Effects of nanoporosity on the mechanical properties and applications of aerogels in composite structures

Aerogels are ultralight solids with nanoporous structure and are one of the world’s lightest materials available in the market. It is a dry gel, principally made up of 99.8% of air and weighing just around three times that of air. The first aerogels were realized in 1931, when Kistler (J Phys Chem 36:52-64, 1932) attempted to remove liquid from a wet gel. It started out with the testing of the hypothesis that the liquid in a jelly can be replaced by a gas so as to avoid the collapse of the wet gel. He postulated that it was possible to slowly expand the supercritical fluid within a gel and obtain an air-filled non-collapsed gel structure. He subsequently succeeded in producing silica aerogels with densities in the range 20-100 kg/m3, as well as aerogels of alumina, tungsten, ferric, and stannic oxides. Today, silica aerogel is frequently used in nanocomposites for their light weight and excellent thermal insulating properties. In this chapter, we document some of the silica aerogel-filled carbon composite sandwich structures we have recently developed and also numerically examine the underlying mechanisms which enable silica aerogels to possess extreme insulation properties and especially how pore size plays a major role.