Electrostatic self-assembly effect of Fe₃O₄ nanoparticles on performance of carbon nanotubes in cement-based materials

The beneficial effect of carbon nanotubes (CNTs) to enhance the electrical conductivity and piezoresistivity of cement-based materials was highly contingent upon its dispersion. To achieve an appropriate dispersion of CNTs, ultrasonication, high-speed stirring, and chemical dispersion were commonly used, which raises the risk of structural damage of CNTs caused by the excessive energy. In this study, electrostatic self-assembly of Fe3O4 nanoparticles on CNTs was employed to efficiently disperse CNTs. To optimize the dispersion effect of conductive fillers in cement paste, the mix proportions including sodium dodecyl sulfate (SDS) concentration, CNTs concentration, and Fe3O4/CNTs ratios were adjusted. The dispersion degree and electrical property were evaluated by UV-vis absorption and zeta potential. In addition, the effect of self-assembled conductive filler dosage on the electrically conductive property of cement pastes was examined. The results show that the occurrence of electrostatic self-assembly was proved by the change of zeta potential, and the grape-bunch structure was observed by transmission electron microscopy. Further, the optimal proportions of self-assembled conductive fillers were 0.20 wt% SDS concentration, 0.05 wt% CNTs concentration, and 1:1 Fe3O4/CNTs ratio. The self-assembled conductive filler dosage between 0.02 and 0.10 wt% can effectively improve the electrical conductivity of cement paste with up to 68% reduction of resistivity.