Ionic-Liquid-Mimetic Surface Engineering of WS₂ Nanosheets via Amine-Phosphate Functionalization for Enhanced Tribological Performance

Eco-friendly two-dimensional (2D) nanolubricants have emerged as promising candidates for advanced functional materials. However, challenges such as poor dispersion stability and weak interfacial adhesion limit their widespread application. Herein, we developed a method to tailor WS₂ nanosheets functionalized with γ-aminopropyltriethoxysilane (γ-APS), enhancing their interaction with phosphate ester groups from di(2-ethylhexyl) phosphate (DEPS), which leads to the creation of gel-like WS₂-NH-DEPS additives with excellent dispersive and tribological properties in polyalphaolefin (PAO6). Specifically, a 0.5 wt % WS₂-NH-DEPS/PAO6 dispersion achieves the reduction of ∼40% in the coefficient of friction (COF) and the decrease of ∼70% in the wear scar diameter (WSD) compared to pure PAO6. Surface analysis reveals that the unique structure of exfoliated WS₂ nanosheets and their synergistic interactions with phosphonate groups facilitate the formation of a hybrid protective film composed of embedded WS₂ nanosheets, phosphoric acid compounds, and other oxides such as FeO_X, FeNO_X, and FeSO_X to enhance the tribological performance, providing essential insights for developing nanomaterial-based lubricants in advanced mechanical systems.