Quantitative Method for Analyzing Dendritic Carbon Nanotube Agglomerates in Dispersions Using Differential Centrifugal Sedimentation

Dispersion of carbon nanotubes (CNTs) in liquids is a crucial process in the fabrication of advanced CNT-based materials. However, quantitative evaluation of the dispersed CNTs remains one of the least investigated aspects of CNTs. In this study, we found that the Stokes diameter of single-walled carbon nanotube (SWCNT) agglomerates depends on the rotational velocity in the differential centrifugal sedimentation analysis. The phenomenon can be explained by considering the buoyancy caused by the density difference between the density gradient liquid and the solvent held by SWCNT agglomerates. A single settling velocity equation of a spherical uniform porous particle explains the sedimentation of SWCNT agglomerates very well. Consequently, the size and the porosity of the dendritic SWCNT agglomerates in solution are quantitatively measured by changing the rotational velocity of the centrifugation and/or the concentration of the density gradient liquid.