Tribological behavior and structural change of the LB film of MoS2 nanoparticles coated with dialkyldithiophosphate

The LB film of MoS2 nanoparticles coated with dialkyldithiophosphate (DDP) was prepared on a copper-coated glass substrate. The tribological behavior of the surface-modified MoS2 nanoparticle LB film against GCr15 bearing steel (SAE 52100) was evaluated with a one-way reciprocating friction tester, and the structural change of the LB film during rubbing process was investigated with a Fourier transform infrared (FTIR) microscope and X-ray photoelectron spectroscope (XPS). It has been found that MoS2 nanoparticle LB film shows a considerably decreased friction coefficient and increased wear resistance in sliding against steel. Tribochemical changes were involved during the friction process of the LB film against GCr15 bearing steel, including the disordering and partial or even complete decomposition of the modifier DDP at sliding cycles above 5000. However, the inorganic nanocores of MoS2 kept unchanged after sliding even for 5000 cycles, though they experienced oxidation when heated to 300°C in air. Thus, the improved tribological behavior of DDP coated-MoS2 nanoparticles is attributed to the lubricity of DDP modifier at low sliding cycles and the load-carrying capacity and lubricity of MoS2 nanocores at increased sliding cycles.