gel (rus. гель) — (from Latin “gelo” (solidifying) or “gelatus” (frozen, motionless)): 1) in colloid chemistry – a disperse system with a liquid medium in which particles of the dispersed phase form a spatial structural grid; 2) in polymer chemistry – infusible and insoluble product of polycondensation or polymerisation.

Description

Gel is a jelly-like body that can maintain its shape and is characterised by its elastic behaviour. The spatial grid is formed by particles of the dispersed phase that are interconnected by means of intermolecular interaction.

Gels can be formed by coagulation of sols, when contacts between the particles are easily and reversibly destroyed by mechanical and thermal effects (see sol-gel transition). All gels are divided into hydrogels and organogels having water and organic compounds, respectively, as the dispersion medium. Drying of gels, depending on the method of removing the dispersion medium, results in obtaining aerogels, ambigels, cryogels and xerogels, significantly differing in density and micromorphological characteristics.

Most gels are thermodynamically unstable and prone to aging, which is accompanied by changes (mostly shrinkage and compaction) of the spatial grid.

Examples of substances that form gels are: amorphous aluminium hydroxide (gel) of varying composition Al2O3·nH2O, silica hydrogels (nSiO2·mH2O). Their drying results in alumogel and silica gel, respectively – porous materials used as sorbents and catalyst carriers.

In chemistry and polymer technology gels are water-swollen ion exchange resins, cross-linked dextrans (sephadexes) and polyacrylamides; liquid hydrocarbons – swollen copolymers of styrene and divinylbenzene, as well as rubber materials based on natural and some synthetic rubbers, hydrogels of gelatin, agar, polyvinyl alcohol; organogels of some cellulose ethers and acrylonitrile.

Authors

  • Eremin Vadim V.
  • Shlyakhtin Oleg A.
  • Streletskiy Alexey V.

Source

  1. Gels // Chemical encyclopedia (in Russian). V. 1. — M.: Sovetskaja ehnciklopedija, 1988. p. 513.

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