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Gold-ionic liquid nanofluids with preferably tribological properties and thermal conductivity.

Wang B, Wang X, Lou W, Hao J - Nanoscale Res Lett (2011)

Bottom Line: 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.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.Our results should open new avenues to utilize Au NPs and ILs in tribology and the high-temperature heat transfer field.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China. wjlou@licp.cas.cn.

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.

No MeSH data available.


Related in: MedlinePlus

The preparation process and stabilization mechanism of the sample 4. I: the AuCl4- was reduced by sodium borohydride (NaBH4) and Au NPs modified by CTABr were quickly obtained; II: after standing for more than 5 months, the modified Au NPs could still exhibit ultrahigh stability due to the electrostatic repulsions and steric hindrances between different Au NPs.
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Figure 5: The preparation process and stabilization mechanism of the sample 4. I: the AuCl4- was reduced by sodium borohydride (NaBH4) and Au NPs modified by CTABr were quickly obtained; II: after standing for more than 5 months, the modified Au NPs could still exhibit ultrahigh stability due to the electrostatic repulsions and steric hindrances between different Au NPs.

Mentions: Based on characterization of Au NPs, the preparation process and stabilization mechanism of the sample 4 are shown in Figure 5. First, the NaBH4 reduced the AuCl4- into Au NPs quickly and effectively. CTABr molecules specifically adsorbed on the Au NPs can form surface ion pairs through the attachment of Br- ions to the Au surfaces and the electrostatic interactions between the cationic CTABr headgroups and the Br- layer, which has been verified in a two-phase system [25]. Then, the Au NPs modified by CTABr dispersed in ILs possessed ultrahigh stability due to the electrostatic repulsions and steric hindrances among different Au NPs. Thus, the sample 4 can keep stable and homogeneous after standing for more than 5 months. While the partial aggregation of samples 5, 6, and 7 of Table 1 within 1 week indicates that this process cannot make high concentration Au nanofluids stable owing to the low solubility of CTABr in [Bmim][PF6].


Gold-ionic liquid nanofluids with preferably tribological properties and thermal conductivity.

Wang B, Wang X, Lou W, Hao J - Nanoscale Res Lett (2011)

The preparation process and stabilization mechanism of the sample 4. I: the AuCl4- was reduced by sodium borohydride (NaBH4) and Au NPs modified by CTABr were quickly obtained; II: after standing for more than 5 months, the modified Au NPs could still exhibit ultrahigh stability due to the electrostatic repulsions and steric hindrances between different Au NPs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211321&req=5

Figure 5: The preparation process and stabilization mechanism of the sample 4. I: the AuCl4- was reduced by sodium borohydride (NaBH4) and Au NPs modified by CTABr were quickly obtained; II: after standing for more than 5 months, the modified Au NPs could still exhibit ultrahigh stability due to the electrostatic repulsions and steric hindrances between different Au NPs.
Mentions: Based on characterization of Au NPs, the preparation process and stabilization mechanism of the sample 4 are shown in Figure 5. First, the NaBH4 reduced the AuCl4- into Au NPs quickly and effectively. CTABr molecules specifically adsorbed on the Au NPs can form surface ion pairs through the attachment of Br- ions to the Au surfaces and the electrostatic interactions between the cationic CTABr headgroups and the Br- layer, which has been verified in a two-phase system [25]. Then, the Au NPs modified by CTABr dispersed in ILs possessed ultrahigh stability due to the electrostatic repulsions and steric hindrances among different Au NPs. Thus, the sample 4 can keep stable and homogeneous after standing for more than 5 months. While the partial aggregation of samples 5, 6, and 7 of Table 1 within 1 week indicates that this process cannot make high concentration Au nanofluids stable owing to the low solubility of CTABr in [Bmim][PF6].

Bottom Line: 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.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.Our results should open new avenues to utilize Au NPs and ILs in tribology and the high-temperature heat transfer field.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China. wjlou@licp.cas.cn.

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.

No MeSH data available.


Related in: MedlinePlus