Comparative investigation of carbon nanotubes dispersion using surfactants: A molecular dynamics simulation and experimental study

Poor dispersion is a major obstacle limiting the practical application of carbon nanotubes (CNTs) in composites. A comparative analysis of the dispersion ability of six representative surfactants for CNTs was conducted using both molecular dynamics (MD) simulations and experimental investigations. The dispersion stability of the surfactant-assisted CNTs was characterised via ultraviolet–visible spectroscopy, surface potential analysis, and transmission electron microscope. The chemical structures of the surfactants and CNTs-surfactant ratios directly affected the adsorption behaviours of surfactants on CNTs surface, thus exerting significant impacts on the final dispersion effect. The interaction energy analysis showed that Triton X-100 and sodium dodecyl benzenesulfonate (SDBS) exhibited the strongest interaction with CNTs with respect to other surfactants, whereas sodium dodecyl sulfate (SDS) displayed the weakest interaction. The van der Waals forces were the main driving forces of this adsorption process. Several structural factors, such as the presence of benzene rings and long alkyl chains, were important and favourable in enhancing the adsorption efficiency of surfactants on CNTs surface. The MD simulation results also revealed that different concentrations of surfactants in the system led to different adsorption behaviours, as low amounts of surfactants tended to exhibit random adsorption without a particular orientation on CNTs surface. Based on the experimental results, Triton X-100 and SDBS showed the strongest dispersion ability, which was consistent with the MD calculation results. Notably, excess amounts of surfactants above the optimum amount caused the entanglement and agglomeration of CNTs owing to the interaction between unfavourable micelles. This study provides an effective guidance for the selection of optimal surfactants for CNTs dispersion.