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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]

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]