Impact of the molecular architecture of polycarboxylate superplasticizers on the dispersion of multi-walled carbon nanotubes in aqueous phase

The working mechanism of carbon nanotube (CNT) dispersion by distinct methacrylate ester-based polycarboxylates (PCEs), all of which are highly efficient cement dispersants, was elucidated. Such duplex functionality of the PCE saves introducing an extra surfactant, which might cause severe adverse reactions in cement-based matrices. Eight PCEs exhibiting well-defined architectures were synthesized, characterized by gel permeation chromatography, and their influence on the dispersion capability of CNTs was assessed. The PCEs varied systematically with respect to their backbone length, grafting density, and side-chain length. Using optical microscopy, it was found that at a mass ratio of CNT:PCE = 1:1, pronounced differences manifested themselves in the state of the macro-dispersions, depending on the PCE architecture. However, a clear correlation between PCE structure and dispersing efficiency could not be established. A subsequent study applying equivalent numbers of PCE molecules revealed clear differences in the individual PCEs’ dispersibilities. The most efficient PCEs consisted of a long backbone combined with a high side-chain density. Lower side-chain densities as well as short backbones resulted in pronounced reduction in CNT-dispersing ability. Regarding side-chain length, no significant effect was found. Finally, a model for the dispersing mechanism leading to deagglomeration of the CNTs was proposed.