Friction and Wear Performance of Ionic Liquid-Functionalized MoS2 Nanosheets as Lubricant Additives

Abstract Surface functionalization can enhance the dispersibility and lubrication performance of molybdenum disulfide (MoS2) nanosheets in lubricating oil. Herein, MoS2 nanosheets were functionalized with a quaternary phosphonium ionic liquid ([P888A]DEHP) via ultraviolet-induced thiol-ene click chemistry. The functionalized MoS2 nanosheets (MoS2-PETMP/[P888A]DEHP) exhibited improved dispersibility in polyethylene glycol 200 (PEG-200). Tribological tests demonstrated that the addition of 0.5 wt% MoS2-PETMP/[P888A]DEHP reduced the friction coefficient by 18.85% and the wear volume by 65.59%. This improved performance originated from dual roles of [P888A]DEHP in facilitating interlayers slip within MoS2 nanosheets and forming tribochemical films on the contact surfaces. This work exemplifies how to improve the tribological properties of MoS2 nanosheets through surface functionalization.