Bundling dynamics of single walled carbon nanotubes in aqueous suspensions

A simple optical method based on absorption of monochromatic light to investigate the dynamics of single walled carbon nanotube (SWCNT) suspensions is described. The well dispersed suspensions display a complex behavior, exhibiting peaks due to resonant scattering from SWCNT bundles with increasing diameters as a function of time. The results indicate that the bundling of SWCNTs initiates almost immediately after termination of sonication (after ∼0.1 h) and continues to increase up to a critical time (∼10 h), above which precipitation according to the Stokes relationship occurs. The absorbance behavior can be explained by the depletion of the effective medium as well as the Mie scattering from growth of bundles. A semiquantitative analysis of the experimental data based on the Mie theory of light scattering from cylindrical particles allows the extraction of diameters at the nucleation and growth of SWCNT bundles. The bundling dynamics have been correlated with the electrical properties such as the sheet resistance and transistor characteristics of the SWCNT thin films. Our work is a useful step toward reproducible solution processed electronics because it provides a simple method to monitor the quality of SWCNT suspensions in real time and correlate it to device characteristics.