Optimizing Graphene-Enhanced Poly-Alpha-Olefin Oils: The Role of Additive Geometry and Concentration in Lubricity Performance Across Simulation Conditions

Abstract

Abstract. Graphene is well known as an excellent solid lubricant and one of the most effective additives. Enhancing the lubricity of polyalphaolefin (PAO) oils with graphene additives significantly increases their potential applications. Due to its diverse effects, graphene additives continue to be the subject of intensive and ongoing research. The aim of this study is to use molecular dynamic simulations to identify conditions under which graphene additives significantly enhance lubricating performance. Various graphene shapes, including square, rectangular, and fishbone, and their different sizes are considered. Friction behavior is analyzed based on additive concentration and tribofilm formation. To evaluate their influence, PAO oils with molecules containing 1, 3, and 7 branches are examined. Additionally, the study investigates the effects of temperature and sliding velocity on lubrication. The findings indicate that graphene's shape and size significantly affect the friction coefficient. Small square-shaped graphene provides the best lubrication, exhibiting both a low friction coefficient and high stability. PAO lubricants with molecules containing a higher number of branches demonstrate greater stability and improved lubrication, observed across additive concentrations ranging from 2 wt% to 10 wt%. Variations in the results stem from interactions between PAO molecules and graphene sheets. When graphene sheets within the tribofilm align along the sliding direction and maintain extensive contact with the slider, tribofilm lubricity is significantly enhanced, leading to a substantial reduction in the friction coefficient. The findings emphasize the crucial role of graphene sheet geometry and PAO molecular structure in lubrication efficiency, revealing the optimal conditions for achieving significant friction reduction across various investigative parameters.