SDS Surfactants on Carbon Nanotubes: Aggregate Morphology

Abstract

Although carbon nanotubes have attracted enormous research interest, their practical application is still hindered, primarily, by the difficulty of separating them into samples monodispersed in diameter, chirality, and length. Recent advances show that ultracentrifugating carbon nanotube dispersions stabilized by surfactants is a promising route for achieving the desired separation. For further perfectioning this procedure it is necessary to know how surfactants adsorb on nanotubes of different diameters, which determines the nanotube-surfactant aggregate effective density and the nanotube-nanotube potential of mean force. Because only limited experimental data are available to elucidate these phenomena, we report here an extensive all-atom molecular dynamics study on the morphology of sodium dodecyl sulfate (SDS) surfactant aggregates adsorbed on (6,6), (12,12), and (20,20) single walled carbon nanotubes at room conditions. Our calculations reveal that the nanotube diameter is the primary factor that determines the morphology of the aggregates because of a competition between the entropic and energetic advantage encountered by the surfactants when they wrap one nanotube, and the enthalpic penalty faced during this process due to bending of the surfactant molecule. The data are in qualitative agreement with the neutron scattering results reported by Yurekli et al. [J. Am. Chem. Soc. 2004, 126, 9902], and for the first time provide an atomic-level description helpful in designing better separation, as well as stabilization techniques for aqueous carbon nanotube dispersions.

Carbon nanotubes for ultrafast fibre lasers

“…Individual CNTs migrate into surfactant layers matching their density during the ultracentrifugation process (with acceleration g > 100,000). Assuming that the surfactant interacts with all dispersed CNTs equally, irrespective of their conductivity type or geometry, the buoyant density of the resulting suspension depends only on CNT diameter [155]. To achieve selection by conductivity type, one should apply two surfactants with both different density and reactivity for either s-or m-CNTs.…”

Optimizing sonication parameters for dispersion of single-walled carbon nanotubes

“…The two main methods developed to functionalize SWCNTs are categorized as either covalent or non-covalent functionalization [11][12][13]. The biggest advantage of covalent functionalization is that it allows for a high solubility of SWCNTs in most solvents [12,14].…”

“…So far, lots of effort has been focused on the study of the properties of surfactants with a 0301-0104/$ -see front matter Ó 2012 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.chemphys.2012.08.020 variety of concentrations [11,14,25]. Moreover, molecular dynamic simulations have also been applied to investigate the basic interactions between the SWCNTs, surfactant and water molecules [13].…”

Evaluation of Thin Film Surface Shape as a Function of Dispersant Concentration in Carbon Nanotube Thin Film Fabrication via the Electrospray Method

“…The surfactants used are diverse, but it has been reported that by placing CNT aggregates in an aqueous solution of SDS, the hydrophilicity of the hydrophobic CNT surface can be increased. Thus, the dispersion due to ultrasonic treatment becomes more effective [20][21][22][23][24][25].…”