Self-Dispersed Crumpled Graphene Nanoparticles for LubricationPublic
Ultrafine particles are often used as lubricant additives because they can enter tribological contacts to reduce friction and protect surfaces from wear. They tend to be more stable than molecular additives under high thermal and mechanical stresses during rubbing. However, in lubricant oil, ultrafine particles tend to aggregate together to reduce the effective dispersed concentration. Although the surfactants could bind to nanoparticle surface and facilitate their dispersion in lubricant oil, they could be rubbed off or decomposed under the harsh tribological conditions. Therefore, the lubrication performance will be compromised. And it is highly desirable for these particles to remain well dispersed in oil without relying on molecular ligands. Previously, our lab discovered that the nano-meter sized crumpled graphene balls which have unique aggregation resistance property and here we report the use of crumpled graphene balls as a high-performance additive that can significantly improve the lubrication properties of polyalphaolefin base oil. Due to the aggregation resistant property, the tribological performance of crumpled graphene balls is only weakly dependent on their concentration in oil and readily exceeds that of other carbon additives such as graphite, reduced graphene oxide, and carbon black. Notably, polyalphaolefin base oil with only 0.01–0.1 wt % of crumpled graphene balls outperforms a fully formulated commercial lubricant in terms of friction and wear reduction. Further, crumpled graphene balls were also evaluated as additives for commercially lubricant oils. They were found to improve the wear reduction of the commercially available oils at oil temperature ranging from room temp to 90C. However, the crumpled graphene balls did not significantly change the oils’ friction reduction, suggesting that the current formulation will not be negatively affected by crumpled graphene balls, probably due to its aggregation resistance and no interferences with other molecular additives. On the other hand, it could further improve the wear reduction by being added into the commercial lubricant oil. In conclusion, crumpled graphene has great potential as a lubricant additive material. Because of their unique particle shape and aggregation resistance property, crumpled graphene balls can reduce the friction and wear between metal mechanical parts, showing improvements over other carbon-based additives and a fully formulated commercial lubricant. Finally, crumpled graphene balls can be easily introduced into commercially available lubricants to further enhance their lubrication performance, especially in wear reduction.
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