Nanoconfinement induced anomalous water diffusion inside carbon nanotubes

• Published in: Microfluidics and nanofluidics 2011-06, Vol.10 (6), p.1359-1364
• Main Authors: Ye, Hongfei, Zhang, Hongwu, Zheng, Yonggang, Zhang, Zhongqiang
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Biomedical Engineering and Bioengineering; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diffusion coefficient; Diffusion in nanoscale solids; Diffusion in solids; Engineering; Engineering Fluid Dynamics; Exact sciences and technology; Materials science; Nanoscale materials and structures: fabrication and characterization; Nanotechnology; Nanotechnology and Microengineering; Nanotubes; Physics; Short Communication; Transport properties of condensed matter (nonelectronic)
• ISSN: 1613-4982; 1613-4990
• DOI: 10.1007/s10404-011-0772-y

The diffusion mechanism and coefficient of water confined in carbon nanotubes (CNTs) of diameter ranging from 8 to 54 Å are studied by molecular dynamics simulations. It is found that the motions of water molecules inside the CNTs of diameter smaller than 12.2 Å follow a two-stage diffusion mechanism. Initially, the water diffusion exhibits a long-time super- or sub-diffusion mechanism, and thereafter it transits to the single-file type inside the (6, 6) CNT and shifts to the Fickian type inside the larger CNTs. As for the CNTs of diameter larger than 12.2 Å, the diffusion of the confined water occurs through the Fickian mechanism, which is identical to that of the bulk water. The simulation results further reveal that the diffusion coefficient of the confined water is non-monotonically dependent on the diameter, which can be ascribed to the double-edged effect of CNTs, i.e., the surface effect and the size effect.