Synthesis, Optimization and Characterization of Flexible Hybrid-Silica Aerogels

Kurzfassung

This master thesis is a continuation of a project module with research proposal where the optimization of hybrid-silica aerogels in relationship with precursors ratios, acid or base catalyst, gelation temperature, and washing was analyzed and discussed. The main goal is to find correlations between the synthetic pathway of hybrid-silica aerogels and their thermal, mechanical, and hydrophobic properties by modifying the concentration and ratios of catalysts, precursors, solvent, and other relevant parameters like temperature. Hybrid-silica aerogels have been previously studied by Hayase and the German Aerospace Center (DLR - Deutsches Zentrum für Luft- und Raumfahrt) due to their low bulk density and high flexibility. The monoliths are prepared by using a mixture of the two different precursors methyl trimethoxysilane [CH3Si(OCH3)3, MTMS] and dimethyl dimethoxysilane [(CH3)2Si(OCH3)2, DMDMS]. They exhibit low thermal conductivities (12-15 mW/mK), low density values (0.1 g/cm3), high porosity and high surface area. Since the first report of hybrid-silica aerogels, many researchers have been working on the characterization and improvement of their properties. By using different molar ratios, different catalysts, or different gelation and aging times or temperatures. The properties of aerogels can be manipulated and controlled. As a result of their properties, the use in different applications can be analyzed, more specifically thermal and mechanical purposes. In the last years, thermal insulation has become an interesting topic concerning energy efficiency and saving. Every year new policies are proposed to create sustainable and environmental-friendly products and reduce global warming. However, the commercialization of hybrid-silica aerogels for thermal insulation has not been widespread, as the material faces some challenges in terms of water sensitivity and durability. In the case of hybrid-silica aerogels, the mechanical strength and elasticity have shown a remarkable performance after ambient pressure drying. Additionally, the whole synthetic process has been simplified in the last years. With this, the optimization of these aerogels in a shorter time span is possible, which also favors the applications of these materials into specific fields like aircraft manufacturing. Here it can be used to build the inner structure of the airplane cabin to reduce the overall weight and therefore consuming less fuel. Other further applications of hybrid-silica aerogels can be in the piping industry, cryogenic applications, and casting.