DFT method study on lubricant properties of disulfide compounds as extreme pressure additive

The molecular geometries optimization and electronic structures of fourteen disulfide compounds had been investigated by density functional theory (DFT) at 6-31G basis set level. The active atoms and active bonds of tribochemical reaction were obtained according to frontier molecular orbital theory, and the interaction energy of chemical adsorption between disulfides and metal surfaces were calculated. The structure-property relationship had been discussed with satisfactory results. The calculated results indicated that the S-S bond and C-S bond of compounds are trended to be broken when organic disulfide compounds interact with a metal, and the order of anti-wear properties for disulfide compounds: diphenyldisulfide >dibenzyldisulfide>di-n-dodecyldisulfide >di-n-octyldisulfide >di-n-butyldisulfide>diethyldisulfide, the extreme pressure properties of DBDS is superior to that of DPDS. The predicted results based on quantum chemical calculations are in excellent agreement with friction and wear test results.