Sonication Power for Length Control of Single-Walled Carbon Nanotubes in Aqueous Suspensions Used for 2-Dimensional Network Formation
Control over the average length of single-walled carbon nanotubes (SWNTs) in suspension is of critical importance to characterizing and developing flexible, transparent thin films that use percolative transport to achieve reproducibility in electronic properties. This paper demonstrates how the average length of SWNTs in aqueous suspensions can be controlled by the conditions used to form (sonication) and purify (low-G centrifugation) the dispersions. The effect of ultrasonic probe sonication, which was used to disperse SWNT bundles into suspension, on the length and extent of defects on the nanotubes was investigated via atomic force microscopy (AFM) and confocal Raman spectroscopy, respectively. Quantitative information about the suspension concentration and the effect of sonication power on unbundling the SWNTs was obtained via UV-vis and near-IR spectroscopy, respectively. To obtain a clear understanding of the effect of sonication power on SWNT suspensions, repeated low-G centrifugation cycles were used to remove impurities such as bundles of SWNTs, amorphous carbon, and catalyst nanoparticles. This nonoxidizing purification method, which was performed prior to all analyses, allows direct determination of the effect of sonication power on defect formation.