Dynamic Covalent Polymer-Nanoparticle Networks as High-Performance Green Lubricants: Synergetic Effect in Load-Bearing Capacity

Although conventional lubricant additives containing sulfur and phosphorus elements have been widely utilized to lower friction and wear, harmful emissions caused by the lubrication processes have resulted in serious environmental concerns. In this work, a series of polymer-nanoparticle networks have been in situ constructed in base oil by coupling phenylboronic ester-containing telechelic polymers and silica or titania nanoparticles via dynamic B-O covalent bonds. These sulfur- and phosphorus-free composites appear as the form of oleogels, wherein the nanoparticles show long-time dispersible stability. Ball-on-disc reciprocating sliding tribological tests display that the dynamic covalent networks give rise to remarkable reductions of the base oil in coefficient of friction (up to 52%) and wear volume (up to 93%). Moreover, high bearing loads of the polymer-nanoparticle composites are readily realized at 1100 N, which is higher than those of the telechelic polymers (900 N) or nanoparticles (600 N) alone. Such positive cooperativity in load-bearing capacity originates from nanometric thick tribofilms containing both B2O3 and beta-SiC or TiC formed at the rubbing interfaces. The present concept of combining nanoparticles with dynamic covalent chemistry provides a promising approach to create high-performance green lubricants.