Dialkyl Dithiophosphate-Functionalized Gallium-Based Liquid-Metal Nanodroplets as Lubricant Additives for Antiwear and Friction Reduction
Baoluo He, Sha Liu, Sha Liu, Xiangyuan Zhao, Jianxi Liu, Qian Ye, Shujuan Liu, Shujuan Liu, Weimin Liu
Abstract
The escalation in industrial demand and environmental concerns has necessitated the development of high-performance nanoadditives—the driving force behind advanced lubricating oil used in engineered systems. Herein, dialkyl dithiophosphate (DDP)-functionalized gallium-based liquid-metal (GLM) nanodroplets—DDP@GLMs, were prepared with an average size of about 178 nm and used as effective lubricant additives for tribological properties such as friction and wear reduction. Polydopamine-coated GLM nanodroplets (PDA@GLMs) can simply be prepared by means of sonication of liquid metal in bulk in Tris aqueous solution of dopamine, followed by modification by a commercial lubricating additive (DDP) via Michael addition. The DDP@GLMs exhibited exceptional stability in poly(alphaolefin) (PAO) base oil and remained stable for more than 5 days. The tribological properties of DDP@GLM additives were evaluated under varied conditions. It can be seen that the as-obtained DDP@GLMs demonstrated remarkable friction reduction and wear resistance abilities while operating as lubricating additives. The high load-carrying property is seen reaching a value as high as 1050 N with the frictional coefficient befalling less than 0.1 and the corresponding wear volume loss being decreased by 96%. The tribological properties seem attributable to the formation of a protective film (oxides of Ga, In, Fe, ferrous sulfide, and iron phosphate) on the interfaces of friction pairs. This study establishes a reliable basis for simple preparation of functional GLM nanodroplets and the manner of their implementation as lubrication additives.