Hybrid sol-gel-derived polymers: Applications of multifunctional materials

The homogeneous combination of inorganic and organic moieties in a single-phase material provides unique possibilities to tailor the mechanical, electrical, and optical properties with respect to numerous applications. The synthetic pathway follows the well-known sol-gel procedure. Nevertheless, the establishment of defined hybrid products necessitates a basic understanding of the underlying chemistry as well as of the parameters influencing the processing techniques. Modern spectroscopy provides versatile tools, e.g., multinuclear NMR experiments and Raman scattering to investigate the sol-gel processing of organo(alkoxy)silanes in their co-condensation reactions with main group or transition metal alkoxides as well as in their copolymerization reactions with each other or with organic molecules. This almost infinite modular design concept has led to the industrial application of coatings for transparent plastics, glasses, and metals to prevent these substrates from mechanical abrasion, permeation, or corrosion or to achieve decorative functions. Further passive optical properties can be realized by generating submicrometer surface patterns. By the integration of organic or inorganic dopants, like dyes or nanoparticles, highly sophisticated multifunctional hybrid polymers or nanocomposites are accessible and have become important to achieve active optical functions, e.g. switching, light harvesting, or storage media. Recently developed porous and dense bulk hybrid polymers have shown that the range of possible applications is not limited to surface refinement by coatings. This contribution reviews the present status as well as the perspectives of these types of advanced materials.