Nanotube concentration

Similarly, Cherukuri et al. used the near-IR fluorescence of individualized semiconducting SWNTs to study their blood elimination kinetics and biodistribution in rabbits.127 The pluronic copolymer-coated SWNTs were intravenously administered into rabbits at a dose of 20 pg S WNT per kilogram of body mass. The pluronic coating was found to be displaced by blood protein within seconds, as indicated by changes in the near-IR emission spectra. The nanotube concentration in the blood semm decreased exponentially with a half-life of 1 h, and no adverse effects were observed in terms of the rabbit behavior and the pathological examination. At 24 h post administration, significant concentrations of nanotubes were found only in the liver.127... 

The conductivity of the alloys as a function of nanotube concentration is shown in Fig. 5.9. P30T is an insulator with a conductivity 10-8 S/m. The conductivity increases monotonically with nanotube concentration. However the rate of increase is relatively small at low concentrations. It increases dramatically above 12% concentration. Above this concentration the nanotubes are close enough so that percolation becomes possible. The fit of the percolation theory is shown by the solid line. 

Figure 19.9 shows the thermal conductivity vs. nanofiller (nanotube) weight concentration in the polymeric oil (polyalphaolefin oil). It is clearly seen that thermal conductivity increases with increasing nanotube concentration. The curve tends to saturate at high concentrations (>10 wt%). 

Rheological research has shown that the nanocomposites (nanogreases) exhibit pseudoplastic behavior, which has a typical power law response and a definable yield stress. It provides convincing evidence that a metastable network structure is formed inside the nanocomposite with high nanofiller (nanotube) concentrations. 

Zaidi B, Bouzayen N, Wery J, Alimi K. Annealing treatment and carbon nanotubes concentration effects on the optical and vibrational properties of single walled carbon nanotubes functionalized with short oligo-n-vinyl carbazole. Mater Chem Phys 2011 126(l-2) 417-23. 

Plasma treatment provides a new approach to functionalize nanoparticle and nanotube surface for heat transfer nanofluid preparation without using stabilizing agents. More experimental investigation is very necessary to optimize the plasma treatment process in terms of plasma chemistry, plasma operating conditions, and proper plasma apparatus design. As pointed out in this entry, besides nanoparticle and nanotube concentration, the enhanced interfacial interactions between nanoparticles and/or carbon nanotubes with base fluids could be another important factor that contributed to the thermal conductivity increase observed in heat transfer nanofluids. A detailed characterization of the nanofluids with the aid of theoretical simulations will help us to understand the fundamental mechanisms for the observed heat transfer enhancement. 

Peddini et al. [9] used oxidized multiwalled carbon nanotubes (MWCNTs) as reinforcement in SBR matrices to improve the rheological properties and thus the elastomer performances in tires. Materials containing 15% MWCNTs proved to have the highest dispersion. In a further study [10], the group assessed the tensile stress-stain behavior of the resulted composites, showing that the stress is reduced with the increase of the nanotube concentration. 

Figure 6.12. Dependence of electrical conductivity on nanotube concentration in SWNT/PMMA nanocomposites. Reproduced from [87] with permission from Elsevier...

Recently, Boland et al utilized AFM to evaluate the mechanical properties of individual SWNT/PVA electrospun composite fibers prepared on a silicon surface pre-patterned with trenches [133]. These nanofibers were prepared with different loadings of SWNTs and had radii between 20 and 40 nm. Individual fiber sections were pinned across the trenches and laterally loaded by an AFM tip to yield mechanical response curves. A simple model was exploited to extract the tensile mechanical properties from the lateral force-displacement data. Depending on the fiber composition, the optimum tensile properties were reached when the nanotubes concentration was around 0.05 vol%, with the observed maximal strength and moduli of 2.6 and 85 GPa, respectively. Such optimized fibers break at strains of -4% and exhibit fracture toughness of up to 27 MJ/m, ... 

The effects of CNT s surface chemistry on the bubble density were also studied (Chen et al., 2012). In their study, the oxidized CNTs (M20 and MlOO) were functionalized by grafting with glycidyl phenyl ether (GPE) (Figure 1.14a). The GPE functionalized CNTs (P20 and PlOO) would have the same aspect ratio as the parent oxidized CNTs. They found that at the same nanotube concentration, the nanocomposite foams with GPE grafted CNTs had a bubble density several times higher than that of nanocomposite foams with oxidized CNTs under a series of foaming... 

It was established that the electrical conductivity of DWNTs/CA increases with nanotube concentration and reaches 8.1 S/cm at the highest content studied (8 mass%). A similar trend was observed by the same authors for the thermal conductivity of DWNTs/CA (Worsley, Satcher, and Baumann, 2009). Further, the study was extended to the fabrication of SWNTs/CA containing up to 55 mass% nanotubes (Worsley, Pauzauskie et al., 2009). Interestingly, above 20 mass%, the microstructure of aerogel changed from a network of carbon nanoparticles to a network of randomly oriented filament-like formations. Hence, at high SWNT concentrations, the majority of nanoparticles are located on the surface of the SWNTs and interconnect the nanotube bundles. In other words, above concentrations of 20 mass%, SWNTs dominate the microstructure of aerogels and determine their... 

Valentino, O., Samo, M., Rainone, N.G., Nobile, M.R., CiambeUi, P., Neitzert, H.C., Simon, G.P., 2008. Influence of the polymer structure and nanotube concentration on the conductivity and rheological properties of polyethylene/CNT composites. Physica E Lowdimensional Systems and Nanostructures 40, 2440—2445. 

Figure 347 Effect of the nanotube concentration in PAO on the friction coefficient at 0.83 GPa. These results show an optimal concentration of about 1 wt%...

Nanoparticle loadings (i.e., contents) vary significantly and depend on application. For example, carbon nanotube concentrations on the order of 5 wt% can lead to significant increases in strength and stiffness. However, between 15 and 20 wt% of carbon nanotubes are required to produce electrical conductivities necessary for some applications (e.g., to protect a nanocomposite structure from experiencing electrostatic discharges). 

Figure 8.6 shows a representative set of stress-strain curves for the 12 1 melt-drawn samples at each nanotube concentration. The addition of nanotubes significantly alters the stress-strain behavior of the fibers. The ultimate stress, yield stress and modulus increase with the addition of nanotubes. In contrast, the ultimate elongation slightly decreases with the addition of nanotubes. The significant increases in ultimate and yield stress combined with a small decrease in ultimate elongation lead to the observed increases in toughness. 

Figure 8.7 shows the results for the tensile toughness (Fig. 8.7a), modulus (Fig. 8.7b) and yield stress (Fig. 8.7c) as a function of nanotube concentration (from 0 to 3 wt%) and orientation (no draw, or unoriented, and oriented with a draw ratio of 12 1, 23 1 and 24 1). The white bars represent undrawn samples, the black bars represent fibers melt-drawn to a 12 1 ratio, the vertical striped bars represent fibers that are melt and then cold drawn to a 23 1 ratio, and the horizontal striped bars represent fibers coupled melt/solid drawn to a 24 1 ratio. The error bars are based on the standard error of ten samples tested at each concentration level. Because of the difficulty of drawing the PP/3 wt% MWNT samples to the 24 1 draw ratio, homogeneous samples could not be collected. In both the tensile toughness and modulus, optimal... 

Table 8.4 Summary of mechanical properties for PP and composite samples as a function of nanotube concentration and fiber draw ratio...

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