ion ordering. Room temperature ionic liquids (RTILs) form crystal-like structures in nanogaps, surprisingly reducing friction. This offers a new way to design tunable lubrication devices.
Area of Science:
- Materials Science
- Tribology
- Computational Chemistry
Background:
- Room temperature ionic liquids (RTILs) are tunable lubricants.
- Electric fields can alter RTIL properties for device applications.
Purpose of the Study:
- Investigate how RTIL composition affects ionic layer ordering in nanogaps.
- Understand the relationship between ionic liquid structure and friction under confinement.
- Explore electric field control over RTIL ordering and friction.
Main Methods:
- Nonequilibrium molecular dynamics atomistic simulations.
- Analysis of ionic liquid structure and ordering in nanoconfined geometries.
- Correlation of structural ordering with tribological properties (friction).
Main Results:
- Anion geometry and surface properties dictate ionic liquid ordering: crystal-like structures form with [BF4]- and [NTf2]- anions, while [C2SO4]- forms disordered layers.
- Counterintuitively, increased ordering (crystallization) in confined RTILs leads to decreased friction.
- Surface polarity can be manipulated to activate or inhibit RTIL crystallization, offering friction control.
Conclusions:
- The molecular structure of RTIL anions and surface characteristics significantly influence lubricant ordering under confinement.
- A mechanism for tunable friction in nanoconfined ionic liquids is demonstrated, where increased order reduces friction.
- Electric field-induced control over RTIL crystallization provides a pathway for developing advanced, tunable lubrication systems.
