From Big Medical Encyclopedia

SUSPENSIONS (Latin suspensio lifting, suspension) — disperse systems, in to-rykh a dispersion medium serves liquid, and a dispersed phase — solid particles with the sizes exceeding 10 - 5 see Suspensions of cells (erythrocytes, bacteria, etc.) Pages are. Many pharmaceuticals use in medical practice in the form of S. (see. Dosage forms ). The high-concentrated S. called by pastes apply in medicine and perfumery. Villages of pigments in water and organic liquids use as dyes in histology and for other purposes. Are of exclusively great importance of S. in the nature and the equipment. Many geological and soil processes are connected with S.'s education and their physical. - chemical transformations (formation of sedimentary breeds, soils, formation of deltas of the rivers, etc.). Cement and limy S. widely apply in construction business. In production of rubber, stonewares, papers, photographic materials, etc. also use Page.

Properties C. as coarse-dispersion systems in many respects differ from properties sols (see), representing extremely high-disperse systems, particle sizes of a dispersed phase to-rykh are ranging from 10 - 5 to 10 - 7 see S.'s Particles reflect or refract light owing to what they are seen at microscopy, and S. mutna, both in reflected, and in a transmitted light. S.'s particles are not capable to diffusions (see) therefore S. do not find osmotic pressure (see). Paper, glass, ceramic filters do not pass

S. S. particles — kinetic unstable systems that is shown depending on density of a dispersed phase and a dispersion medium in sedimentations (see) or emerging (flotation) of particles. Speed of particle sedimentation considerably increases in S. during the centrifuging (see).

To properties C., the general with properties of sols, existence of electric charge and, therefore, the electrokinetic potential of particles belongs. The last can be measured on the speed of particle motion of S. in the field of direct electric current and has size approximately same, as at colloid particles (see. Colloids ). Electric charge of particles of S. as well as colloid particles, resulting from preferential adsorption of the ions which are in a dispersion medium or owing to dissociation of ionizable group of a surface of particles of S., is one of factors of aggregate stability of Page. Aggregate stability of S. is gained also in that case when their particles are covered with solvation shells (if a dispersion medium is water — hydrated covers), i.e. the covers consisting of molecules of a dispersion medium (see Solvation). Solvation shells around S.'s particles arise during the wetting of particles a dispersion medium. Therefore hydrophilic powders, napr, powders of quartz, chalk, aluminum hydroxide, well water wet, form agregativno steady S. in water; the soot having water repellency and which is well moistened by benzene gives steady S. in benzene. If extent of wetting of particles is small and solvation shells around particles are not formed, then S. will agregativno be unstable that is shown by adhesion of particles under the influence of intermolecular forces of adhesion in larger units and their separation (subsidence or emerging) from a dispersion medium. This process similar to coagulation of sols, sometimes call flocculation (see). At flocculation of the concentrated S., especially with asymmetric particles of a dispersed phase, often there are structured systems, similar to gels (see), possessing a thixotropy (see). Hydrophilic powders in unpolar liquids, napr, in benzene, or hydrophobic powders in polar liquids, napr, in water, form agregativno unstable S. Odnako these S. it is possible to make agregativno steady by addition to a dispersion medium of poverkhnostnoaktivny substances (see. Detergents ). Molecules of such substances, napr, olein to - you, being adsorbed on S.'s particles, do possible education around particles of solvation shells.

Villages receive as well as sols, method condensation (see) or method dispersions (see).

Bibliography: Voyutsky S. S. Course of colloid chemistry, M., 1975; Figurov-s to and y N. A. Sedimetric analysis, M. — JIj, 1948.

V. P. Mishin.