Mechanical Characterization Of Aerogels
As multifunctional porous nanostructured materials (e.g., thermally/acoustically insulating), aerogels are derived from their vast porosity and their high specific surface area and may also hold exceptional specific mechanical properties under certain conditions as well. In this chapter, the mechanical characteristics of aerogels are discussed in detail. First, the mechanical characterization of traditional aerogels is summarized, and then, the mechanical behavior of polymer crosslinked silica and vanadia (X-aerogels), as well as organic aerogels, is presented. Finally, the acoustic attenuation property is briefly discussed for polyurea aerogel. In polymer crosslinked aerogels, a few-nanometer-thick conformal polymer is coating on secondary particles, while the pores is not clogging, which thus preserves the multifunctionality of the native framework and improves the mechanical strength. The mechanical properties were characterized under both quasi-static loading conditions (dynamic mechanical analysis, compression, and flexural bending testing) and high-strain-rate loading conditions using a split Hopkinson pressure bar. We evaluated the effects of strain rate, mass density, loading–unloading, moisture concentration, and low temperature on the mechanical properties of aerogels. Digital image correlation was used to analyze the surface strains through ultrahigh-speed images for calculation of properties such as dynamic Poisson's ratio. A remarkable result is that crosslinked vanadia aerogels remain ductile even at −180 °C, indicating a property derived from interlocking and sintering-like fusion of skeletal nanoworms during compression. Due to the substantial improvement in the mechanical properties of X-aerogels with a small amount of polymeric crosslinking agent, purely polymeric aerogels with similar X-aerogel nanostructures were investigated. Therefore, in this chapter, the mechanical properties of organic aerogels including polyurea and polyurethane aerogels were also studied. Furthermore, a special attention has been carried out on the acoustic attenuation of polyurea aerogels by means of normal incidence sound transmission loss measurements. Polyurea aerogels showed unprecedented high sound transmission losses over a broad range of frequencies, a trend that clearly breaks the empirical "Mass Law" nature of the conventional acoustic materials.
H. Luo et al., "Mechanical Characterization Of Aerogels," Springer Handbooks, pp. 197 - 229, Springer, Jan 2023.
The definitive version is available at https://doi.org/10.1007/978-3-030-27322-4_8
Keywords and Phrases
Acoustic attenuation; Aerogel; Mechanical characterization; Nanostructure; Polyurea; Polyurethane; Silica; Vanadia
International Standard Serial Number (ISSN)
Article - Journal
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01 Jan 2023