Production of different kinds of aerogel varies a bit. In general aerogel derive from a gel in which the liquid component of the gel has been replaced with gas.
But a gel precursor is a chemical or mixture of chemicals that can be activated toward molecular nucleation into small colloidal particles. A gel forms when a solution of these dispersed nanoparticle colloids (also called “sols”) are induced to form a semi-solid form via interparticle condensation. At the gel point, the liquid phase within a gel structure is not able to diffuse freely and will not flow or change shape if the volume is tilted on an axis.
When the chemistry approach is designed correctly, the solid in the wet gel phase can define a high surface area network of pores that confine the liquid within the structure. Aspen Aerogels processes various materials to contain liquid filled pores that average about ten nanometers (a nanometer is 1/100,000th the diameter of a human hair). The size of the pores can be controlled during the production process.
Če je gel ustvarjen iz vodne faze, se poltrdna snov imenuje hidrogel, vodo pa je pred sušenjem potrebno zamenjati z organskim raztopilom.
If the gel is formed from a water phase, the resulting semi-solid is called a hydrogel, and the water must be exchanged with organic solvent prior to drying. If the gel is formed within an alcohol phase, the resulting semi-solid is called an alcogel, and can be dried directly. This is accomplished by increasing the temperature and pressure of the solvent phase inside of the gel structure beyond its critical point.
This “supercritical” extraction condition lowers the surface tension between the liquid and the solid pore surfaces so that depressurization of the system at temperatures above the critical temperature leaves the pore structure filled with gas.