Surface-to-Volume Ratio of Ganglia Trapped in Small-Pore Systems Determined by Pulsed-Field Gradient Nuclear Magnetic Resonance

Pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) measurements of hydrocarbon diffusion are shown to provide a quantitative measure of the surface-to-volume (s/v) characteristics of slowly dissolving hydrocarbon ganglia, trapped in a water-saturated porous medium, for systems with pore sizes below the limit of spatial resolution of magnetic resonance imaging (MRI). The porous medium is in the form of a packed bed of glass ballotini. The PFG NMR approach is validated in two ways. First, both MRI and PFG analyses are performed on the same system containing ballotini with a diameter of 1 mm. The s/v ratio of the dissolving ganglia determined by the two methods is the same to within the accuracy of the experimental data. Second, below the spatial resolution limit of MRI, PFG NMR alone is used to characterize the s/v ratios of ganglia entrapped in two packings of ballotini with diameters 0.1 and 0.5 mm, respectively. The s/v data are then included into a one-dimensional advection-dispersion model of the ganglia dissolution process. The resultant mass transfer coefficients obtained are in agreement with those obtained, under the same conditions of aqueous superficial flow rate, following MRI analysis of hydrocarbon dissolution in larger pore structures. Copyright 2001 Academic Press.     

Pore-scale study of nonaqueous phase liquid dissolution in porous media using laser-induced fluorescence

Little quantitative, experimental pore-scale information exists regarding nonaqueous phase liquid (NAPL) ganglia undergoing dissolution in porous media. By using refractive index matched fluids and porous media, we have been able to nonintrusively visualize NAPL dissolution (at constant capillary numbers) in three dimensions using laser-induced fluorescence. The results provide dynamic, quantitative information regarding ganglia surface area, volume, position, and shape. It appears that ganglia smaller than a few pore volumes are spheroid, whereas larger ganglia exhibit a fractal area to volume scaling. Evidence of ganglia breakup is found for all capillary numbers studied. Mobilization, however, is only important at higher capillary numbers.     

Roles of pH and acid type in the anodic growth of porous alumina

Several theoretical models have been formulated to explain the growth of porous structures in anodized alumina. Using some basic assumptions, these models predict the size and shape of the pores in the anodic porous alumina as functions of pH and voltage. Additionally, they address issues of stability in the pore growth. In this work, we have carried out a systematic experimental investigation to study the stability phase diagram as a function of pH and applied voltage. We also obtain the dependence of pore dimensions on the pH, voltage, and acid type. Based on our results, and insight gained from recent chemical analysis of the porous alumina anodization process, we conclude that the models must include an appropriate weighting factor to account for the oxidation and dissolution mechanism during the pore formation.     

Matrix polyelectrolyte microcapsules: new system for macromolecule encapsulation

A new approach to fabricate polyelectrolyte microcapsules is based on exploiting porous inorganic microparticles of calcium carbonate. Porous CaCO3 microparticles (4.5-5.0 microns) were synthesized and characterized by scanning electron microscopy and the Brunauer-Emmett-Teller method of nitrogen adsorption/desorption to get a surface area of 8.8 m2/g and an average pore size of 35 nm. These particles were used as templates for polyelectrolyte layer-by-layer assembly of two oppositely charged polyelectrolytes, poly(styrene sulfonate) and poly(allylamine hydrochloride). Calcium carbonate core dissolution resulted in formation ofpolyelectrolyte microcapsules with an internal matrix consisting of a polyelectrolyte complex. Microcapsules with an internal matrix were analyzed by confocal Raman spectroscopy, scanning electron microscopy, force microscopy, and confocal laser-scanning fluorescence microscopy. The structure was found to be dependent on a number of polyelectrolyte adsorption treatments. Capsules have a very high loading capacity for macromolecules, which can be incorporated into the capsules by capturing them from the surrounding medium into the capsules. In this paper, we investigated the loading by dextran and bovine serum albumin as macromolecules. The amount of entrapped macromolecules was determined by two independent methods and found to be up to 15 pg per microcapsule.     

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。     

膨胀石墨微观孔结构的特点及其表征

膨胀石墨是一种疏松多孔的颗粒状新型碳材料［1，2］．由于在膨化过程中产生了丰富的孔结构，新鲜表面大为增加[3，4]，因此具有很好的吸附性能．探讨这种新材料孔结构的特征对于深入研究其吸附行为有重要意义．但目前尚没有对膨胀石墨孔结构进行系统研究的报导，本文采用低温N     

Construction by molecular dynamics modeling and simulations of the porous structures formed by dextran polymer chains attached on the surface of the pores of a base matrix: characterization of porous structures

Significant increases in the separation of bioactive molecules by using ion-exchange chromatography are realized by utilizing porous adsorbent particles in which the affinity group/ligand is linked to the base matrix of the porous particle via a polymeric extender. To study and understand the behavior of such systems, the M3B model is modified and used in molecular dynamics (MD) simulation studies to construct porous dextran layers on the surface of a base matrix, where the dextran polymer chains and the surface are covered by water. Two different porous polymer layers having 25 and 40 monomers per main polymer chain of dextran, respectively, are constructed, and their three-dimensional (3D) porous structures are characterized with respect to porosity, pore size distribution, and number of conducting pathways along the direction of net transport. It is found that the more desirable practical implications with respect to structural properties exhibited by the porous polymer layer having 40 monomers per main polymer chain, are mainly due to the higher flexibility of the polymer chains of this system, especially in the upper region of the porous structure. The characterization and analysis of the porous structures have suggested a useful definition for the physical meaning and implications of the pore connectivity of a real porous medium that is significantly different than the artificial physical meaning associated with the pore connectivity parameter employed in pore network models and whose physical limitations are discussed; furthermore, the methodology developed for the characterization of the three-dimensional structures of real porous media could be used to analyze the experimental data obtained from high-resolution noninvasive three-dimensional methods like high-resolution optical microscopy. The MD modeling and simulations methodology presented here could be used, considering that the type and size of affinity group/ligand as well as the size of the biomolecule to be adsorbed onto the affinity group/ligand are known, to construct different porous dextran layers by varying the length of the polymeric chain of dextran, the number of attachment points to the base matrix, the degree of side branching, and the number of main polymeric chains immobilized per unit surface area of base matrix. After the characterization of the porous structures of the different porous dextran layers is performed, then only a few promising structures would be selected for studying the immobilization of adsorption sites on the pore surfaces and the subsequent adsorption of the bioactive molecules onto the immobilized affinity groups/ligands.     

A new method to determine pore size and its volume distribution of porous solids having known atomistic configuration

A simple method, based on Monte Carlo integration, is presented to derive pore size and its volume distribution for porous solids having known configuration of solid atoms. Because pores do not have any particular shape, it is important that we define the pore size in an unambiguous manner and the volume associated with each pore size. The void volume that we adopt is the one that is accessible to the center of mass of the probe particle. We test this new method with porous solids having well defined pores such as graphitic slit pores and carbon nanotubes, and then apply it to obtain the pore volume distribution of complex solids such as disordered solids, rectangular pores, defected graphitic pores, metal organic framework and zeolite.     

Quantitative information on pore size distribution from the tangents of comparison plots

The comparison plot obtained from the nitrogen adsorption data has a similar shape to that of the curve of accumulating pore volume of a solid. The intrinsic nature of this relation is discussed. It is known that the derivatives of the accumulating pore volume with respect to the pore size are the pore size distribution (PSD) of the solid. Thus, the tangent curve of the comparison plot can display, at least qualitatively, the PSD of a solid, over a wide range of pore sizes (from approximately 1 to 50 nm) because the comparison plot is applicable to both micropores and mesopores. Quantitative pore structure information can be derived from the comparison plots by establishing a relationship between the t value and the pore size from the samples with uniform pore structure and known pore sizes, such as MCM-41 and alumina pillared clay samples. A calculation procedure to derive quantitative PSD from the comparison plots is suggested, giving reasonable results. This study proposes concise and reliable methods based on the comparison plots to derive information on pore structure in porous solids.     

Polymer/Ag composite microspheres produced by water-in-oil-in-water emulsion polymerization and their application for a preservative

Nanosized Ag particles were entrapped successfully in multihollow porous poly(methyl methacrylate) (PMMA) microspheres by water-in-oil-in-water emulsion polymerization. The structure of the PMMA/Ag microspheres prepared was characterized by scanning electron microscopy and X-ray powder diffraction analysis. It was found that the Ag nanoparticles were impregnated in the inner voids of the microspheres and they had a face-centered cubic structure. In the preservation test, the PMMA/Ag microspheres showed a powerful antibacterial performance, indicating that the Ag ions released effectively through the nanosized pore channel of the PMMA wall.     

以陶瓷纤维为基材的硅胶吸附材料的制备与性能

以陶瓷纤维纸为基材，经水玻璃浸泡，絮凝剂沉积，盐酸调节pH值得到陶瓷纤维基硅胶吸附材料：探讨水玻璃浓度、絮凝剂浓度，盐酸浓度等条件对硅胶吸附剂吸附性能的影响：采用扫描电镜(SEM)，多孔介质孔隙分析仪揭示吸附材料的表面形貌、比表面积及孔径大小。实验结果显示：当水玻璃浓度为26．67wt%，絮凝剂浓度为15wt％，盐酸浓度为0．5mol／L时，吸附剂具有较好的吸附性能：硅胶能较好分散在纤维表面及其空隙中，BET比表面积为347．4m^2／g，总孔容为0．20295cm^2／g，其中，微孔所占比例为50．54％，平均孔径为，微孔0．4939nm，中孔3．907nm。     

Determination of Morphological Properties of Swellable Solids by Size Exclusion Chromatography

Many technically interesting porous solids, e.g. ion exchangers or adsorbents for catalysis, are swellable polymers, i.e. the pore structure depends on the solvent medium. A method based on exclusion chromatography, permits determination of the pore size and pore size distribution in the swollen state.—Size exclusion chromatography, also referred to as gel permeation, gel filtration, or molecular sieve chromatography, is a widely employed method for the separation of dissolved substances—mostly polymer mixtures—according to their molecular size. Porous solids are used as stationary phase. Conversely, pore sizes and other structural data can be determined by exclusion chromatography. This application requires a series of standards (polymer samples) of known molecular weight. As a simple and rapid method, it has already proven valuable for such determinations in the case of rigid solids; in the case of swellable solids, this constitutes the sole method by which the pore structure can be characterized: classical methods require dry samples.     

微介孔材料的孔结构分析表征

孔材料的研究是当今热点问题之一，而关于孔的结构特性如比表面积、孔容、孔尺寸及分布等相关参数的确定，对于一些研究者可能存在着认知盲区.以实验室自制的孔材料为例，应用Nova 1000e型比表面积测试仪进行相关测试，并采用不同方法获得材料的孔结构参数.试验结果表明，非定域密度泛函理论（NLDFT）和骤冷固体密度泛函理论（QSDFT）可获取较为全面的材料孔结构参数，分析过程简便快捷.     

聚乳酸蜂窝状多孔膜的形成与控制

以单一组分聚L-乳酸(PLLA)为成膜材料,利用水辅助法制备了聚乳酸(PLLA)蜂窝状多孔膜.利用扫描电镜(SEM)和原子力显微镜(AFM)观察多孔膜形貌.研究溶剂、溶液浓度、环境温度和湿度等因素对所成多孔膜结构的影响.实验结果表明,高湿度环境和具有一定浓度的聚合物溶液是制备蜂窝状多孔膜的必要条件.溶剂的挥发性是形成规整蜂窝状孔结构的关键因素.环境相对湿度由43%增加到91%,PLLA多孔膜的孔径由(1.75±0.24)μm增加到(11.50±1.43)μm,且孔呈现六边形的蜂窝状结构.扫描电镜断面和AFM表明:膜表面形成了深度约为1.8μm的单层孔结构.通过控制溶液浓度、环境温度和湿度等因素来控制膜的表面形貌及其所成蜂窝状孔的大小.最佳的成膜条件为溶剂CH2Cl2,湿度75%RH,温度34℃,浓度3 wt%.讨论了蜂窝状多孔膜的形成机理.     

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.     

Adsorption, structure and dynamics of benzene in ordered and disordered porous carbons

Molecular simulations are used to study the adsorption, structure, and dynamics of benzene at 298 K in atomistic models of ordered and disordered nanoporous carbons. The ordered porous carbon is a regular slit pore made up of graphene sheets. The disordered porous carbon is a structural model that reproduces the morphological (pore shape) and topological (pore connectivity) disorder of saccharose-based porous carbons. As expected for pores of a regular geometry, the filling occurs at well-defined pressures which are an increasing function of the pore width H. In contrast, in qualitative agreement with experimental data for activated carbon fibers, the filling of the disordered carbon is continuous and spans over a large pressure range. The structure and dynamics of benzene in the disordered carbon also strongly depart from that for the slit pore geometry. While benzene in the slit graphite nanopores exhibits significant layering, benzene in the disordered porous carbon exhibits a liquid-like structure very close to its bulk counterpart. Both the ordering and self-diffusivity of benzene in the graphite nanopores depend in a complex manner on the pore width. The dynamics is either slower or faster than its bulk counterpart; our data show that the self-diffusivity decreases as the number of confined layers n divided by the pore width H increases (except for very small pore sizes for which benzene crystallizes and is necessarily slower than the liquid phase). The dynamics of benzene in the disordered porous carbon is isotropic and is much slower than that for the graphite slit nanopores (even with the smallest slit nanopore considered in this work). The results above show that the adsorption, structure, and dynamics of benzene confined in disordered porous carbons cannot be described in simple terms using an ideal model such as the slit pore geometry.     

Entrapping enzyme in a functionalized nanoporous support

The enzyme organophosphorus hydrolase (OPH) was spontaneously entrapped in carboxylethyl- or aminopropyl-functionalized mesoporous silica with rigid, uniform open-pore geometry (30 nm). This approach yielded larger amounts of protein loading and much higher specific activity of the enzyme when compared to the unfunctionalized mesoporous silica and normal porous silica with the same pore size. When OPH was incubated with the functionalized mesoporous silica, protein molecules were sequestered in or excluded from the porous material, depending on electrostatic interaction with the charged functional groups. OPH entrapped in the organically functionalized nanopores showed an exceptional high immobilization efficiency of more than 200% and enhanced stability far exceeding that of the free enzyme in solution. The combination of high protein loading, high immobilization efficiency and stability is attributed to the large and uniform pore structure, and to the optimum environment introduced by the functional groups.     

Tuning particle morphology of mesoporous silica nanoparticles for adsorption of dyes from aqueous solution

Spherical and rod mesoporous silica nanoparticles with hexagonal mesostructure were prepared using the modified Stöber method. The morphology, size and internal pore structure can be controlled by simple changing of surfactant concentration and water:ethanol molar ratio. Monodispersed spheroid MCM-41 was obtained at 40 °C under basic conditions using cetyltrimethylammonium bromide (C₁₆TAB) as template. Obtained materials were characterized by X-ray diffraction (XRD), nitrogen physisorption (BET), transmission electron microscopy (TEM) and scanning electronic microscopy (SEM). The results reveal that the pore volume and surface area increase when the amount of C₁₆TAB increases whereas the pore diameter and particle size decrease. However, the use of ethanol as cosolvent led to an increase in the particles’ size. Moreover, the addition of a 3-aminopropyltriethoxysilane greatly influenced the final particle shape. The material was effectively used for the removal of two fluorescent dyes (Hoechst 33342 and rhodamine 6g) from aqueous solution. Adsorption isotherm models, Langmuir, Freundlich and Temkin were used to simulate the equilibrium data. The Langmuir model was found to fit the experimental data better than others models.