Influence of Boundaries of Nanoporous Crystals on Molecular Exchange under the Conditions of Single-File Diffusion

Schüring, Andreas; Vasenkov, Sergey; Fritzsche, Siegfried

doi:10.1021/jp052314k

Cited by 17 publications

(26 citation statements)

References 28 publications

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“…Hummer et al , observed that the transport of water molecules occurs in bursts, although later studies of transport on lattices reveal that the pulsatory transport seems to be an universal feature of single-file systems, irrespective of the details of the interaction between particles. , As pointed out by Karger et al in the context of diffusion of molecules inside zeolites, the question of what conditions SFD (in the sense defined above) would be observed in finite systems is quite subtle. The answer depends crucially on factors such as interactions among the diffusing particles, effects of boundaries (closed boundaries or whether there is an exchange of particles with a bath), nature of the dynamics (deterministic or stochastic), and the time scale at which one is probing the dynamics. − In the case of water molecules inside carbon nanotubes, the strong hydrogen bonding between neighboring water molecules plays an important role in the dynamics. As shown by Hummer and co-workers, ,, the hydrogen bonding facilitates the formation of long chains of water molecules.…”

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Single-File Diffusion of Water Inside Narrow Carbon Nanorings

et al. 2010

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We use atomistic molecular dynamics (MD) simulations to study the diffusion of water molecules confined inside narrow (6,6) carbon nanorings. The water molecules form two oppositely polarized chains. It is shown that the effective interaction between these two chains is repulsive in nature. The computed mean-squared displacement (MSD) clearly shows a scaling with time Deltatheta(2)(t) approximately t(1/2), which is consistent with single-file diffusion (SFD). The time up to which the water molecules undergo SFD is shown to be the lifetime of the water molecules inside these chains. Simulations of "uncharged" water molecules inside the nanoring show the formation of several water chains and yield SFD. These observations conclusively prove that the diffusion is Fickian when there is a single chain of water and SFD is observed only when two or more chains are present.

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Single-File Diffusion of Water Inside Narrow Carbon Nanorings

et al. 2010

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“…In the restricted diffusion regime, a(t) f 0 at sufficiently long t. Molecular-exchange dynamics in open-ended channels can be accessed by the tracer exchange technique. 56,78 Tracer exchange monitors the uptake of labeled molecules by a porous material which is initially saturated with unlabeled molecules (or vice versa). The tracer exchange function is defined as…”

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confidence: 99%

“…For simple exclusion interaction in a single-file system, mutual exchange of positions in the lattice is prohibited, and the unrestricted RW process breaks down. The time-scaling of the mean-squared displacement (MSD) then enters the SFD regime, depending on the density. ,− The single-file criterion for spherically shaped molecules with collision diameter σ c in smooth, rigid channels with cylindrical symmetry and internal diameter d is d ≥ σ c ≥ d /2. Channels formed by macrocycle 1 fulfill the single-file criterion.…”

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confidence: 99%

“…Molecular-exchange dynamics in open-ended channels can be accessed by the tracer exchange technique. , Tracer exchange monitors the uptake of labeled molecules by a porous material which is initially saturated with unlabeled molecules (or vice versa). The tracer exchange function is defined as where n ads ( t ) is the number of labeled molecules adsorbed after time t .…”

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confidence: 99%

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Crystalline Bis-urea Nanochannel Architectures Tailored for Single-File Diffusion Studies

et al. 2015

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Urea is a versatile building block that can be modified to self-assemble into a multitude of structures. One-dimensional nanochannels with zigzag architecture and cross-sectional dimensions of only ∼3.7 Å × 4.8 Å are formed by the columnar assembly of phenyl ether bis-urea macrocycles. Nanochannels formed by phenylethynylene bis-urea macrocycles have a round cross-section with a diameter of ∼9.0 Å. This work compares the Xe atom packing and diffusion inside the crystalline channels of these two bis-ureas using hyperpolarized Xe-129 NMR. The elliptical channel structure of the phenyl ether bis-urea macrocycle produces a Xe-129 powder pattern line shape characteristic of an asymmetric chemical shift tensor with shifts extending to well over 300 ppm with respect to the bulk gas, reflecting extreme confinement of the Xe atom. The wider channels formed by phenylethynylene bis-urea, in contrast, present an isotropic dynamically average electronic environment. Completely different diffusion dynamics are revealed in the two bis-ureas using hyperpolarized spin-tracer exchange NMR. Thus, a simple replacement of phenyl ether with phenylethynylene as the rigid linker unit results in a transition from single-file to Fickian diffusion dynamics. Self-assembled bis-urea macrocycles are found to be highly suitable materials for fundamental molecular transport studies on micrometer length scales.

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“…The surface external resistance has been attributed to the crossing of a potential barrier[3], or to the probability to stick to the surface [9,10], According to Ruthven [7] the temperature rise that accompanies the strongly exothermic adsorption of small molecules, can influence the kinetics of adsorption. Misinterpretation of experiments is then also possible, see refs.…”

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confidence: 99%