Effects of Density Tuning on Porous Structure and Compression Mechanics of Flexible Silica Aerogels via X-Ray Tomography

Kurzfassung

Aerogels are open-porous, lightweight materials exhibiting remarkable properties, such as high specific surface area and low thermal and sound velocity. Although they can be synthesized from various precursor materials, their practical applications are limited by their brittleness and high production cost. These challenges have been addressed by the development of flexible aerogels, which enable broader practical use and lower costs through the avoidance of expensive specialized drying procedures. One particularly promising silica aerogel, created by Kanamori and Hayase, combines high mechanical flexibility coupled with inherent hydrophobicity, enabling applications from drug delivery to insulation at cryogenic conditions. Subsequent research by Steffens demonstrated further optimization via density tuning, which our recent study confirmed also preserves elasticity at cryogenic temperatures. However, prior investigations revealed signs of diminishing flexibility in this aerogel with increasing maximum compressive strains. This issue is especially challenging because the microporous structure precludes physisorption analysis, leaving critical structural data inaccessible. Key questions thus arise: What mechanisms drive the non-elastic deformation at high strains and how is it influenced by density tuning? To address these questions, this study examines the deformation of porous structures in flexible silica aerogels using X-ray tomography. Aerogels of varying densities undergo quasistatic and cyclic compressive mechanical testing, with deformations tracked via X-ray. Slice-analysis of these deformations provides characteristic data on true pore structure, including sizes, lengths, and thicknesses. Additionally, digital volume correlation further elucidates potential non-elastic features. Collectively, these insights promise to accelerate the tuning and development of flexible aerogels for practical deployment.