Catalysis

Engineering

Polymer chemistry

Materials science

Solubility

Biodegradation

Lubricant

Alkyl

Chemical engineering

Lubrication

Cationic polymerization

Organic chemistry

Phosphonium

Composite material

Tribology

Corrosion

Chemistry

Viscosity

Ionic liquid

Thermal stability

Halide

Tribology International

Phosphonium-based room temperature ionic liquids (P-RTILs) offer outstanding lubricant properties. Studies have shown that the cationic chain length and anionic ring size significantly affect the performance of P-RTIL lubricants by altering properties, such as viscosity, density, thermal stability, wettability, and solubility. Functionalized moieties further improve their performance. However, the presence of halide groups could introduce corrosion and toxicity, which could be minimized by non-halide anions with large alkyl-chain-carrying cations to optimize both corrosion and tribological performance of P-RTILs. In this review, state-of-the-art research of P-RTILs is summarized from the lubrication perspective, covering their synthesis, properties, lubricant-relevant mechanisms, and performance matrices. Finally, the potential for developing a circular economy enabled by the biodegradability, recovery, and alternative applications of P-RTILs is discussed.

Recent progress on phosphonium-based room temperature ionic liquids: Synthesis, properties, tribological performances and applications