Synthesis of microsphere-loaded porous polymers by combining emulsion and dispersion polymerisations in supercritical carbon dioxide.

Highly porous materials were produced by acrylamide polymerisation templated by supercritical CO(2)-in-water emulsions using new fluorinated glycosurfactants. Properties of the resulting polymer scaffolds were tuned by performing dispersion polymerisations within their cavities filled with supercritical CO(2).

Morphological models of complex ordered materials based on inhomogeneously clipped Gaussian fields.

Clipping a Gaussian random field at a level that is position-dependent yields statistically inhomogeneous morphologies, relevant to many ordered nanostructured materials. The one-point and two-point probability functions of the morphology are derived, as well as a general relation between the specific surface area and the gradient of the clipping function. The general results are particularized for the comprehensive analysis of small-angle x-ray scattering and nitrogen adsorption of SBA-15 ordered mesoporous silica.

Multiscale image analysis of microcellular solids: application to hybrid silica xerogels.

A general methodology is proposed to characterize microcellular solids, the structure of which consists of a three-dimensional network of filamentary structures. The analysis is based on transmission electron microscopy observation of the filaments individually and of their spatial arrangement. The micrographs are analyzed with grey-tone digital image analysis techniques, such as opening granulometry and correlation analysis. The methodology is applied to hybrid organic-inorganic low-density silica solids synthesized by the sol-gel method with an organically modified co-reactant. The quantitative impact of the co-reactant on each structural level of the structure is assessed quantitatively.

Structure of silica xerogels synthesized with organoalkoxysilane co-reactants hints at multiple phase separation.

The microstructure of hybrid silica xerogels synthesized by the base-catalyzed polymerization of tetraethoxysilane (TEOS) in ethanol in the presence of 3-aminopropyltriethoxysilane (AES) and of 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) as co-reactants, and dried in subcritical conditions, is analyzed. A thorough structural characterization of the samples is performed combining nitrogen adsorption, small-angle X-ray scattering (SAXS), and transmission electron microscopy coupled with digital image analysis. The use of these methods shows that, for both co-reactants, the xerogels are made of macropores supported by filaments, with each filament being formed of smaller structures. The quantitative impact of the additive on each structural level is assessed. The data are compared with a previous time-resolved SAXS study conducted during the formation of the gels (J. Phys. Chem. B 2004, 108, 8983-8991). The results are analyzed in the framework of a double phase separation model.

Assessment of the 3D localization of metallic nanoparticles in Pd/SiO2 cogelled catalysts by electron tomography.

The purpose of this study is to analyze the localization of palladium nanoparticles within their silica support, in two heterogeneous catalysts synthesized by the sol-gel process, with different metal loadings. Electron tomography demonstrates that the palladium particles are localized deep inside the silica skeleton. The use of digital image analysis further shows that the dispersion of palladium is optimal in the sample with the lowest loading. The particles are regularly spaced in the middle of the silica skeleton, with a distance between them comparable to the diameter of the struts of silica.

Nitrogen adsorption on silica xerogels or the odd look of a t plot.

Nitrogen adsorption in some silica xerogels leads to t plots that cannot be interpreted by the occurrence of capillary condensation or by the filling of micropores. Their particular appearance stems from the unique columnar structure of these samples at the nanometer scale, by which the adsorbent surface has a positive curvature. A standard thermodynamic approach allows the phenomenon to be exploited to characterize the samples.