Dispersion of Single-Walled Carbon Nanotubes in Ketone Solvents and Effects of Sonication

In recent years, carbon nanotubes (CNTs) have been intensively studied because of their excellent electrical, thermal, physical, and chemical properties [1,2]. However, CNTs generally form bundles due to strong van der Waals forces, which results in low solubility and processability [3]. Therefore, a number of methods have been developed to disperse CNTs in water and organic solvents, including chemical modification through sidewall functionalization [4,5] and physical modification using dispersants such as surfactants [6-8], aromatic molecules [9], and polymers [10,11]. While the use of dispersants can disperse CNTs without introduction of defects, absolute removal of dispersants from CNTs is quite difficult. Consequently, residual dispersants lower the electrical properties of CNTs because most dispersants are electrically insulating organic molecules [12]. Several organic solvents can disperse CNTs in the absence of dispersants. For example, o-dichlorobenzene [13,14] and polar aprotic solvents, such as N-methylpyrrolidinone [15], N,Ndimethylformamide [16], and N,N-dimethylacetamide [17], are known to disperse CNTs without any additives. However, such solvents are quite limited and most of them have high boiling points (over 100°C), relatively high viscosity, and toxicity. Hence, it is demanded to disperse CNTs in common and widely used organic solvents such as alcohols, ketones, and ethers. In this study, we have found that ketone solvents, acetone and methyl ethyl ketone (MEK), can disperse single-walled CNTs (SWCNTs) without any additives. SWCNT dispersions were prepared by sonication of SWCNTs in ketone solvents. The dependence of the sonication time on the SWCNT concentration was examined. Furthermore, the effects of sonication in ketone solvents on SWCNTs were evaluated with respect to the defect generation and the electrical properties.