Parametric analysis of sonication and centrifugation variables for dispersion of single walled carbon nanotubes in aqueous solutions of sodium dodecylbenzene sulfonate

Abstract

Dispersion of single-walled carbon nanotubes with the aid of surfactants has become a common procedure for generating aqueous solutions containing a high fraction of individualized nanotubes, though methodologies vary greatly among the literature. A parametric study was performed in order to analyse the effect of ultracentrifugation temperature, duration and applied force on dispersions of arc-discharge nanotubes in sodium dodecylbenzene sulfonate. The amount of metallic impurities remaining after varying levels of centrifugation was investigated by electron microscopy and X-ray spectroscopy. The effect of intensity and duration of exposure to ultrasound was also examined. Solutions were characterized with UV–vis–NIR absorbance spectroscopy, Raman spectroscopy and atomic force microscopy in order to find optimal ranges of these parameters for this particular system. In general, optimal conditions were accomplished via tip sonication at a power below 0.6 W mL −1 to deliver around 450 J mL −1 to the solution, followed by centrifugation at ∼120 × 10 3 g for 1–2 h. The scission of nanotubes was found to follow a power law such that the average length of the ensemble decreased proportional to t −0.38 under continuous tip sonication, while the relationship between mean nanotube length and the Raman D:G ratio was approximately linear for both 1.58 and 2.33 eV excitation.