Dispersion of different carbon-based nanofillers in aqueous suspension by polycarboxylate comb-type copolymers and their influence on the early age properties of cementitious matrices

Abstract

The dispersion behaviour of different carbon-based nanofillers in deionized (DI) water was investigated in the study at hand by using polycarboxylates as surfactants. Carbon nanotubes (CNTs), carbon black (CB) and expanded graphite (EG) were firstly characterized in respect of their morphology. Subsequently, they were dispersed in DI water using two polycarboxylate (PCE) comb-type copolymers which differed in length of their chemical backbones. Optical microscopy and light transmission analysis during centrifugation disclosed a clear difference in the dispersibility among the nanofillers under investigation. Small CB particles showed excellent dispersion in DI water even with no surfactant. CNT was dispersed significantly better than EG, whereby the PCE with the longer backbone yielded better filler dispersion in both cases. After incorporating the carbon nanofillers into a cementitious matrix, interestingly, the highest compressive and flexural strengths at an early age were measured for the CNT samples with worse filler dispersion. This effect is explained by the role of the PCE and the aspect ratio of the carbon nanofiller, both of which determine the microstructure in the hardened cement-based matrix collaboratively.