Gold/1-butyl-3-methylimidazolium hexafluorophosphate (Au/[Bmim][PF6]) nanofluids containing different stabilizing\r\nagents were fabricated by a facile one-step chemical reduction method, of which the nanofluids stabilized by\r\ncetyltrimethylammonium bromide (CTABr) exhibited ultrahighly thermodynamic stability. The transmission electron\r\nmicroscopy, UV-visible absorption, Fourier transform infrared, and X-ray photoelectron characterizations were\r\nconducted to reveal the stable mechanism. Then, the tribological properties of these ionic liquid (IL)-based gold\r\nnanofluids were first investigated in more detail. In comparison with pure [Bmim][PF6] and the nanofluids\r\npossessing poor stability, the nanofluids with high stability exhibited much better friction-reduction and anti-wear\r\nproperties. For instance, the friction coefficient and wear volume lubricated by the nanofluid with rather low\r\nvolumetric concentration (1.02 Ã?â?? 10-3%) stabilized by CTABr under 800 N are 13.8 and 45.4% lower than that of\r\npure [Bmim][PF6], confirming that soft Au nanoparticles (Au NPs) also can be excellent additives for high\r\nperformance lubricants especially under high loads. Moreover, the thermal conductivity (TC) of the stable\r\nnanofluids with three volumetric fraction (2.55 Ã?â?? 10-4, 5.1 Ã?â?? 10-4, and 1.02 Ã?â?? 10-3%) was also measured by a\r\ntransient hot wire method as a function of temperature (33 to 81Ã?°C). The results indicate that the TC of the\r\nnanofluid (1.02 Ã?â?? 10-3%) is 13.1% higher than that of [Bmim][PF6] at 81Ã?°C but no obvious variation at 33Ã?°C. The\r\nconspicuously temperature-dependent and greatly enhanced TC of Au/[Bmim][PF6] nanofluids stabilized by CTABr\r\ncould be attributed to micro-convection caused by the Brownian motion of Au NPs. Our results should open new\r\navenues to utilize Au NPs and ILs in tribology and the high-temperature heat transfer field.
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