SWNTs aqueous dispersion

PEDOT with and without the dopant PSS has been the most commonly used conductive polymer for SWNT composites. De et al prepared composite films by vacuum filtration from aqueous dispersions with PEDOT PSS as the matrix and both arc and HiPCO SWNTs as the filler. The optimal performance was observed for a 80 nm thick film containing 60 wt /o arc SWNTs, with a sheet resistance of 80 Q sq at 75 /o transmittance. Electromechanical testing showed these films to be stable under flexing and cycling. Later, a modified PEDOT copolymer with enhanced solubility, perchlorate-doped poly(3,4-ethylenedioxythiophene)-Z /ock-poly(ethyleneox-ide) (P-PEDOT-b-PEO) was used to disperse SWNTs and then to fabricate conductive nanocomposites via vacuum filtration method.The sheet resistance of the composite film was approximately 600 Q sq with 80 /o transmittance. 

However, using an appropriate surfactant in water can be cheaper than using DMF and NMP, which also exhibit the disadvantage of high boiling points. The most common surfactants are sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulphate (SDS). Aqueous dispersion of SWNTs in the presence of the water-soluble perylene derivatives has also been reported. After the nanotubes are dispersed in a solvent, the buckypaper can usually be fabricated by a simple Buchner filtration[22]. 

Figure 17 Vials (6 ml) containing aqueous dispersions of (left to right) SDS-high-pressure carton monoxide process (HiPCO) SWNTs at 0.5 mg ml" and Triton X-100-HiPCO SWNTs at 0.8 mg ml" after sifting for 5 days, and SDBS-HiPCO SWNTs at 20 mg ml" after sifting for 2 months. Adapted with permission from Islam, M. F. Rojas, E. ...

Some of the better solvents for pure SWNTs are the amide-containing ones, like DMF or N-methylpyrrolidone, but they still do not permit full dissolution, just dispersion (Boul et al., 1999 Liu et al., 1999). The addition of surfactants to carbon nanotube suspensions can aid in their solubilization, and even permit their complete dispersion in aqueous solution. The hydro-phobic tails of surfactant molecules adsorb onto the surface of the carbon nanotube, while the hydrophilic parts permit interaction with the surrounding polar solvent medium. 

Detergents have been used for simple solubilization of SWNTs in aqueous solution. Ionic detergents such as SDS will coat the nanotube surface and expose the negatively charged sulfonate groups to the surrounding aqueous environment, thus allowing SWNT dispersion in aqueous... 

Other groups have achieved CNT forest assemblies by electrostatic SWNT-COO / Fe interactions also starting with shortened CNTs. The assembly process involves sequential substrate dipping in dilute Nafion and aqueous FeCl3 solutions followed by DMF-assisted precipitation of the nafion-adsorbed Fe to produce thin FeO(OH)/FeOCl nanocrystals. Subsequent immersion into a DMF disperse nanotube suspension produces the forest assembly that is driven by acid-base neutralization [12, 61, 121[. 

Aqueous solution of SWNTs was suspended with different types of surfactants a) anionic (SDS) (CH3(CH2)ii(S04) Na+), b) cationic (hexadecyltrimethylammonium bromide (CTAB) (CH3(CH2)i5N+(CH3)3Br) and c) and non-ionic (Tween-80) H(Et-0)n0(C4H602CH0HCH20 CO(Ci8H23). Surfactants SDS and CTAB were purchased from Serva , Tween-80 from Shuchard (Germany). 0.05 mg/mL nanotube dispersion with surfactant was mixed and then the suspension was sonicated for 40 minutes. A concentration of surfactants in water solution was 1%. Water was prepared by distillation and then passed through Multi-Q system. The deionized water has resistance 18 MO. 

Lu et al7 applied the vacuum filtration fabrication to the comparison of films of as-purified SWNTs and separated metallic SWNTs (approximately 85% purity in metallicity). In the fabrication, the two nanotube samples were each dispersed into an aqueous solution of SDS. A porous alumina membrane was used as filter in the vacuum filtration of the suspended SWNTs. After filtration, the film on the filter was washed repeatedly with deionized water to remove the surfactant SDS, for which the progress in surfactant removal via... 

The fabrication of a solution of CNTs with good dispersion and stability has been of great interest because most of the potential applications of SWNTs are based on solution processes such as spin coating and dip coating." " The physical adsorption on to the nanotube surface of surfactants and/or macromolecules has been shown as a possible way to stabilize SWNTs in both aqueous and organic media. 

Choi et al. successfully dispersed CNTs with different contents in Nafion solution to form homogeneous composites [27]. Then CNT/Nafion composite films were prepared by doctor blade method. SEM images suggested that the SWNTs were homogeneously dispersed in the Nafion matrix, indicating that wrapping of the SWNTs by the Nafion in an aqueous solution is effective. Hewitt etal. prepared the PVDF/CNT composite film with different content of CNTs by adding PVDF into the CNTs dimethylacetamide (DMAC) solution [28]. 

Powder of ag-SWNTs can be easily dispersed into water in the presence of CUR-N" or CUR-SOj with the aid of sonication, the solution color becoming dark as the sonication time progressed. The resultant aqueous solution is stable for more than one-month without forming any precipitate probably due to the electrostatic repulsion among the composites. The NIR-VIS spectral feature of the solution was similar to that of the SWNT/SPG composite solution, suggesting that CUR-N" " would wrap an individual SWNT fiber in the helical cavity. The fact is also supported by TEM and AFM observations (Fig. 37B). 

Organic nanocomposite dispersions of PANI-SWNT are prepared by in situ synthesis of polyaniline as shown in Scheme - 3. Ammonium persulfate is added to aqueous phase and aniline in xylene is added from the top. After rigorous stirring, the system is then left idle, during which phase inversion occurs. No traces of SWNT were observed in the aqueous phase. The nanocomposite dispersion is then taken from the top and washed with excess amount of xylene. The filtered material is then dried imder dynamic vacuum at 60 °C for more than 24 hours. 

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