From Big Medical Encyclopedia

GELS (Latin gelo I stiffen) — the gelatinous or firm colloid systems consisting of the dispersion medium concluded in spatial structure (a grid, a framework) formed by the particles of a dispersed phase connected with each other.

Jellies gelatin, an agar, pectin, silicon to - you can be G.'s examples; such food stuffs as curdled milk, kissels, jelly, fruit jelly, cheese, bread, etc. Especially widely G. are presented in vegetable and animal organisms — all dense fabrics of organisms, napr, muscular and nervous, connecting fabrics, a vitreous of an eye, different biol, membranes are examples of difficult G.

Existence of internal spatial structure gives to G. properties of solids: they possess a certain form, edges can change only under the influence of external forces.

The nature of particles of a dispersed phase and mechanical characteristics of G. formed by them cause G.'s division on brittle and elastic.

Brittle G. are, as a rule, formed at coagulation of lyophobic sols (see), napr, hydrosols of vanadium pentoxide, ferric hydroxide, silicon dioxide, etc. Coupling of particles in spatial structure in such G. happens in separate points under the influence of vandervaal-sovy forces of an attraction. Brittle G. represent heterogeneous, two-phase systems. Owing to rigidity of particles of a dispersed phase and the framework formed by them brittle G.' volume during the drying or absorption of liquids by them, napr, at an ovodneniya, changes a little therefore brittle G. call also not bulking up. During rather full removal of a dispersion medium by drying from gelatinous brittle G. receive the high-porous solids sometimes called by xerogels, which are good sorbents (e.g., silica gel). Brittle G. contain a large number of capillaries therefore these G. can absorb significant amounts of various liquids moistening them.

Elastic G., or jellies, are formed at gelatination of solutions of high-molecular compounds. Spatial structure in this case results from coupling of flexible macromolecules. Thanks to their flexibility absorption or removal of a dispersion medium (solvent) from elastic G. is followed by considerable change of its volume. Absorption of liquids by elastic G. is processes selective concerning the nature of liquid and is always followed by increase in their volume — swelling (see) therefore elastic G. call also bulking up. Elastic G. represent homogeneous single mixing systems. Typical examples of elastic G. are G. gelatin, an agar, rubber and many other polymers and biopolymers.

Depending on the nature of a dispersion medium (water, alcohol, glycerin, etc.) hydrogels, alcogels, glycerogels, etc. distinguish.

When communication between particles of a dispersed phase in a space grid of G. fragile, G. show property thixotropies (see), i.e. can pass reversibly into sol or solution at mechanical influence (stirring, hashing). The sols or solutions of polymers received thus in the late state are gelatinated again.

Can undergo process of aging, a so-called syneresis; at the same time there is a reduction of volume of G. at preservation of its form; a part of a dispersion medium (solvent) separates.

Are widely applied in mikrobiol., dignity. - a gigabyte. and a wedge, laboratories for preparation of mediums, for carrying out some types electrophoresis (see), immunoelectrophoresis (see) and for gel filtering (see). Poliakrilamidny, agar and starched G. are used as carriers at an electrophoresis in laboratory diagnosis of such diseases as rheumatism, a myocardial infarction, pneumonia, schizophrenia, a thalassemia, etc.

Filtering of urine through gel of G-25 sephadex is applied to early diagnosis of pregnancy (release of the conjugated estrogen).

Bibliography: Weiss A. Macro-molecular chemistry of gelatin, the lane with English, M., 1971; In about yu c To and y S. S. Kurs of colloid chemistry, M., 1975, bibliogr.; P and p to about in S. P * Gelatinous condition of polymers, M., 1974.

V. P. Mishin.