Dialkyl Dithiophosphate-Functionalized Gallium-Based Liquid-Metal Nanodroplets as Lubricant Additives for Antiwear and Friction Reduction

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.