Preparation Of Alkylated Sulfur Doped Graphene Oxide And Study On Its Tribological Properties

Lubrication is mainly used to eliminate direct contact between two sliding parts to reduce friction and wear.Lubricating oil has been widely used in various fields.In order to effectively achieve the effect of lubricating oil in all kinds of environments,diversified functional lubricating additives have received more and more attention.Due to its special structure and excellent physical and chemical properties,graphene has caused worldwide research boom since its discovery.In recent years,researchers have discovered that this new two-dimensional carbon material can be used as an excellent lubricant additive.In this paper,alkylated graphene(R-GO)with variable alkyl chain length(Cn,n=4,8,12,18)was successfully prepared by amidation reaction which was conducted with alkylamine and graphene oxide.Then,through sulfonation reaction,alkylated sulfur doped graphene(RS-GO and SR-GO)was prepared.The effect of oxidation time,alkyl carbon chain length and synthetic methods on the product were studied separately.Through FT-IR,Raman,XPS,TEM and TGA characterization results,the composition and structure differences of RS-GO and SR-GO were analyzed.It was found that SR-GO had loaded with more sulfur and RS-GO had branced with more alkyl carbon chains.The prepared RS-GO and SR-GO were investigated as lubricant additives in lubricating oils for their dispersion and tribological properties.The dispersion experiment of alkylated sulfur doped graphene in the lubricating oil indicates that the longer the oxidation reaction time,the longer the alkyl carbon chain branched on its surface,then the better dispersibility the alkylated sulfur doped graphene has.Besides,its dispersibility in lubricating oil decreases as its concentration increases.The synthesis method had no significant effect on the dispersion properties of SR-GO and RS-GO.There was no obvious difference in its dispersion test results.The tribological experiments of alkylated sulfur doped graphene in lubricating oil showed that the tribological properties of RS-GO and SR-GO in lubricating oil lifted with oxidation degree increasing.Among them,after 24 h oxidation reaction,sulfur-doped graphene modified by octylamine(Cn,n=8)has the best antifriction and antiwear performance in lubricating oil,and its best score is to cut the wear spot diameter and the average friction coefficient by 43.2% and 44.9% respectively in 928 lubricating oil.And 14.1%,30.0% in PAO4 oil.Due to the different sulfur content of loaded,the octadecylamine-modified sulfur-doped graphene has better extreme pressure property in the lubricating oil,and its upper limit can enhance PB values by 12 kg and 24 kg in the 928 lubricating oil and PAO4 base oil,respectively.The lubrication mechanism of alkylated sulfur-doped graphene was proposed by analyzing the tribological experiments results of SR-GO and RS-GO in lubricating oil and associating with SEM and EDS characterization.