From sol-gel to aerogels and cryogels

Pajonk, G.M.; Repellin-Lacroix, M.; Abouarnadasse, Sadik; Chaouki, Jamal; Klavana, Danilo

doi:10.1016/0022-3093(90)90106-v

Cited by 62 publications

(28 citation statements)

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“…The extraction can then be performed at relatively low temperature 8,9 , albeit at high pressure. Freeze drying methods 10,11 first freeze the wet gel at low temperature and then allow the solvent to sublimate directly to a vapor form, again avoiding crossing the liquid-vapor phase line. The ambient pressure method uses surfactants to reduce the surface tension effects or polymers to strengthen the nanostructure, followed by drying of the wet gel at ambient pressure [12][13][14][15][16] .…”

Section: Si(och 3 ) 4 + H 2 Omentioning

confidence: 99%

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

Carroll

Anderson

Gorka

2014

JoVE

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A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10 -3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/ pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes. Video LinkThe video component of this article can be found at

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Section: Si(och 3 ) 4 + H 2 Omentioning

confidence: 99%

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

Carroll

Anderson

Gorka

2014

JoVE

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“…2,3 The wet gel structure frequently exhibits a mass fractal feature 4 consisting of a continuous solid network imbibed in a liquid phase, which can occupy until about 95 to 98 % of the volume sample. 5,6 Drying is the most critical step of the sol-gel processing for obtaining monoliths or if the textural properties of the wet gels are intended to be preserved. 7 Supercritical drying ͑aerogels͒, freeze drying ͑criogels͒, and evaporation drying ͑xerogels͒ 1 are the usual methods in dried gels production.…”

Section: Introductionmentioning

confidence: 99%

Small-angle x-ray scattering study of the structural evolution of the drying of sonogels with the liquid phase exchanged by acetone

et al. 2004

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The structural evolution on the drying of wet sonogels of silica with the liquid phase exchanged by acetone, obtained from tetraethoxisilane sonohydrolysis, was studied in situ by small-angle x-ray scattering ͑SAXS͒. The periods associated to the structural evolution as determined by SAXS are in agreement with those classical ones established on basis of the features of the evaporation rate of the liquid phase in the obtaining of xerogels. The wet gel can be described as formed by primary particles ͑microclusters͒, with characteristic length a ϳ0.67 nm and surface which is fractal, linking together to form mass fractal structures with mass fractal dimension Dϭ2.24 in a length scale ϳ6.7 nm. As the network collapses while the liquid/vapor meniscus is kept out of the gel volume, the mass fractal structure becomes more compacted by increasing D and decreasing , with smoothing of the fractal surface of the microclusters. The time evolution of the density of the wet gels was evaluated exclusively from the SAXS parameters , D, and a. The final dried acetone-exchanged gel presents Porod's inhomogeneity length of about 2.8 nm and apparently exhibits an interesting singularity D →3, as determined by the mass fractal modeling used to fit the SAXS intensity data for the obtaining of the parameters and D.

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“…The term "cryogel" was first introduced into the field of inorganic materials by Klvana and Pajonk [1][2][3], who considered cryogels, together with xerogels and aerogels, as one of the possible drying products of SiO 2 .nH 2 O-and Al 2 O 3 .nH 2 Obased hydrogels. In their experiments, freezing and freeze-drying of wet gels were used to avoid pore collapse due to the extreme surface tension effects of water removal during atmospheric drying and to retain most of the tiny morphological features of gels in the dried state.…”

Section: Introductionmentioning

confidence: 99%

Inorganic Cryogels

Shlyakhtin¹

2014

Polymeric Cryogels

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From sol-gel to aerogels and cryogels

Cited by 62 publications

References 1 publication

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

Small-angle x-ray scattering study of the structural evolution of the drying of sonogels with the liquid phase exchanged by acetone

Inorganic Cryogels

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