Mechanical Characterization of Aerogels

Abstract

Aerogels are multifunctional porous nanostructured materials (e.g., thermally/acoustically insulating) derived from their vast internal empty space and their high specific surface area. Under certain conditions, aerogels may also have exceptional specific mechanical properties as well. The mechanical characteristics of aerogels are discussed in this chapter. First, we summarize work conducted on the mechanical characterization of traditional aerogels, and second, we describe the mechanical behavior of polymer crosslinked aerogels. In polymer crosslinked aerogels, a few nanometer thick conformal polymer coating is applied on secondary particles without clogging the pores, thus preserving the multifunctionality of the native framework while improving mechanical strength. The mechanical properties were characterized under both quasi-static loading conditions (dynamic mechanical analysis, compression, and flexural bending testing) as well as under high strain rate loading conditions using a split Hopkinson pressure bar. The effects of strain rate, mass density, loading–unloading, moisture concentration, and low temperature on the mechanical properties were evaluated. Digital image correlation was used to measure the surface strains through analysis of images acquired by ultrahigh-speed photography for calculation of properties including dynamic Poisson’s ratio. Among remarkable results described herewith, crosslinked vanadia aerogels remain ductile even at −180°C, a property derived from interlocking and sintering-like fusion of skeletal nanoworms during compression.