62. AEROGEL-

♤ Aerogel is a synthetic porous material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and thermal conductivity. It is nicknamed frozen smoke, solid smoke, solid air or blue smoke owing to its translucent nature and the way light scatters in the material; however, it feels like expanded polystyrene (styrofoam) to the touch.

♤ Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly drawn off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. The first aerogels were produced from silica gels.

♤ Despite their name, aerogels are rigid, dry materials and do not resemble a gel in their physical properties; the name comes from the fact that they are derived from gels.Aerogels are good thermal insulators. Owing to its hygroscopic nature, aerogel feels dry and acts as a strong desiccant. The slight color it does have is due to Rayleigh scattering of the shorter wavelengths of visible light by the nanosized dendritic structure. This causes it to appear smoky blue against dark backgrounds and yellowish against bright backgrounds. Aerogels by themselves are hydrophilic, but chemical treatment can make them hydrophobic.