"When the tide of misfortune moves over you, even jelly will break your teeth."
Persian proverb
Gels arejellylike colloidal substances that have a liquid body containing a network of interconnecting 2-5 nanometer nanoparticles surrounding 100-nanometer pores. If the liquid is carefully removed and replaced by a gas, you have an aerogel. These are light, low-density solid foams, sometimes called "frozen smoke."
Steven S. Kistler (1900-1975), a chemical engineer at the College of the Pacific in California, was investigating the gels produced by the acidic condensation of aqueous sodium silicate. He noticed that gels shrank and cracked as they dried, due to the high surface tension of the water they contained. Kistler managed to stop the volume reduction by replacing the water with low-surface-tension alcohol. The end-product, aerogel, was simply the unshrunk, microporous, solid component of the original gel.
In the late 1970s French rocket engineers considered aerogels—whose 99 percent air content makes them ideal thermal insulators—as a safe storage medium for rocket fuels. Their silica aerogel was cheap and easily produced, using a tetramethylorthosilicate base and methanol hydrolization. The Stardust space mission— which collected comet dust—also used aerogels.
