PSS-stabilized SWCNTs

In order to ascertain the additive nature of the absorbances of PEDOT PSS and SWCNTs, samples were prepared by simply mixing known concentrations of the PEDOT PSS latex and SDS-stabilized SWCNTs. The absorbance spectra were then analyzed and compared to a mathematical addition of the separate spectra collected for both components individually. It was seen that for the case in which the PEDOT PSS latex and SDS-stabilized SWCNTs are simply mixed, the final absorbance level is the same as the mathematical summation of the two constituents individual absorbance spectra (additive nature). The absorbance of the PEDOT PSS-stabilized SWCNTs, with similar concentrations, was always lower than that of the SDS-stabilized SWCNTs with added PEDOT PSS. This substantiates the non-additive nature of the absorbances of the SWCNTs and PEDOT PSS in this case. For this reason, it is difficult to say for certain that the degree of exfoliation is higher or lower when comparing the two surfactants. 

There is a marked difference between the micrographs of SDS-and PEDOT PSS-stabilized SWCNTs. The speckled background in Figure 6.3 (ii), is most likely due to the PEDOT PSS present in the system that is film-forming during the preparation of the TEM grid. 

The percolation thresholds observed for composites prepared with a PS matrix and SDS- and PEDOT PSS-stabilized SWCNTs are shown in Figure 6.4 [Q. The linear fittings oft and cpp (ii) using the statistical percolation law are given in Figure 6.4 (ii). The statistical percolation law is given as ... 

Figure 6.4 (i) Percolation thresholds for composites prepared with SDS-stabilized SWCNTs (squares) and PEDOT PSS-stabilized SWCNTs (stars). Arrows indicate applicable axes and the horizontal line corresponds to the measured conductivity of PEDOTrPSS. (ii) Linear fittings of t and (Pp (R values are 0.99). (Reprinted with permission from RSC Publishing). 

The introduction of AuNPs into PS/SWCNT composites has not shown to significantly alter the ultimate conductivity of these composites. In the case of only one studied hybrid system made from PSS-stabilized SWCNTs decorated with AuNPs, the addition of the gold particles to the PS/SWCNT composite seems to slightly reduce the percolation threshold. But in all other systems, no effect of the addition of AuNPs... 

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... 

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]. 

Composites with varying loadings of SDS- and PEDOT PSS-stabilized Carbolex SWCNTs were prepared. Percolation thresholds, along with the control system (PS/PEDOT PSS blend), were constructed and are given in Figure 6.15. 

Figure 6.15 Percolation threshold of PEDOT PSS-stabilized (stars) and SDS-stabilized (squares) Carbolex SWCNTs, and the insulator-conductor transition of PEDOT PSS/PS (control, circles). Arrows indicate applicable axes. (Reprinted with permission from ACS Publishing).

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. 

For Method 1, PEDOT PSS was used as a surfactant for the dispersion of SWCNTs in an aqueous environment [similar system to that reported previously]. This dispersion was subsequently blended with a PS latex stabilized with SDS. This case is illustrated in Figure 6.8 [A]. 

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