Triobological Behavior of Pickering Emulsions Stabilized with Alkylamine Edge-functionalized Graphene Oxide

Yang, HM; Li, JS; Zeng, XQ

Zeng, XQ (reprint author), Univ Chinese Acad Sci, Chinese Acad Sci, Shanghai Adv Res Inst, Shanghai 200120, Peoples R China.

CHINA SURFACE ENGINEERING, 2019; 32 (5): 151

Abstract

In order to explore the potential application of graphene oxide (GO) in the field of metalworking fluid, GO was synthesized by improved Hummers' method, followed by edge-functionalization with n-octanylamine, and Pickering emulsions based on functionalized GO were constructed. The oil-water interfacial behaviors of functionalized GO at liquid-liquid interfaces, together with the tribological behaviors of GO-based Pickering emulsions at solid-liquid interfaces were respectively studied. The interfacial tension of functionalized GO at different oil-water interfaces was studied by full-automatic interfacial tension tester. And the interfacial lubricating properties of GO-based Pickering emulsions on CoCrMo alloy and 304 stainless steel were studied by UMT-tribolab and white light interferometer. To clarify the lubricating mechanism of GO-based Pickering emulsions, the composition of lubricating films on metal friction pairs was analyzed by Micro-Raman and XPS. The results show that the friction-reducing properties of GO-based Pickering emulsions are better than that of base emulsion, and alkylamine functionalized GO shows better lubrication performance on CoCrMo alloy than on that 304 stainless steel. Compared with base emulsion, when the friction counterpart is CoCrMo alloy, GO emulsion can reduce the average friction coefficient and the steel ball wear rate by 35.9% and 46.7% respectively, while Oct-N-GO emulsion can reduce the average friction coefficient (COF) and the wear rate of steel ball by 48.7% and 73.0% respectively. The mechanism analysis shows that the good interfacial wettability of functionalized GO enables its Pickering emulsion to form a better interfacial lubricating film on metal surfaces. The alkylamine chains at GO edges are more prone to be sheared during friction, which reduces the interfacial shear force and results in reducing friction. At the same time, the lubricating film formed by Oct-N-GO contains higher content of C-O-C/C-OH and C=O, which can adsorb or fill the metal surfaces and play an anti-wear role.

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