Abstract: The aim of this study was to investigate the effects of competitive adsorption of mono-isostearate (FM-1), butyltriphenyl thiophosphate (AW-1) and acid thiophosphate (AW-2) on the friction properties of vehicle gear oil. The friction properties of AW-1, AW-2, FM-1, and their composite systems were evaluated using SRV tester and surface analysis was conducted using S neox three-dimensional confocal white light interferometer, while the adsorption behavior of antiwear and friction modifier on steel surfaces was examined quartz crystal microbalance with dissipation (QCM-D). The results revealed that both AW-1 and AW-2 had stable wear resistance, while FM-1 had no wear resistance. In the combination of AW-1 and FM-1, the competition of adsorption sites leads to antagonistic effect, and the wear resistance of AW-1 deteriorated significantly. When AW-2 was mixed with FM-1, FM-1 regulated the adsorption configuration through steric hindrance effect, which inhibited the possibility of forming brittle FeS film between sulfur element in AW-2 molecule and metal surface, while retaining the anti-wear properties of P element in AW-2.

Key words: phosphorothioate, glycerol monoisostearate, adsorption behavior, QCM-D, gear oil