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Research Papers

One-Pot Shear Synthesis of Gallium, Indium, and Indium–Bismuth Nanofluids: An Experimental and Computational Study OPEN ACCESS

[+] Author and Article Information
Anne K. Starace

National Renewable Energy Laboratory,
15013 Denver West Parkway,
Golden, CO 80401
e-mail: anne.starace@nrel.gov

Joongoo Kang

National Renewable Energy Laboratory,
15013 Denver West Parkway,
Golden, CO 80401
e-mail: Joongoo.Kang@nrel.gov

Junyi Zhu

National Renewable Energy Laboratory,
15013 Denver West Parkway,
Golden, CO 80401
e-mail: jyzhu@phy.cuhk.edu.hk

Judith C. Gomez

National Renewable Energy Laboratory,
15013 Denver West Parkway,
Golden, CO 80401
e-mail: Judith.Gomez@nrel.gov

Greg C. Glatzmaier

National Renewable Energy Laboratory,
15013 Denver West Parkway,
Golden, CO 80401
e-mail: Greg.Glatzmaier@nrel.gov

1Corresponding author.

Manuscript received May 21, 2014; final manuscript received June 7, 2014; published online July 8, 2014. Assoc. Editor: Abraham Wang. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States Government purposes.

J. Nanotechnol. Eng. Med 4(4), 041004 (Jul 08, 2014) (6 pages) Paper No: NANO-14-1039; doi: 10.1115/1.4027854 History: Received May 21, 2014; Revised June 07, 2014

Nanofluids are often proposed as advanced heat transfer fluids. In this work, using a one-step nanoemulsification method, we synthesize gallium, indium, and indium–bismuth nanofluids in poly-alpha-olefin (PAO). The size distributions of the resulting nanoparticles are analyzed using transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis of the alloy nanoparticles indicates that their composition is the same as that of the bulk alloy. It was found that oleylamine stabilizes both gallium and indium particles in PAO, while oleic acid is effective for gallium particles only. The microscopic adsorption mechanism of surfactants on gallium and indium surfaces is investigated using density functional theory (DFT) to understand why oleylamine is effective for both metals while oleic acid is effective for gallium only.

Nanofluids have an array of applications, as described well in a recent review article [1]. An application that is of particular interest is the use of nanofluids as advanced heat transfer fluids. The suspension of nanoparticles in a fluid can increase the thermal conductivity of the fluid by 3–161%, depending on the amount and thermal conductivity of nanoparticles added [2-6]. Additionally, in solar thermal applications, the nanoparticles can absorb energy from sunlight directly, resulting in a more efficient transfer of energy than the current state of the art [7,8].

A one-pot synthesis of nanofluids is desirable because it eliminates the chemical waste that accompanies the removal, and subsequent washing, of the nanoparticles from the solution in which they are formed before placing them in the desired base fluid. Han et al. have devised a one-pot synthesis of nanofluids that used the high shear of an ultrasonic probe to break up bulk liquid metal immersed in a fluid into nanoparticles [9]. Ultrasonication has been used as an energy source in the chemical production of nanoparticles [10]; however, the use of ultrasonication to physically form nanoparticles seems to be a new method. Han et al. demonstrated this technique with indium in PAO using “a PAO aminoester” as the surfactant. To our knowledge, this technique has not been demonstrated for the production of other types of nanoparticles. In this work, we reproduce this synthesis method with different nanoparticle materials and investigate the mechanism and reproducibility of this method.

Experimental Methods.

The base fluid, surfactant, and material from which the nanoparticles were made were placed in a multiport flask with one port fitted to the sonicator probe and the others allowing a flow of nitrogen through the flask. The flask was submerged in an oil bath maintained at a selected temperature. The mixture was sonicated with an ultrasonic processor (Vibracell model VC-750). The sonicator was alternately pulsed for 5 s and paused for 5 s. Sonication was continued until 10 min after the bulk material from which the nanoparticles were being made was no longer visible. Typically, the total sonication time (including the 5 s pauses) was around 30 min. If an appropriate surfactant was used, the sonication process produced a nanofluid. A portion of this nanofluid was reserved so that the length of time it remains suspended can be monitored. The remaining nanofluid was mixed with hexanes, centrifuged, and decanted. This process was repeated four times, typically, until a nanoparticle powder was isolated.

For XRD analysis, a portion of the nanoparticle powder was mixed with a volatile solvent to make a paste, which was spread on a glass slide and allowed to dry. XRD patterns were measured using a Rigaku x-ray diffractometer at 0.020 deg per step, 40 kV, and 250 mA. For TEM analysis, a portion of the nanoparticle powder was mixed with a volatile solvent to make a dilute nanofluid. A droplet of the dilute nanofluid was placed on a TEM grid or a TEM grid was dipped in the nanofluid and the grid was allowed to dry. TEM analysis was performed in a Philips CM200 TEM. We aimed to measure the particle size of at least 50 particles for each nanofluid made.

Calculation Methods.

We performed first-principles DFT calculations of molecular adsorption of oleic acid and oleylamine on Ga and In surfaces. The DFT simulation of metal nanoparticles in liquid phase is formidable because it requires the large system size (more than 10,000 atoms) and long simulation time for the ensemble average of the adsorption of surfactants on liquid metal surfaces. Thus, we used Ga and In surfaces in solid phases for the adsorbent to gain insights into microscopic interactions between surfactants and metal surfaces. For the adsorption surface, we selected the (010) surface of Ga crystalline phase with space group Bmab. For In phase (space group I4/mmm), the (111) surface was chosen, because this surface is commonly observed experimentally [11]. The adsorption strength of surfactants on metal surfaces was determined by calculating the adsorption energy (Eads) of surfactants, which is defined as Eads = E(metal–surfactant) – E(bare metal) – E(surfactant molecule). Here, E(metal–surfactant) is the DFT total energy of surfactants adsorbed on a metal surface, while E(bare metal) and E(surfactant molecule) are the total energies of a surfactant-free metal surface and a single, isolated surfactant molecule, respectively. Periodic boundary conditions were employed to simulate the adsorption of surfactants on metal surfaces. The areal densities of surfactants on the Ga and In surfaces in our DFT study are 0.47 molecule/nm2 and 0.36 molecule/nm2, respectively. For the selected areal densities, the surfactant molecules are well separated from each other on metal surfaces. DFT total energies were calculated within the generalized gradient approximation (GGA-PBE) [12] to DFT, as implemented in the vasp package [13]. Our DFT calculations employed the projector augmented wave method [14,15] with an energy cutoff of 400 eV for the plane wave part of the wave function.

Nanofluids were made from bulk gallium, indium, and indium–bismuth eutectic alloy (66.3 wt. % In and 33.7 wt. % Bi) with PAO as the base fluid. The selection of a suitable surfactant began with the gallium/PAO system. When no surfactant was present, a suspension of gallium particles formed during sonication, but the gallium crashed out of solution within minutes without sonication. Methyl-6-amionhexanoate hydrochloride did not stabilize the gallium particles in PAO while oleic acid, oleylamine, and fumed silica (Aerosil90 from Evonik-Degussa) did. When 1-butyl-3-methylimidazolium tetrafluoroborate was used as both the solvent and the surfactant with gallium particles, a nanofluid was not formed. While fumed silica stabilized the gallium particles in PAO, it did not stabilize them in silicon oil (Dynalene 600). Interestingly, the gallium/PAO suspension stabilized with fumed silica remained in suspension the longest. One year and ten months after synthesis, the suspension was still opaque, though some solids were present at the bottom of the container. The suspensions stabilized with traditional surfactants completely separated into clear, colorless PAO on top with the nanoparticles on bottom within four months.

Table 1 shows the salient properties of the nanofluids made in PAO. The histograms collected, from which the average, standard deviation, minimum, and maximum particle diameters were calculated, are presented in the Appendix. Example micrographs are shown in Fig. 1. Let us first examine the nanofluids made with all three measured parameters (surfactant concentration, bath temperature, and sonicator amplitude) the same, namely, Ga-4-i, Ga-4-ii, and Ga-4-iii nanofluids in Table 1. All three had the same minimum particle diameter of 5 nm. Two, the Ga-4-ii and Ga-4-iii, had nearly the same average particle diameter (77 nm and 76 nm, respectively) while Ga-4-i had a much larger average diameter of 206 nm. Ga-4-i also had the largest standard deviation of particle diameters, 349, compared with 281 and 203 for Ga-4-ii and Ga-4-iii, respectively.

Looking at the entire dataset, there are no clear trends between surfactant concentration, bath temperature or sonication amplitude and the average, minimum, or maximum particle size. There is also no clear correlation between the number of particles measured and either the average, minimum or maximum particle size.

Now, let us compare pairs of data that differ by only one parameter. Looking at Ga-1, the Ga-4s, and Ga-5, there is no trend between the surfactant concentration and the average particle size. Looking at the Ga-4s and Ga-6, it is the case that the nanofluid with the higher bath temperature has the larger average particle size. However, when considering the large standard deviations on these measurements, it is not clear that the particles are a distinctly different size. Comparing Ga-1 to Ga-2 and Ga-3 to Ga-4i-iii, we see that the average particle size decreases as the sonicator amplitude decreases, but again the high standard deviations nullify the discrepancy.

Comparing Ga-1 with Ga-8, we see that when oleylamine is used as the surfactant, the average particle size, standard deviation of the particle size, minimum particle size, and maximum particle size are all substantially larger than when oleic acid is used as a surfactant. However, comparing Ga-6 with Ga-9, the opposite effect is seen—in this case, with a higher bath temperature and higher surfactant concentration, the nanofluid made with oleic acid has larger average and maximum particle sizes than when oleylamine is used. The minimum particle diameter, 4 nm and 5 nm, are effectively the same for both surfactants. Looking at the histograms of Ga-6 and Ga-9, Ga-6 has nanoparticles in the size range of 4–13 nm and just over 150 nm to just over 2500 nm, and no nanoparticles in the size range in between 13 and 150 nm. This is in contrast to the Ga-9 histogram, which is almost continuous from its minimum to its maximum.

Figure 2 shows the XRD spectrum of the bulk In-Bi alloy and along with the XRD spectrum of the nanoparticles created from the bulk In-Bi alloy. Both spectra include all of the same peaks, though their relative intensities vary, indicating that the nanoparticles have the same structure and composition as the bulk starting material.

This new “shear synthesis” method has been shown to produce gallium and In-Bi alloy nanoparticles in addition to indium nanoparticles. Furthermore, this method produces nanoparticles with a yield of effectively 100%; seemingly, all of the bulk material used to make the nanoparticles is converted to nanoparticles in the process if the sonication is allowed to proceed for a sufficiently long time. However, with the settings used here, the method produces a broad range of nanoparticle sizes. From this limited study, it is unclear what effect the bath temperature and surfactant concentration have on the resulting particles. It seems likely that the bath temperature would change size of the resulting nanoparticles because it changes the viscosity of the PAO. The Taylor formula describing the formation of droplets through shear states that a continuous phase with a larger viscosity will produce smaller droplets, all else being equal [16]. This suggests that the higher the bath temperature, and hence the lower the continuous phase viscosity, the larger the average particle size would be. Additionally, the increased bath temperature increases the diffusion of both the particle and the surfactant, increasing the frequency of both nanoparticle–nanoparticle and nanoparticle–surfactant collisions. Considering the effects of the surfactant concentration, we know that the smaller the nanoparticles, the larger the total surface area between the nanoparticles and the fluid is for the same initial mass of nanoparticle material. Thus, if the surfactant concentration were too low, there would be a particle diameter below which it would be impossible for all of the particles to be stabilized by the surfactant. In this case, the particles would agglomerate to form an interfacial area small enough to be covered by surfactant or fall out of solution. Since we do not see a correlation between the surfactant concentration and particle size, we might assume that all the surfactant concentrations used were above this threshold. Once above this threshold, the surfactant might still have an effect on the process by changing the viscosity and surface tension of the fluid.

We have several concerns about the sampling of the particles for particle size analysis. It is difficult to prove that the particles measured are a representative sample of the particles in the nanofluid. For instance, certain particle sizes may preferentially absorb to the walls of the container the nanofluid is in or to the pipet used to extract the nanofluid for TEM analysis. We samples the nanofluid both by taking a drop of the nanofluid, with a pipette, and placing it on a TEM grid to dry, as well as by dipping, with tweezers, a TEM grid into the nanofluid. We saw no noticeable difference with one method versus the other. However, in both cases, there is the concern that only a certain range of particle sizes would adhere to the grid. In one sample set, we also used ethanol instead of hexanes to wash the centrifuged nanoparticles and saw no noticeable difference in the result, suggesting that the solvent did not preferentially suspend the same range of nanoparticle sizes, or that both solvents had the same preferential effect.

The fact that the XRD spectra of the bulk and nanomaterials include all of the same peaks suggests that no phase separation (into pure indium, pure bismuth, or a different alloy ratio) occurs during the sonication process and that the nanoparticles have the same indium to bismuth ratio as the bulk starting material.

Finally, we discuss the adsorption mechanisms of oleic acid and oleylamine on Ga (010) and In (111) surfaces using DFT calculation results. As discussed in Results, it was found that oleylamine stabilizes both Ga and In particles in PAO, while oleic acid only works for Ga particles. Figure 3 shows the adsorption geometry of oleylamine on Ga and In surfaces. The adsorption occurs through the N lone-pair electrons of oleylamine on both metal surfaces. The bond length between N and the nearest surface atom is dN–Ga = 2.28 Å and dN–In = 2.59 Å. The adsorption energy (Eads) of oleylamine is −0.44 eV/molecule and −0.21 eV/molecule for the Ga and In surfaces, respectively. The negative Eads indicates that the adsorption state is energetically favorable.

Unlike the case of oleylamine, oleic acid exists in a dimer form that is paired through the hydrogen bonding between the carboxylic groups of the molecules (Fig. 4(a)); Refs. [17,18]. Therefore, the hydrogen bonding should be first broken for each oleic acid monomer to be adsorbed on a metal surface. The hydrogen-bond energy of the oleic acid dimer is calculated to be 1.19 eV/pair. We first focus on the adsorption of an oleic acid monomer on metal surfaces. We found that for both Ga and In surfaces, an oleic acid monomer binds to the surface via the lone pair of the oxygen atom of the carboxylic group, as shown in Fig. 4(b) for the Ga surface. The bond length is dO–Ga = 2.36 Å and dO–In = 2.94 Å. The adsorption energy Eads of oleic acid monomer is −0.42 and −0.28 eV/molecule for the Ga and In surfaces, respectively. We note that the physisorption strength of oleic acid is almost same as that of oleylamine on each metal surface. However, when the Eads is referenced to the energy of oleic acid dimer as Eads = E(metal-oleic acid monomer) − E(metal surface) − ½ E(oleic acid dimer), it becomes positive, Eads(Ga) = 0.18 eV/molecule and Eads(In) = 0.31 eV/molecule, indicating that the physisorption of oleic acid is not energetically possible on both Ga and In surfaces.

The “shear synthesis” of metal nanoparticles requires high temperature and high shear stress near the probe tip of sonication for the break-up of liquid metal into nanoparticles. So, the sonication can be intense enough to dissociate small amount of solvent and/or surfactant. When the sonication starts with the N2 gas flowing, a significant increase in the thermal conductivity of the gas was detected using an Agilent G3388A detector. The enhanced thermal conductivity can be attributed to H2 evolution from the dehydrogenation of PAO and/or oleic acid. Our DFT calculations suggest that chemisorption of oleic acid on Ga surfaces may occur if H atoms of the carboxylic groups of oleic acid dimers are dissociated to form H2 during the shear synthesis. The proposed chemisorption geometry of oleic acid is shown in Fig. 4(c). Once oleic acid is dehydrogenated around the sonication tip, it strongly binds to the Ga (010) surface via a pair of O–Ga bonds with dO-Ga = 2.10 and 2.17 Å, which are substantially shorter than the single O–Ga bond of the physisorption state in Fig. 4(a) (dO–Ga = 2.36 Å). The Eads of the chemisorption state, which is referenced to the energies of oleic acid dimers and bare Ga surface, is 0.10 eV/molecule, which is 0.08 eV/molecule lower than that of the physisorption state. In our model, H2 molecule is weakly physisorbed on the Ga surface. In fact, H2 is in a gas phase at high temperature, and thus the free energy change of the chemisorption process can be negative. For In surface, the Eads of the chemisorption state of oleic acid dimer is calculated to be 0.27 eV/molecule. Therefore, it would be less likely that such chemisorption can occur on In surface considering the weak In–O bonding and associated large Eads.

Using high shear as a one-pot, effectively 100% yield synthesis method for nanofluids seems to be a generalizable technique, as long as a suitable combination of surfactant, base fluid, and nanoparticle are used. However, with the parameters used in this work, the method created a broad range of particle sizes.

Our DFT calculations show that for both oleic acid and oleylamine, the adsorption strength of surfactant on Ga surface is much stronger than on In surface. The adsorption of oleylamine is energetically favorable with the binding energy of 0.44 eV and 0.21 eV for Ga (010) and In (111) surfaces, respectively. To the contrary, the hydrogen-bond induced dimerization of oleic acid molecules makes the physisorption of oleic acid monomers on metal nanoparticles energetically difficult. However, when oleic acid is dehydrogenated around the sonication tip due to high temperature and shear stress, the dehydrogenated surfactant can strongly bind on Ga surface, enabling the suspension of Ga nanoparticles in PAO.

We would like to thank Jun Wang for many helpful discussions.

This work was supported by the Laboratory Directed Research and Development (LDRD) Program at the National Renewable Energy Laboratory. NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC.

Appendix
Taylor, R., Coulombe, S., Otanicar, T., Phelan, P., Gunawan, A., Lv, W., Rosengarten, G., Prasher, R., and Tyagi, H., 2013, “Small Particles, Big Impacts: A Review of the Diverse Applications of Nanofluids,” J. Appl. Phys., 113(1), p. 011301. [CrossRef]
Beck, M. P., Yuan, Y., Warrier, P., and Teja, A. S., 2008, “The Effect of Particle Size on the Thermal Conductivity of Alumina Nanofluids,” J. Nanopart. Res., 11(5), pp. 1129–1136. [CrossRef]
Saidur, R., Kazi, S. N., Hossain, M. S., Rahman, M. M., and Mohammed, H. A., 2011, “A Review on the Performance of Nanoparticles Suspended With Refrigerants and Lubricating Oils in Refrigeration Systems,” Renewable and Sustainable Energy Rev., 15(1), pp. 310–323. [CrossRef]
Shaikh, S., Lafdi, K., and Ponnappan, R., 2007, “Thermal Conductivity Improvement in Carbon Nanoparticle Doped PAO Oil: An Experimental Study,” J. Appl. Phys., 101(6), p. 064302. [CrossRef]
Kang, H., Kim, S., and Oh, J., 2006, “Estimation of Thermal Conductivity of Nanofluid Using Experimental Effective Particle Volume,” Exp. Heat Transfer, 19(3), pp. 181–191. [CrossRef]
Zhang, X., Gu, H., and Fujii, M., 2006, “Effective Thermal Conductivity and Thermal Diffusivity of Nanofluids Containing Spherical and Cylindrical Nanoparticles,” J. Appl. Phys., 100(4), p. 044325. [CrossRef]
Otanicar, T. P., Patrick, P. E., Prasher, R. S., Rosengarten, G., and Taylor, R. A., 2010, “Nanofluid-Based Direct Absorption Solar Collector,” J. Renewable Sustainable Energy, 2(3), p. 033102. [CrossRef]
Otanicar, T. P., Phelan, P. E., Taylor, R. A., and Tyagi, H., 2011, “Spatially Varying Extinction Coefficient for Direct Absorption Solar Thermal Collector Optimization,” ASME J. Sol. Energy Eng., 133(2), p. 024501. [CrossRef]
Han, Z. H., Cao, F. Y., and Yang, B., 2008, “Synthesis and Thermal Characterization of Phase-Changeable Indium/polyalphaolefin Nanofluids,” Appl. Phys. Lett., 92(24), p. 243104. [CrossRef]
Chen, H.-J., and Wen, D., 2011, “Ultrasonic-Aided Fabrication of Gold Nanofluids,” Nanoscale Res. Lett., 6. [CrossRef]
Heyraud, J. C., and Métois, J. J., 1986, “Surface Free Energy Anisotropy Measurement of Indium,” Surf. Sci., 177, pp. 213–220. [CrossRef]
Perdew, J. P., Burke, K., and Ernzerhof, M., 1996, “Generalized Gradient Approximation Made Simple,” Phys. Rev. Lett., 77, pp. 3865–3868. [CrossRef]
Kresse, G., and Furthmüller, J., 1996, “Ab initio Calculations of the Cohesive, Elastic, and Dynamical Properties of CoSi2 by Pseudopotential and All-Electron Techniques,” Phys. Rev. B, 54(3), pp. 1729–1734. [CrossRef]
Blöchl, P. B., 1994, “Projector Augmented-Wave Method,” Phys. Rev. B, 50, 17953. [CrossRef]
Kresse, G., and Joubert, D., 1999, “From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method,” Phys. Rev. B, 59, pp. 1758–1775. [CrossRef]
Taylor, G. I., 1934, “The Formation of Emulsions in Definable Fields of Flow,” Proc. R. Soc. A, 146(858), pp. 501–523. [CrossRef]
Garland, E. R., Rosen, E. P., Clarke, L. I., and Baer, T., 2008, “Structure of Submonolayer Oleic Acid Coverages on Inorganic Aerosol Particles: Evidence of Island Formation,” Phys. Chem. Chem. Phys., 10, pp. 3156–3161. [CrossRef]
McGinty, S. M., Kapala, M. K., and Niedziela, R. F., 2009, “Mid-Infrared Complex Refractive Indices for Oleic Acid and Optical Properties of Model Oleic Acid/Water Aerosols,” Phys. Chem. Chem. Phys., 11, pp. 7998–8004. [CrossRef] [PubMed]
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References

Taylor, R., Coulombe, S., Otanicar, T., Phelan, P., Gunawan, A., Lv, W., Rosengarten, G., Prasher, R., and Tyagi, H., 2013, “Small Particles, Big Impacts: A Review of the Diverse Applications of Nanofluids,” J. Appl. Phys., 113(1), p. 011301. [CrossRef]
Beck, M. P., Yuan, Y., Warrier, P., and Teja, A. S., 2008, “The Effect of Particle Size on the Thermal Conductivity of Alumina Nanofluids,” J. Nanopart. Res., 11(5), pp. 1129–1136. [CrossRef]
Saidur, R., Kazi, S. N., Hossain, M. S., Rahman, M. M., and Mohammed, H. A., 2011, “A Review on the Performance of Nanoparticles Suspended With Refrigerants and Lubricating Oils in Refrigeration Systems,” Renewable and Sustainable Energy Rev., 15(1), pp. 310–323. [CrossRef]
Shaikh, S., Lafdi, K., and Ponnappan, R., 2007, “Thermal Conductivity Improvement in Carbon Nanoparticle Doped PAO Oil: An Experimental Study,” J. Appl. Phys., 101(6), p. 064302. [CrossRef]
Kang, H., Kim, S., and Oh, J., 2006, “Estimation of Thermal Conductivity of Nanofluid Using Experimental Effective Particle Volume,” Exp. Heat Transfer, 19(3), pp. 181–191. [CrossRef]
Zhang, X., Gu, H., and Fujii, M., 2006, “Effective Thermal Conductivity and Thermal Diffusivity of Nanofluids Containing Spherical and Cylindrical Nanoparticles,” J. Appl. Phys., 100(4), p. 044325. [CrossRef]
Otanicar, T. P., Patrick, P. E., Prasher, R. S., Rosengarten, G., and Taylor, R. A., 2010, “Nanofluid-Based Direct Absorption Solar Collector,” J. Renewable Sustainable Energy, 2(3), p. 033102. [CrossRef]
Otanicar, T. P., Phelan, P. E., Taylor, R. A., and Tyagi, H., 2011, “Spatially Varying Extinction Coefficient for Direct Absorption Solar Thermal Collector Optimization,” ASME J. Sol. Energy Eng., 133(2), p. 024501. [CrossRef]
Han, Z. H., Cao, F. Y., and Yang, B., 2008, “Synthesis and Thermal Characterization of Phase-Changeable Indium/polyalphaolefin Nanofluids,” Appl. Phys. Lett., 92(24), p. 243104. [CrossRef]
Chen, H.-J., and Wen, D., 2011, “Ultrasonic-Aided Fabrication of Gold Nanofluids,” Nanoscale Res. Lett., 6. [CrossRef]
Heyraud, J. C., and Métois, J. J., 1986, “Surface Free Energy Anisotropy Measurement of Indium,” Surf. Sci., 177, pp. 213–220. [CrossRef]
Perdew, J. P., Burke, K., and Ernzerhof, M., 1996, “Generalized Gradient Approximation Made Simple,” Phys. Rev. Lett., 77, pp. 3865–3868. [CrossRef]
Kresse, G., and Furthmüller, J., 1996, “Ab initio Calculations of the Cohesive, Elastic, and Dynamical Properties of CoSi2 by Pseudopotential and All-Electron Techniques,” Phys. Rev. B, 54(3), pp. 1729–1734. [CrossRef]
Blöchl, P. B., 1994, “Projector Augmented-Wave Method,” Phys. Rev. B, 50, 17953. [CrossRef]
Kresse, G., and Joubert, D., 1999, “From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method,” Phys. Rev. B, 59, pp. 1758–1775. [CrossRef]
Taylor, G. I., 1934, “The Formation of Emulsions in Definable Fields of Flow,” Proc. R. Soc. A, 146(858), pp. 501–523. [CrossRef]
Garland, E. R., Rosen, E. P., Clarke, L. I., and Baer, T., 2008, “Structure of Submonolayer Oleic Acid Coverages on Inorganic Aerosol Particles: Evidence of Island Formation,” Phys. Chem. Chem. Phys., 10, pp. 3156–3161. [CrossRef]
McGinty, S. M., Kapala, M. K., and Niedziela, R. F., 2009, “Mid-Infrared Complex Refractive Indices for Oleic Acid and Optical Properties of Model Oleic Acid/Water Aerosols,” Phys. Chem. Chem. Phys., 11, pp. 7998–8004. [CrossRef] [PubMed]

Figures

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Fig. 1

Examples of TEM micrographs of (a) gallium and (b) indium particles used to measure particle sizes

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Fig. 2

XRD spectra of bulk In–Bi alloy (bottom trace) and In–Bi nanoparticles (top trace)

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Fig. 3

Adsorption of oleylamine on (a) Ga (010) and (b) In (111) surfaces. The areal densities of the adsorbates on the Ga and In surfaces are 0.47 molecule/nm2 and 0.36 molecule/nm2, respectively.

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Fig. 4

Adsorption of oleic acid on Ga (010) surfaces. (a) Dimeric structure of oleic acid. Possible adsorption structures for (b) physisorption and (c) chemisorption of oleic acid on the Ga surfaces. The areal density of the adsorbates is 0.47 molecule/nm2.

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Fig. 5

Particle size histogram of nanofluid Ga-1

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Fig. 6

Particle size histogram of nanofluid Ga-2

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Fig. 7

Particle size histogram of nanofluid Ga-3

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Fig. 8

Particle size histogram of nanofluid Ga-4-i

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Fig. 9

Particle size histogram of nanofluid Ga-4-ii

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Fig. 10

Particle size histogram of nanofluid Ga-4-iii

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Fig. 11

Particle size histogram of nanofluid Ga-5

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Fig. 12

Particle size histogram of nanofluid Ga-6

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Fig. 13

Particle size histogram of nanofluid Ga-6

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Fig. 14

Particle size histogram of nanofluid Ga-8

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Fig. 15

Particle size histogram of nanofluid Ga-9

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Fig. 16

Particle size histogram of nanofluid I-1

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Fig. 17

Particle size histogram of nanofluid In–Bi-1-i

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Fig. 18

Particle size histogram of nanofluid In–Bi-1-ii

Tables

Table Grahic Jump Location
Table 1 Properties of nanofluids made with PAO

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