Multi-Walled Carbon Nanotube Covalently Bound to MoS2 Microflowers in Polyalphaolefins as Low Friction Oil

Abstract

Friction and wear cause substantial energy losses and premature failure of mechanical components, and effective lubricant additives are critical to mitigate these issues under boundary lubrication. Physical blending remains the dominant approach for MoS2/multi-walled carbon nanotube (MWCNTs) hybrid lubricant additives, yet it suffers from weak interfacial adhesion, asynchronous tribo-evolution, and phase separation. To address these limitations, we construct a covalently bonded one-dimensional/two-dimensional heterostructure by one-step hydrothermal in situ growth of MoS2 nanosheets on hydroxylated MWCNTs skeletons, which simultaneously confines the MoS2 microflowers to a reduced average diameter (from 1.11 to 0.36 μm) and forms robust C−S covalent heterointerfaces, overcoming the structural brittleness of pristine MoS2, severe MWCNTs entanglement, and interfacial delamination of physically blended systems. After systematic optimization, the hybrid with a 2:1 MoS2-to-MWCNTs mass ratio at 0.5 wt % loading in polyalphaolefin 10 delivers the optimal comprehensive performance. Under reciprocating ball-on-disk contact with a maximum Hertzian pressure of 1.73 GPa, this formulation reduces the average friction coefficient and specific wear rate by 51.9% and 59.1% relative to neat base oil, respectively, with synergistic effect indices of 26.8% for friction reduction and 32.1% for wear resistance. A C−S bond-regulated three-stage tribochemical mechanism is proposed, in which tribo-oxidized MoO3, intact MWCNTs, and exfoliated MoS2 jointly build a robust self-healing hierarchical tribofilm that sustains the synergistic lubrication. This work provides a feasible interface-engineering strategy for high-performance carbon/transition metal dichalcogenide hybrid lubricant additives.