Parametric analysis of sonication and centrifugation variables for dispersion of single walled carbon nanotubes in aqueous solutions of sodium dodecylbenzene sulfonate Adam J. Blanch, Claire E. Lenehan, Jamie S. Quinton * Smart Surface Structures Group, Flinders Centre for NanoScale Science and Technology, School of Chemical and Physical Sciences, Flinders University, G.P.O. Box 2100, Adelaide, SA 5001, Australia ARTICLE INFO Article history: Received 16 May 2011 Accepted 21 July 2011 Available online 28 July 2011 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 individ- ualized 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 dodecyl- benzene 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 sys- tem. 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. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanotubes (CNTs) are emerging as a promising candi- date for many applications, however the nature of as-pro- duced CNT material presents a considerable barrier to realising the potential offered by these nanostructures. CNTs in the raw ‘soot’ provided by most bulk synthesis methods interact strongly with one another through van der Waals forces, and thus exist primarily in large aggregates such as ropes, matts or bundles [1]. Impurities such as graphitic and amorphous carbon as well as metal catalyst particles are of- ten present in significant quantities, while the nanotubes themselves may consist of a diverse range of lengths, diame- ters and electronic properties, providing a largely heteroge- neous starting material [2–4]. CNTs are inherently insoluble in water, and while organic solvents may disperse nanotubes to some degree, individualized CNTs are usually only ob- tained at low concentrations [5]. Consequently, much effort has been directed towards the dispersion and subsequent sorting of CNTs through a variety of methods [6]. Initial dis- persion is generally accomplished either by chemical modifi- cation of the nanotube sidewall or through non-covalent functionalization with a dispersant [7]. The former, while effective, has been shown to inhibit or even destroy the intrinsic electronic properties of the nanotube by disrupting the conjugated p structure of the carbon lattice [8]. On the 0008-6223/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2011.07.039 * Corresponding author. E-mail address: jamie.quinton@flinders.edu.au (J.S. Quinton). CARBON 49 (2011) 5213 – 5228 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon