What are aerogels?
Aerogels are a unique class of open-pore polymer foams that can be prepared from either organic or inorganic precursors. Aerogels are typically prepared using sol-gel chemistry, starting with liquids that form tiny sol particles, which eventually connect together in chain-like fashion to make a semi-solid gel. When the solvent is removed from the wet gel and replaced by air in a manner that does not collapse the delicate gel structure, a solid aerogel results. What makes the aerogels unique is their nano-sized structure; they consist of particles and pores both of which are smaller than wavelengths of visible light. This unique nano-structure is responsible for many of the unusual acoustic, mechanical, optical and thermal properties observed for aerogels
With the lowest density, highest thermal insulation, lowest refractive index, dielectric constant and sound speed, and highest surface area per unit volume of any solid, aerogels exhibit an amazing range of properties which are not observed in any other kind of material. The following table summarizes physical properties of typical silica aerogels