Abstract
Gold/1-butyl-3-methylimidazolium hexafluorophosphate (Au/[Bmim][PF6]) nanofluids containing different stabilizing agents were fabricated by a facile one-step chemical reduction method, of which the nanofluids stabilized by cetyltrimethylammonium bromide (CTABr) exhibited ultrahighly thermodynamic stability. The transmission electron microscopy, UV-visible absorption, Fourier transform infrared, and X-ray photoelectron characterizations were conducted to reveal the stable mechanism. Then, the tribological properties of these ionic liquid (IL)-based gold nanofluids were first investigated in more detail. In comparison with pure [Bmim][PF6] and the nanofluids possessing poor stability, the nanofluids with high stability exhibited much better friction-reduction and anti-wear properties. For instance, the friction coefficient and wear volume lubricated by the nanofluid with rather low volumetric concentration (1.02 × 10-3%) stabilized by CTABr under 800 N are 13.8 and 45.4% lower than that of pure [Bmim][PF6], confirming that soft Au nanoparticles (Au NPs) also can be excellent additives for high performance lubricants especially under high loads. Moreover, the thermal conductivity (TC) of the stable nanofluids with three volumetric fraction (2.55 × 10-4, 5.1 × 10-4, and 1.02 × 10-3%) was also measured by a transient hot wire method as a function of temperature (33 to 81°C). The results indicate that the TC of the nanofluid (1.02 × 10-3%) is 13.1% higher than that of [Bmim][PF6] at 81°C but no obvious variation at 33°C. The conspicuously temperature-dependent and greatly enhanced TC of Au/[Bmim][PF6] nanofluids stabilized by CTABr could be attributed to micro-convection caused by the Brownian motion of Au NPs. Our results should open new avenues to utilize Au NPs and ILs in tribology and the high-temperature heat transfer field.
Highlights
Gold nanoparticles (Au NPs) are always the hotspot of scientific research owing to their unique chemical and physical properties [1,2], high chemical stability and potential applications in optics, catalysts, sensors, and biology [3]
We investigated the tribological and thermal conductivity (TC) properties of the novel Au/[Bmim][PF6] nanofluids, and two major strategies are pursued in our studies: (1) the effects of the stability of nanofluids on their properties, and (2) the improvements of properties of [Bmim][PF6] induced by the introduction of low amount of Au nanoparticles (Au NPs)
The Au/[Bmim][PF6] nanofluids with changeable stabilities were synthesized by a facile Brust-Schiffrin method at room temperature
Summary
Gold nanoparticles (Au NPs) are always the hotspot of scientific research owing to their unique chemical and physical properties [1,2], high chemical stability and potential applications in optics, catalysts, sensors, and biology [3]. The stable Au NPs in water or organic solvents have been successfully fabricated using functionalized ILs or surfactants as capping agents and their optical, electrical, catalytic, biological, and thermal properties have been widely studied [4,5,16,17,18]. The tribological properties of the Au/[Bmim][PF6] nanofluids with changeable stabilities were detailedly evaluated in our present work Due to their potential applications as generation heat transfer fluids, the TC of Au nanofluids has been studied as a function of temperature and Au NP content [16,17,18]. Collected from sample 4 by centrifugation in order to disclosure the stabilization mode of Au NPs in the existence of CTABr. Figure 2 shows the TEM images, the selected area electron diffraction (SAED) pattern and size distribution of Au NPs obtained from sample 4. The diffraction rings corresponding to (111), (200), (220), (311), and (331) crystal planes have been marked out, respectively
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