Temperature- and pH-Dependent Dispersion of Highly Purified Multiwalled Carbon Nanotubes Using Polycarboxylate-Based Surfactants in Aqueous Suspension

Multiwalled carbon nanotubes (MWCNTs) were synthesized by chemical vapor deposition and subsequently purified by applying a high-temperature annealing process. The annealed material was characterized using Raman spectroscopy. Next, the interaction of the annealed MWCNTs with polycarboxylate (PCE) comb-copolymer surfactants was studied regarding the quality of dispersion in water, with a focus on the influence of the critical parameters temperature and pH. Optical micrographs and integral light-transmission measurements revealed that both temperature and pH strongly impact the dispersion quality of the MWCNTs. Dynamic light scattering and zeta potential measurements of aqueous solutions of the diluted PCE samples proved that conformational changes occur in dependence on temperature as well as pH. Moreover, it was found that specific molecular conformations strongly affect their efficiency to disperse MWCNTs. On the basis of these experimental findings, a scheme illustrating the consequences of PCE coiling and stretching on successful CNT dispersion in water is presented.