From quasi-static to dynamic loading: Temperature and density effects in flexible silica aerogels

Flexible silica aerogels are highly porous lightweight materials with an unique flexibility, rendering them suitable for multifunctional applications in diverse fields, including aerospace and energy storage. However, such applications generally demand cryogenic conditions that require elastic flexibility and mechanical stability across a wide range of temperatures and dynamic mechanical stresses. This study investigates the viscoelastic behavior of flexible silica aerogels as well as the impact of tunable synthesis parameters, such as dilution and aging time, under dynamic mechanical and cryogenic conditions. Quasi-static testing revealed enhanced stiffening of the aerogels with increasing density as well as with decreasing temperature. The results further demonstrate power-scaling relations between the elastic modulus and density, with exponents ranging between 2–3 for long-aged samples, but extraordinarily 5–8 for short-aged ones. Dynamic mechanical analysis (DMA) revealed low energy dissipation and minor temperature sensitivity, suggesting that flexible silica aerogels have potential application in aviation or liquefied gas storage. The quasi-static and dynamic mechanical response could be tailored towards lower densities without sacrificing material stiffness by increasing aging time. Storage modulus peaks as well as differential scanning calorimetry (DSC) results both indicate short-term stiffening around −100 to −150 °C. This phenomenon can be hypothesised to be related to glass transitions or nitrogen interaction. It is recommended that further combined DMA and DSC studies are conducted to fully harness the potential of flexible silica aerogels in practical cryogenic applications.