title: Transition from single-file to Fickian diffusion for binary mixtures in single-walled carbon nanotubes.
abstract: The transition from single-file diffusion to Fickian diffusion in narrow cylindrical pores is investigated for systems of rigid single-walled armchair carbon nanotubes, solvated with binary mixtures of Lennard-Jones fluids (Ar/Ne, Ar/Kr, and Ar/Xe). A range of effects is examined including the mixture concentration, the size ratio of the two components, and the nanotube diameter. The transition from single-file to Fickian diffusion in varying carbon nanotube diameters is analyzed in terms of the Fickian self-diffusivity and the single-file mobility of the mixture components. It is found that the single-file to Fickian carbon nanotube transition diameter is a unique property of the individual molecule's diameter and remains unchanged regardless of the mixture composition. In applications of binary mixtures, each component may crossover from single-file to Fickian diffusion in a different carbon nanotube diameter, giving rise to bimodal diffusion in some nanotubes. This transition allows for one species to diffuse in single-file while the other diffuses by a Fickian mechanism, yielding orders of magnitude difference between the self-diffusional rates of the two molecules. This phenomenon might be further extended to alter the diffusional motion of molecules in nanoporous materials.
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou 310027, People's Republic of China.
authors.forename: Qu
authors.initials: Q
authors.lastname: Chen
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Moore
authors.forename: Ying-Chun
authors.initials: YC
authors.lastname: Liu
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Roussel
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Tao
authors.initials: T
authors.lastname: Wu
authors.forename: Keith E
authors.initials: KE
authors.lastname: Gubbins