Preparation of Low-Density Aerogels at Ambient Pressure

Abstract

Low density aerogels have numerous unique properties which suggest a number of applications such as ultra high efficiency thermal insulation. However, the commercial viability of these materials has been limited by the high costs associated with drying at high pressures (supercritical), low stability to water vapor, and low mechanical strength. Normally, critical point drying is employed to eliminate the surface tension and hence, the capillary pressure, of the pore fluid to essentially zero. However, we show that by employing a series of aging and surface derivatization steps, the capillary pressure and gel matrix strength may be controlled such that gel shrinkage is minimal during rapid drying at ambient pressure. The properties (density, surface area, pore size, SAXS) of aerogel monoliths prepared from base catalyzed silica gels using this technique, supercritical CO2 drying, and supercritical ethanol drying are compared. An additional advantage of this approach is that the final gels are hydrophobic.

An overview on silica aerogels synthesis and different mechanical reinforcing strategies

“…The organic group will allow the aerogel to spring back to its original wet gel size without resulting in any crack within the gel. Other methods involve changing the capillary force experienced by the network through surface modification of the silica with alkyl groups, and providing a surface with lack of Si\OH groups [108]. Here, the general goal for the surface treatment is to produce a more hydrophobic surface by reacting the surface hydroxyl groups with hydrophobic reagents, such as [(CH 3 ) 3 -Si-OR] [109,110], or hexamethyldisilazane [111,112].…”

Aerogel-based thermal superinsulation: an overview

“…Thanks to the induced spring-back effect [77], thermal conductivities equivalent to these of large silica aerogel plates can be achieved with ambient dried analogues today. Furthermore, as a consequence of these direct/indirect sylilation processes, the dried materials exhibit hydrophobic properties.…”

Graphene oxide reinforced high surface area silica aerogels

“…In order to exploit aerogels commercially, cost effective drying routes are required. Consequently, many upsurges in aerogel research have focused on the determination of alternative preparation routes [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”