Polyoxometalate-Based Composites as High-Performance Lubricant Additives for Friction and Wear Reduction

Conventional small-molecule additives, inherently limited in thermal, chemical, and mechanical stability, raise environmental concerns in lubricated systems. Nanoparticles, by contrast, offer superior stability but suffer from poor dispersibility in base oils, a critical bottleneck that restricts their application in tribological contacts. Intermediate in size between small-molecule additives and nanoparticles, polyoxometalates (POMs) possess high stability. Herein, we report the synthesis of oil-dispersible POM-based composites via the acid-base reaction between sulfur-free or elemental-sulfur-derived polyisobutylene monosuccinimide and phosphomolybdic acid (PMA) or phosphotungstic acid (PTA). The resulting composites form stable micellar aggregates in oil, with the polyisobutylene corona encapsulating the POMs and ensuring long-term colloidal stability. SRV-IV oscillating reciprocating tribological evaluation reveals that the sulfur-derived POM composites exhibit excellent friction-reduction and antiwear properties, with load-bearing capacity exceeding 1200 N. This superior lubrication performance arises from the formation of nanoscale protective tribofilms that comprise in-situ-generated MoS2 or WS2. The present supramolecular platform, combining POMs with sulfur-derived and oil-compatible polymers, enables systematic development of high-performance lubricant additives via interfacial tribochemistry.