Preparation and Structure-Performance Relationship of Choline Heterocyclic Dicarboxylate Ionic Liquid lubricants

Lubricating additives Ch₂Hdc were synthesized in situ by a reaction between choline and heterocyclic dicarboxylic acids in water. The structure-activity relationship between the performance, tribological property, corrosion performance, aquatic toxicity, and the additives molecular framework were investigated. The results showed that the kinematic viscosity of the aqueous solution increased as the raising of the additive (Ch₂Hdc) concentration. Moreover, when the molecular structure of Ch₂Hdc had low symmetry and high polarity, the viscosity increase was relatively large. This was due to that, when the additive molecule had higher polarity, the intermolecular interaction was greater, and it led to the larger viscosity of the solution. The tribological test results showed that the friction-reducing and anti-wear performance of the aqueous solution was related to the adsorption capacity of Ch₂Hdc molecular on the metal surface of the friction pairs. Effective lubricating protective films formed by the Ch₂Hdc which had higher polarity and strong adsorption capacity. When the concentration of the Ch₂Hdc was relatively high, the friction-reducing performance of the aqueous solution was inversely related to its viscosity, and the anti-wear performance was positively related to its viscosity. It was because that the lubricant viscosity was higher, the internal friction of the lubricant was larger. As a result, it showed a higher friction coefficient, i.e. poor friction reducing performance. The results of corrosion experiments showed that the corrosion of water was reduced obviously by Ch₂Hdc. The results of toxicity tests showed that the toxicities of Ch₂Hdc to green algae and sea shrimp were much less than traditional ionic liquid L-B104.