| Summary: | Hybrid molybdenum disulfide (MoS<sub>2</sub>)-MXene (Ti<sub>3</sub>C<sub>2</sub>) was added as an additive in SAE 5W-40-based engine oil in an attempt to reduce interfacial friction between contact surfaces. It was found that the coefficient of friction (COF) and wear scar diameter (WSD) were reduced by 13.9% and 23.8%, respectively, with the addition of 0.05 wt.% MoS<sub>2</sub>-Ti<sub>3</sub>C<sub>2</sub> compared to base engine oil due to the interlaminar shear susceptibility of MXene. However, we postulate that the high surface energy and presence of -OH, -O and -F functional groups on the surfaces limited the dispersibility and stability of MXene in base oil, while high activity of MoS<sub>2</sub> nanoparticles due to large surface area and vigorous Brownian motion prompted fast settling of nanoparticles due to gravitational force. As such, in the present study, hybrid MoS<sub>2</sub>-Ti<sub>3</sub>C<sub>2</sub> were amine-functionalized to attain stability in SAE 5W-40-based engine oil. Experimental findings indicate that amine-functionalized 0.05 wt.% MoS<sub>2</sub>-Ti<sub>3</sub>C<sub>2</sub> exhibited higher COF and WSD, i.e., 12.8% and 12.3%, respectively, compared to base oil added with 0.05 wt.% unfunctionalized MoS<sub>2</sub>-Ti<sub>3</sub>C<sub>2</sub>. Similarly, Noack oil volatility was reduced by 24.6% compared to base oil, indicating reduced oil consumption rate, maximal fuel efficiency and enhanced engine performance for a longer duration.
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