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Pore Morphology (pore + morphology)

Distribution by Scientific Domains
Polymers and Materials Science66%

Selected Abstracts

Lattice Monte Carlo and Experimental Analyses of the Thermal Conductivity of Random-Shaped Cellular Aluminum

ADVANCED ENGINEERING MATERIALS, Issue 10 2009
Thomas Fiedler
The effective thermal conductivity of open- and closed-cell aluminium foams with stochastic pore morphologies has been determined by numerical, analytical and experimental methods. A three dimensional analysis technique has been used where numerical calculation models are generated based on 3D computed tomographic (CT) reconstructions. The resulting three dimensional grid models are used for thermal Lattice Monte Carlo (LMC) analyses. The second part of this paper addresses experimental measurements of open-cell M-pore® and closed-cell Alporas® cellular aluminium. Finally, results obtained using both approaches are compared to classical analytic predictions. [source]

DIATOM SILICA BIOMINERALIZATION: AT NANOSCALE LEVEL A CHEMICALLY UNIFORM PROCESS

JOURNAL OF PHYCOLOGY, Issue 2000
E. G. Vrieling
Using a high-brilliance synchrotron X-ray source, combined small- and wide-angle X-ray scattering (SAXS and WAXS) was applied to study nanoscale characteristics, in particular pore size in the range of 3 to 65 nm, of a variety of unialgal cultures of centric and pennate diatoms, and of mixed diatom populations sampled in the field. Results of scattering analysis were compared with details of pore size, structure and orientation visible at the electron microscopic level. WAXS patterns did not reveal any crystalline phase or features of microcrystallinity (resolution 0.07 to 0.51 nm), which implies a totally amorphous character of the SiO2 matrix of the frustule material. SAXS data (resolution 3 to 65 nm) provided information on geometry, size, and distribution of pores in the silica. Overall, two pore regions were recognized that were common to the silica of all samples: the smallest (d less than 10 nm) regularly spaced and shaped spherically, the larger (up to 65 nm) being cylinders or slits. Apparently, at a nanoscale level diatomaceous silica is quite homologous among species, in agreement with the chemical principles of silica polymerization under the conditions of pH and precursor concentrations inside the silicon deposition vesicle. The final frustule "macro"-morphology is of course species-specific, being determined genetically. Synthetically-derived MCM-type silicas have a similarly organized pore distribution in an amorphous silica matrix as we found in all diatom species studied. We therefore suggest that organic molecules of a kind used as structure-directing agents to produce these artificial silicas play a role in the nucleation of the silica polymerization reaction and the shaping of pore morphology inside the silicon deposition vesicle of diatoms. Structure-directing molecules now await isolation from the SDV, followed by identification and characterisation by molecular techniques. [source]

Fabrication of Gradient Pore TiO2 Sheets by a Novel Freeze,Tape-Casting Process

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007
Linlin Ren
Gradient pore structure TiO2 sheets were fabricated by a novel freeze,tape-casting process. Aqueous TiO2 ceramic slurries were prepared by the traditional tape-casting processing and were then cast onto an aluminum foil carrier. The slurries were immediately frozen on the substrate, whose temperature was about ,18°C. After freezing completely, the green sheets were then dried in a lyophilizer. Freeze,tape casting led to formation of a gradient pore microstructure of the TiO2 sheet. The results showed that the solid loading of slurry considerably affected the pore microstructure, pore morphology, and the porosity. Solid loadings of 10, 20, 30, 40, and 50 wt% slurries were used, respectively, and the gradient pore structure TiO2 sheets with different porosities of 75%,88% were obtained. [source]

Blending Chitosan with Polycaprolactone: Porous Scaffolds and Toxicity

MACROMOLECULAR BIOSCIENCE, Issue 9-10 2007
Aparna R. Sarasam
Abstract The preparation and characterization of porous scaffolds from chitosan-PCL blends by freeze extraction, freeze gelation and freeze drying is reported. Using freeze extraction, stable structures were obtained only from PCL, but these were not porous. No stable scaffolds were obtained using the freeze gelation process. Stable scaffolds of chitosan/PCL mixtures could not be obtained using 77% acetic acid by any of these techniques. With 25% aqueous acetic acid, stable scaffolds of chitosan/PCL mixtures were obtained by the freeze drying technique. The stability and pore morphology of freeze dried scaffolds were dependent on the relative mass ratio of chitosan and PCL. A chorioallantoic membrane assay showed that formed 3D chitosan/PCL mixtures were not toxic to vasculature. [source]

Effect of Surface Modification on the Synthesis of Pore-Filling Polymeric Monoliths in Microfiltration Membranes Made from Poly(propylene) and Poly(ethylene terephthalate)

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 3 2007
Abdus Salam
Abstract The effect of pre-modification on the interaction of macroporous substrates (membranes) with mainly micro- and mesoporous polymer monoliths has been studied. Bulk, porous polymer monoliths were synthesized to optimize the synthesis conditions and their pore morphology, and the data were used as benchmark for this study. Pre-modification of the entire pore surface of PP microfiltration membranes and PET track-etched membranes by UV-initiated grafting with PEGMA was performed using well-established methods, including coating with the photo-initiator, benzophenone. Subsequently, these membranes were functionalized by filling the pores with porous polymer monoliths from MAA and EDMA and compared with membranes that had been functionalized without the pre-modification step. The materials were characterized mainly by the degree of grafting, SEM and by the gas-adsorption-isotherm method. The DG values, after composite-membrane preparation under identical conditions, were not influenced by the pre-modification. However, it could be clearly seen from the SEM images that the pre-modification step prevents the formation of voids at the monolith-membrane pore interface. Larger specific surface area and pore volume values for composite membranes, prepared after pre-modification, fully support the SEM results. Especially large differences in pore structure between the two different composite membranes were found in the mesopore range. The results of this study indicate that it is possible to prepare porous, composite membranes where the trans-membrane transport is exclusively controlled by the pore and surface structure of a functional polymeric monolith, for example, made from a molecularly-imprinted polymer. [source]

Hybrid metal/silicon nanocomposite systems and their catalytic activity

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2009
Sergej Polisski
Abstract In this work we studied the reduction of metal salts and their mixtures on extended hydrogen-terminated porous silicon surfaces. For these experiments we employed salts of Au, Ag, Pt and their mixtures. We show that the size and shape of resulting metal and metal alloy nanoparticles depends on the pore morphology. This has been confirmed by transmission electron microscopy measurements and plasmon resonance experiments. Finally we demonstrate catalytic activity of formed Pt nanoparticles in PSi matrix via monitoring the conversion of carbon monoxide. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]