Gas Transport in Porous Media: Simulations and Experiments on Partially Densified Aerogels

The experimental density dependence of gas (argon and nitrogen) permeability of partially densified silica aerogels in the Knudsen regime is quantitatively accounted for by a computer model. The model simulates both the structure of the sintered material and the random ballistic motion of a point particle inside its voids. The same model is also able to account for the densit y dependence of the specific pore surface as measured from nitrogen adsorption experiments.Comment: RevTex, 11 pages + 5 postscript figures appended using "uufiles". Published in Europhys. Lett. 29, p. 567 (1995

Effect of porogen solvent on the synthesis of nickel ion imprinted polymer materials prepared by inverse suspension polymerization

Ion-imprinted polymers (IIPs) for nickel were synthesized by inverse suspension copoly-merization of vinylbenzyl iminodiacetic acid (VbIDA) with ethyleneglycol dimethacrylate (EDMA) in the presence of nickel(II) ions with various porogen solvents to study their impact on the IIPs properties. They were prepared with mixtures of acetonitrile and dimethylsulfoxide (DMSO), 50/50%v/v, for IIP-A/D and 2-methoxyethanol and DMSO, 50/50%v/v, for IIP-M/D. The structure and properties of these polymers were compared with those of IIP-D previously prepared with pure DMSO as porogen solvent. Although IIP-A/D and IIP-M/D were less porous than IIP-D, they presented better nickel adsorption properties and selectivity towards Zn2+, Co2+ and Pb2+. This is assumed to be the result of the stabilization of the ligand-metal complex during the polymerization process. Moreover, the nickel binding capacities of the prepared IIPs in competitive conditions are remarkably high (184 mu mol/g for IIP-D, 170 mu mol/g for IIP-A/D and 174 mu mol/g for IIP-M/D). The impact of the VbIDA chelating monomer was highlighted by comparing the adsorption properties of a copolymer of methyl methacrylate (MMA) and EDMA with NIP-D. It was proved that the methacrylic polymer matrix has low binding properties. (C) 2016 Elsevier Ltd. All rights reserved.Peer reviewe

Root canal hydrophobization by dentinal silanization: Improvement of silicon-based endodontic treatment tightness

A new strategy to improve silicon-based endodontic treatment tightness by dentine hydrophobization is presented in this work: root dentine was silanized to obtain a hydrophobic dentine-sealer interface that limits fluid penetration. This strategy was based on the grafting of aliphatic carbon chains on the dentine through a silanization with the silane end groups [octadecyltrichlorosilane (OTS) and octadecyltriethoxysilane]. Dentine surface was previously pretreated, applying ethylenediaminetetraacetic acid and sodium hypochlorite, to expose hydroxyl groups of collagen for the silane grafting. Collagen fibers exposure after pretreatment was visible with scanning electron microscopy, and Fourier transform infrared (FTIR) spectroscopy showed their correct exposition for the silanization (amide I and II, with 1630, 1580, and 1538 cm⁻¹ peaks corresponding to the vibration of C=O and C--N bonds). The grafting of aliphatic carbon chains was confirmed by FTIR (peaks at 2952 and 2923 cm⁻¹ corresponding to the stretching of C--H bonds) and by the increasing of the water contact angle. The most efficient hydrophobization was obtained with OTS in ethyl acetate, with a water contact angle turning from 51° to 109°. Gas and liquid permeability tests showed an increased seal tightness after silanization: the mean gas and water flows dropped from 2.02 × 10⁻⁸ to 1.62 × 10⁻⁸ mol s⁻¹ and from 10.8 × 10⁻³ to 5.4 × 10⁻³ µL min⁻¹, respectively. These results show clear evidences to turn hydrophilic dentine surface into a hydrophobic surface that may improve endodontic sealing. Copyright © 2013 Wiley Periodicals, Inc

Combining mercury thermoporometry with integrated gas sorption and mercury porosimetry to improve accuracy of pore-size distributions for disordered solids

The typical approach to analysing raw data, from common pore characterization methods such as gas sorption and mercury porosimetry, to obtain pore size distributions for disordered porous solids generally makes several critical assumptions that impact the accuracy of the void space descriptors thereby obtained. These assumptions can lead to errors in pore size of as much as 500%. In this work, we eliminated these assumptions by employing novel experiments involving fully integrated gas sorption, mercury porosimetry and mercury thermoporometry techniques. The entrapment of mercury following porosimetry allowed the isolation (for study) of a particular subset of pores within a much larger interconnected network. Hence, a degree of specificity of findings to particular pores, more commonly associated with use of templated, model porous solids, can also be achieved for disordered materials. Gas sorption experiments were conducted in series, both before and after mercury porosimetry, on the same sample, and the mercury entrapped following porosimetry was used as the probe fluid for theromporometry. Hence, even if one technique, on its own, is indirect, requiring unsubstantiated assumptions, the fully integrated combination of techniques described here permits the validation of assumptions used in one technique by another. Using controlled-pore glasses as model materials, mercury porosimetry scanning curves were used to establish the correct correspondence between the appropriate Gibbs–Thomson parameter, and the nature of the meniscus geometry in melting, for thermoporometry measurements on entrapped mercury. Mercury thermoporometry has been used to validate the pore sizes, for a series of sol–gel silica materials, obtained from mercury porosimetry data using the independently-calibrated Kloubek correlations. The pore sizes obtained for sol–gel silicas from porosimetry and thermoporometry have been shown to differ substantially from those obtained via gas sorption and NLDFT analysis. DRIFTS data for the samples studied has suggested that the cause of this discrepancy may arise from significant differences in the surface chemistries between the samples studied here and that used to calibrate the NLDFT potentials

Molecular dynamics simulation of the early stages of the synthesis of periodic mesoporous silica

We present results of detailed atomistic modeling of the early stages of the synthesis of periodic mesoporous silica using molecular dynamics. Our simulations lead to the proposal of a mechanism that validates several previous experimental and modeling studies and answers many controversial issues regarding the synthesis of mesoporous silicas. In particular, we show that anionic silicates interact very strongly with cationic surfactants and, significantly adsorb on the surface of micelles, displacing a fraction of previously bound bromide counterions. This induces an increase in micelle size and also enhances silica condensation at the micelle surface. The presence of larger silica aggregates in solution further promotes the growth of micelles and, by binding to surfactant molecules in different micelles, their aggregation. This work demonstrates the crucial role played by silica in influencing, by way of a cooperative templating mechanism, the structure of the eventual liquid-crystal phase, which in turn determines the structure of the porous material

Mesoporous Titania Gels Prepared from Titanous Chloride and Ammonia: SEM, Nitrogen Adsorption, Thermoporometry and Mercury Porosimetry Studies

Pore-size distribution studies were carried out employing nitrogen adsorption, mercury porosimetry and thermoporometry techniques on two titania gels prepared from titanous chloride and ammonia using oxygen gas as the oxidizing agent. These gels were also characterized by scanning electron microscopy and X-ray diffraction. After heat-treatment at 340 °C and 520 °C, the gels were found to possess the anatase structure, being predominantly mesoporous in nature as indicated by nitrogen adsorption studies and α S -plots. Very good agreement was observed between the BJH pore-size distribution analysis data and the thermoporometry pore-size determinations. Comparable results were also obtained by mercury porosimetry. The validity of thermoporometry as a viable and reliable technique for pore structure analysis was ascertained

Functionalized ordered nanoporous polymeric materials: From the synthesis of diblock copolymers to their nanostructuration and their selective degradation

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Adsorption et co-adsorption CO2/H2O sur des silices mésoporeuses fonctionnalisées ou modifiées

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The use of nanoporous materials for mechanical energy dissipation

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