Porous morphology

The challenge for modeling the water balance in CCL is to link the composite, porous morphology properly with liquid water accumulation, transport phenomena, electrochemical kinetics, and performance. At the materials level, this task requires relations between composihon, porous structure, liquid water accumulation, and effective properhes. Relevant properties include proton conductivity, gas diffusivihes, liquid permeability, electrochemical source term, and vaporizahon source term. Discussions of functional relationships between effective properties and structure can be found in fhe liferafure. Because fhe liquid wafer saturation, 5,(2)/ is a spatially varying function at/o > 0, these effective properties also vary spatially in an operating cell, warranting a self-consistent solution for effective properties and performance. 

After phase separation, the creation of an isolated porous morphology is achieved by holding the sample at a temperature in the rubbery state, thus enabling for high diffusion rates well above the boiling point of the solvent. On the other hand the temperature must kept below the decomposition temperature of the network. Thus removal of the low molecular weight liquid is achieved by... 

These theoretical calculations predict that the generation of a porous morphology leads to a decrease in modulus and yield strength, and are in good agreement with experimental data. Furthermore, the calculation of stress distribution, which takes into account the interaction of randomly dispersed voids, predicts the buildup of local stress concentrations which in turn can initiate shear banding. 

In a second series of experiments, similar materials were prepared with I wt % catalyst to investigate the influence of morphology on the toughening. In addition to the two heat treatments to generate solvent-modified and macroporous epoxies as presented before, a third heat treatment was carried out to give a semi-porous morphology. A brief heating above Tg and under vacuum results in partial solvent removal. The differences in the three heat treatments is clearly revealed with density measurements as shown in Fig. 48. 

The finely porous morphology of the membrane shown in Figure 16 is characteristic of a dope mixture containing a combination of solvents with individual specific gravities in the same order of... 

Similarly to MIP monoliths, MIP membranes are of interest for their highly porous morphology inducing a high permselectivity. Indeed, porous imprinted membranes could overcome the problems associated with the limited accessibility of the recognition sites of the traditional bulk imprinted polymers as well as with the lack of selectivity of usual commercial membranes. 

Microcellular foams can be produced by thermally induced phase separation (TIPS) [47, 74, 76], The induced spinodal decomposition can be optimized to generate, e.g., polylactide scaffolds with the porous morphology and physicomechanical characteristics of a foam. Interesting materials can be constructed in a simple process. These materials exhibited bundles of channels with a diameter of 400 pm. The internal walls of the tubular macropores have a porous substructure with pore diameters of " 10 pm. It appears to be remarkable that the channels have a preferential... 

The inner porous morphology of these resins is distinguished by interconnected channels that form a porous network, which pervades the rigid, significantly cross-linked polymer matrix [205], These materials are often synthesized by suspension polymerization [206], where a polymerization mixture which includes a cross-linking monomer, a functional comonomer or comonomer, an initiator, and a porogenic agent is polymerized. 

Fig. 16.3. Scanning electron micrographs of cross-sections of a MIP-filled capillary column. The super-porous morphology of the polymer monolith can be seen. Micrometre-sized globular units of macroporous MIP surrounded by interconnecting super-pores (left). A superpore of about 7 pm in width (above, right). Covalent attachments of the MIP to the capillary wall (below, right). Reprinted from [39] Copyright (1997), with permission from American Chemical Society.

Based upon the relative positions of the size distributions of sites and bonds, a classification of porous structures has been proposed [5] and five types have been recognized. During the course of a capillary process each pattern of the confined phases is astonishingly characteristic within each type of structure. The fingerprint of porous morphology is embodied in (ji and is present in all kinds of capillary processes [1]. 

The radius of surface curvature relative to the width of space charge layer determines the sensitivity of reactions to surface roughness, the distribution of reactions on the surface. It is the principal factor in the formation of pores in semiconductors and the porous morphology. 

It has been demonstrated that the release of citric acid from PHEMA hydrogels hinders the formation of calcium phosphates, especially hydroxyapatites. Because of this inhibitory effect, the calcium phosphate phases formed during in vitro calcification were mainly present as non-apatite phases, possibly MCPM and DCPD. The porous morphology of the outer surface of the spherical calcium phosphate deposits could be due to the dissolution of precipitates in the presence of citric acid. The results obtained after subcutaneous implantation ofPHEMA and PHEMA containing citric acid in rats confirmed the resistance of PHEMA-citric acid to calcification. The calcium phosphate deposits which formed in vivo consisted mainly of Ca2+ and OH deficient hydroxyapatites. However, it is not yet known whether or not the differences between the calcium phosphate phases found in vivo and in vitro arise from the presence of proteins/peptides in the in vivo calcifying medium. 

Figure 1.2 Plan view image of a 4H-SiC Si-face sample, off-cut 8° towards [1210], photoelectrochemically etched to obtain the triangular porous morphology. About 2 pm of material was removed by RIE prior to imaging. The exposed channels apparently propagate preferably along (1210) directions. Reproduced from Y. Shishkin etal.,J. Appl. Phys., 96(4), 2311-2322. Copyright (2004), the American Institute of Physics...

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