Structural and mechanical characterization of ultra-low-density aerogels

This work presents an experimental study on the multi-scale relationship between structure and mechanical behavior. Peculiar low-density silica aerogels, in the range 0.02–0.09 g.cm −3 , are studied using compression tests (cyclic uniaxial and oedometer), dynamic mechanical analysis (DMA), atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The compression results show strain dependent internal friction, peaking at low strains before decreasing with densification while the structural characterization reveals silica nanoparticles with a radius of 2 nm. The AFM results exhibit localized mechanical heterogeneity, featuring both stiff elastic and adhesive responses. The post compression Scanning Electron Microscopy (SEM) images confirm irreversible plastic deformation of the aerogel network. The density modulus relation is extended to low-density silica aerogels (exponent 3.17). These results highlight new insights into the deformation mechanisms and energy dissipation of aerogels. They provide guidelines for the design of very low-density aerogels with tuned properties.