Octadecanethiol-grafted molybdenum disulfide nanosheets as oil-dispersible additive for reduction of friction and wear

• DOI: 10.1016/j.flatc.2017.06.004
• Publication Date: 2017-06-17T14:17:06Z
• Authors: Sangita Kumari; Harshal P. Mungse; Rashi Gusain; Niranjan Kumar; Hiroyuki Sugimura; Om P. Khatri
• Keywords: Molybdenum disulfide; Dispersion stability; Petrochemical

Abstract Molybdenum disulfide (MoS2) easily shears at the contact interfaces because of weak interplaner interaction and exhibits high mechanical strength, which promises its potential for tribological applications. However, poor dispersibility of MoS2 in the lube oils has been a great challenge. Herein, a facile and scalable hydrothermal approach is presented to synthesize the MoS2 nanosheets and then chemically functionalized with octadecanethiol (ODT). The structural defects and vacant sulfur sites on the Mo-atoms of MoS2 nanosheets are targeted for grafting of ODT via Mo-S dative linkage. The chemical and structural features of MoS2-ODT are characterized by FTIR, XPS, XRD and HRTEM analyses. The dispersion stability of MoS2-ODT nanosheets in the polyol ester lube oil is examined by UV–Visible spectroscopy. The van der Waals interaction between the octadecyl chain of MoS2-ODT and oleate chains of polyol ester lube oil facilitates the dispersion of MoS2-ODT nanosheets. Tribological results revealed that minute dosing (0.05 mg.mL−1) of thoroughly dispersed MoS2-ODT nanosheets, as an additive to polyol lube oil, significantly reduced the friction and the wear of steel tribo-pair. The uninterrupted supply of MoS2-ODT nanosheets on the tribo-contacts, formation of MoS2 thin film on tribo-interfaces, ease of shearing driven by weak van der Waals interaction between MoS2 lamellae and high mechanical strength of MoS2, collectively enhanced the tribo-performance, when thoroughly dispersed MoS2-ODT was used as an additive to the polyol lube base oil.