The microscopic aggregation behavior of lubricant additives,especially demulsifier EO-PO(ethylene oxide and propylene oxide copolymer) and diphenylamine antioxidant (DPA),anti-wear and extreme pressure additive sulfurized hydrocarbons (S4),and compound containing phosphate and nitrogen (PN),corrosion inhibitor (T561) in n-octane/water,was studied by the all-atomic molecular dynamics simulation method.The behavior of EO-PO molecules and additive molecules at the oil-water interface was explored by analyzing the interfacial morphology,density distribution,interface thickness,radial distribution function,and hydrogen bond energy.The results show that each additive molecule forms a corresponding interfacial film at the oil-water interface,which makes the oil-water mixed emulsion more stable than the single oil-water system,indicating that each additive also plays a certain role in emulsification while serving as a functional additive.EO-PO molecules have stronger hydrophilicity than additive molecules,which can replace the additive molecules interacted with water on the interface,so as to destroy the stability of the interfacial film and completely separate the oil phase and water phase.Therefore,for oil-water emulsion,EO-PO molecules have an obvious demulsification effect.In each system containing different additives,EO-PO molecules interact with water to varying degrees.In the system containing PN and DPA molecules,EO-PO molecules have greater damage to its interfacial film,showing better demulsification effect.