Ionic liquids (ILs) have emerged as potential lubricants in 2001. Subsequently, there has been tremendous research interest in ILs from the tribology society since their discovery as novel synthetic lubricating materials. This also expands the research area of ILs. Consistent with the requirement of searching for alternative and eco-friendly lubricants, IL lubrication will experience further development in the coming years. Herein, we review the research progress of IL lubricants. Generally, the tribological properties of IL lubricants as lubricating oils, additives and thin films are reviewed in detail and their lubrication mechanisms discussed. Considering their actual applications, the flexible design of ILs allows the synthesis of task-specific and tribologically interesting ILs to overcome the drawbacks of the application of ILs, such as high cost, poor compatibility with traditional oils, thermal oxidization and corrosion. Nowadays, increasing research is focused on halogen-free ILs, green ILs, synthesis-free ILs and functional ILs. In addition to their macroscopic properties, the nanoscopic performance of ILs on a small scale and in small gaps is also important in revealing their tribological mechanisms. It has been shown that when sliding surfaces are compressed, in comparison with a less polar molecular lubricant, ion pairs resist "squeeze out" due to the strong interaction between the ions of ILs and oppositely charged surfaces, resulting in a film that remains in place at higher shear forces. Thus, the lubricity of ILs can be externally controlled in situ by applying electric potentials. In summary, ILs demonstrate sufficient design versatility as a type of model lubricant for meeting the requirements of mechanical engineering. Accordingly, their perspectives and future development are discussed in this review.

Ionic liquid lubricants: when chemistry meets tribology

Fundamental importance of ionic interactions in the liquid phase: A review of recent studies of ionic liquids in biomedical and pharmaceutical applications

Cutting fluid corrosion inhibitors from inorganic to organic: Progress and applications

Review of the toxic effects of ionic liquids

Towards superior lubricity and anticorrosion performances of proton-type ionic liquids additives for water-based lubricating fluids

The ecotoxicity and tribological properties of choline amino acid ionic liquid lubricants

The synthesis and tribological properties of dicarboxylic acid ionic liquids

In situ preparation of multifunctional additives in water

Anti-corrosion benzotriazole ionic liquid (IL, BTAP4444) was synthesized by neutralizing 1H-benzotriazole (BTAH) with terabutylphosphonium hydroxide (P4444OH). The physicochemical and tribological properties of BTAP4444 were measured and the results indicated that it had good lubricating properties for steel/steel, steel/copper and steel/aluminum friction pairs in reducing the friction coefficient and wear volume, especially when it worked for the steel/copper friction pair both at room temperature (RT) and 100 °C. Good performances were also found in terms of its anti-corrosion ability, thermal and hydrolysis stability, and viscosity temperature characteristics compared with commercially available synthetic oil poly-alpha-olefin (PAO 10) and traditional IL 1-butyl-3-methyl imidazolium tetrafluoroborate (bmimBF4). The designing purpose of BTAP4444 is to enhance the anti-corrosion ability of the IL lubricant attributed to the introduction of a nitrogen heterocyclic structure, 1H-benzotriazole, which is normally used as antirust and corrosion inhibitor in mechanical engineering. The corrosion test results confirm our assumption and BTAP4444 shows excellent anti-corrosion ability for all the used friction pairs including steel/steel, steel/copper and steel/aluminum contacts.

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Study on the synthesis and tribological properties of anti-corrosion benzotriazole ionic liquid

The depletion of petroleum resources and the intensification of environmental problems have necessitated the development of renewable products from bio-based chemicals instead of petroleum resources. Herein, a new kind of ester lubricating oil, isooctyl furan dicarboxylate (isooctyl-FD), was prepared from bio-based 2, 5-furandicarboxylic acid. The structure of isooctyl-FD was evaluated using nuclear magnetic resonance imaging and high-resolution mass spectroscopy. Its physicochemical and tribological properties including thermal and oxidation stabilities, flash point and pour point, viscosity and viscosity index, and friction-reducing and anti-wear properties were systematically evaluated. The results show that isooctyl-FD has comparable thermal and oxidation stability to the synthetic ester lubricating oil, isooctyl sebacate (isooctyl-S). Its friction-reducing and anti-wear properties are superior to isooctyl-S; however, its viscosity-temperature and low-temperature properties are inferior to isooctyl-S.

/pdf/lubricating-properties-of-ester-oil-prepared-from-bio-based-4yvx8zvujh.pdf

Shuai Zhang

Papers

The ecotoxicity and tribological properties of choline amino acid ionic liquid lubricants

The synthesis and tribological properties of dicarboxylic acid ionic liquids

In situ preparation of multifunctional additives in water

Study on the synthesis and tribological properties of anti-corrosion benzotriazole ionic liquid

Lubricating properties of ester oil prepared from bio-based 2, 5-furandicarboxylic acid