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Special Issue "Diffusion in Micropores and Mesopores 2013"

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Porous Materials".

Deadline for manuscript submissions: closed (31 May 2013)

Special Issue Editors

Guest Editor
Dr. Sergey Vasenkov

Department of Chemical Engineering, University of Florida, 423 ChE Bldg., PO Box 116005, Gainesville, FL 32611, USA
Website | E-Mail
Fax: +1 352 392 9513
Interests: transport in porous materials with hierarchy of pore sizes; dynamics in room temperature ionic liquids; single-file diffusion in nanochannels; separations of greenhouse gases
Guest Editor
Dr. Christian Chmelik

Department of Interface Physics, University of Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
Website | E-Mail
Phone: +49 341 9732531
Fax: +49 341 9732549
Interests: micro-imaging of diffusion in nanoporous materials; host-guest interactions; mixture diffusion; reaction-diffusion patterns

Special Issue Information

Dear Colleagues,

Detailed understanding of transport properties of mesoporous and microporous materials is essential for a wide range of applications involving transport of molecules and ions in pore networks of these materials. Such applications include catalysis, separations, molecular storage and sensor development. A truly remarkable progress was recently made in the development and fabrication of novel mesoporous and microporous materials such as mesoporoussilicas, metal-organic framework materials (MOFs), single wall carbon nanotubes and zeolites. In additional to materials with uniform or similar pore sizes, also hierarchical and hybrid porous solids were introduced. Functionalization of pore walls with various types of active groups allows for optimization of porous solids for different types of applications. All this complexity in the structural properties of novel porous materials leads to a complexity in intrapore transport. Recent studies of sorbate diffusion in mesoporous and microporous materials resulted in fascinating discoveries related to normal diffusion, and also anomalous diffusion, such as single-file diffusion in nanochannels. Such discoveries become possible due to most recent development of many new experimental techniques allowing monitoring molecular transport on various length scales of displacements under different experimental conditions and by the further development and application of multiscale computer simulations.

Prof. Dr. Sergey Vasenkov
Dr. Christian Chmelik
Guest Editors

Submission

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed Open Access monthly journal published by MDPI.

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Keywords

  • microporous
  • mesoporous
  • hierarchical materials
  • sorbate diffusion
  • permeation
  • transport optimization

Published Papers (6 papers)

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Research

Open AccessArticle Antithrombogenicity of Fluorinated Diamond-Like Carbon Films Coated Nano Porous Polyethersulfone (PES) Membrane
Materials 2013, 6(10), 4309-4323; doi:10.3390/ma6104309
Received: 31 May 2013 / Revised: 14 June 2013 / Accepted: 24 September 2013 / Published: 27 September 2013
Cited by 5 | PDF Full-text (1035 KB) | HTML Full-text | XML Full-text
Abstract
A nano porous polyethersulfone (PES) membrane is widely used for aspects of nanofiltration, such as purification, fractionation and dialysis. However, the low-blood-compatibility characteristic of PES membrane causes platelets and blood cells to stick to the surface of the membrane and degrades ions diffusion
[...] Read more.
A nano porous polyethersulfone (PES) membrane is widely used for aspects of nanofiltration, such as purification, fractionation and dialysis. However, the low-blood-compatibility characteristic of PES membrane causes platelets and blood cells to stick to the surface of the membrane and degrades ions diffusion through membrane, which further limits its application for dialysis systems. In this study, we deposited the fluorinated-diamond-like-carbon (F-DLC) onto the finger like structure layer of the PES membrane. By doing this, we have the F-DLC films coating the membrane surface without sacrificing the membrane permeability. In addition, we examined antithrombogenicity of the F-DLC/PES membranes using a microfluidic device, and experimentally found that F-DLC drastically reduced the amount of blood cells attached to the surface. We have also conducted long-term experiments for 24 days and the diffusion characteristics were found to be deteriorated due to fouling without any surface modification. On the other hand, the membranes coated by F-DLC film gave a consistent diffusion coefficient of ions transfer through a membrane porous. Therefore, F-DLC films can be a great candidate to improve the antithrombogenic characteristics of the membrane surfaces in hemodialysis systems. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Open AccessArticle The Mechanism of Pseudomorphic Transformation of Spherical Silica Gel into MCM-41 Studied by PFG NMR Diffusometry
Materials 2013, 6(9), 3688-3709; doi:10.3390/ma6093688
Received: 1 July 2013 / Revised: 16 August 2013 / Accepted: 19 August 2013 / Published: 26 August 2013
Cited by 7 | PDF Full-text (860 KB) | HTML Full-text | XML Full-text
Abstract
The pseudomorphic transformation of spherical silica gel (LiChrospher® Si 60) into MCM-41 was achieved by treatment at 383 K for 24 h with an aqueous solution of cetyltrimethylammonium hydroxide (CTAOH) instead of hexadecyltrimethylammonium bromide (CTABr) and NaOH. The degree of transformation was
[...] Read more.
The pseudomorphic transformation of spherical silica gel (LiChrospher® Si 60) into MCM-41 was achieved by treatment at 383 K for 24 h with an aqueous solution of cetyltrimethylammonium hydroxide (CTAOH) instead of hexadecyltrimethylammonium bromide (CTABr) and NaOH. The degree of transformation was varied via the ratio of CTAOH solution to initial silica gel rather than synthesis duration. The transformed samples were characterized by N2 sorption at 77 K, mercury intrusion porosimetry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thus, MCM-41 spheres with diameters of ca. 12 μm, surface areas >1000 m2 g−1, pore volumes >1 cm3 g1 and a sharp pore width distribution, adjustable between 3.2 and 4.5 nm, were obtained. A thorough pulsed field gradient nuclear magnetic resonance (PFG NMR) study shows that the diffusivity of n-heptane confined in the pores of the solids passes through a minimum with progressing transformation. The final product of pseudomorphic transformation to MCM-41 does not exhibit improved transport properties compared to the initial silica gel. Moreover, the PFG NMR results support that the transformation occurs via formation and subsequent growth of domains of <1 μm containing MCM-41 homogeneously distributed over the volume of the silica spheres. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Figures

Open AccessArticle Drift in Diffusion Gradients
Materials 2013, 6(8), 3598-3609; doi:10.3390/ma6083598
Received: 27 June 2013 / Revised: 23 July 2013 / Accepted: 13 August 2013 / Published: 19 August 2013
Cited by 9 | PDF Full-text (393 KB) | HTML Full-text | XML Full-text
Abstract
The longstanding problem of Brownian transport in a heterogeneous quasi one-dimensional medium with space-dependent self-diffusion coefficient is addressed in the overdamped (zero mass) limit. A satisfactory mesoscopic description is obtained in the Langevin equation formalism by introducing an appropriate drift term, which depends
[...] Read more.
The longstanding problem of Brownian transport in a heterogeneous quasi one-dimensional medium with space-dependent self-diffusion coefficient is addressed in the overdamped (zero mass) limit. A satisfactory mesoscopic description is obtained in the Langevin equation formalism by introducing an appropriate drift term, which depends on the system macroscopic observables, namely the diffuser concentration and current. The drift term is related to the microscopic properties of the medium. The paradoxical existence of a finite drift at zero current suggests the possibility of designing a Maxwell demon operating between two equilibrium reservoirs at the same temperature. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Open AccessArticle Charged Polymers Transport under Applied Electric Fields in Periodic Channels
Materials 2013, 6(7), 3007-3021; doi:10.3390/ma6073007
Received: 3 June 2013 / Revised: 10 July 2013 / Accepted: 11 July 2013 / Published: 19 July 2013
PDF Full-text (2454 KB) | HTML Full-text | XML Full-text
Abstract
By molecular dynamics simulations, we investigated the transport of charged polymers in applied electric fields in confining environments, which were straight cylinders of uniform or non-uniform diameter. In the simulations, the solvent was modeled explicitly and, also, the counterions and coions of added
[...] Read more.
By molecular dynamics simulations, we investigated the transport of charged polymers in applied electric fields in confining environments, which were straight cylinders of uniform or non-uniform diameter. In the simulations, the solvent was modeled explicitly and, also, the counterions and coions of added salt. The electrophoretic velocities of charged chains in relation to electrolyte friction, hydrodynamic effects due to the solvent, and surface friction were calculated. We found that the velocities were higher if counterions were moved away from the polymeric domain, which led to a decrease in hydrodynamic friction. The topology of the surface played a key role in retarding the motion of the polyelectrolyte and, even more so, in the presence of transverse electric fields. The present study showed that a possible way of improving separation resolution is by controlling the motion of counterions or electrolyte friction effects. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Open AccessArticle Diffusion Study by IR Micro-Imaging of Molecular Uptake and Release on Mesoporous Zeolites of Structure Type CHA and LTA
Materials 2013, 6(7), 2662-2688; doi:10.3390/ma6072662
Received: 2 May 2013 / Revised: 12 June 2013 / Accepted: 17 June 2013 / Published: 4 July 2013
Cited by 16 | PDF Full-text (1216 KB) | HTML Full-text | XML Full-text
Abstract
The presence of mesopores in the interior of microporous particles may significantly improve their transport properties. Complementing previous macroscopic transient sorption experiments and pulsed field gradient NMR self-diffusion studies with such materials, the present study is dedicated to an in-depth study of molecular
[...] Read more.
The presence of mesopores in the interior of microporous particles may significantly improve their transport properties. Complementing previous macroscopic transient sorption experiments and pulsed field gradient NMR self-diffusion studies with such materials, the present study is dedicated to an in-depth study of molecular uptake and release on the individual particles of mesoporous zeolitic specimens, notably with samples of the narrow-pore structure types, CHA and LTA. The investigations are focused on determining the time constants and functional dependences of uptake and release. They include a systematic variation of the architecture of the mesopores and of the guest molecules under study as well as a comparison of transient uptake with blocked and un-blocked mesopores. In addition to accelerating intracrystalline mass transfer, transport enhancement by mesopores is found to be, possibly, also caused by a reduction of transport resistances on the particle surfaces. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Open AccessArticle Interactions and Diffusion of Methane and Hydrogen in Microporous Structures: Nuclear Magnetic Resonance (NMR) Studies
Materials 2013, 6(6), 2464-2482; doi:10.3390/ma6062464
Received: 9 May 2013 / Revised: 4 June 2013 / Accepted: 5 June 2013 / Published: 17 June 2013
Cited by 2 | PDF Full-text (728 KB) | HTML Full-text | XML Full-text
Abstract
Measurements of nuclear spin relaxation times over a wide temperature range have been used to determine the interaction energies and molecular dynamics of light molecular gases trapped in the cages of microporous structures. The experiments are designed so that, in the cases explored,
[...] Read more.
Measurements of nuclear spin relaxation times over a wide temperature range have been used to determine the interaction energies and molecular dynamics of light molecular gases trapped in the cages of microporous structures. The experiments are designed so that, in the cases explored, the local excitations and the corresponding heat capacities determine the observed nuclear spin-lattice relaxation times. The results indicate well-defined excitation energies for low densities of methane and hydrogen deuteride in zeolite structures. The values obtained for methane are consistent with Monte Carlo calculations of A.V. Kumar et al. The results also confirm the high mobility and diffusivity of hydrogen deuteride in zeolite structures at low temperatures as observed by neutron scattering. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)

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