Diffusion in nanopores: correlating experimental findings with “first-principles” predictions

Abstract Measurement of molecular diffusion in nanoporous host materials, which are typically inhomogeneous and anisotropic, often involves an intricate web of factors and relations to be taken into account since the associated diffusivities are a function of the diffusion path of the guest molecules during a given observation time. Depending on the observation time, therefore, the result of the experimental measurement can point to completely different conclusions about the underlying diffusion phenomena. The risk of misinterpretation of the experimental data, by correlating them with irrelevant phenomena, may be reduced if there is an option to compare the data with the results of totally independent measurements. The present communication addresses this issue with reference to the particular potentials of pulsed field gradient NMR and microimaging by infrared microscopy as techniques of microscopic diffusion measurement.

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Diffusion in Nanoporous Materials: Novel Insights by Combining MAS and PFG NMR

Processes ◽

10.3390/pr6090147 ◽

2018 ◽

Vol 6 (9) ◽

pp. 147 ◽

Cited By ~ 12

Author(s):

Jörg Kärger ◽

Dieter Freude ◽

Jürgen Haase

Keyword(s):

Molecular Diffusion ◽

Diffusion Path ◽

Magic Angle Spinning ◽

Observation Time ◽

Time Interval ◽

Magic Angle ◽

Sample Tube ◽

Pulsed Field ◽

Pfg Nmr ◽

Nuclear Magnetic

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) allows recording of molecular diffusion paths (notably, the probability distribution of molecular displacements over typically micrometers, covered during an observation time of typically milliseconds) and has thus proven to serve as a most versatile means for the in-depth study of mass transfer in complex materials. This is particularly true with nanoporous host materials, where PFG NMR enabled the first direct measurement of intracrystalline diffusivities of guest molecules. Spatial resolution, i.e., the minimum diffusion path length experimentally observable, is limited by the time interval over which the pulsed field gradients may be applied. In “conventional” PFG NMR measurements, this time interval is determined by a characteristic quantity of the host-guest system under study, the so-called transverse nuclear magnetic relaxation time. This leads, notably when considering systems with low molecular mobilities, to severe restrictions in the applicability of PFG NMR. These restrictions may partially be released by performing PFG NMR measurements in combination with “magic-angle spinning” (MAS) of the NMR sample tube. The present review introduces the fundamentals of this technique and illustrates, via a number of recent cases, the gain in information thus attainable. Examples include diffusion measurements with nanoporous host-guest systems of low intrinsic mobility and selective diffusion measurement in multicomponent systems.

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Molecular Diffusion Measurement in Lipid Bilayers over Wide Concentration Ranges: A Comparative Study

ChemPhysChem ◽

10.1002/cphc.200700611 ◽

2008 ◽

Vol 9 (5) ◽

pp. 721-728 ◽

Cited By ~ 105

Author(s):

Lin Guo ◽

Jia Yi Har ◽

Jagadish Sankaran ◽

Yimian Hong ◽

Balakrishnan Kannan ◽

...

Keyword(s):

Comparative Study ◽

Lipid Bilayers ◽

Molecular Diffusion ◽

Diffusion Measurement

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Molecular Diffusion Processes in Crystalline Microporous Materials

MRS Proceedings ◽

10.1557/proc-527-481 ◽

1998 ◽

Vol 527 ◽

Author(s):

G. Sastre ◽

A. Corma ◽

C. R. A. Catlow

Keyword(s):

Molecular Dynamics ◽

Chemical Composition ◽

Diffusion Coefficients ◽

Molecular Diffusion ◽

Diffusion Processes ◽

Diffusion Path ◽

Microporous Structure ◽

Microporous Material ◽

Para Xylene ◽

Channel Systems

ABSTRACTAtomistic Molecular Dynamics are used to simulate diffusion of hydrocarbons inside the microporous structure of siliceous zeolite CIT-I, with chemical composition SiO2. CIT-1 is a crystalline microporous material containing channels formed by rings containing 12 and 10 Si atoms (Figure 1). The dimensions of these two channel systems are sufficient to cause substantial differences in the diffusion of para-xylene and ortho-xylene. Diffusion coefficients as a function of loading of each isomer, and activation energies have been calculated from the simulations. The effect of the isomer size in the diffusion path is also analysed.

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First-principles investigation of copper diffusion barrier performance in defective 2D layered materials

Nanotechnology ◽

10.1088/1361-6528/ac4879 ◽

2022 ◽

Author(s):

Manareldeen Ahmed ◽

Yan Li ◽

Wenchao Chen ◽

Erping Li

Keyword(s):

Barrier Layer ◽

Diffusion Barrier ◽

First Principles ◽

Energy Barrier ◽

2D Materials ◽

Diffusion Path ◽

Layered Materials ◽

Vacancy Defects ◽

2D Layered Materials ◽

Barrier Performance

Abstract This paper investigates the diffusion barrier performance of 2D layered materials with pre-existing vacancy defects using first-principles density functional theory. Vacancy defects in 2D materials may give rise to a large amount of Cu accumulation, and consequently, the defect becomes a diffusion path for Cu. Five 2D layered structures are investigated as diffusion barriers for Cu, i.e., graphene with C vacancy, hBN with B/N vacancy, and MoS2 with Mo/2S vacancy. The calculated energy barriers using climbing image - nudged elastic band show that MoS2-V2S has the highest diffusion energy barrier among other 2D layers, followed by hBN-VN and graphene. The obtained energy barrier of Cu on defected layer is found to be proportional to the length of the diffusion path. Moreover, the diffusion of Cu through vacancy defects is found to modulate the electronic structures and magnetic properties of the 2D layer. The charge density difference shows that there exists a considerable charge transfer between Cu and barrier layer as quantified by Bader charge. Given the current need for an ultra-thin diffusion barrier layer, the obtained results contribute to the field of application of 2D materials as Cu diffusion barrier in the presence of mono-vacancy defects.

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First-Principles Investigation of Atomic Hydrogen Adsorption and Diffusion on/into Mo-doped Nb (100) Surface

Applied Sciences ◽

10.3390/app8122466 ◽

2018 ◽

Vol 8 (12) ◽

pp. 2466 ◽

Cited By ~ 7

Author(s):

Yang Wu ◽

Zhongmin Wang ◽

Dianhui Wang ◽

Jiayao Qin ◽

Zhenzhen Wan ◽

...

Keyword(s):

First Principles ◽

Atomic Hydrogen ◽

Energy Barrier ◽

Hydrogen Adsorption ◽

Hydrogen Permeation ◽

Diffusion Path ◽

Interstitial Site ◽

Octahedral Interstitial Site ◽

Tetrahedral Interstitial Site ◽

And Diffusion

To investigate Mo doping effects on the hydrogen permeation performance of Nb membranes, we study the most likely process of atomic hydrogen adsorption and diffusion on/into Mo-doped Nb (100) surface/subsurface (in the Nb12Mo4 case) via first-principles calculations. Our results reveal that the (100) surface is the most stable Mo-doped Nb surface with the smallest surface energy (2.75 J/m2). Hollow sites (HSs) in the Mo-doped Nb (100) surface are H-adsorption-favorable mainly due to their large adsorption energy (−4.27 eV), and the H-diffusion path should preferentially be HS→TIS (tetrahedral interstitial site) over HS→OIS (octahedral interstitial site) because of the correspondingly lower H-diffusion energy barrier. With respect to a pure Nb (100) surface, the Mo-doped Nb (100) surface has a smaller energy barrier along the HS→TIS pathway (0.31 eV).

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Impending Collision Judgment from an Egocentric Perspective in Real and Virtual Environments: A Review

Perception ◽

10.1177/0301006619861892 ◽

2019 ◽

Vol 48 (9) ◽

pp. 769-795 ◽

Cited By ~ 4

Author(s):

Ilja T. Feldstein

Keyword(s):

Virtual Environments ◽

Observation Time ◽

Field Of View ◽

Spatial Distance ◽

Driving Experience ◽

Factors Affecting ◽

The Past ◽

Technical Factors ◽

Potential Factors ◽

Experimental Findings

The human egocentric perception of approaching objects and the related perceptual processes have been of interest to researchers for several decades. This article gives a literature review on numerous studies that investigated the phenomenon when an object approaches an observer (or the other way around) with the goal to single out factors that influence the perceptual process. A taxonomy of metrics is followed by a breakdown of different experimental measurement methods. Thereinafter, potential factors affecting the judgment of approaching objects are compiled and debated while divided into human factors (e.g., gender, age, and driving experience), compositional factors (e.g., approaching velocity, spatial distance, and observation time), and technical factors (e.g., field of view, stereoscopy, and display contrast). Experimental findings are collated, juxtaposed, and critically discussed. With virtual-reality devices having taken a tremendous developmental leap forward in the past few years, they have been able to gain ground in experimental research. Therefore, special attention in this article is also given to the perception of approaching objects in virtual environments and put in contrast to the perception in reality.

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New experimental findings and biofilm modelling concepts

Water Science & Technology ◽

10.2166/wst.1995.0280 ◽

1995 ◽

Vol 32 (8) ◽

pp. 133-140 ◽

Cited By ~ 3

Author(s):

Oskar Wanner

Keyword(s):

Mixed Culture ◽

Molecular Diffusion ◽

Volume Fraction ◽

Mathematical Functions ◽

Phase Volume Fraction ◽

Microbial Species ◽

Biofilm Model ◽

New Findings ◽

Experimental Side ◽

Experimental Findings

About ten years ago a mathematical model was presented which describes the spatial distribution and development in time of microbial species in mixed-culture biofilms. The model was based on the continuum approach and was one-dimensional in space. These two concepts still are the basis of practically all biofilm models used today. On the experimental side some remarkable new findings have been made in the past years: transport of dissolved components in the biofilm is not always due to molecular diffusion only, transport of particulate components can not be exclusively related to the net growth rates of the microbial species in the biofilm, the liquid phase volume fraction (porosity) in the biofilm is not a constant, and simultaneous attachment and detachment of cells and particles at the biofilm surface is an essential process. These experimental findings had a significant impact on our notion of biofilm systems and called for the integration of new processes in the original mixed-culture biofilm model. The new processes can reproduce most of the experimental observations, however, they are described by empirical mathematical functions. Their mechanisms and significance for biofilm behavior have not been completely elucidated yet. Thus, the extended mixed-culture biofilm model represents primarily a tool for research on biofilm processes.

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Systematic first principles calculations of the effects of stacking faults defects on the 4H-SiC band structure

MRS Proceedings ◽

10.1557/proc-1246-b03-07 ◽

2010 ◽

Vol 1246 ◽

Cited By ~ 1

Author(s):

Massimo Camarda ◽

pietro delugas ◽

Andrea Canino ◽

Andrea Severino ◽

nicolo piluso ◽

...

Keyword(s):

First Principles ◽

Density Functional ◽

Stacking Faults ◽

Perfect Crystal ◽

First Principles Calculations ◽

Electronic Band ◽

Functional Theory ◽

Experimental Findings ◽

Electronic Band Structures ◽

Formation Energies

AbstractShockley-type Stacking faults (SSF) in hexagonal Silicon Carbide polytypes have received considerable attention in recent years since it has been found that these defects are responsible for the degradation of forward I-V characteristics in p-i-n diodes. In order to extend the knowledge on these kind of defects and theoretically support experimental findings (specifically, photoluminescence spectral analysis), we have determined the Kohn-Sham electronic band structures, along the closed path Γ-M-K-Γ, using density functional theory. We have also determined the energies of the SSFs with respect to the perfect crystal finding that the (35) and (44) SSFs have unexpectedly low formation energies, for this reason we could expect these two defects to be easily generated/expanded either during the growth or post-growth process steps.

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