Dispersing Carbon Nanotubes with Ionic Surfactants under Controlled Conditions: Comparisons and Insight

Abstract

A fundamental understanding of the mechanisms involved in the surfactant-assisted exfoliation and dispersion of carbon nanotubes (CNTs) in water calls for well-controlled experimental methodologies and reliable comparative metrics. We have assessed the ability of several ionic surfactants to disperse single and multiwalled carbon nanotubes, resorting to a stringently controlled sonication-centrifugation method for the preparation of the dispersions. The CNT concentration was accurately measured for a wide range of surfactant concentration, using combined thermogravimetric analysis and UV-vis spectroscopy. The obtained dispersibility curves yield several quantitative parameters, which in turn allow for the effects of nanotube morphology and surfactant properties (aromatic rings, chain length, headgroup charge, and cmc) to be assessed and rationalized, both in terms of dispersed nanotube mass and surface area. The data also indicate that the CNT-surfactant association follows patterns that are markedly different from other equilibrium processes governed by hydrophobicity (such as micellization); in particular, the surfactant concentration needed for maximum dispersibility, c(s,max), and the number of surfactant molecules per unit CNT area at c(s,max) are shown to depend linearly on chain length. The results further suggest that the presence of micelles in the exfoliation process is not a key factor either for starting CNT dispersibility or attaining its saturation value.

Surfactant-mediated dispersions of carbon nano-onions in aqueous solution

“…Zeta-potential analyses were carried out to determine the CNO surface charge in the surfactant dispersions, thus providing information about their stability. In fact, particles showing zeta-potential values higher than |30| mV are generally stable as the repulsion forces hinder the material aggregation [19,29]. Cationic and anionic surfactants are expected to confer opposite zeta-potential values to the stabilized materials as a consequence of their different surface charge [29,30].…”

“…In fact, particles showing zeta-potential values higher than |30| mV are generally stable as the repulsion forces hinder the material aggregation [19,29]. Cationic and anionic surfactants are expected to confer opposite zeta-potential values to the stabilized materials as a consequence of their different surface charge [29,30]. In particular, the CTAB quaternary ammonium heads and the COO − and sulfonate heads of DCAS and SDBS are presumed to impart, respectively, positive and negative charge to the CNO surface, preventing their aggregation.…”

Structural and mechanical properties of free-standing multiwalled carbon nanotube paper prepared by an aqueous mediated process

“…In this case, refluxing in the surfactant medium plays an important role in generating outer nanoscale irregularities which improve the intermolecular bonding and hence the mechanical property. Secondly, the surfactant helps in dispersing the CNTs which ultimately improves the uniformity of CNTs in the suspension and allows more entanglement [51]. The mechanical property analysis of oxidized refluxed CNT bucky paper is showing the significant improvement.…”

Impact of size control of graphene oxide nanosheets for enhancing electrical and mechanical properties of carbon nanotube–polymer composites

“…Based on the data in Fig. 3(a), the critical W GO /W MWCNT ratios are calculated using linear regression statistics 53 and plotted as a function of GO size in Fig. 3(b).…”