Carbon nanotubes suspensions

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. 

Zhou, W., Islam, M.F., Wang, H., Ho, D.L., Yodh, A.G., Winey, K.I., and Fischer, J.E. (2004) Small angle neutron scattering from single-wall carbon nanotube suspensions Evidence for isolated rigid rods and rod networks. Chem. Phys. Lett. 384, 185-189. 

Wang H, Christopherson GT, Xu ZY, Porcar L, Ho DL, Fry D, Hobbie EK (2005). Shear-SANS study of single-walled carbon nanotube suspensions.Chem. Phys. Lett. 416 182-186. 

Mishra SR, Rawat HS, Mehendale SC, Rustagi KC, Sood AK, Bandyopadhyay R, Govindaraj A, Rao CNR (2000) Optical limiting in single-walled carbon nanotube suspensions. Chem. Phys. Lett. 

S. Ramesh, R.K. Saini, C. Kittrell, W.E. Billups, W.W. Adams, R.H. Hauge, RJi. Smalley, and M. Pasquali, Viscoelasticity of single wall carbon nanotube suspensions, Macrorrwlecules, 37, 154 (2004). 

Hasegawa, N. Okamoto, H. Kato, M. Usuki, A. (2000) Preparation and Mechanical Properties of Polypropylene-Clay Hybrids based on Modified Polypropylene and Organophilic Clay. /. Aypl. Polym. Sci. Vol.78, No.ll, p>p.l918-1922 Huxtable, S. Cahill, D. Shenogin, S. Xue, L. Ozisik, R. Barone, R Usrey, M. Strano, M. Siddons, G. Shim, M. Keblinski, P. (2003) Interfadal Heat Flow in Carbon Nanotube Suspensions. Nat. Mater. Vol.2, No.ll, pp.731-734 Hyatt, J. (1984) Liquid and Supercritical Carbon Dioxide as Organic Solvents. J. Org. Chem. Vol.49, No.26, pp.5097-5101... 

C. Lin, J.W. Shan, Ensemble-averaged particle orientation and shear viscosity of single-wall-carbon-nanotube suspensions under shear and electric fields, Phys. Fluids, 2010, 22, 022001. 

It was shown that even in the absence of attractive interparticle interactions, shear forces can make aggregates of the particles interacting by large friction forces (Switzer lii and Klingenberg 2003). For example, flow-induced aggregation has been observed for stiff fibers (Schmid et al. 2000) and carbon nanotube suspensions (Khalkhal et al. 2011). 

Huxtable ST, CahiU DG, Shenogin S, Keblinski P, et al. Interfacial heat flow in carbon nanotube suspensions. Nat Mater October 2003 2 731. ... 

Fan Z, Advani SG (2007) Rheology of multiwall carbon nanotube suspension. J Rheol 51... 

Huxtable, S. T., et al. (2003). Interfacial Heat Flow in Carbon Nanotube Suspensions. Nature materials, 2(11), 731-734. 

Alpatova, A.L. et al. (2010) Single-walled carbon nanotubes dispersed in aqueous media via noncovalent functionalization effect of dispersant on the stability, cytotoxicity, and epigenetic toxicity of nanotube suspensions. Water Research, 44 (2), 505-520. 

Rothen-Rutishauser, B. et al. (2010) Relating the physicochemical characteristics and dispersion of multiwalled carbon nanotubes in different suspension media to their... 

Fischer, J.E., Johnson, A.T., Luzzi, D.E., Therien, M., Winey, K.I., and Yodh, A.G. Carbon nanotube-derived materials High-quality suspensions of single-wall carbon nanotubes. Poster Materials Research Science and Engineering Center, University of Pennsylvania. 

Carbon nanotubes have been also used as a macromolecular scaffold for Gdm complexes. An amphiphilic gadolinium(III) chelate bearing a C16 chain was adsorbed on multiwalled carbon nanotubes (264). The resulting suspensions were stable for several days. Longitudinal water proton relaxivities, r] showed a strong dependence on the GdL concentration, particularly at low field. The relaxivities decreased with increasing field as predicted by the SBM theory. Transverse water proton relaxation times, T2, were practically independent of both the frequency and the GdL concentration. An in vivo feasibility MRI study has been... 

Transient transmittance of single-walled carbon nanotubes (SWNTs) in suspension was modulated at two periods of T40 and 21 fs, corresponding to the RBM and G mode, respectively [54,55]. The amplitude and the frequency of the coherent RBMs exhibited a clear excitation-wavelength dependence (Fig. 2.15) [54]. The different frequencies were attributed to SWNTs with different diameters coming to the excitonic resonance. The FT spectra of the coherent RBMs in Fig. 2.15 had noticeable differences from the resonant Raman spectra, such as the different intensities and better frequency resolution. 

As with fullerenes, carbon nanotubes are also hydrophobic and must be made soluble for suspension in aqueous media. Nanotubes are commonly functionalized to make them water soluble although they can also be non-covalently wrapped with polymers, polysaccharides, surfactants, and DNA to aid in solubilization (Casey et al., 2005 Kam et al., 2005 Sinani et al., 2005 Torti et al., 2007). Functionalization usually begins by formation of carboxylic acid groups on the exterior of the nanotubes by oxidative treatments such as sonication in acids, followed by secondary chemical reactions to attach functional molecules to the carboxyl groups. For example, polyethylene glycol has been attached to SWNT to aid in solubility (Zhao et al., 2005). DNA has also been added onto SWNT for efficient delivery into cells (Kam et al., 2005). 

Chromatographic approaches have been also used to separate nanoparticles from samples coupled to different detectors, such as ICP-MS, MS, DLS. The best known technique for size separation is size exclusion chromatography (SEC). A size exclusion column is packed with porous beads, as the stationary phase, which retain particles, depending on their size and shape. This method has been applied to the size characterization of quantum dots, single-walled carbon nanotubes, and polystyrene nanoparticles [168, 169]. Another approach is hydro-dynamic chromatography (HDC), which separates particles based on their hydro-dynamic radius. HDC has been connected to the most common UV-Vis detector for the size characterization of nanoparticles, colloidal suspensions, and biomolecules [170-172]. 

In many cases the potential application of single-walled carbon nanotubes is associated with solubility of this nanomaterial in different solvents. Unfortunately, nanotubes are poorly soluble in the most of organic solvents and are insoluble in water, and this fact especially hinders biological using SWNT. Weak solubility of SWNT is a result of substantial van der Waals attractions between nanotubes aggregated in bundles. To solve nanotubes in water without any covalent functionalization, a surfactant would be added into aqueous solution, and then this mixture is suspended by sonication. It is supposed that the sound wave splits bundles in aqueous solution. A surfactant in suspension adsorbed onto the nanotube surfaces precludes aggregation of nanotubes in bundles. 

Recent reports show unexpected information on the role of free radicals in the health effects of nanotubes currently employed in many industries.31 Unlike asbestos and most toxic particles, nanotubes do not release but blunt free radicals, which are considered one of the features imparting toxicity to particulates. Multi-wall carbon nanotubes (MWCN) in aqueous suspension do not generate oxygen or carbon centered free radicals detectable with the spintrapping technique. Conversely, when in contact with an external source of hydroxyl (HO) or superoxide radicals (CL h MWCN exhibit a remarkable radical scavenging capacity (Figure 3). It is therefore possible that the inflammatory reaction reported in vivo should be ascribed to MWCN features other than particle derived free radical generation. 

Synthesis of Vinyl Polymer/ Carbon Nanotube Nanocomposites Prepared by Suspension Polymerization and Their Properties... 

Keywords Carbon nanotube, nanocomposite, radical polymerization, suspension polymerization, in-situ polymerization, electrorheology. 

Presence of conductive carbon nanotubes can significantly change the composite particles properties. One example is documented in Figure 8.9 (16) MMA suspension polymerized together with MWCNT. 

Table 8.2. The amount of adsorbed carbon nanotubes on the surface of suspension polymers PS and PMMA with various surfactants, and electrical conductivities of prepared compression moulded discs-type specimens (61)...

As the chapter has shown, suspension polymerization in the presence of carbon nanotubes can be an efficient tool for the preparation of materials suitable for a broad spectrum of applications. As the properties of the resulting material can be to a certain level tailored to the requirements, it is a promising area for research and industry. 

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