OPALECTION(lat. opalus opal) - the phenomenon of light scattering by colloidal systems and solutions of macromolecular substances, observed in reflected light. O. is due to the diffraction of light produced by colloidal particles or macromolecules.

Measurement of O.'s intensity, made with the help of nephelometers and special photometers, is widely used in determining the concentration of proteins, lipids, nucleic acids, polysaccharides and other macromolecular substances in biol, liquids, as well as in measuring a mol. weight (mass) of biopolymers in solutions and micellar mass of colloidal particles (see Nephelometry). The phenomenon of diffraction light scattering is the basis for determining the size and shape of colloidal particles using an ultramicroscope (see); it is a reliable sign for distinguishing colloidal solutions from true solutions of low molecular weight substances. Opalescence explains the turbidity of colloidal solutions and solutions of high molecular weight substances in their side illumination, as well as the different color of the same colloidal solution when viewed in transmitted and reflected light. So, for example, colloidal solutions of sulfur in transmitted light are transparent and have a red color, in reflected light they are cloudy and colored blue.

O. of colloidal solutions of gold was first studied by Faraday (M. Faraday) in 1857. This phenomenon was studied in more detail by J. Tyndall, who published in 1869 the results of his observations. He discovered that in the dark the path of a strong beam of light passing through any colloidal solution, when viewed from the side, looks like a luminous cone (the so-called Tyndall cone).

Theoretically, the O. phenomenon was substantiated by J. W. Rayleigh in 1871. For spherical, non-conductive electric current particles whose dimensions are small compared to the wavelength of the light incident on them, Rayleigh derived the following equation:

where I is the light intensity observed in the direction perpendicular to the incident light beam; n is the number of light-scattering particles per unit volume; v is the volume of the particle, λ is the wavelength of the incident light; I 0 - the intensity of the initial beam of light; K is a coefficient of proportionality, the value of which depends on the difference between the refractive indices of light of the dispersed phase and the dispersion medium and on the distance from the particles to the observer.

If the light passing through the colloidal system is not monochromatic, then short-wavelength rays are scattered to a greater extent, which explains the different coloring of the colloidal solutions when observed in transmitted and reflected light.

Light scattering produced by coarsely dispersed systems (suspensions and emulsions) differs from optical scattering in that it is observed not only in reflected but also in transmitted light and is due to the reflection and refraction of light by microscopic particles. It is easy to distinguish O. from fluorescence (see) by introducing a red light filter on the path of the beam, which, delaying the short-wave part, quenches fluorescence, but does not eliminate O.

Bibliography: Voyutsky S. S. Kurs colloid chemistry, M., 1975; Y and rgyo n-with about n with B. Natural organic macromolecules, trans. from English, p. 72, Moscow, 1965; Williams W. and Williams X.’ Physical chemistry for biologists, trans. from English, p. 442, M., 1976.

ELECTROKINETIC PROPERTIES OF COLLOIDS

Electrokinetic phenomena are divided into two groups: direct and reverse. The direct ones include those electrokinetic phenomena that occur under the action of an external electric field(electrophoresis and electroosmosis). The reverse is called electrokinetic phenomena, in which, during the mechanical movement of one phase relative to another, a electric potential(percolation potential and sedimentation potential).

Electrophoresis and electroosmosis were discovered by F. Reiss (1808). He discovered that if two glass tubes are immersed in wet clay, filled with water and electrodes are placed in them, then when a direct current is passed, clay particles move towards one of the electrodes.

This phenomenon of movement of particles of the dispersed phase in a constant electric field was called electrophoresis.

In another experiment, the middle part of a U-shaped tube containing water was filled with crushed quartz, an electrode was placed in each elbow of the tube and passed D.C.. After some time, in the knee, where the negative electrode was located, a rise in the water level was observed, in the other - a drop. After turning off the electric current, the water levels in the elbows of the tube were equalized.

This phenomenon of movement of a dispersion medium relative to a stationary dispersed phase in a constant electric field is called electroosmosis.

Later, Quincke (1859) discovered a phenomenon inverse to electroosmosis, called the percolation potential. It consists in the fact that when a fluid flows under pressure through a porous diaphragm, a potential difference arises. Clay, sand, wood, and graphite were tested as diaphragm materials.

The phenomenon, the reverse of electrophoresis, and called the sedimentation potential, was discovered by Dorn (1878). When particles of the quartz suspension settled under the action of gravity, a potential difference arose between the levels of different heights in the vessel.

All electrokinetic phenomena are based on the presence of a double electric layer at the boundary of the solid and liquid phases.

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18. Special optical properties of colloidal solutions due to their main features: dispersion and heterogeneity. On optical properties dispersed systems greatly influenced by the size and shape of the particles. The passage of light through a colloidal solution is accompanied by such phenomena as absorption, reflection, refraction and scattering of light. The predominance of any of these phenomena is determined by the ratio between the particle size of the dispersed phase and the wavelength of the incident light. AT coarse systems mainly the reflection of light from the surface of the particles is observed. AT colloidal solutions particle sizes are comparable to the wavelength visible light, which determines the scattering of light due to the diffraction of light waves.

Light scattering in colloidal solutions manifests itself in the form opalescence– a matte glow (usually of bluish hues), which is clearly visible against a dark background with side illumination of the sol. The cause of opalescence is the scattering of light on colloidal particles due to diffraction. Opalescence is associated with a phenomenon characteristic of colloidal systems - Tyndall effect: when a beam of light is passed through a colloidal solution from directions perpendicular to the beam, the formation of a luminous cone in the solution is observed.

Tyndall effect, Tyndall scattering - optical effect, scattering of light during the passage of a light beam through an optically inhomogeneous medium. It is usually observed as a luminous cone (Tyndall's cone) visible against a dark background.

It is typical for solutions of colloidal systems (for example, metal sols, dilute latexes, tobacco smoke), in which particles and their environment differ in refractive index. A number of optical methods for determining the size, shape and concentration of colloidal particles and macromolecules are based on the Tyndall effect. .

19. Zoli - these are poorly soluble substances (salts of calcium, magnesium, cholesterol, etc.) existing in the form of lyophobic colloidal solutions.

A Newtonian fluid is a viscous fluid that obeys Newton's law of viscous friction in its flow, that is, the tangential stress and velocity gradient in such a fluid are linearly dependent. The proportionality factor between these quantities is known as the viscosity.

Newtonian fluid continues to flow even if external forces are very small, as long as they are not strictly zero. For a Newtonian fluid, viscosity, by definition, depends only on temperature and pressure (and also on chemical composition, if the liquid is not pure), and does not depend on the forces acting on it. A typical Newtonian fluid is water.

A non-Newtonian fluid is a fluid in which its viscosity depends on the velocity gradient. Typically, such liquids are highly inhomogeneous and consist of large molecules that form complex spatial structures.

The simplest illustrative household example is a mixture of starch with a small amount of water. The faster the external impact on the binder macromolecules suspended in the liquid, the higher its viscosity.

Opalescence critical opalescence - a sharp increase in the scattering of light by pure substances (gases or liquids) in critical conditions, as well as solutions when they reach critical mixing points. It is explained by a sharp increase in the compressibility of a substance, as a result of which it increases number density fluctuations, on which light(transparent substance becomes cloudy).

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See what "OPALECTION" is in other dictionaries:

Scattering Dictionary of Russian synonyms. opalescence n., number of synonyms: 1 scattering (18) ASIS synonym dictionary. V.N. Trishin ... Synonym dictionary

CRITICAL A sharp increase in the scattering of light by pure substances in critical states ... Physical Encyclopedia

An optical phenomenon in which the sun appears reddish and distant objects (distance) appear bluish. It is caused by the presence of the smallest dust particles in the air; most often and most strongly observed in the masses of marine tropical air ... Marine Dictionary

Iridescent play of colors, characteristic of opals and other gels, apparently due to the cellular structure. O. of crystalline minerals, for example, quartz, is usually associated with an abundance of regularly faceted voids. Geological dictionary: in 2 volumes. M.: Nedra. Under … Geological Encyclopedia

opalescence- a sharp increase in the scattering of light in the environment, clouding of the environment ... Source: METHODOLOGY FOR EXPRESS ASSESSMENT OF THE ENVIRONMENTAL SITUATION AT A MILITARY FACILITY (approved by the Ministry of Defense of the Russian Federation on 08.08.2000) ... Official terminology

opalescence- and, well. opalescence, germ. Opaleszenz lat. see opal + suffix escentia denoting weak action. physical The phenomenon of light scattering by a turbid medium, due to its optical inhomogeneity. Krysin 1998. Opalescent. Liquid air when we ... ... Historical Dictionary of Gallicisms of the Russian Language

opalescence- Milky or pearl color or luster of the mineral. [English Russian Gemological Dictionary. Krasnoyarsk, KrasBerry. 2007.] Topics gemology and jewelry production EN opalescence … Technical Translator's Handbook

opalescence- is the scattering of light by a colloidal system in which the refractive index of the particles of the dispersed phase differs from the refractive index of the dispersion medium. general chemistry: textbook / A. V. Zholnin ... Chemical terms

Opalescence 1) an optical phenomenon consisting in a sharp increase in the scattering of light by pure liquids and gases when a critical point is reached, as well as solutions in critical points mixing. The reason for the phenomenon is a sharp increase ... Wikipedia

- (opal + lat. escentia suffix meaning weak action) phases. the phenomenon of light scattering by a turbid medium due to its optical inhomogeneity; observed, for example, when illuminating most colloidal solutions, as well as in substances in ... ... Dictionary foreign words Russian language