MWNT

The yield strengths of defect-free SWNTs may be higher than that measured for Bacon s scroll structures, and measurements on defect-free carbon nanotubes may allow the prediction of the yield strength of a single, defect-free graphene sheet. Also, the yield strengths of MWNTs are subject to the same limitations discussed above with respect to tube slippage. All the discussion here relates to ideal nanotubes real carbon nanotubes may contain faults of various types that will influence their properties and require experimental measurements of their mechanical constants. 

Fig. la. Low-resolution TEM photograph of a bent MWNT showing kinks along the inner radius of the bend resulting from bending stress that exceeds the elastic limit of the tube. 

Since most SWNTs have diameters in the range of 1 -2 nm, we can expect them to remain cylindrical when they form cables. The stiffness constant of the cable structures will then be the sum of the stiffness constants of the SWNTs. However, just as with MWNTs, the van der Waals binding between the tubes limits tensile strength unless the ends of all the tubes can be fused to a load. In the case of bending, a more exact... 

Because direct calculation of thermal conductivity is difficulty 1], experimental measurements on composites with nanotubes aligned in the matrix could be a first step for addressing the thermal conductivity of carbon nanotubes. High on-axis thermal conductivities for CCVD high-temperature treated carbon fibers have been obtained, but have not reached the in-plane thermal conductivity of graphite (ref. [3], Fig. 5.11, p. 115). We expect that the radial thermal conductivity in MWNTs will be very low, perhaps even lower than the c-axis thermal conductivity of graphite. 

Recently, TsHs has been encapsulated within single-walled (SWNTs) and multiwalled carbon nanotubes (MWNTs) with internal diameters of 0.8-8 nm. It was shown that the best results were obtained when the internal diameters (1.4—1.5 nm for SWNTs and 1.0-3.0 nm for MWNTs) slightly exceeded the diameter of TsHs (1.2 nm). T8H8 was introduced in the gas phase and reacted with the nanotubes through van der Waals interactions. ... 

Chemical pretreatments with amines, silanes, or addition of dispersants improve physical disaggregation of CNTs and help in better dispersion of the same in rubber matrices. Natural rubber (NR), ethylene-propylene-diene-methylene rubber, butyl rubber, EVA, etc. have been used as the rubber matrices so far. The resultant nanocomposites exhibit superiority in mechanical, thermal, flame retardancy, and processibility. George et al. [26] studied the effect of functionalized and unfunctionalized MWNT on various properties of high vinyl acetate (50 wt%) containing EVA-MWNT composites. Figure 4.5 displays the TEM image of functionalized nanombe-reinforced EVA nanocomposite. 

Soot deposited on the chamber wall contained mostly carbonaceous particles, where no MWNTs were contained. The deposits on the cathode consist of two portions the inside is black fragile core and the outside hard shell. The inside include MWNTs scad poljd ral graphitic nanoparticles. The outer-shell part ojnsisted of the crystd of graphite. 

Fig. 2. The SEM images of (a) the raw sample, (b) the purified MWNTs and (c) the TEM image of the purified MWNTs...

Fig. 3. Raman spectra of MWNTs synthesized under dififenrat sure (a) 250 Totr, (b) 500 Torr, (c) 760Torr...

Therefore the cap of the MWNTs was removed using the purification proems. 

Fig. 3 shows the Raman spectra of the MWNT samples as a flmction of helium pressure. The peaks around 1280 cm", called the D-mode, are Imown to be attributed la amorphous carbons and defects of nanotubes, whereas the pe around 1600 cm", called the G-mode, are known to be due to the graphitic structure of carbon atoms. The G-mode of produced MWNTs was shifted to a lower wave number region (1595 cm" ) by the strain of the forming tube [6]. The intensity of MWNTs synftiesized under 250 Torr was lower than at other pressure. And the ratio of the G-mode to the D-mode was the hi t at pressure of 500 Torr. The highest purity of MWNTs was obtained when the pressure of helium is 500 Torr. 

Fig. 4 shows the SEM images of SWNTs purified by the thermal oxidation and acid-treated. Fig. 4(a) shows a SEM image of the raw soot. In addition to the bundle of SWNTs, carbonaceous particles are shown in the figure. These stractural features mi t be causal by various in the arcing process because of an inhomogeneous distribution of catalysts in the anodes [7]. It can be seen that the appearance of SWNTs was curled and quite different fiom that of MWNTs. Fig. 4(b) shows a decrease of amorphous carbons after oxidation. The basic idea of the selective etching is that amorphous carbons can be etched away more easily than SWNTs due to the faster oxidation reaction rate [2]. Since the CNTs are etched away at the same time, the yield is usually low. The transition metals can be etched away by an add treatment. Fig. 4(c) shows the SEM image of the acid-treated sample, where the annealed sample was immersed in 10 % HCl. 

Pt/MWNT) [20,21], fine and homogeneous Pt nanoparticles deposited on MWNTs were obtained when pure EG was used as the solvent or less water (<5vol.%) was introduced. With the increase in water content, aggregation of the metal nanoparticles occurred, the average particle size increased and the particle size distribution became wider. 

Table 2. Effect of water content in EG on the particle size of Pt nanoparticles deposited on MWNTs.

MWNTs were found to be cytotoxic in human skin fibroblasts (HSF42) and human epidermal keratinocytes (HEK) [42-44], whereas SWNTs were toxic in human keratinocyte (HaCaT) cultures [25, 26, 45]. Reduced cell proliferation and oxidative stress were reported also in epithelial (HeLa) cells [45] and murine epidermal cells (JB6 P + ) [46] upon incubation with SWNTs. 

Only a few in vivo dermal toxicity studies have been reported so far. Huczko and Lange [50] evaluated the potential of raw CNTs to induce skin irritation by conducting two routine dermatological tests (patch test on 40 volunteers with allergy susceptibilities and Draize rabbit eye test on four albino rabbits). Koyama etal. [51] showed the biological responses to four different types of carbon nanotubes (SWNTs, two types of MWNTs with different diameters, and cup-stacked carbon nanotubes) after their subcutaneous implantation in mice. Both tests [50, 51] showed no or poor irritation effects. However, the in vitro studies in epidermal cell lines exposed to CNTs, and also a more recent report on the toxic outcomes of topical exposure of mice to SWNTs [46], have raised concerns over these assessments. Clearly, this is an area requiring further scientific evaluation. 

Following their preliminary study in 2001 [63], Huczko et al. published a followup study in 2005 [66]. In this investigation, five different samples of MWNTs... 

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