Which is better? Experimental and simulation analyses of the chemical modification of carbon nanotubes to improve their dispersion in water

I Montes-Zavala and EO Castrejon-Gonzalez and V Rico-Ramirez and E Perez and DA Santamaria-Razo and JA Gonzalez-Calderon, JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY, 42, 1338-1349 (2021).

DOI: 10.1080/01932691.2020.1763179

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.

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