Exploring the Effect Mechanism of Alkyl Chain Lengths on the Tribological Performance of Ionic Liquids

In this work, four kinds of imidazole phosphate ionic liquids (ILs) with different anionic and cationic alkyl chain lengths were synthesized. The physicochemical properties and tribological performance of ILs were evaluated. The experimental results revealed that the tribological properties of ILs were positively correlated with the cationic chain length and negatively correlated with the anionic chain length. The effect mechanism can be summarized in two aspects: on the one hand, anions with shorter alkyl chain lengths possess stronger adsorption performance and better film forming ability on the friction pair surfaces, which makes the ILs form more robust and stable lubricating film; on the other hand, ILs with longer cationic alkyl chain lengths possess milder tribo-chemical reactions, which can effectively enhance the tribological performance and decrease the corrosion wear.