HiPCO SWCNTs exfoliated

Consequently, stopping the sonication when the maximum amount of exfoliable CNTs has been unbundled [e.g., at 100,000 J for HiPCO SWCNTs] should prevent further cutting of the SWCNTs, though SWCNT surface damage may not be particularly minimized. 

The purified CNTs were exfoliated by sonication. Grossiord et al. followed this process by UV-Vis spectroscopy, and compared this individualization with the exfoliation of non-purified CNTs. The results are plotted in Figures 3.13 and 3.14 for two HiPCO SWCNT... 

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

These two experimental observations point out that the purified CNTs are more bundled at the end of the exfoliation than the as-produced CNTs. This was confirmed by SEM images of the purified HiPCO SWCNTs of the high quality batch, which showed that these... 

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 exfoliation of Carbolex SWCNTs was performed with both SDS and PEDOT PSS. The UV-Vis absorption spectra revealed a profile from which it was apparent that the final absorbance level reached was similar for dispersions prepared with SDS and PEDOT PSS, unlike that previously seen for HiPCO SWCNTs.This suggests that the electronic interaction between the Carbolex SWCNTs and PEDOT PSS is different from that observed for HiPCO SWNCTs. Examining their respective absorption spectra, as well as using Raman spectroscopy one can examine the difference in electronic structure of the SWCNTs. 

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. 

Figure 3.13 Evolution of the value of the absorbance of the peak located at 272 nm for an aqueous 0.1 wt% HiPCO CNT dispersion, containing 1 wt% of SDS. The SWCNTs for which the exfoliation behavior is monitored here come from a lower quality batch, and are exfoliated either before ( ) or after purification (O).

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