Quantized Friction across Ionic Liquid Thin Films

TL;DR

This study investigates how the layered nano-structure of ionic liquids influences their lubrication properties by measuring friction across films of controlled thickness, revealing multiple friction regimes linked to the number of ion layers.

Contribution

It provides the first detailed correlation between ionic liquid nano-structure and frictional behavior at atomic scales.

Findings

Multiple friction-load regimes identified

Friction coefficients vary with ion layer number

Layer composition affects lubrication properties

Abstract

Ionic liquids, salts in the liquid state under ambient conditions, are of great interest as precision lubricants. Ionic liquids form layered structures at surfaces, yet it is not clear how this nano-structure relates to their lubrication properties. We measured the friction force between atomically smooth solid surfaces across ionic liquid films of controlled thickness in terms of the number of ion layers. Multiple friction-load regimes emerge, each corresponding to a different number of ion layers in the film. In contrast to molecular liquids, the friction coefficients differ for each layer due to their varying composition.