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A new route to aerogels: Monolithic silica cryogels

“…The shift of mesopore size toward larger values may actually have turned most mesopores into macropores. All the new textural features encountered in cryogels (higher percentage macroporosity, larger mesopores and wider and more complex mesopore size distributions) are consistent with the idea that the cryogel pore structure is modified by frozen solvent crystals in the gel network [17]. Textural and porosity characterization reveals that the monolithicity in our materials is linked to a homogeneous porosity system, either made of simple cylindrical pores (M and E6 cryogels) or, similar to aerogels, spherical pores connected by cylindrical channels (Tm cryogels).…”

“…More recently, freeze-drying methods have often been mentioned as a possible approach for drying gels [13,14], but it is generally believed that cryogels prepared by this procedure can only be obtained as powders. Nevertheless, a significant amount of work has been carried out in the field of cryogels [15], from pioneering work on silica cryogels [16,17], to carbon [18,19], alumina [20] and zirconia [21] cryogels. The resultant cryogels usually have high surface area and porosity, but, as mentioned above, they are obtained as powders [22] or thin layers [15].…”

Silica aerogels prepared via rapid supercritical extraction: Effect of process variables on aerogel properties

“…Freeze drying the wet gel results in cryogels. Pajonk et al [5] and Kalinen et al [6] describe the process for making cryogels, which results in a non-transparent powder. In the case of freeze drying, Kalinen et al report that the microstructure of their cryogels is governed by the size of ice microcrystals that are formed during the freeze drying process.…”

Analysis of a rapid supercritical extraction aerogel fabrication process: Prediction of thermodynamic conditions during processing

“…Ambient pressure drying techniques usually include the use of surfactants [15], aging to stiffen the microstructure [16] or manipulation of the surface chemistry [17]. There has also been work using freeze drying, whereby the solvent is sublimated from the wet gel [18,19].…”