Tribological Interaction of Plasma-Functionalized Polytetrafluoroethylene Nanoparticles with ZDDP and Ionic Liquids

Polytetrafluoroethylene (PTFE) nanoparticles were coated with consecutive plasma deposited siliceous and methacrylate coatings. Secondary zinc dialkyldithiophosphate (ZDDP), phosphonium cation and phosphate anion ionic liquid (IL), and IL with phosphonium cation and dithiophosphate anion were mixed with the functionalized nanoparticles. Tribological studies were carried out for seven separate formulations including base oil, oils with only additives, and oils with additives and functionalized PTFE particles. Results indicate strong synergistic interactions of ZDDP and ILs with functionalized nanoparticles providing enhanced friction and wear performance. Chemical analysis of the tribofilms using X-ray photoelectron spectroscopy and X-ray absorption near edge structure spectroscopy indicates functionalized PTFE nanoparticles interact synergistically with ZDDP and ILs to form silicon- and fluorine-doped tribofilms resulting in superior tribological performance.