Influence of Base oil Polarity on the Tribological Performance of Surface-Active Engine Oil Additives

Abstract

Friction, wear and tribo lm growth of organic friction modi ers (glycerol monooleate and oleamide), antiwear additive (ZDDP) and binary additive system comprising the organic friction modi ers and ZDDP were studied in polyalphaole n (PAO) and ester oil. The mechanisms underlying base oil polaritydependent frictional performance of the OFM and AW additives at high temperature (140 oC), either singly or in combination, was investigated in the light of chemical composition analysis of the tribo lms post friction measurements using energy-dispersive X-ray spectroscopy (EDX), static and dynamic timeof-ight secondary ion mass spectrometry (ToF-SIMS). Depending on the rubbing conditions, the boundary friction coe cient of the binary additive systems were found to be either lower than that of individual additives or to lay between the values for the individual additives. Chemical composition analysis of the tribo lms indicated that the nature of base oil controlled interactions between ZDDP and OFM and consequently adsorption and reactive tribo lm formation in the boundary lubrication layer.Surface roughness and wear scar width measured post tribological tests using 3D surface pro ler showed improved wear performance in both PAO and ester-based additive formulations.

Lubricant performance against white etching areas (WEAs) formation in AISI 52100 bearing steel under cyclic compressive loading

“…Researchers 36 state that some of the degradation occurring in the lubricants is below the detectable limit of FTIR. Therefore, the oils were subjected to ESR spectroscopy for further analysis.…”

Adsorption Behavior of TEMPO-Based Organic Friction Modifiers during Sliding between Iron Oxide Surfaces: A Molecular Dynamics Study

“…38 Many studies demonstrated that high adsorbed masses or thick films result in low friction and wear, possibly due to the high surface coverage and packing density. 17,20,43 In contrast, a few recent studies reported that adsorbed masses evidently affect the initial friction but not the steady-state friction, 30 and fast adsorption kinetics is effective at reducing friction and wear rather than high adsorbed masses. 35 A recent study also suggests that complete surface coverage is not necessary for effective friction reduction.…”

“…The adsorption kinetics depends on the chemical structure of not only the functional groups and alkyl chains of OFMs but also of lubricating oils because adsorption involves a process of OFM molecules diffusing onto the solid surfaces from the lubricating oils. ,− The literature shows that, on ferrous substrates, OFMs with carboxylic acid and amine groups are generally more effective than with alcohol and ester groups. , It was reported that, compared with a single functional group, multiple functional groups lead to strong adsorption owing to the multisite adsorption or chelate effect and thereby high adsorbed masses; however, the steric hindrance caused by the large size could slow down the adsorption kinetics. , Longer alkyl chains were found to result in thicker boundary films, , and linear saturated alkyl chains are believed to result in ordered and close-packed boundary films compared with branched and unsaturated ones . Many studies demonstrated that high adsorbed masses or thick films result in low friction and wear, possibly due to the high surface coverage and packing density. ,, In contrast, a few recent studies reported that adsorbed masses evidently affect the initial friction but not the steady-state friction, and fast adsorption kinetics is effective at reducing friction and wear rather than high adsorbed masses . A recent study also suggests that complete surface coverage is not necessary for effective friction reduction .…”

Tribological performance of polymeric friction modifiers under sliding rolling contact condition

“…6 The frictional performance of OFM is shown to be a function of its molecular structure and external factors such as load, temperature, sliding speed, nature of solvent and substrate material. 1,2,[7][8][9][10][11][12] Glycerol Mono-oleate (GMO) and oleamide are the most commonly used OFMs. 13,14 Even though they are effective in reducing friction, the boundary films formed by them can be brushed off under harsh contact conditions.…”

“…The contrasting result suggests that these surface-active molecules are effective under specific operating conditions. 12 The most commonly used organo-molybdenum compounds are molybdenum dialkyldithiophosphate and molybdenum dialkyldithiocarbamate. 18 Even though they are effective in reducing friction, they can produce hazardous lubricant discharge and therefore are not environmentally friendly.…”