Improving the properties of flexible hybrid-silica aerogels: addition of pores for a more lightweight material

Silica aerogels with their remarkable properties such as low density and thermal conductivity are prime candidates for a wide range of different applications, such as insulation materials in aviation. While pure silica aerogels are very brittle and difficult to handle, adapting the sol-gel process can result in organic-inorganic hybrid-materials with a high mechanical flexibility and a good hydrophobicity while still retaining a remarkable insulation performance. They were first investigated by Hayase et al. and are based on methyltrimethoxysilane (MTMS) and dimethoxydimethylsilane (DMDMS). For aviation applications the properties of this aerogel still have to be improved. Starting with recipes patented by the German Aerospace Center (DLR), the synthesis route was first investigated towards varying precursors and their ratios, using different solvents and mixtures, as well as testing a wide range of surfactants and catalysts. Mechanical, thermal, chemical and morphological properties of the samples were analyzed. With this presentation we will report on a set of experiments reducing the density. In a first approach gas bubbles were included in the aerogel network by distributing nitrogen gas into the sol during the gelation process. And in a second one the formation of large-scale pores was carried out using suitable filler-materials which can later be removed during washing processes. Both attempts result in an even lighter lightweight material and in addition lead to improved thermal and acoustic insulation performance, while still retaining a high mechanical flexibility and a good hydrophobicity. Those resulting aerogels can possibly outperform the state-of-the-art compressed fiberglass-mats in aviation applications