Branch-chain length modulated graphene oxides for regulating the physicochemical and tribophysical properties of pickering emulsions

[Display omitted] To save energy and meet the demand of advanced manufacturing technology, great efforts on the development of new technologies and materials are made to reduce or even eliminate friction and wear. Of particular interests, the graphitic materials are very promising. In this study, graphene oxide (GO) based Pickering emulsions are developed as a novel water-based lubrication system. Alkylamines with varied branch-chain lengths (C = 0, 4, 8) are designed to functionalize GOs at edges (fGOs: GO-0, GO-4, GO-8), and the correlation between molecular structure and physicochemical behaviors of fGOs is systematically investigated. Results show that fGO without branch-chain exhibits a better ability to reduce the interfacial tension than those with branch-chains at various oil-water interfaces. The fGO microstructure, frictional pair material and surface roughness all contribute to the tribophysical performances of Pickering emulsion at liquid-solid interfaces. Lubricating performances decrease with the increasing branch-chain length for secondary amines modulated GO. The difference in material hardness or surface roughness leads to severe wear at the steel-steel interface, while at the steel-polymer interface, despite of a big difference in material hardness, the system falls into a stable and less-wear regime due to the formation of polymer transfer films. Micro-IR and XPS analysis of worn surfaces infer that fGOs are decomposed during shearing to produce oxygen-containing groups and alkylamines, and the film forming capability of fGOs is GO-4 > GO-8 > GO-0.