Optimization of Sonication Parameters for Homogeneous Surfactant-Assisted Dispersion of Multiwalled Carbon Nanotubes in Aqueous Solutions

The current study provides answers to two critical open questions concerning homogeneity of aqueous suspensions of carbon nanotubes by ultrasonic processing. The first is the dependence of tube dispersion quality on sonication duration and intensity, and the second is the identification of the appropriate conditions for retaining the highly desirable initial aspect ratio of the free-standing tubes in the dispersed state. A straightforward methodology based on nanotube agglomerate size analysis by liquid mode laser diffraction is suggested for quantifying the effects of sonication parameters on tube length and sample polydispersity. The technique, which is superior to currently suggested methods in that analysis of larger representative volumes is allowed and tube sedimentation effects are avoided, was tested across surfactant-assisted aqueous suspensions of multiwalled carbon nanotubes, while no apparent factors limit application to other types of suspensions. A ruling rationale for distinguishing between entangled states and individually suspended modes is presented, and the effects of surfactant concentration are discussed in the text. For the particular MWCNTs and experimental conditions investigated herein, an energy density rate of 7.7 J min(-1) mL(-1) applicable for a duration of 90 min was found optimum for achievement of suspension homogeneity without significant tube aspect ratio impairment.