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

Abstract

Multiwalled carbon nanotubes (MWCNTs) were synthesized by chemical vapor deposition and subsequently purified by applying a hightemperature 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 lighttransmission 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.

Multi-walled carbon nanotube dispersion methodologies in alkaline media and their influence on mechanical reinforcement of alkali-activated nanocomposites

“…The anionic surfactant was the commercially available superplasticizer, MasterRheobuild 30 (BASF, Germany), based on sodium ß-naphthalene sulfonic acid formaldehyde. The naphthalene sulfonate was added as surfactant/dispersant for MWCNT dispersion purposes not for rheology and strength modifications, due to its stability and functionality in alkali-activated materials in addition to its dispersion capabilities [35,36,47,[39][40][41][42][43][44][45][46].…”

“…These procedures are far away from real liquid alkaline conditions. For example, one view showed higher dispersibility of MWCNTs in alkaline pH solutions [35], but in contrast, other researchers concluded that CNT suspensions will not maintain the stability in highly alkaline media [36]; or a medium with neutral pH can be an optimum environment for MWCNT dispersion [37]. Simulation of MWCNT exposure to diluted sodium silicate furthermore confirmed the agglomeration and instability of CNTs in such environments [38].…”

Electrical Joule heating of cementitious nanocomposites filled with multi-walled carbon nanotubes: role of filler concentration, water content, and cement age

“…The nanofillers were dispersed in DI water with the aid of a highrange water reducing admixture MasterRheobuild 30 based on naphthalene sulfonate (NS) from BASF, Germany. Ultrasonication was applied in an ice bath [33,34] using a Bandelin Sonopuls 3100 instrument combined with a sonotrode VS70T (Bandelin, Berlin/Germany). An ultrasonication time of only 5 min at 70% was chosen to prevent possible damage to the MWCNT structures [35].…”