cryogel (rus. криогель) — 1) in chemistry and technology of inorganic materials – a highly porous monolithic or powdered product of freeze drying of frozen suspensions and gels and their subsequent heat treatment; 2) in chemistry and technology of high-molecular compounds – a product of low temperature effect (freezing, thawing) on solutions and colloidal dispersions of polymers and monomers, often followed by freeze-drying; 3) in medicine – a jelly-like fraction of blood plasma formed when the plasma is slowly cooled to a temperature of about +4ºC.

Description

The typical cryogel structure is formed during freezing, when the formation of relatively large crystals of solvent, usually ice, results in the displacement of solid particles into the space between them and in concentration of the suspension. In freezing of colloidal solutions the concentrating leads to the formation of a gel. Removal of the frozen solvent by sublimation leads to the formation of frame structures with large (up to hundreds of micrometres) pores in place of the removed ice crystals. The structural elements of the frame structure are composed of solid (usually nanosized) particles of the suspension. As a result, inorganic cryogels, in contrast to the polymer cryogels, are characterised by a bimodal distribution of porosity, in which the second peak corresponds to mesopores. Directional crystallisation of ice allows the creation of materials with large cylindrical pores and mesoporous frame walls; such carriers are promising for the creation of highly effective catalysts. The specific surface area of cryogels typically ranges from 300-400 m2/g (transition metal hydroxides) to 700-800 m2/g (carbon and silica cryogels).

Elastic highly porous frame structures with a pore size of tens or hundreds of micrometres based on dried polymeric cryogels are used as carriers of enzymes and immobilised cells in biocatalysis and biotechnology.

Important derivatives of polymeric cryogels are carbon cryogels obtained by carbonisation. They are used as sorbents and electrode materials of supercapacitors (carbon aerogels).

The removal of cryogel-forming blood plasma proteins by continuous mode cryo-filtration of the blood plasma produces a well-defined therapeutic effect in the treatment of rheumatoid arthritis.

Illustrations

Microphotograph of SiO2 cryogel produced by a transmission electron microscope. Auth
Microphotograph of SiO2 cryogel produced by a transmission electron microscope. Author: Oleg A. Shlyakhtin, Lomonosov Moscow State University. From personal files.

Author

  • Shlyakhtin Oleg A.

Sources

  1. Pajonk G.M. et al. From sol-gel to aerogels and cryogels // J. Non-Crystalline Solids. 1990. V. 121. P. 66–67.
  2. Lozinsky V. I. Cryogels on the Basis of Natural and Synthetic Polymers: Preparation, Properties and Applications// Wiley, 2002. V. 33. 252 pp.
  3. Shlyakhtin O. A., Young-Jei Oh, Inorganic cryogels for energy saving and conversion // J. Electroceramics. 2009. V. 23. P. 452–461.

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