Abstract

This work combines molecular dynamics with experimental results to explain the behavior of the two main functionalization alternatives of carbon nanotubes (acidification and silanization) when they are dispersed in water. It was observed that the presence of carboxyl and hydroxyl groups in the carbon nanotubes improves the interaction with the aqueous medium by 22% in comparison with the pristine and silanized material. This indicates that the process of acidifying carbon nanotubes to improve their dispersion in aqueous systems is preferable and it is not necessary to employ an additional silanization stage. Experimental studies show that the silanization process induces partial stability because of the positive charges on the surface material, whereas the acidified system is stable for up to 24 hours. On the one hand, pristine and silanized nanotubes show the formation and rupture of the agglomerates; on the other hand, the acidified system shows a behavior similar from that of water, since appropriate interactions occur between the nanotubes and the water molecules. Computational studies were used to evaluate the performance of the systems by calculating the diffusion coefficient and the potential energy of the system. The energy of the system relates to intermolecular interactions between the species involved; greater intermolecular forces guarantee a better integration of the nanotubes, since the forces do not represent an impediment either for the medium to flow or for the nanomaterial to diffuse within the medium. In addition, the distribution of the charge on the surface of the carbon nanotubes guarantees repulsion between them, improving colloidal stability.

摘要

这项工作将分子动力学与实验结果相结合，以解释碳纳米管的两种主要功能化替代物（酸化和硅烷化）分散在水中时的行为。据观察，与原始和硅烷化材料相比，碳纳米管中羧基和羟基的存在将与水性介质的相互作用提高了 22%。这表明酸化碳纳米管以改善它们在水性体系中的分散的方法是优选的，并且没有必要采用额外的硅烷化阶段。实验研究表明，由于表面材料上带有正电荷，硅烷化过程会引起部分稳定性，而酸化系统可稳定长达 24 小时。一方面，原始和硅烷化的纳米管显示了团聚体的形成和破裂；另一方面，酸化系统表现出与水相似的行为，因为纳米管和水分子之间发生了适当的相互作用。计算研究用于通过计算系统的扩散系数和势能来评估系统的性能。系统的能量与所涉及物种之间的分子间相互作用有关；更大的分子间力保证了纳米管更好的整合，因为这些力并不代表介质流动或纳米材料在介质内扩散的障碍。此外，碳纳米管表面的电荷分布保证了它们之间的排斥，