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The goal of the work is to investigate the flow pattern of MoS 2 nanoparticles, which influences the lubrication properties of the lubricant. The tribological behavior of MoS 2 nanoparticles was studied in unidirectional or reciprocating ball-on-disk sliding tribometer. Friction reduction of 0.25 wt% MoS 2 nanoparticles in reciprocating mode reached 53.1% compared with that of base oil; whereas the friction coefficient of 0.25 wt% MoS 2 nanoparticles in unidirectional mode was similar with that of base lubricant (about 0.18). Flow pattern results of MoS 2 nanoparticles around contact area show that particles piled up heavily in the inlet of contact zone in unidirectional mode, leading to starved lubrication. However, loose net-like aggregations were formed in reciprocating mode, benefiting to reduce friction and wear. [ABSTRACT FROM AUTHOR]

The goal of the work is to investigate the lubrication mechanism of MoS 2 nano sheet. Polyisobutyleneamine Succinimide (PIBS) provides the steric repulsion to disperse nanoparticles in oil due to its long carbon chain. In the present study, the tribological behavior of nano-MoS 2 sheet mixed with different percentages of PIBS was explored. The dispersed state and the mode of nano-MoS 2 sheet entering the contact point were studied. Ball-on-disk results illustrated that the COF of nano-MoS 2 in paraffin oil with free of PIBS was 26.2% compared with those containing 3 wt% PIBS, and the reduction of wear depth reached 41.9%. The nano-MoS 2 sheets with 3 wt% PIBS were in discrete state in paraffin oil, which moved with side flow and could not enter the contact area to cause poor lubrication. Aggregation of particles took place in the case of low PIBS concentration and without PIBS, it entered the contact area and formed well-distributed MoS 2 tribofilm to reduce friction and wear. [ABSTRACT FROM AUTHOR]

Layered boric acid (BA) nanoparticle was considered as a promising 'green' lubricant additive due to its bio-degradable. However, its unclear lubrication mechanism and poor dispersion stability cause serious concerns for practical applications. Here, highly oil-dispersed alkyl-functionalized BA nanoparticles with size of about 100 nm were fabricated using a scalable strategy. The friction coefficient reached to around 0.11 with the addition of BA nanoparticles, about 30% lower than that of base oil (0.16). Tribological tests show that the wear reduction reached 40%, and the scuffing load capacity was improved by about 3 times. Lubrication mechanism investigation by molecular dynamics (MD) simulation shows that BA molecules preferentially adsorbed on the friction interface through hydrogen bond. A compact net-like adsorption layer from the decomposed nanoparticles, as well as boron-containing tribofilm, was formed on the rubbing surface to enhance lubrication performance. These solid evidences make BA nanoparticle to be a very promising candidate in practical applications as high performance green additive. Image 1 • MD simulation demonstrates the key role of hydrogen bond at friction interface. • Boric acid (BA) molecule preferentially adsorbed on the sliding surface. • Alkyl-functionalized BA nanoparticles were fabricated using a simple strategy. • The oil suspension with BA nanoparticles remains stable for more than 2 months. • Scuffing load capacity was improved by 3 times with the addition of BA nanoparticles. [ABSTRACT FROM AUTHOR]

The commonly accepted interlayer shear mechanism for layered materials as oil additives remains a challenge with the emergence of two-dimensional materials. In this work, the lubrication effectiveness of MoS 2 and BN nanosheets with a similar size was investigated as oil additives using block-on-ring tests. BN nanosheets reveal remarkable anti-wear performance and a reduction of wear depth of about 50%, whereas, the expected friction and wear reduction were not found for MoS 2 nanosheets. X-ray photoelectron spectroscopy (XPS) investigation indicates the generation of boron-based tribofilm for BN nanosheets and MoS 2 -complex tribofilm for MoS 2 nanosheets. Together with the thermal stability analysis, we found that it is the high strength tribofilm with high oxidation resistance, but not the layer structure, that plays a critical role in lubrication enhancement. This study highlights the advance of 'depositing tribofilm' mechanism in novel additive design. Image 1 • Layered materials with similar size and shape were selected. • Expected friction and wear reduction was not found for MoS 2 nanosheets in this study. • BN nanosheets reveal the remarkable anti-wear property with strong tribofilm strength. • It is a challenge to explain the results by using interlayer shear mechanism. • Depositing tribofilm mechanism would be preferable for novel particle additive design. [ABSTRACT FROM AUTHOR]