Influence of the molecular structure on the tribological properties of choline-based ionic liquids as water-based additives under current-carrying lubrication

In this work, four types of choline/fatty acid ionic liquids were synthesised and used as water-based lubricant additives in an ethylene glycol system, and the tribological behaviours of the mixtures were investigated under the control of an applied electric field. Under current-carrying lubrication, the friction and wear resistances of the steel friction pair lubricated with the ionic liquid-added lubricant became more pronounced. As the number of double bonds in the fatty acid structure increases, the molecular compactness decreases, and the friction-reduction performance is affected. Mechanistic analyses indicated that the [Ch][SA] ionic liquid can strongly adsorb to the metal surface and form a tribochemical reaction film during the friction process, leading to excellent tribological properties.