Pore classification in the characterization of porous materials: A perspective

The original version of the article was published in Cent. Eur. J. Chem., Vol. 5(2), (2007), pp. 385–395. It can be also found online at: http://dx.doi.org/10.2478/s11532-007-0017-9. Unfortunately, the original version of this article contains mistakes in the Acknowledgements section. There should be: This work was supported by Grants 240/08/0016 of Institute of Chemical Technology, 257 Prague, 104/06/1079 of Czech Science Foundation and MSM6046137308 of Ministry of Education, Youth and Sports of the Czech Republic. The online version of the original article can be found at     

Pore structure characterization of organic-inorganic materials by inverse size exclusion chromatography

Summary In Inverse Size (or Steric) Exclusion Chromatography (ISEC) measurements, the investigated material is used as a stationary phase in a chromatographic column and the elution volumes of a series of standard solutes with different molecular size are measured. By an appropriate choice of mobile phase and type of standard solutes, specific (enthalpic) interactions between investigated material and solutes are eliminated so that the elution volumes depend on the porous structure of the column filling only. Then, a mathematical treatment of elution data can provide detailed information on both the macropores and the microporous structure of e.g. a swollen polymer gel in a polymer that is grafted onto silica. The basic principle of the evaluation of porosimetric information from chromatographic data is the assumption that the real porous structure of an investigated sample can be modelled as a collection of discrete pore fractions, each containing pores of different but uniform size and of simple geometrical shape. Problem then is to determine the combination of volumes of these fractions which yields the best agreement between computed and experimental values of the elution volumes of standard solutes. It is possible to perform the ISEC measurements either in an organic solvent or non-solvent (e.g. tetrahydrofuran or methanol) or in water, depending on the compatibility of the investigated material with the respective environment. For non-polar polymers, like copolymers of styrene and divinylbenzene, the use of tetrahydrofuran as the mobile phase with alkanes and polystyrenes as standard solutes has been recommended. Alternative ISEC investigation of the same material in an organic and an aqueous environment can provide additional information on its lipo- or hydrophilicity. This method has provided specific information, not obtainable by mercury porosimetry, when modifying silica by a coupling agent, polymerizing different monomers to different extents.     

表面作用力孔流通模型计算高分子滤过膜孔径大小及分布的方法

综述了一种建立在表面作用力孔流通模型基础上计算高分子多孔滤过膜孔径大小及分布的方法。     

Study on porous silk fibroin materials: 3. Influence of repeated freeze–thawing on the structure and properties of porous silk fibroin materials

The influence of repeated freeze–thawing on pore structural characteristics and physical properties of porous silk fibroin materials prepared by freeze drying were studied. It showed that when quick‐frozen silk fibroin solution was repeatedly thawed and frozen before being vacuum dried, thus pore size of prepared porous silk fibroin materials increased from 67 µm to about 120 µm, and pore density decreased from 80 per square millimeter to about 28 per square millimeter; at the same time compression ratio and moisture permeability increased from 22.7% and 230 g/m² hr to about 33.7% and 308 g/m² hr, respectively, tensile strength and dissolvability in hot water decreased from 20.2 N/cm² and 42.7% to about 12.5 N/cm² and 26.1%, respectively. Both the times of repeated thawing and the thawing temperature had a certain influence on the above‐mentioned pore characteristic parameters and physical properties. Copyright © 2001 John Wiley & Sons, Ltd.     

Numerical Study of Pore Sizes Distribution in Gels

We introduce a new numerical technique for the calculation of the pore size distribution in two-dimensional disordered systems. Our method is based on a triangulation technique which allows a closer measurement of pores surface without any morphological hypothesis.In this work, we focus our calculations in simulated gels. Such materials are modeled in two different conditions: by means of the Diffusion-Limited and Reaction-Limited Cluster-cluster Aggregation algorithms, DLCA and RLCA, respectively. In both situations, when the particles concentration decreases, the average pores size increases. The more compact cluster in RLCA, compared with DLCA, is consistent with the pore size distribution we have calculated. The simulated mean pore size is quantitatively in agreement with experimental data from literature.     

Capillary condensation of adsorbates in porous materials

Hysteresis in capillary condensation is important for the fundamental study and application of porous materials, and yet experiments on porous materials are sometimes difficult to interpret because of the many interactions and complex solid structures involved in the condensation and evaporation processes. Here we make an overview of the significant progress in understanding capillary condensation and hysteresis phenomena in mesopores that have followed from experiment and simulation applied to highly ordered mesoporous materials such as MCM-41 and SBA-15 over the last few decades.     

Predicting adsorption isotherms of asphaltenes in porous materials

In this paper we present a molecular thermodynamics approach for the modeling of adsorption isotherms of asphaltenes adsorbed on Berea sandstone, Bedford limestone and dolomite rock, using a model for bulk asphaltenes precipitation and a quasi-two-dimensional approach for confined fluids [E. Buenrostro-González, C. Lira-Galeana, A. Gil-Villegas, J. Wu, AIChE J., 50 (2004) 2552–2570; A. Martínez, M. Castro, C. McCabe A. Gil-Villegas, J. Chem. Phys. 126 (2007) 074707, respectively], both based on the Statistical Associating Fluid Theory for Potentials of Variable Range [A. Gil-Villegas, A. Galindo, P.J. Whitehead, S.J. Mills, G. Jackson, A.N. Burgess, J. Chem. Phys. 106 (1997) 4168–4186]. The theory is applied to model adsorption isotherms from experimental data of asphaltenes extracted from a dead sample of heavy crude oil from a Mexican reservoir. The theoretical results give the right Langmuir Type II adsorption isotherms observed experimentally. The model requires the determination of ten molecular parameters related to the size of the particles and the square-well potentials used to describe the particle–surface and particle–particle interactions at the bulk and adsorbed phases. Nine parameters are taken from previous published results about the behavior of asphaltenes in bulk phases and the adsorption of several molecular fluids onto activated carbon and graphite surfaces. The remaining parameter, the energy strength of the particle–surface interaction, is adjusted to reproduce the experimental data, obtaining values that are consistent with Molecular Mechanics calculations for asphaltenes adsorbed on different surfaces and solutions. Although the agreement between theory and experiments shows some deviations at low bulk concentrations, the model reproduces adsorption data at high concentrations where other semi-empirical approaches fail.     

金属-有机框架材料孔结构的初步理论评估

金属-有机框架材料在气体吸附/分离方面具有广泛的应用, 因而引起国内外学者的广泛关注。本文以6种代表性的MOFs为例简单介绍了利用理论工具研究MOFs孔结构的方法。     

金属-有机框架材料孔结构的初步理论评估

金属-有机框架材料在气体吸附/分离方面具有广泛的应用,因而引起国内外学者的广泛关注。本文以6种代表性的MOFs为例简单介绍了利用理论工具研究MOFs孔结构的方法。     

Atomic Force Microscope Studies of Membranes: Surface Pore Structures of Diaflo Ultrafiltration Membranes

Noncontact atomic force microscopy (AFM) has been used to investigate the surface pore structure of eight Diaflo ultrafiltration membranes covering a range of nominal molecular weight cutoff (MWCO) from 3000 to 300,000 and manufactured from three different polymer types. Excellent high resolution images were obtained. Analysis of the pore images gave quantitative information on the surface pore structure, in particular the pore size distribution and surface roughness. Such data is compared to that obtained by other techniques. Noncontact AFM is a facile and informative means of studying the surface structure of porous materials such as synthetic membranes.     

利用体积排阻快速原位表征整体固定相的孔结构

利用体积排阻色谱原理,在自制的径向色谱柱上,测定了具有窄分子量分布且已知平均分子量418～190 000的聚苯乙烯标准品的保留数据,这些数据可用于计算柱子的外部(55．1％)、内部(4．9％)和总孔隙率以及整体材料孔尺寸分布的信息。此种技术用于整体填料孔结构的表征,具有无破坏性、原位、快速的特点。整体固定相的外部和总孔隙率高于颗粒填充柱,表明整体柱的高通透性;流速与压力关系的分析,证明了整体固定相在高流速下具有低背压的特征。     

氩吸附法研究多级孔分子筛的孔结构

采用不同方法分别制备了双介孔分子筛、介微孔分子筛及介孔沸石材料,利用氩吸附法并结合XRD技术表征了多级孔分子筛的孔结构。探讨了适用于多级孔分子筛的孔径分布计算方法,揭示了不同类型吸附等温线与孔径分布、孔型及孔容等之间的关系。研究表明,对于多级孔分子筛、微孔和介孔的孔径分布分别用SF法和BJH法计算较适宜,全孔分析可用NLDFT法计算。通过对TS-1介孔沸石的孔结构分析发现, TPAOH 在改性制备介孔TS-1的过程中起到了生成介孔及促进二次晶化的双重作用。     

孔径渐变的有序介孔炭的合成及电化学应用

以SBA-15为模板,硼酸为孔道扩张剂,蔗糖为碳源制备了一系列孔径渐变的有序硼杂介孔炭材料,并研究了其电化学电容性能。氮气静态吸附测试表明,当硼酸物质的量分数从0%增大到75%时,介孔炭的孔径从3.3nm增大至8.1nm,并保持有序的介孔结构。电化学测试表明,在KOH电解液中,硼杂介孔炭比电容明显高于未掺杂硼有序介孔炭,孔道有序性和孔径大小共同影响了炭材料的电容性能。当硼酸物质的量分数为50%时,炭材料的比电容性能最优。     

Pore size distribution of unsupported SnO2 membranes prepared by sol-gel process

Unsupported SnO₂ membranes were prepared by sol-gel process and characterized by N₂ adsorption-desorption isotherms and X-ray diffraction. Results show that the texture of dried samples does not change appreciably with the concentration of electrolyte. All of the pore size range used in ultrafiltration process was screened using sintering temperature between 300 and 700°C.     

A Facile Method for the Preparation of Monodisperse Beads with Uniform Pore Sizes for Cell Culture

This paper describes a facile method for the preparation of porous gelatin beads with uniform pore sizes using a simple fluidic device and their application as supporting materials for cell culture. An aqueous gelatin droplet containing many uniform toluene droplets, produced in the fluidic device, is dropped into liquid nitrogen for instant freezing and the small toluene droplets evolve into pores in the gelatin beads after removal of toluene and then freeze‐drying. The porous gelatin beads exhibit a uniform pore size and monodisperse diameter as well as large open pores at the surface. Fluorescence microscopy images of fibroblast‐loaded gelatin beads confirm the attachment and proliferation of the cells throughout the porous gelatin beads.     

Pore size in one‐step swelling and polymerization of monodisperse polymer beads

Crosslinked polystyrene beads were prepared at low swelling ratios by one‐step swelling and polymerization method. Pore size of the beads was observed based on the GPC calibration curves. It is found that: (1) the pore size increases as the swelling ratio decreases; (2) when a good solvent is used as the porogen the pore size increases with the crosslinking monomer content; and (3) at high crosslinking monomer content the pore size does not depend on the porogen solubility. The effects are discussed in terms of polymer miscibility, including phase separation between the seed and bead polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3270–3277, 2000     

双峰孔分布薄壁中孔碳的便捷制备

以廉价的γ-氧化铝为模板制备薄壁中孔碳材料,且可在制备过程中方便地对碳材料的孔结构、微孔率等参数进行调控.以原位聚合的酚醛树脂为碳源取代蔗糖,简化了制备流程.制得的碳材料不仅可以较好地复制氧化铝模板的孔结构,且比表面积比以蔗糖为碳源的样品显著提高.在此基础上,选用模板堆积孔径与模板自身直径差异较大的长棒状氧化铝为模板,成功地以一种模板、经过一次聚合-碳化过程制备出了具有双峰孔分布(PSD)结构的薄壁碳材料,两个峰分别位于4 nm附近的较小中孔区和13 nm附近的较大中孔区.此外,所得碳材料的比表面积(>1800 m2·g-1)和孔容(>4.5 cm3·g-1)均很高,而微孔率却较低,具有优异的中孔特性.将所得碳材料用作电化学电容器的电极,电容可达200 F·g-1,且当电流密度从0.1 A·g-1升至1.0 A·g-1时,比电容仅衰减10%,表现出良好的电容性能.     

Controlling Pore Size and its Distribution of γ-Al2O3 Nanofiltration Membranes

The preparation process of γ-A12O3 nanofiltration membranes were studied by N2 absorption and desorption test and retention rate vs thickness gradient curve method. It was found that template and thermal treatment were key factors for controlling pore size and its distribution.Under the optimized experimental conditions, the BJH (Barret-Jovner-Halenda) desorotion average pore diameter, BJH desorption cumulative volume of pores and BET (Brunauer-Emmett-Teller)surface area of obtained membranes were about 3.9 nm, 0.33 cm3/g and 245 m2/g respectively, the pore size distribution was very narrow. Pore size decreased with the increasing of thickness and no evident change after the dense top layer was formed. The optimum thickness can be controlled by retention rate vs thickness gradient curve method.     

介孔二氧化硅的扩孔及其氨基功能化

利用嵌段共聚物聚环氧乙烷-聚环氧丙烷-聚环氧乙烷(P123)作为胶束模板,均三甲苯(TMB)为扩孔剂,在强酸条件下制备出了一系列大孔径的介孔二氧化硅材料,获得了一种泡状新型结构的硅材料;通过N2吸附-脱附、高分辨透射电镜(HTEM)等手段对这种新型结构的材料进行了表征,综合考察了扩孔剂的用量、酸的浓度以及水热处理温度对...     

Effects of molecular weight on macropore sizes and characterization of porous hydroxyapatite ceramics fabricated using polyethylene glycol: mechanisms to generate macropores and tune their sizes

Hydroxyapatite (HAp) is a raw material used to fabricate scaffolds. Scaffolds are required to be porous to facilitate nutrient flow and vascularization. This study aims to produce porous HAp ceramics with macropores (>200 μm) and bioactivity and tune their macropore size. Polyethylene glycol (PEG) with molecular weights of 400, 3,400, and 8,300 was used to generate macropores. The macropore size increased as the molecular weight of PEG increased. In this method, emulsions were formed by hydrophobic PEG binding HAp nanoparticles during chemical syntheses. Water foams, as a core of the emulsion, were transformed into steam, and the steam expanded under heat treatment. Macropores were generated by the evaporation of the steam and consolidation of HAp nanoparticles. The difference in the molecular weight of PEG did not affect cell adhesion to the porous HAp ceramics. Cells adhered well to and spread widely on the HAp ceramics regardless of macropore size.