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 shutdown 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 disperse 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 is an optical effect, the scattering of light when a light beam passes 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 OPALECTION - 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 the number of density fluctuations in it increases, on which light is scattered (a transparent substance becomes cloudy).

Big Encyclopedic Dictionary. 2000 .

Synonyms:

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

Moonshine, which we are used to seeing on the screens, does not mean ideal at all. In "Moonshine" it is cloudy, but the correct drink has no color. The question arises: why did the moonshine become cloudy (opalescent) at the exit?

Generally speaking, there was a violation of the technology for preparing the drink. Let's take a closer look at each of the possible causes of cloudy moonshine. There will be 5 in total!

1. Spray blower

In this case, you could make one of two common mistakes - you poured too much mash or the mash began to foam a lot (as a result of excessive heating, which led to the mash boiling and subsequently entering the cooler / refrigerator / coil).

But here the spray has occurred, what to do?

Finish distillation;
Disassemble the moonshine;
Clean the machine.

Only then can you continue to make moonshine on your equipment, and the muddy moonshine that has turned out before can be re-distilled.

How not to repeat the spray:

Fill the cube with mash not completely, but only ¾ (70-75%);
Watch the heating temperature, the manufacturer installs a thermometer on most cubes;
Wash the moonshine after each distillation, do it carefully;
Clean the mash with bentonite (before the first distillation!).

2. The presence of fusel oils

Fusel oils are various impurities that form during the fermentation process.

Here you do not need special tools to get rid of them. However, this does not mean at all that cleaning moonshine has become easier. After all, you are waiting for a double distillation with separation into fractions (it is also called fractional)! This way you can minimize the appearance of turbidity.

Clue:

The head fraction, as a rule, is considered the first 10-12% of absolute alcohol. It, like the tail, contains fusel oils.

In turn, the tail fraction begins to go when the temperature in the cube reaches 95°C.

Conclusion:

Select a body up to 92°C cubed, so you will definitely get a 100% quality product.

3. Hard water

We have written more than once that it is necessary to take a responsible approach to the choice of water for diluting moonshine! Since water can contain in its composition a huge amount of salts and impurities, which, after dilution, precipitate.

Remember, in the water used in home brewing, the salt content should be minimal and not exceed 1 mg-eq / l.

Breeding moonshine with tap and distilled water is not allowed!

Water with high hardness should be allowed to settle for 1-2 days.

The cause of turbidity may also be hidden in the wrong dilution procedure:

It is necessary to pour distillate into water, and not vice versa
When diluting moonshine, the temperature of both liquids should be the same and be in the range of 10-20 ° C.

4. Wrong containers

We are talking about all the containers used in the process of preparation and storage: fermentation containers, cubes of moonshine stills and dishes for collecting and storing alcoholic beverages.

The main rule of absolutely all home distillers and brewers is to disinfect the equipment every time before using it!

With regards to the storage of moonshine, only glass containers are suitable.

5. Imperfections of the moonshine still

We are talking about both shortcomings in the design and in the materials from which it is made. So, low-quality materials can enter into an oxidation reaction, which proceeds especially rapidly with high acidity of the mash. After oxidation, the distillate is not only cloudy, but also yellow.

With such violations, the opalescence of moonshine may not occur immediately, but only after a few days!

There is only one advice here - any moonshine that you want to use or just buy, at least, should be made of food grade stainless steel.

Purification of moonshine

As we said earlier, cloudy moonshine can be “reanimated”. The main thing is to understand the cause of the appearance of opalescence and to exclude its occurrence in the future.

If you properly clean cloudy moonshine, then you will retain its taste and restore transparency!

So, cleaning methods:

1. Redistillation

As you understand from the name, you need to distill the moonshine a second time with division into fractions. Just remember to dilute it with water to 20-30% vol.

2. heating

Perhaps the easiest way to clean, but with a flaw - you will not always get the desired transparency.

You need to heat the distillate to 70°C, then cool it down sharply. in this way you will achieve a precipitation that is easily filtered out.

Be careful, heated moonshine is highly flammable.

3. Cooling

If you have an aluminum pot and a roomy freezer, then this method is just right for you.

Pour the cloudy moonshine into a saucepan, cover and place in the freezer for 12-15 hours. During this period, fusel oils will freeze to the surface of the pan, and alcohol will remain liquid, as it has a lower freezing point.

4. Charcoal cleansing

If you want to purposefully make cloudy moonshine, then here are a few simple ways opalescent alcoholic drink at home:

Add whey in a ratio of 5-15 ml per 500 ml of moonshine;
Add powdered milk in the ratio of 2-7 grams per 0.5 liter;
Add a few drops of vegetable oil to 1 liter of alcohol.

The quality of the alcoholic beverage will not change when performing these methods!

Visually opalescence is defined as the glow of microscopic inclusions, forming a cloudy suspension. Because the we are talking not about radiation, but about the reflection of light by microparticles, there is a belief in the philistine environment: for the appearance of opalescence, it is required that every single particle of the suspension is a miniature flat "mirror".

The subtlety of the effect opalescence consists partly in the size, partly in the form, partly in the light transmission of the "mirrors" that form the suspension. If the linear size of the reflecting surface is so small that it is comparable to the wavelength of light, we will observe the reflection from such a particle as a poorly distinguishable point surrounded by an iridescent glow.

A similar effect is also observed when the "mirror" is an uneven surface with relief defect sizes close to the light wavelength. Only then does the light passing through the suspension split into colored flashes at millions of refraction points and merge into a milky white glow - which gives opalescence.

The background environment also plays an important role in the opalescence of precious stones. The refraction of light at the boundaries of media is especially decorative in quartz, corundum, and other transparent minerals. Solid transparent media are ideal for fixing fine-fibrous molecular structures, each of which forms a regular polyhedron.

The most beautiful opalescence is observed precisely when the role of "mirrors" and "light filters" that form an opaque suspension in the stone is played by silica polyhedrons.

A classic example of aesthetic opalescence can serve... The stone, mined near the Pacific coast of the United States, is saturated with chemically bound water. Many molecules of silicon dioxide, which form the basis of the stone, are attached to several molecules of water. Optically dense molecular groups in an array of silica change the light transmission properties of the stone, giving rise to the phenomenon of opalescence.

exhibits slightly less opalescence than butte opal. The difference arises from the fact that part of the water contained in silica goes to the oxidation of impurity iron.

Noticeable pronounced opalescence and at the shard Australian opal. However, the distribution of opalescent layers is uneven, and zones of high light transmission create the illusion of a local glow of the gem. Australian opal's natural color palette, aged in nature's blue tones, highlights reflected light. makes an ordinary shard of silica a precious stone.

Foggy haze of classic opalescence makes the iridescent glow of the round cabochon enigmatic and mysterious. In the absence of a haze of scattered light, this stone would hardly have produced such a stunning impression.

The nature of the opalescence of rose quartz and violet-pink amethyst is identical to the mechanism of light scattering by opals. No wonder: mineralogically, opals and quartz are siblings.