EMULSIONS

From Big Medical Encyclopedia

EMULSIONS (emulsio, singular; lat. emulsum which is milked dry) — disperse systems with a fluid dispersion medium and a liquid dispersed phase. Process of receiving E. — emulsification — has big fiziol. value at absorption and assimilation by an organism of fats (see), which only in the form of E. can be split hydrolytic by lipases (see), and also at education biol. membranes (see Membranes biological), ensuring normal functioning of many enzymes (see), etc. Some pharmaceuticals subject to dispersion (see) and apply in the form of emulsions (see. Dosage forms). AA. are widely used in the food industry, at production of cosmetics, pesticidal drugs, in a radiology, the photo, soap manufacture, production of dyes, lubricant cooling liquids, etc. Whole milk, cream, natural latex of rubber-bearing plants, crude oil represent emulsions.

Distinguish lyophilic and lyophobic E. Liofilnye E. — colloid systems (see Colloids), for to-rykh the equilibrium, not changing in time particle distribution by the sizes, i.e. thermodynamic stability is characteristic (see Thermodynamics). A typical example of lyophilic emulsions are micellar solutions of colloid surfactants and solutions of the high-molecular compounds (see) having the sites which are sharply differing on polarity; proteins treat such systems, e.g., (see). Lyophilic E. are formed spontaneously.

Lyophobic E. are characterized by an unstable state of particles (drops) of a liquid dispersed phase. They are divided, in turn, into two types: straight lines — with drops of unpolar liquid in the polar environment (like «oil in water») — and the return, or invert (like «water in oil»). Change of structure lyophobic E. or external impact on them can be led to transformation of a direct emulsion into the return and vice versa. It is possible to determine type of an emulsion by its conductivity (at an emulsion, in a cut a dispersion medium is water, conductivity is many orders higher than conductivity of the return E.), on blendability with polar and non-polar solvents (see) or to dissolve polar and unpolar dyes (see). Lyophobic E. are formed at emulsification or owing to condensation formation of drops of a dispersed phase in peresyshchenny solutions or fusions.

Emulsification can be made by dispersion or polycondensation (see Condensation in chemistry). Lyophobic E. arise also at electric emulsification. Mechanical dispersion E. it is carried out by hashing by means of mixers, a transmission of mixes of phases E. through narrow gaps between solid surfaces in so-called colloid mills. Dispersion by means of ultrasound is widely applied. At condensation emulsification a dispersed phase E. it is formed of the fluid particles which are gradually enlarged at first to the size of a particle of colloids (0,001 — 0,1 microns) and further to the sizes of large drops. It results from supersaturation of homogeneous solution of liquid in liquid (see Solutions) owing to decrease in their mutual solubility at addition to such solution of the third liquid or at its cooling is up to one temperature lower than critical.

Lyophobic straight lines E. thermodynamic are unstable, the droplets of liquid forming in such E. a dispersed phase, at collision inevitably merge. This process called by a koalestseption (see) continues until droplets do not merge in a continuous layer. Stabilization such E. it is made by substances-emulsifiers, action to-rykh is based on reduction of size of interfacial surface intention (see) and increase in dispersion of drops of a dispersed phase. As emulsifiers usually serve ionogenic poverkhnostnoaktivny substances (see Detergents), to the Crimea soaps belong (see) with an ionizable group of CO O of Na, sulphonates, with an ionizable group of S03Na, hydrocarbon radicals with

a carbon chain length from 12 to 18 carbon atoms. Molecules of such emulsifiers of a difilna, i.e. have identical affinity to polar (water) and unpolar (oil) liquid. They are adsorbed on an interface of two phases so that the carbon chain of the hydrocarbon radical is shipped in oil, and its polar group is in water. An ionizable group of emulsifier, dissociating in water, forms organic anion, e.g. R — SOO“ where R — the hydrocarbon radical. Thereof on a surface of droplets of oil there is a double electric layer causing stability diluted E. — unstructured liquids, the dispersed phase in to-rykh makes apprx. 1%. In concentrated E. — the structured systems — the layer of molecules of emulsifier on a surface of drops of a dispersed phase is a factor of stability: high viscosity and mechanical strength of the layer of molecules of emulsifier adsorbed on them prevent merge of drops. Such layer can b*yt is formed as ionogenic (anionic, cation-active, ampholytic), and nonionic emulsifiers. Emulsifiers divide into two groups depending on that what formation of type E. they cause. Emulsifiers for E. direct type are usually more hydrophilic and are better dissolved in water, than in oil. Them are long-chain hydrophilic connections of both polar, and unpolar type: salts of alkali metals and carboxylic to - t, alkylsulfates, alkylsulfonates, vegetable adhesives, proteins, carbohydrates (polysaccharides). Oleophilic emulsifiers, soluble in organic environments — fat to - you, fatty alcohols, ethyl cellulose, the alkyd resins — usually form E. return type. Also thinly crushed substances, not soluble in liquids of both phases can be emulsifiers. Solid hydrophilic emulsifiers for E. direct type are clays and hydroxides, carbonates and sulfates of metals, for E. the return type as emulsifiers serve powder of the soot which is formed at combustion of gas and sulfides of heavy metals (oleophilic solid emulsifiers). The principle of effect of solid emulsifiers consists in formation of the layer on a surface of particles of a dispersed phase interfering coalescence.

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Type and stability E. depend by nature emulsifier. If in E. to enter the reagents changing the nature of emulsifier, there can be E. Ustoychivost E. address depends also on a quantitative ratio of a dispersion medium and a dispersed phase. AA., containing insignificant quantity of a dispersion medium, have the increased stability since the drops of a dispersed phase divided only by a pellicle of a dispersion medium are practically not mobile. To destruction E. addition of dezemulgator, change of reaction of the environment promote (see. Hydrogen ion exponent) and its electrolytic structure (see Electrolytes), influence on E. electric field, gravitation and heating. In the equipment process of destruction E. is not less important, than their receiving, it is used, e.g., in the petrochemical industry during the processing of crude oil.

The emulsifying properties of bile acids (see) allow them to carry out one of the main functions — transfer of lipids in an aqueous medium. Already in fabrics pechen and (see) with the participation of bilious to - t are formed (or finally form) the micelles which received the name of a lipidic complex of bile (see). Thanks to inclusion in this

complex the lipids cosecreted by a liver and nek-ry another low solubility substances in water are transferred to intestines as a part of bile in a look? homogeneous solution. Salts bilious to - t participate in intestines in emulsification of fat. They are a part of the emulsifying system (a saturated monoglyceride + unsaturated fat to - that + salt bilious to - you), playing in it a role of the stabilizing emulsifier. After a lipolysis a lipase products of this splitting — monoglycerides and fat to - you — form micellar solution. Thanks to emulsifiers — salts bilious to - the t — in intestines arises steady E., micelles a cut contain cleavage products of fat, cholesterol and phospholipids. In such look these substances from particles of a dispersed phase of an emulsion (i.e. from the place of hydrolysis of lipids) are transferred to the soaking-up surface of an intestinal epithelium (see Absorption). In the form of micellar solution in went. - kish. a path also fat-soluble vitamins arrive (see). At experimental removal of bile from intestines and impossibility of convertion of fat of food in the emulsified state absorption of lipids in intestines decreases by 50%, besides, the phenomena of a vitamin deficiency (see), including a hypovitaminosis K.

Biol develop. membranes of live organisms are under construction according to the mechanism of education lyophilic E. Basic structural elements biol. membranes — phospholipids (see Phosphatides) in an aqueous medium represent micellar solutions. During the processing of such solutions ultrasound forms so-called liposomes, the double lipidic layer to-rykh (bisly) is similar to structure of a dimolecular layer of natural membranes. Liposomes widely use for studying of properties of biological membranes, and also for introduction to an organism of missing enzymes at replaceable enzymotherapy (see).

Blood serum at a row fiziol. and patol. states represents fatty E. Stepen of stability such E. serves as the informative test in laboratory diagnosis during the phenotyping of giperlipoproteinemiya (see L and-poproteidy).

Carry an alimentary lipemia to these states (see) or the lipemia which was a consequence of the strengthened mobilization fat to - t from fat depos (at starvation, blood loss, heavy anemias, a diabetes mellitus, pancreatitis, damages of the kidneys which are followed by a nephrotic syndrome, glycogenoses), whether at stimulation of synthesis -

poproteid of very low density or delay of their catabolism, whether-poproteidlipazy and also at genetically caused insufficiency of enzyme (see).

Bibliography: Clayton V. Emulsions,

the lane with English, M., 1950; L and p and t about in Yu. S. Colloid chemistry of polymers, Kiev, 1984; Phenotyping of giperlipoproteidemiya, sost. A. N. Klimov, etc., M., 1975; Shch at-kin E. D., Pertsov A. V. and Amelina E. A. Colloid chemistry, M., 1982.

N. V. Prokazova.

Яндекс.Метрика