Investigation on the robust adsorption mechanism of alkyl-functional boric acid nanoparticles as high performance green lubricant additives

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.