Evaluation of the porous structures of new polymer packing materials by inverse size-exclusion chromatography

A highly cross-linked porous polymer resin based on styrene-divinylbenzene matrix with pores created by the use of micellar imprinting technique was used as chromatographic packing material. Its performance as a column packing material in inverse size-exclusion chromatography was compared with a non-imprinted resin of the same polymer matrix. The porous structures (the pore size and the porosity) of the resins in the dry and wet states and their relationships with the elution volume of probe solutes (alkanes and polystyrene standards) were established. Characteristic properties of the resins such as specific pore volume, specific surface area and porosity are compared with results obtained by other methods of characterization such as mercury intrusion porosimetry, solvent regain and nitrogen sorption. The results show that the new porous resin can be used in the separation of small molecules. The separation is based on the size of the molecules, and the larger pores (meso- and macropores) in the porous resin can provide a much easier access to the smaller pores (micropores) which are useful in the chromatographic separations.     

Nondestructive technique for the characterization of the pore size distribution of soft porous constructs for tissue engineering

Polymer scaffolds tailored for tissue engineering applications possessing the desired pore structure require reproducible fabrication techniques. Nondestructive, quantitative methods for pore characterization are required to determine the pore size and its distribution. In this study, a promising alternative to traditional pore size characterization techniques is presented. We introduce a quantitative, nondestructive and inexpensive method to determine the pore size distribution of large soft porous solids based on the on the displacement of a liquid, that spreads without limits though a porous medium, by nitrogen. The capillary pressure is measured and related to the pore sizes as well as the pore size distribution of the narrowest bottlenecks of the largest interconnected pores in a porous medium. The measured pore diameters correspond to the narrowest bottleneck of the largest pores connecting the bottom with the top surface of a given porous solid. The applicability and reproducibility of the breakthrough technique is demonstrated on two polyurethane foams, manufactured using the thermally induced phase separation (TIPS) process, with almost identical overall porosity (60-70%) but very different pore morphology. By selecting different quenching temperatures to induce polymer phase separation, the pore structure could be regulated while maintaining the overall porosity. Depending on the quenching temperature, the foams exhibited either longitudinally oriented tubular macropores interconnected with micropores or independent macropores connected to adjacent pores via openings in the pore walls. The pore size and its distribution obtained by the breakthrough test were in excellent agreement to conventional characterization techniques, such as scanning electron microscopy combined with image analysis, BET technique, and mercury intrusion porosimetry. This technique is suitable for the characterization of the micro- and macropore structure of soft porous solids intended for tissue engineering applications. The method is sensitive for the smallest bottlenecks of the largest continuous pores throughout the scaffold that contributes to fluid flow.     

Pore Modification in Porous Ceramic Membranes With Sol-Gel Process and Determination of Gas Permeability and Selectivity

Summary: The aim of the study was to investigate the variation in total surface area, porosity, pore size, Knudsen and surface diffusion coefficients, gas permeability and selectivity before and after the application of sol-gel process to porous ceramic membrane in order to determine the effect of pore modification. In this study, three different sol-gel process were applied to the ceramic support separately; one was the silica sol-gel process which was applied to increase porosity, others were silica-sol dip coating and silica-sol processing methods which were applied to decrease pore size. As a result of this, total surface area, pore size and porosity of ceramic support and membranes were determined by using BET instrument. In addition to this, Knudsen and surface diffusion coefficients were also calculated. After then, ceramic support and membranes were exposed to gas permeation experiments by using the CO₂ gas with different flow rates. Gas permeability and selectivity of those membranes were measured according to the data obtained. Thus, pore surface area, porosity, pore size and Knudsen diffusion coefficient of membrane treated with silica sol-gel process increased while total surface area was decreasing. Therefore, permeability of ceramic support and membrane treated with silica sol-gel process increased, and selectivity decreased with increasing the gas flow rate. Also, surface area, porosity, pore size, permeability, selectivity, Knudsen and surface diffusion coefficients of membranes treated with silica-sol dip coating and silica-sol processing methods were determined. As a result of this, porosity, pore size, Knudsen and surface diffusion coefficients decreased, total surface area increased in both methods. However, viscous flow and Knudsen flow permeability were detected as a consequence of gas permeability test and Knudsen flow was found to be a dominant transport mechanism in addition to surface diffusive flow owing to the small pore diameter in both methods. It was observed that silica-sol processing method had lower pore diameter and higher surface diffusion coefficient than silica-sol dip coating method.     

高分子辅助倒相法制备聚乙烯醇多孔膜

采用高分子辅助倒相法制香了多孔的ＰＶＡ－ＰＶＡｃ膜,并测得其孔隙率,最大孔径,平均孔径及孔径分布。研究了影响这些孔特性的各种因素,在扫描电镜下考察了多孔膜的微观形态,制得的膜孔隙率可调节,孔径分布窄。     

Ellipsometric determination of the structure of nanoscale porous layers

A new ellipsometric method is proposed to measure adsorption in thin layers directly in a stream of vapors of volatile liquid and inert gas at atmospheric pressure. The method enables the determination of the main structural parameters of nano- and microporous materials: the average pore size, pore surface, size pore distribution, and the total porosity of sorbents. A procedure to find the Young modulus in nanoscale porous layers with the use of a spectroellipsometer is described.     

碱溶法制备高孔隙度多孔微球

提出并研究了以碱溶侵蚀提高多孔硅球孔隙度的新方法,研究了碱液浓度、处理温度、反应时间与洗除量的关系。结果表明,随着NaOH浓度的提高,不仅洗除量加大,而且硅胶的溶解速度亦少许增大,其主要原因是由于某些孔结构的塌陷导致了细屑的脱除。温度升高和处理时间延长会导致洗除量增大。随着洗除量的增加,硅胶的比孔容呈线性增大,但其外观仍为均匀的球形,且直径亦未见明显变化。选用粒径4~5 μm、孔径8 nm、比孔容1.4 cm3/g的多孔硅胶,采用1.25 mol/L NaOH水溶液、室温(25 ℃)处理3.0 h,制备了粒径4~5 μm、孔径14 nm、比孔容3.2 cm3/g的高孔隙度多孔硅胶,其孔隙度从75%增加到88%。     

Low Dielectric Constant Organosilicate Films Prepared by Sol-Gel and Templating Methods

Low dielectric constant organosilicate films with controllable microstructure have been successfully synthesized by multiple-step sol-gel process and templating method, which are the two basic methods to establish porous network in the films. Ultra-low dielectric constant (k) of around 2.0 can be achieved for both films. The microstructure such as porosity, pore interconnection and pore size of the two types of the films have been studied and compared. It has been found that the sol-gel films have a higher level of porosity comparing to the templating films to obtain the same k value. The sol-gel film has a majority of closed pores with pore size around 5 nm. The templating film has a closed pore structure with pore size around 10 nm. Preliminary results present a very positive prospective for intermetal dielectric applications.     

A mini-review of polymeric porous membranes with vertically penetrative pores

Membrane separation technology plays a pivotal role in modern industry and scientific research. The key to developing and improving membrane separation processes lies in designing and fabricating customized porous membranes with specific physical parameters, including pore diameter, porosity, pore size distribution, pore length (membrane thickness), pore geometry, and pore connectivity. Polymeric porous membranes with vertically-penetrative-pores (PPMVs) represent a distinct category among the available membranes due to their unique characteristics such as short transport path, small trans-membrane resistance, and simple pore geometry, as compared to other porous membranes with sponge-like channels. In practical applications, PPMVs offer several advantages, including achieving higher flux rates, facilitating easier unidirectional transport, and enabling harmless biological extraction. Moreover, PPMVs can serve as ideal model systems for theoretical investigations on the fundamental mechanisms of separation and transport in academic research. With substantial advancements in fabrication technologies and application fields of PPMVs in recent years, it warrants a comprehensive perspective. In this mini-review, we provide an overview of widely used fabrication methods for PPMVs, discuss their primary applications, and address the existing challenges and opportunities.     

Characterization of the surface charge property and porosity of track-etched polymer membranes

As an important property of porous membranes, the surface charge property determines many ionic behaviors of nanopores, such as ionic conductance and selectivity. Based on the dependence of electric double layers on bulk concentrations, ionic conductance through nanopores at high and low concentrations is governed by the bulk conductance and surface charge density, respectively. Here, through the investigation of ionic conductance inside track-etched single polyethylene terephthalate (PET) nanopores under various concentrations, the surface charge density of PET membranes is extracted as ∼−0.021 C/m² at pH 10 over measurements with 40 PET nanopores. Simulations show that surface roughness can cause underestimation in surface charge density due to the inhibited electroosmotic flow. Then, the averaged pore size and porosity of track-etched multipore PET membranes are characterized by the developed ionic conductance method. Through coupled theoretical predictions in ionic conductance under high and low concentrations, the averaged pore size and porosity of porous membranes can be obtained simultaneously. Our method provides a simple and precise way to characterize the pore size and porosity of multipore membranes, especially for those with sub-100 nm pores and low porosities.     

In situ monitoring of atomic layer deposition in nanoporous thin films using ellipsometric porosimetry

Ellipsometric porosimetry (EP) is a handy technique to characterize the porosity and pore size distribution of porous thin films with pore diameters in the range from below 1 nm up to 50 nm and for the characterization of porous low-k films especially. Atomic layer deposition (ALD) can be used to functionalize porous films and membranes, e.g., for the development of filtration and sensor devices and catalytic surfaces. In this work we report on the implementation of the EP technique onto an ALD reactor. This combination allowed us to employ EP for monitoring the modification of a porous thin film through ALD without removing the sample from the deposition setup. The potential of in situ EP for providing information about the effect of ALD coating on the accessible porosity, the pore radius distribution, the thickness, and mechanical properties of a porous film is demonstrated in the ALD of TiO(2) in a mesoporous silica film.     

Colloid-templated multisectional porous polymeric fibers

A fabrication method for porous polymeric fibers (PPFs) is reported. We show that a multisectional colloidal crystal can be assembled within a microcapillary by alternating dipping into colloidal solutions of varying size. Subsequent infiltration with curable polymer and washing with suitable solvents results in porous fibers with a cylindrical cross section. Along the length of the fiber, alternating sections of controlled length, pore size, and pore size distribution exist. These fibers present interesting materials for neural scaffolding, catalysis, and possibly photonics if produced with a high degree of crystallinity. The surface pores and bulk porosity of the fibers are characterized by variable-pressure scanning electron microscopy (vp-SEM). Careful analysis shows that the surface pores vary with the colloidal template diameter and polymer infiltration time.     

Supramolecular engineering of intrinsic and extrinsic porosity in covalent organic cages

Control over pore size, shape, and connectivity in synthetic porous materials is important in applications such as separation, storage, and catalysis. Crystalline organic cage molecules can exhibit permanent porosity, but there are few synthetic methods to control the crystal packing and hence the pore connectivity. Typically, porosity is either 'intrinsic' (within the molecules) or 'extrinsic' (between the molecules)--but not both. We report a supramolecular approach to the assembly of porous organic cages which involves bulky directing groups that frustrate the crystal packing. This generates, in a synthetically designed fashion, additional 'extrinsic' porosity between the intrinsically porous cage units. One of the molecular crystals exhibits an apparent Brunauer-Emmett-Teller surface area of 854 m(2) g(-1), which is higher than that of unfunctionalized cages of the same dimensions. Moreover, connectivity between pores, and hence guest uptakes, can be modulated by the introduction of halogen bonding motifs in the cage modules. This suggests a broader approach to the supramolecular engineering of porosity in molecular organic crystals.     

Controllable porous fluorinated polyimide thin films for ultralow dielectric constant interlayer dielectric applications

In this paper, silica microspheres were used as template to prepare porous fluorinated polyimide (FPI) thin films from polyamic acid (PAA, precursor of FPI) and silica colloid solution. The strong hydrogen-bonding interaction between silica microspheres and PAA chains have improved the dispersion of silica microspheres in N,N-Dimethylformamide (DMF) solution, resulting in the high weight content of silica template in PAA/silica colloid solution, and thus giving rise to the formation of porous FPI films with maximum porosity of 35%. The interior microstructures of the resultant porous FPI thin films were investigated. It is found that the porous FPI thin films have interconnected “ink-bottle-type” porous structure, and the pore size, porosity could be precisely controlled by the diameter and weight content of silica microspheres, respectively. Although both the tensile strength and young modules declined with the increasing porosity, the high level void of the porous FPI films endowed the FPI ultralow dielectric constant of 1.84 when the porosity increased to 35%. Furthermore, the mechanical and dielectric properties of the porous FPI films were closely related to the microstructures and porosity, indicating the desired properties could be controlled to meet the application in the microelectronics.     

Sintering effects related to filtration properties of porous continuously gradient ceramic structures

A single-step processing method has been previously established to prepare porous alumina microstructures by a controlled sedimentation technique whereby fine powder from an aqueous suspension consolidates over a casting slab. Metastable surface chemical control of the suspension properties was able to produce a highly porous flat disc structure with a continuously increasing mean pore size from top to bottom. Formation of this gradient structure was facilitated by using a relatively broad particle size distribution. Top layer pore sizes less than 50 nm have been achieved. Without modification, these structures are suitable for use as ultrafiltration media.The present work presents a comparison of properties and performance data for samples made with the above mentioned functionally gradient characteristics, to samples made with a more uniform microstructure. The effects of sintering time and temperature were analysed in view of overall porosity, pore size distribution and the extent of densification from the green state. These results are presented along with permeation measurements from a filtration test module.     

Preparation of porous polylactide microspheres by emulsion‐solvent evaporation based on solution induced phase separation

Porous polylactide (PLA) microspheres were fabricated by an emulsion‐solvent evaporation method based on solution induced phase separation. Scanning electron microscopy (SEM) observations confirmed the porous structure of the microspheres with good connectivity. The pore size was in the range of decade micrometers. Besides large cavities as similarly existed on non‐porous microspheres, small pores were found on surfaces of the porous microspheres. The apparent density of the porous microspheres was much smaller than that of non‐porous microspheres. Fabrication conditions such as stirring rate, good solvent/non‐solvent ratio, PLA concentration and dispersant (polyvinyl alcohol, PVA) concentration had an important influence on both the particle size and size distribution and the pore size within the microspheres. A larger pore size was achieved at a slower stirring rate, lower good solvent/non‐solvent ratio or lower PLA concentration due to longer coalescence time. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrical conductivity of porous media with two-phase saturation

Relations are derived for calculating the electrical conductivity of porous media with two-phase saturation. The considered calculations are based on a capillary-lattice model of a porous medium, the model being composed of several unequally scaled three-dimensional cubic lattices of capillaries. Each lattice may be represented as a large number of analogous cubic cells with the same structure of pore space and a preset pore size distribution over the cells. The distribution of porosity over pore sizes serves as a starting datum for the calculation of all model parameters. The number and scale of lattices are determined by the peculiarities of this distribution. The possibilities of practical use of the considered model are shown by the example of experimental data on samples of porous rocks. The results obtained, in particular, suggest that the model is applicable to solving problems of applied geophysics relevant to determining the saturation of rocks with water and hydrocarbons.     

新型多孔莫来石纤维陶瓷负载La0.8Sr0.2CoO3-δ钙钛矿催化剂

 利用空气挤压排液成型法在 1250 ℃下制得了高孔隙率高热稳定性的莫来石纤维陶瓷. 这种多孔莫来石纤维陶瓷具有较均匀的孔分布,并且孔隙率高达96.22%. 以这种多孔陶瓷为载体制备了负载型La0.8Sr0.2CoO3-δ钙钛矿催化剂,该催化剂对NO氧化CO表现出很好的催化活性和稳定性. 在催化剂中掺入贵金属Pd之后,催化剂的催化活性得到了很大的提高.     

On the Geometry and Topology of 3D Stochastic Porous Media

The nature of geometric and topological information contained in statistical correlation functions was investigated systematically using simulated porous media, generated by the level-cut of Gaussian random fields. Pore space partitioning techniques based on multiorientation scanning were implemented to determine the pore and neck size distributions, coordination number distribution, and genus of a number of model porous media. These results were correlated with the statistical properties (porosity and correlation function) of the microstructure, revealing for the first time the extent of morphological diversity of a broad class of stochastically reconstructed porous media. It was found that the dominant factor explaining microstructural variability among the media studied is the dimensionless length of spatial correlation. Accordingly, the resolution at which the void space is discretized during simulation was shown to affect significantly the resulting pore and neck size distributions and specific genus. It was also found that the average coordination number of simulated porous media is independent of correlation length, but decreases slightly with decreasing porosity. Copyright 2000 Academic Press.     

Characterization of aluminium surface treatments by means of gas adsorption measurements

Adsorption measurements were used to determine the specific surface area of a.c. electrolytically grained aluminium and the porosity distribution diagram of porous anodized aluminium. Alternating current electrolytic graining of aluminium is used to increase the specific surface area for the preparation of litho sheets or capacitor foil. The specific surface area S (calculated by the BET procedure from the nitrogen adsorption isotherm) was studied as a function of the graining frequency between 0.1 and 1000 Hz. The results were related to the graining morphology by comparing them with scanning electron microscopy micrographs. It is concluded that in contrast to the more common surface investigation techniques the method can be used to measure quantitatively the gain in surface area after such a treatment as a.c. electrolytic graining. In the second part of the paper the pore size distribution diagrams are calculated from the adsorption isotherm for porous sulphuric acid films. It is shown that the dominant pore diameter corresponds rather well to the pore diameter observed in transmission electron microscopy sectional views. This means that the adsorption method can be applied to study the porosity of the aluminum oxide films. The method was then used to study the influence of the pretreatment on the porous oxide film morphology.     

金属-有机框架材料的荧光探测应用进展

金属-有机框架材料(metal-organic frameworks,MOFs)是一类由金属离子或金属离子簇与有机配体自组装而成的杂化多孔材料。 极高的比表面积和孔隙率,组成和结构可调节等特点赋予该材料灵活的设计性和丰富的功能性。 金属-有机框架材料的金属离子、有机配体和装载的客体分子等皆可作为发光中心,并能对离子或小分子产生特异性荧光响应,因此在荧光探测方面有广泛应用。 本文主要综述了近年来金属-有机框架材料在荧光探测方向的研究进展以及应用前景。