Pore properties

Table 7.1 shows the pore properties of several polymer monolithic columns prepared from styrene/DVB, methacrylates, and acrylamides along with the feed porosity and column efficiency, summarized from several recent publications. Some important points seem to be clearly shown in Table 7.1, especially by the comparison of the properties between methacrylate-based polymer monoliths and silica monoliths. 

Voets T, Prenen J, Fleig A et al 2001 CaTl and the calcium-release activated calcium channel manifest distinct pore properties. J Biol Chem 276 47767-47770 Walker RL, Hume JR, Horowitz B 2001 Differential expression and alternative splicing of TRP channel genes in smooth muscles. Am J Physiol 280 0184-0192 Yue L, Peng J-B, Hediger MA, Clapham DE 2001 CaTl manifests the pore properties of the calcium-release-activated calcium channel. Nature 410 705—709... 

The reason for the high selectivity of zeohte catalysts is the fact that the catalytic reaction typically takes place inside the pore systems of the zeohtes. The selectivity in zeohte catalysis is therefore closely associated to the unique pore properties of zeohtes. Their micropores have a defined pore diameter, which is different from all other porous materials showing generally a more or less broad pore size distribution. Therefore, minute differences in the sizes of molecules are sufficient to exclude one molecule and allow access of another one that is just a little smaller to the pore system. The high selectivity of zeolite catalysts can be explained by three major effects [14] reactant selectivity, product selectivity, and selectivity owing to restricted size of a transition state (see Figure 4.11). 

Gas adsorption (physisorption) is one of the most frequently used characterization methods for micro- and mesoporous materials. It provides information on the pore volume, the specific surface area, the pore size distribution, and heat of adsorption of a given material. The basic principle of the methods is simple interaction of molecules in a gas phase (adsorptive) with the surface of a sohd phase (adsorbent). Owing to van der Waals (London) forces, a film of adsorbed molecules (adsorbate) forms on the surface of the solid upon incremental increase of the partial pressure of the gas. The amount of gas molecules that are adsorbed by the solid is detected. This allows the analysis of surface and pore properties. Knowing the space occupied by one adsorbed molecule, Ag, and the number of gas molecules in the adsorbed layer next to the surface of the solid, (monolayer capacity of a given mass of adsorbent) allows for the calculation of the specific surface area, As, of the solid by simply multiplying the number of the adsorbed molecules per weight unit of solid with the space required by one gas molecule ... 

Jozefaciuk, G. Muranyi, A. Fenyvesi, E. Effect of Cyclodextrins on Surface and Pore Properties of Soil Clay Minerals. Environ. Sci. Technol 2001, 35, 4947-4952. 

The surface areas and pore properties of both the supercritical fluid extracted and the calcined samples were analysed by nitrogen physisorption at 77K using a Quantachrome Auto-Sorbl analyser. The powder X-ray diffraction patterns of both samples were recorded using a SHIMADZU XRD-600 powder X-ray diffractometer, where Cu target Ka-ray was used as the X-ray source. 

Table 1. The surface areas and pore properties of post-synthesis aluminated MCM-41...

The mechanical stability of PSM and AMM-5 samples was investigated by pressing the sample in a die (having a diameter of 16 mm) under different pressures for 15 min. The effects of compression on the surface areas and pore properties of the materials are shown in Table 1. It can be seen that the surface areas of both PSM and AMM-5 samples decrease under high pressure compression. The decrease of surface area, which is proportional to the pressure exerted on the samples, is accompanied with the decrease of pore volume, with no obvious decrease of the pore diameter for both samples. The results indicate that, under high pressure compression, some of the mesoporous channels of MCM-41 have collapsed completely and not constricted to pores of smaller diameter. 

Finite concentration IGC is a useful tool to investigate surface and pore properties. A novel combination of finite concentration IGC and thermal desorption provides the possibility to separate micropore adsorption from surface and mesopore adsorption. This allows the calculation of BET values with physical relevance for highly microporous materials and the consideration of molecular sieve effects. 

Rajagopalan and Luss (1979) developed a theoretical model to predict the influence of pore properties on the demetallation activity and on the deactivation behavior. In this model the change in restricted diffusion with decreasing pore size was included. Catalysts with slab and spherical geometry composed of nonintersecting pores with uniform radius but variable pore lengths were assumed. The conservation equation for diffusion and first-order reaction in a single pore of radius rp is... 

Yue, L., Peng, J. B., Hediger, M. A. and Clapham, D. E., 2001, CaTl manifests the pore properties of the calcium-release-activated calcium channel. Nature 410, 705—9. 

The properties of skeletal Cu-Zn catalysts depend on the composition of the precursor alloy, the composition of the leach solution, and the temperature and time of leaching. Table 6 shows the properties of catalysts used by Friedrich et al. [26]. The leaching conditions used to prepare the catalysts were 323 K, 40wt% NaOH, and sufficient time for complete reaction of the Zn and Al with the NaOH. Thus, the catalysts were fully leached. Table 6 shows that by replacing copper by zinc in the precursor alloy catalysts with increased BET surface areas, decreased pore volumes, decreased pore diameters, and decreased copper crystallite sizes are produced. It also shows the effect of the precursor alloy composition on the surface and pore properties of the catalysts. 

The problem of the interactions between membrane and absorbent solution interests, for instance, the removal of CO2. Reactive absorption liquids, such as amines, that are used for this type of removal, usually wet polyolefin membranes. Wettability depends on the surface tension of the liquid, membrane material, contact angle, and pore properties of the membrane. Possible solutions to this problem are to employ more resistant membrane materials, to use different absorbent liquids, and to deposit a nonporous layer on the membrane surface that prevents any passage of the liquid through pores. In order to do not increase too much the resistance to the mass transport, the layer has to be thin and highly permeable to the gaseous species. The dense skin can be useful also for avoiding any possible contamination of the feed gas by the absorbent (Figure 38.4). 

Prediction of the layer growth kinetics of support layers to be prepared from (sub)micrometer suspensions and sols is, in principle, possible on the basis of Eq. (6.39). Usually, the average pore properties of the substrate, 8i and Rj are known or can be rather easily determined. Estimation of the effective volume fraction of sols, however, may be more difficult as the particles become smaller (see Section 6.2.4). 

The pore properties of cast bulk porous material and coating layers from the same suspension become different above sinter temperatures where intermediate stage sintering in the bulk starts (see Section 6.2.5). At lower temperatures pore properties of free casts determined with Hg porosimetry can be used to compare the pore properties of consolidated dispersion coatings. 

Mather, R.R. (1997). Analysis of pore properties from low pressure hysteresis in nitrogen adsorption isotherms. In Characterisation of Porous Solids IV (B. McEnaney, T.J. Mays, J. Rouquerol, F. Rodriguez-Reinoso, K.S.W. Sing and K.K. Unger, eds). The Royal Society of Chemistry, pp. 314-18. 

Table I compares the pore properties for the starting metakaolln and the LSX pellets, and Figure 6 plots differential pore volume distributions for both materials. The pore distribution data show that the macroporosity of the LSX pellets 1s approximately half that of the starting metakaolln. The difference between pore volumes measured with helium and mercury 1s used as an Indicator for the microporosity of the sample.

Table I. Pore Properties Before and After Conversion to LSX...

Pore Properties of Deep-Fat Fried Chicken Nuggets Coating Formulated from Wheat and Rice Flour Obtained from X-Ray Micro-CT... 

To demonstrate the existence of functional elements responsible for pore properties of channel proteins, peptides with sequences that represent such functional segments are synthesized and their ability to mimic the targeted biological activity is tested by incorporation of the peptides into lipid bilayers. This approach allows rapid determination of which presumed transmembrane helices may form functional channels. The peptides self-assemble in the membrane to generate conductive oligomers, presumably with hydrophobic surfaces that face the phospholipid and hydrophilic residues that fine the pore. Channels of different sizes (oligomeric number) result (37, 48). 

Soil wettability is another important factor besides contamination, which governs water retention and transport processes [97]. Strong interaction of mineral phases with CDs suggests that the properties of the soils may also be seriously affected by CDs, which may have an influence on soil remediation processes. The effect of RM-/9-CD on surface and pore properties of common clay minerals such as bentonite, illite and kaohnite had been studied and it was found that the wettability of the soil decreased at low CD concentration and increased again at the highest load. The increased concentration of CDs reduced the effective radius of the soil bed which improved the average force of interaction among soil particles via water layer, despite the simultaneous decrease of adhesion forces of water to the soil. 

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