Dispersibility and rheological behavior of functionalized silica nanoparticles as lubricant additives

Silica nanoparticles exhibited excellent tribological properties when used as lubricant additives, but the bad dispersity in lubricant limited their application. Also, the influence of nanoparticles on lubricant rheological properties was still unclear. In this paper, hairy silica nanoparticles with different functional groups and different diameters were prepared and tested with their dispersity and rheological behavior as additives to polyalphaolefin 100 (PAO 100). The influence of nanoparticles size and functional group on the rheological properties of PAO with nanoparticles were investigated. Silica nanoparticles with four kinds of functional groups and four different diameters were prepared and dispersed into PAO 100 by a new method based on azeotropic distillation. The average particle sizes of nanoparticles in PAO and during dispersing process were tested to investigate the dispersity of nanoparticles. The viscosity of PAO with different silica nanoparticles was tested by cone-plate viscometer and the influence of nanoparticles on lubricant viscosity was analyzed. It was found that nanoparticles form stable and homogenous solution in PAO using the new method. Functional groups on nanoparticles surface have a strong effect on the dispersity of nanoparticles in PAO lubricant. The viscosity of lubricant increased with the increasing concentration of nanoparticles. Both functional groups and particle size influenced the viscosity behavior of silica nanoparticles as lubricant additives.