Pore space morphology

Equations (6.67) and (6.68) establish relations among local water content, operating conditions, wetting properties, and pore space morphology in the CCL. 

Based on a local dissolution law, the micromechanical approach is able to discuss the effects of the local heterogeneity of the mechanical affinity on the dissolution process and to predict the evolution of the pore space morphology. Whenever it is possible to describe the latter by a scalar parameter , (22) yields its evolution (t) which captures the chemomechanical coupling in so far as it controls the evolution of the poroelastic coefficients in (13). Nevertheless, the implementation of this modelling requires to be able to determine the microscopic strain state along the fluid-solid interface by appropriate micromechanical techniques. 

Experimental techniques commonly used to measure pore size distribution, such as mercury porosimetry or BET analysis (Gregg and Sing, 1982), yield pore size distribution data that are not uniquely related to the pore space morphology. They are generated by interpreting mercury intrusion-extrusion or sorption hysteresis curves on the basis of an equivalent cylindrical pore assumption. To make direct comparison with digitally reconstructed porous media possible, morphology characterization methods based on simulated mercury porosimetry or simulated capillary condensation (Stepanek et al., 1999) should be used. 

In view of the vague experimental situation regarding pore-space morphology, several models of the pore space and... 

SAXS, SANS, porosimetry, and water sorption studies provide ample evidence for the dispersion in pore size and the evolution of the pore size distribution in the PEM upon water uptake. The changes in the pore space morphology upon water uptake translate into variations in transport properties of the PEM, as is well known (Eikerling et al., 1997, 2007a, 2008 Kreuer et al., 2004). There is, however, uncertainty regarding the mechanism of these macroscopic swelling phenomena. 

CGMD simulations have become a viable tool in studying self-organization processes in catalyst layers of PEFCs. Stmctural parameters of interest for such studies involve composition and size distributions of Pt/C agglomerates, pore space morphology, surface wettability, as well as the structure and distribution of ionomer. The latter aspect has important implications for electrochemically active area, proton transport properties, and net electrocatalytic activity of the CL. 

Simulations of physical properties of realistic Pt/support nanoparticle systems can provide interaction parameters that are used by molecular-level simulations of self-organization in CL inks. Coarse-grained MD studies presented in the section Mesoscale Model of Self-Organization in Catalyst Layer Inks provide vital insights on structure formation. Information on agglomerate formation, pore space morphology, ionomer structure and distribution, and wettability of pores serves as input for parameterizations of structure-dependent physical properties, discussed in the section Effective Catalyst Layer Properties From Percolation Theory. CGMD studies can be applied to study the impact of modifications in chemical properties of materials and ink composition on physical properties and stability of CLs. 

Stepanek F, Mmek M, Adler PM (2001) The effect of pore-space morphology on the performance of anaerobic granular sludge particles containing entrapped gas. Chem Eng Sci 56 467- 74... 

FIG. 3 Three-dimensional model of the protein mass distribution of the S-layer of Bacillus stearothermophilus NRS 2004/3a [(a) outer, (b) inner face]. The square S-layer is about 8 nm thick and exhibits a center-to-center spacing of the morphological units of 13.5 nm. The protein meshwork composed of a single protein species shows one square-shaped, two elongated, and four small pores per morphological unit. (Modified from Ref. 7.)... 

Another important point to consider in the interpretation of chemical shifts is the fact that the diffusion path over which xenon travels must be known, as the chemical shifts are averaged if various pore sizes (including extra-particle pore space) are sampled on a time scale rapid compared to the inverse chemical shift differences characteristic of the different pores [12]. Thus the chemical shifts observed may be dependent on the morphology of the sample, depending on the amount of inside versus outside xenon. 

Hildenbrand, A. and Urai, J.L. (2003) Investigation of the morphology of pore space in mudstones - first results. Marine and Petroleum Geology 20, 1185-1200... 

The mineral composition of the soil will also influence the kinetics of gas hydrates dissociation in frozen soils. Our results show, that gas hydrate formations in pore space of samples with montmorillonite particles dissociate less markedly as compared to the samples with kaolinite admixture. This influence may be explained by microstructural specificities of pore hydrate saturated samples but undoubtedly requires additional micro-morphological studies for a full understanding. 

In the model the two coexisting phases are wrell separated and the influence of the interface between them is not included. Therefore, questions of the morphology of the phase-separated liquid in the pore space are beyond the scope of this model. For the experimental system, it is believed that the two coexistent phases form a domain structure on a length scale of the pore size [106], with the domains of the iBA-rich phase [Figs. 4.20(d) or 4.20(dl)j located mostly in rather wide pores or pore junctions of the network [96] and the water-rich domains [Figs. 4.20(c2) or 4.20(d2)] in narrow... 

A Plate 5. Morphological features of kaolinite (dickite) and chlorite, a, b Kaolinite c, d dickite with well-developed crystal faces and of large size (up to 10 pm and above) c-h authigenic chlorites developed in the pore space of sandstones frequently in the form of films or as encrusted fringes around quartz grains. Note that photo g exhibits two chlorite varieties of different origin... 

We now study the morphological and topological characteristics of site-bond-site 3D cubic network model. The following additional assumptions are made about the pore space i. The pore space is a lattice of spherical cavities interconnected by cylindrical channels. The catalytic surface mainly belongs to the voids of the lattice, ii. Active sites are uniformly... 

In [82] different model variants of pore-space evolution (random network, serial and parallel pore models) were compared to each other. A morphology of equally swelling parallel pores gives the most favorable a(w) relations with steepest increase of proton conductivity at small water contents. Results obtained for such a morphology are in good agreement with conductivity data of Dow membranes, which possess shorter pendant sidechains than Nafion. 

Soil is a natural body having variable thicknesses. Soil differs from the parent materials in their morphological, physical and chemical characteristics due to interactions between the lithosphere, hydrosphere, atmosphere and biosphere. It is a mixture of mineral and organic constituents that are in solid, gaseous and aqueous states. In soil, particles are packed loosely, forming a soil structure filled with pore spaces. These pores contain soil solution (liquid) and air (gas). 

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