SWCNT exfoliation

This "excluded volume" concept was further illustrated by Winey and her coworkers who prepared SWCNT/PS nanocomposites by homogeneously coating SWCNTs (exfoliated in aqueous solutions without using surfactant) on the surface of softened flakes or pellets of PS, maintained above the glass transition of the polymer. After processing of the coated PS particles by compression molding, it was shown that SWCNTs were predominantly present in the interfacial volume between the pellets and formed a continuous three-dimensional cellular network. The nanocomposites obtained had conductivity values of the order of 10 S/m for 1 wt% of SWCNTs and a percolation threshold of about 0.2-0.3 wt%, i.e., half of the value of one of the reference samples for which SWCNTs of the same batch were homogeneously dispersed into the same PS matrix by an alternative method. ... 

Noii-purified HiPCO SWCNTs O Purified SWCNTs, exfoliation 1 Purified SWCNTs, exfoliation 2... 

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... 

The majority of studies have used surfactants that wrap around nanocarbons via van der Waals interactions [37]. For instance, surfactants such as sodium dodecylsulfate (SDS) are commonly used to disperse CNTs in aqueous solutions [38,39] while other surfactants, such as Pluorinc-123, are used to mechanically exfoliate graphene from graphite flakes (Fig. 5.4(a)) [40,41]. The polar head group of the surfactant can be used to further hybridize the nanocarbon via a range of covalent or noncovalent interactions [42]. For example, nanoparticles of Pt [43,44] and Pd [45] have been decorated onto SDS-wrapped MWCNTs. Similarly, Whitsitt et al. evaluated various surfactants for their ability to facilitate the deposition of Si02 NPs onto SWCNTs [46,47]. As an exam-... 

In another study by Chae et al., orientation and exfoliation of SWCNTs in polyacrylonitrile (PAN) fibers by gel spinning was studied using Raman spectroscopy, and it was based on the G-band intensity ratio of polarized light and the second- and fourth-order orientation parameters of SWCNT [53]. The Raman intensity ratio for beam-polarized parallel and perpendicular to the fiber axis was 42 for gel spun fiber but 38 for conventional solution spinning and that SWCNT orientation was slightly higher (0.915) than conventional spun fiber (0.90). 

It is indisputable that ILs can be widely applied to functionalize CNTs due to their excellent dispersing power. Recently, liquid-phase exfoliation of CNTs has been reviewed by Coleman [61] however, the dispersion mechanism for CNTs in ILs is still controversial. A cation-jt interaction between nanotubes and imidazolium ions was first proposed by Fukushima and Aida [55,57] to account for the exfoliation of entangled SWCNTs into smaller bundles, even individuals. On the basis of combined results of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectrum, and X-ray diffraction (XRD) analysis, Gilman et al. [81] provided the evidence for a cation-Ti interaction in the imidazolium-treated MWCNTs. Some researchers also cited this interpretation to support their cases [82]. 

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 2.11 High resolution TEM image of a dried solution of 0.05 wt% SWCNT and 1 wt% Gum Arabic, which has been previous sonicated. The arrow shows the location of bifurcation, where the CNTs have started to exfoliate. [From Ref. 89. Reprinted with permission of the American Chemical Society)...

Surfactants — either anionic surfactants such as sodium dodecylsulfate [SDS], or sodium dodecyl benzene sulfate [SDBS], or polysaccharide [Gum Arabic GA] — were first used to disperse, and exfoliate as-produced SWCNTs in water by ultrasonication, and to stabilize the resulting aqueous CNT suspension, see Figure 2.12. The SWCNTs were synthesized by either the AD method [about 30 % of impurities], or by the HiPCO process [having a catalyst particle content of about 5 wt%]. Please note that not only short surfactant molecules, but also polymeric surfactants such as polystyrene sulfonate, or even conductive polymers having a surfactant nature, can also be successfully used to disperse CNTs in water. 

The cryo-TEM micrograph in Figure 3.2a still shows clear aggregates of SWCNTs. Most of the CNTs are still bundled. Some of them have already been exfoliated [thin lines). The small black "dots" are catalyst particles. However, after 130 min sonication, such aggregates and bundles have almost completely disappeared, leaving mostly individual SWCNTs [see Figure 3.2b). 

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