SWCNT dispersions

Addition of carbanions - syntheses of tert-butyl-H-SWCNTs and of tert-butyl-SWCNTs In a nitrogen-purged flask, equipped with a gas inlet and a pressure compensator, 20 mg of HiPCO tubes (1.7 mmol of carbon) was dispersed in 50 mL of anhydrous benzene. To this dispersion 2.5 mL of a 1.7 M solution of tert-butyllithium (4.25 mmol) in hexane were added dropwise over a period of 10 min. Subsequently, the suspension was additionally stirred for 1 h at room temperature and the SWCNT dispersion turned into a black homogeneous solution. The solution was stirred for a further 1 h and subsequently quenched by the addition of... 

A typical experimental procedure suitable for functionalization was described in (44). It includes sonication of SWCNT dispersion in organic solvent (1,2-dichlorbenzene) together with dissolved AIBN for 5 min, which is followed by stirring of reaction mixture for a certain time (1-5 hours) at 75°C. 

Figure 10.4. NIR spectrum of laser-grown SWCNTs dispersed in DMF (0.01 mg/mL). Reprinted with permission from ref 10. Copyright 2009 Elsevier.

The wrapping process is typically carried out in liquid medium a PEI chloroform solution (1.5% w/w) is mixed with the SWCNTs under intense stirring. The blend is then treated with an ultrasonic tip for 1 h at 50% oscillation amplitude and 50% cycle time. The resulting dispersion is subsequently filtered using a 0.2 pm pore size PTFE membrane and dried under vacuum at 60°C to assure total evaporation of the solvent. The wrapped SWCNTs can be characterized by different techniques, and some results are included in Table 10.1. Figure 10.5 shows TEM images of acid-treated SWCNTs dispersed in the compatibilizer. Small nanotube bundles shrouded in PEI can be visualized in the micrographs. 

B) ultrasonication of PEEK/SWCNT dispersion in ethanol (C) melt blending. 

B) PEEK/arc-purified SWCNT 0.5 wt% (C) PEEK/laser-grown SWCNT 1.0 wt% (D) PEEK/laser-grown SWCNT dispersed in PEI 1.0 wt%. The arrows indicate randomly distributed nanotube bundles throughout the matrix. (A) and... 

Dai et al. [90] reported a very interesting work introducing a simple and general approach for noncovalent functionalization of the sidewalls of CNTs for further immobilization of ferritin, streptavidin and biotinyl-3,6-dioxaoetanediamine in a very efficient way. The first step was the noncovalent funetionalization of SWCNTs by irreversible adsorption of a bifimetional moleeule, 1-pyrenebutanoic acid, succinimidyl ester onto the hydrophobie surfaees of SWCNTs dispersed in DMF or methanol. 

Fig. 15.7 (a) Printed elastic conductors on a PDMS sheet. The insets show SWCNTs dispersed in paste and a micrograph of printed eiastic conductors (b) typicai SEM image of the eiastic conductor, in which finer or exfoliated SWCNTs are uniformly dispersed in the rubber and formed well-developed conducting networks ruid (c) a stretchable display that can be spread over arbitrary curved surfaces (Reproduced from Ref [109] with kind permission of Nature Publishing Group)... 

FIGURE 16.5 Luminescence emission spectra and pictures from SWCNTs dispersed with the aid of polyimide in DMF (left) and the PI-NHj-SWCNT in DMF solution (right). The nanotube and polymer contents in the two samples were comparable. (Adapted from Lin, Y. et al., 7. Phys. Chem. B, 109, 14779, 2005.)... 

Initially, molecular combing was used to comb a nanotube over a pair of gold electrodes. Self-assembled monolayers (SAMs) on the electrodes and the silicon substrate were used to help induce the SWCNT (dispersed via sodium dodecyl sulphate [SDS]) to deposit at the correct location the liquid-air meniscus was then used to orient the nanotube across the two electrodes (Fig. 16.2b). This method has the advantage of being easily scalable. However, contact with the nanotube is superior when the electrode is deposited with e-beam lithography over the nanotube. Because molecular combing is a very convenient way to extend nanotubes on the substrate, it is often used in this case as well. These studies have demonstrated... 

The phenomenon of molecular combing of SWCNTs dispersed with SDS was studied further by Ko et a/. They investigated how surface preparation and solution conditions can be used to control the density of nanotubes and demonstrated that, just like DNA,... 

Figure 2.13 Ciyo-TEM image of the mixture of an aqueous Gum Arabic-SWCNT dispersion and of a polystyrene latex. Note the growth of individual or bundles of very few SWCNTs from the Ni-Y catalyst nanoparticles shown by the arrow. Scale bar 100 nm.

The same Carbolex and HiPCO SWCNT dispersions as those previously studied in Section 3.1.2 were examined with UV-Vis spectroscopy. Samples were taken regularly during the sonicating process, diluted and UV-Vis spectra were recorded. Since desorption processes are typically quite slow, it was assumed that the amount of SDS molecules adsorbed on the CNT walls was not significantly influenced by dilution, and UV-Vis spectra were typically immediately recorded after dilution. " Please note that the dilution factor — in other words, the CNT concentration after dilution [i.e., 6.7 x 10 wt% for the standard SWCNT dispersions) — was chosen in such a way that all the UV-Vis absorbance values remained below 1 so that the error inherently present in the measurement itself is reduced. At this dilution, the contribution of scattering can be ignored. " ... 

The UV-Vis spectra recorded for aqueous HiPCO SWCNT dispersions, obtained after different energy-inputs and sonication times, are given in Figure 3.4. The corresponding spectra for Carbolex SWCNTs show a similar development, but exhibit one maximum instead of two around 250-300 nm. This difference indicates that the UV-Vis spectra obtained are specific for the CNT type studied. This is not surprising since the Carbolex and HiPCO CNTs studied... 

Quasi one-dimensional confinement ofthe electronic and phonon states of the SWCNT 7i-electron system causes theCNTdensityof state to show very sharp and characteristic van Hove maxima at energies depending on the CNT diameters and chiralities. As a result, the UV-Vis spectrum of the SDS-CNT dispersions is a superposition of distinct electronic transitions, generated by a variety of SWCNTs with different diameters and chiralities. This is reflected in the separated absorption features (like little humps ) observed in the UV-Vis spectra of the SDS-SWCNT dispersions. These observed features become narrower and narrower as the debundling proceeds. This constitutes an additional indication that CNT individualization from the CNT ropes occurs. It has, indeed, been observed and proven that CNT bundling leads to broadening of spectral features of CNT dispersions. ... 

Figure 3.7 Evolution of the quality factor (, measured by Raman spectroscopy], the CNT length (A, as measured by DLS], and the absorbance at 300 nm of the same SDS-SWCNT dispersions exfoliated at 20 W ( ] plotted in function of the total energy provided.

For Carbolex SWCNTs, it was found that the critical SDS concentration is about 0.06 wt% for a 0.1 wt% Carbolex SWCNT dispersion. For a similar 0.1 wt% HiPCO dispersion, the critical SDS concentration is around 0.17 wt% (see Figure 3.8]. The somewhat higher critical SDS concentration for HiPCO is most probably related to the higher purity of these tubes. It might also be due to the... 

The nature and the quantity of impurities removed are strongly connected to the surfactant type, as well as to the CNT type and batch (notably their density and the homogeneity of the batch). In order to Illustrate this last point, SDS-Carbolex SWCNT and SDS-HiPCO SWCNT dispersions were exfoliated and subsequently centrifuged at... 

The efficiency of PEDOT PSS to stabilize individual SWCNTs in water, without the presence of low molar mass surfactants like SDS, has been shown using a UV-Vis spectroscopy method developed by Grossiord et al. This method was used to determine the optimal [PEDOT PSS) SWCNT ratio. The maximum achievable SWCNT exfoliation was achieved with a (PEDOT PSS) SWCNT ratio of 1 4. The final absorbance level observed in UV-Vis absorption spectra of dispersions after completion of the dispersion process was slightly higher for dispersions prepared with PEDOT PSS as compared to control SDS dispersions. This is most likely linked to a change of the dielectric constant value (s) due to the presence of a new medium in the vicinity of the nanotubes (shifts in absorption spectra are possible in a new chemical environment). Assuming 100% SWCNT exfoliation, the value for of the SDS-stabilized SWCNT dispersions, before 7i-plasmon subtraction, was determined to be 46.4 ml mg" cm at 500 nm, which is similar to reported values. It should be kept in mind that the UV-Vis absorbance spectrum of the PEDOT PSS itself is likely to be influenced by the presence of the SWCNTs. This makes quantitative analysis of these spectra impossible since the final absorbance is not simply a summation of the absorbance of the constituents measured independently (unlike exhibited for... 

To compare the level of individualization, transmission electron microscopy (TEM) was performed on SWCNT dispersions prepared with either SDS or PEDOTiPSS. These TEM micrographs are shown in Figure 6.3. 

Figure 6.3 TEM micrographs of SWCNT dispersions in solutions of (i) SDS and (ii) PEDOT PSS. Scale bar 500 nm for both. (Reprinted with permission from RSC Publishing).

In Method 2, SWCNT dispersions using aqueous solutions of SDS were prepared. The surface of the SWCNT was now decorated with SDS molecules rather than with a polymeric layer, as in Method 1 [the negatively charged head group of SDS is the same as that present in PSS]. Finally, a three-component colloid was prepared by mixing a SDS-stabilized SWCNT dispersion, PS latex [same as for Method 1] and a PEDOT PSS dispersion. Method 2 is illustrated in Figure 6.8 [B]. 

The inclusion of a conductive polymeric component, namely PEDOT PSS, in PS/SWCNT composites to reduce the non-contact resistivity limiting is shown to reduce the percolation threshold and simultaneously increase the ultimate composite conductivity. The ability of PEDOT PSS to stabilize SWCNT dispersions (individualized SWCNTs] was shown. PEDOT PSS/PS/SWCNT composites showed lower percolation thresholds as compared to PS/SWCNT composites. This reduction was modeled assuming a homogeneous deposition of PEDOT PSS over the SWCNT surface. 

To drive the interaction of the QDs and SWCNTs [and subsequently manipulate the percolation threshold], an alternative method in which the QDs are either physi- or chemi-sorbed on a surfactant stabilizing the SWCNT dispersion, or in which the QDs are absorbed onto the SWCNT surface with the use of specific ligands/stabilizing agents, could be used. 

Figure 6.22 Chemical structures of p) PS-b-PDMAEMA and pi) PSS used in the preparation of SWCNT dispersions.

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