Fractionation of carboxylated carbon nanotubes and the corresponding variation in their colloidal behavior

Length dependent dispersibility of carboxylated multi-walled carbon nanotubes is presented using a novel approach where a batch of carboxylated nanotubes was size sorted via ultracentrifugation into different fractions with lengths ranging from 150 to 950 nm. The different fractions had the same tube diameter and degree of oxidation. The dispersibility of the nanotube fractions showed dependence on the length where the longer tubes showed more aggregation in terms of larger particle size, zeta potential and lower critical coagulation concentrations (CCC) in the presence of electrolytes. It is hypothesized that the longer tubes formed a more complex electrostatic double layer that increased their entanglement and aggregation.