Surface - modified oxo clusters and colloids

The control of the micro- and nanostructure of materials is one of the big challenges in materials chemistry. The goal of the project is to investigate the use of surface-modified oxide clusters or particles towards the development of new amorphous materials, particularly nanostructured materials. Objectives are the preparation of molecular clusters to develop the methodology, to study structural aspects and to investigate the reactivity of surface-modified clusters, the correlation of the model systems with the evolution of the gel structures during sol-gel processes, the deliberate derivatization and modification of the surface of oxo clusters and colloidal -oxo particles by functional or non-functional organic groups, the preparation of inorganic- organic hybrid materials using the pre-formed inorganic particles, and the preparation of inorganic particles with core-shell structures as ceramic powders. This approach combines the following advantages: `Me inorganic particles are homogeneously dispersed in the host matrix due to the covalent bonding. This will impair or inhibit aggregation. The inorganic particles are uniform in size, and their particle size can be modulated. Particularly, the advantages and properties of nano-particles can be utilized. This will have important consequences for all materials and processing properties, for which a homogeneous dispersion of the inorganic component or the particle size and size distribution is important, such as rheological mechanical optical electronic and catalytic properties, density, and the shelf life (stability) of solutions, formulations or lacquers. Furthermore, the surface properties and porosity of the materials can be influenced.

Methods were developed to bind reactive organic groups to the surface of metal oxide clusters. The thus modified clusters were used as nanometer-sized inorganic building blocks of defined size and shape for the preparation of a new class of crosslinked polymers. New materials properties are obtained by the combination of the well-defined inorganic building blocks with organic polymers. Conceptually new approaches are needed for the development of materials with new properties or combinations of properties. One of them is the combination of inorganic and organic building blocks on a molecular level. The properties of the so-called inorganic-organic hybrid materials are largely determined by the composition, structure and mutual connection of the building blocks and thus depend to a high degree on chemical parameters of the materials synthesis and the development of suitable molecular precursors. Chemical principles for a new class of hybrid materials were developed in the project, and the feasibility of the approach was shown with selected examples. The new approach is to construct first clusters - assemblies of metal atoms connected by oxygen atoms - of defined size and shape from the molecular precursors and then to use the clusters as pre-fabricated pieces in the materials syntheses. In order to connect the clusters with the organic components of the hybrid material by chemical bonds, suitable organic groups have to be available to the cluster surface. We developed preparative procedures by which such surface-modified clusters can now be obtained. The examples prepared in the project are clusters with spherical, disk-like or rod-like shape and dimensions of the inorganic cluster core between 0.7 and 1.8 nm. The surface of the clusters is covered with polymerizable organic groups. The surface-modified clusters were polymerized with organic co-monomers by classical methods. Structural investigations of the new hybrid polymers showed that the structural integrity of the clusters is preserved upon incorporation in the polymers and that they crosslink the polymer chains very efficiently. A very small cluster proportion is already sufficient to change the properties of the parent polymers decisively. Preliminary investigations of the materials properties showed, for example, that the thermal and mechanical properties are improved, and the solubility in organic solvents is decreased. Already now it can be foreseen that the new hybrid polymers are interesting materials for applications with special application profiles.