Innovative synthesis routes towards hierarchically organized nanostructured materials combined with in-situ SAXS characterization techniques

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Aiming at a better understanding of the formation process of nanostructured materials, we will investigate phase separation phenomena in sol-gel systems on the nano- and micrometer length scale via in-situ small angle X-ray scattering. Highly porous oxides, for example silica, titania, alumina, etc. or mixed silica-metal oxide materials prepared via a novel synthesis route applying metal diolates and comprising a porous network with different levels of hierarchy in the pore sizes will serve as model systems. It is envisioned not only to expand the range of oxidic materials from silica to other transition metal oxides, but also to induce a certain degree of anisotropy into the pore domains, e.g. by mechanical shearing of the sol. Thus, the proposed research comprises three inter-related elements from chemistry and physics: 1.) deliberate network design by tailor-made precursor molecules; 2.) innovative fabrication methods and 3.) detailed characterization of the network development emphazising on in-situ (small angle) X-ray scattering and diffraction. From a chemical point of view, we will develop novel synthetic routes towards highly porous, hierarchically organized transition metal oxide monoliths by applying metal diolates. Metal diolates have the advantage of being processable in purely aqueous solution and thus being compatible with lyotropic liquid crystal phases that will serve as structure-directing agents in the synthesis. As starting compounds the respective alkoxides, e.g. for titania, titanium tetraisopropoxide will be glycolated to give bis(2-hydroxyethyl)titanate as a stable and acid-soluble precursor. This precursor will be processed in the presence of a preformed aqueous lyotropic liquid crystalline phase to yield the oxide with a deliberately designed pore structure. We will demonstrate the high potential of this synthetic approach towards materials with a multimodal pore size distribution by the application of analogous (mixed) metal precursors. From a physical point of view, one focus lies on the structural investigation of the final materials obtained from the glycolated precursor molecules. In addition, previous experiments have shown that contrary to what was expected the lyotropic liquid crystalline phase is not directly templated, but that reorganisation processes occur upon addition of the glycolated precursor. The final network structure is strongly influenced by the mechanism of formation. Therefore, the second focus is on in-situ SAXS measurements, following the structural evolution in the mixture from the sol to the final gel to allow for a deeper understanding of the underlying phase separation processes. Since external parameters such as stirring speed, centrifugation, temperature, etc. have a strong influence on the pore structure, additional measurements are planned comprising shear-induced alignment of the pore system and measurements under different external experimental parameters.