Influence of the molecular structure of a polycarboxylate superplasticiser on the dispersion of graphene oxide in cement pore solutions and cement-based composites

For graphene oxide (GO) to fully exert its reinforcing and toughening functions in cement-based composites, it must be well-dispersed in the cement matrix. In this study, the dispersion behaviour of polycarboxylate superplasticisers (PCEs) with different charge densities and side-chain lengths in the treatment of GO in cement pore solution was studied using ultraviolet spectroscopy, visual sedimentation, and optical microscopy. The results show that all of the molecular structures of PCE can effectively remedy the agglomeration behaviour of GO in cement pore solution. However, for a fixed side-chain length, a higher charge-density PCE structure is better for GO dispersion, and for a fixed charge-density, a longer sidechain is better for GO dispersion. PCEs are adsorbed on the surface of GO through the bridging action of calcium ions (Ca2+) in a cement pore solution. First, the agglomeration of Ca2+ complexed by GO is effectively hindered by steric hindrance due to the side-chains. Second, the carboxyl groups of the PCE main chain complex with Ca2+ to reduce the free Ca(2+ )concentration near the GO sheets. For a fixed side-chain length, a higher charge density promotes GO dispersion by increasing electrostatic repulsion and decreasing the free Ca2+ concentration. For a fixed charge density, a longer side-chain substantially increases steric hindrance and promotes GO dispersion. In general, PCEs with higher charge density and longer side-chains are more suitable for manufacturing GO cement composites. (C) 2020 Elsevier Ltd. All rights reserved.