Influence of alkyl chain length on the tribological performance of choline ionic liquids as water-based lubricating additives under electric field conditions

Abstract

To develop green lubricants and improve the lubricating properties of water, three choline-type ionic liquids with different alkyl chain lengths were designed and synthesised as water-based additives. The tribological behaviour of these ionic liquids as a water-based lubricating additives in an ethylene glycol system was systematically studied under an external electric field. The results show that under current-carrying lubrication, the [Ch][SA] ionic liquid exhibits excellent anti-friction and anti-wear properties with increasing alkyl chain length. Mechanistic analysis showed that the [Ch][SA] ionic liquid could strongly adsorb on the metal surface to form a physical adsorption film. At the same time, during the friction process, the [Ch][SA] ionic liquid forms a dense tribochemical reaction film with the metal substrate, which effectively blocks direct contact between the friction pairs. The excellent anti-friction and anti-wear properties are the result of the synergistic effect of the physical adsorption film and the chemical reaction film.