Water diffusion inside carbon nanotubes: mutual effects of surface and confinement

• Published in: Physical chemistry chemical physics : PCCP 2012-01, Vol.14 (2), p.964-971
• Main Authors: Zheng, Yong-gang, Ye, Hong-fei, Zhang, Zhong-qiang, Zhang, Hong-wu
• Format: Article
• Language: English
• Subjects: Carbon nanotubes; Chemistry; Confinement; Cooperation; Diffusion; Diffusion coefficient; Diffusion effects; Exact sciences and technology; General and physical chemistry; Molecular dynamics; Simulation
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c1cp22622c

The mutual effects of two crucial features of carbon nanotubes (CNTs) (surface and confinement) on the temperature-dependent water diffusion are studied through molecular dynamics simulations. A two-stage diffusion mechanism is detected in the CNTs of diameter smaller than 12.2 , which becomes obscure as the temperature increases. This peculiar phenomenon can be ascribed to the cooperation of the small confinement and the periodic surface. The diffusion coefficient of the confined water exhibits a nonmonotonic dependence on the confinement size and an unexpected increase inside the large CNTs (compared to that of bulk water). These anomalous behaviors can be attributed to the competition of the smooth surface and the small confinement. Considering the mutual effects, an empirical formula is proposed on the basis of two groups of numerical examples, whose results indicate that the confinement effect will dominate over the surface effect until the CNT diameter increases up to 16 , whereas thereafter the surface effect becomes dominant and finally both of them vanish gradually. Mutual effects of special surface and small confinement on the water diffusion inside carbon nanotubes.