Ultrasonic dispersion of multi-walled carbon nanotubes aided by pyrene-polyether dispersants and Al2O3 particles

Carbon nanotube (CNT) aqueous suspensions are attracting considerable attention in conductive, antistatic, electromagnetic shielding coatings and films owning to their environmental safety. However, stable CNT suspensions are difficult to prepare because of the remarkable entanglement between CNTs and their intrinsic hydrophobicity. A new class of amphiphilic dispersants—pyrene butyric acid polyethylene glycol monoester (Py-mPEG)—were prepared through the esterification reaction between 1-pyrene butyric acid and polyethylene glycol monomethyl ether. Varieties of multi-walled carbon nanotubes (MWCNTs) aqueous suspensions were prepared by ultrasonic method using the following dispersants: Py-mPEG, sodium dodecyl benzene sulfonate (SDBS), Py-mPEG/Al2O3, and SDBS/Al2O3. The concentrations of suspended MWCNTs were determined by UV–vis absorption spectroscopy, and the state of suspensions was characterized by scanning electron microscopy (SEM). The non-covalent interactions between MWCNTs and Py-mPEG were investigated by fluorescence emission spectroscopy, and density functional theory calculations. The results showed that MWCNTs were more readily dispersed in Py-mPEG solutions than in SDBS solutions, whereas the Al2O3 particles could further improve the dispersion effect. Particularly, the MWCNT concentration reached 1.363 mg/mL using Py-mPEG (1000 ppm)/Al2O3 (particle size: 5–6 µm) as dispersant. A large number of individual MWCNTs were observed from the SEM images of the suspensions. A diffusion experiment on ink showed that the Al2O3 particles with particle size of 5–6 µm were highly responsive to ultrasound. The entangled MWCNTs could be disintegrated by the collision of particles.