Dispersed systems with a liquid medium. Dispersed medium
KALININGRAD TRADE AND ECONOMICS COLLEGE
branch of the federal state budgetary
educational institution higher vocational education
RUSSIAN ACADEMY OF NATIONAL ECONOMY AND PUBLIC SERVICE
under the PRESIDENT OF THE RUSSIAN FEDERATION
Supporting notes
Topic: “Dispersed systems”
Kaliningrad, 2013
Topic: “Dispersed systems”
Dispersed systems are systems consisting of many small particles distributed in a liquid, solid or gaseous medium.
The dispersed system includes two mandatory components:dispersed phase - crushed substancedispersion medium – a substance in which the dispersed phase is distributed.All dispersed systems are characterized by two main features:
High dispersion.
Heterogeneity.
Dispersed systems
Finely dispersed
Colloidal systems Coarsely dispersed
True Sol Suspensions
Emulsions Gels
Aerosols
Classification of disperse systems
According to the state of aggregation of the phases
Main types of disperse systems
Dispersive medium
By particle size
According to the degree of dispersion, systems are divided into types
Coarsely dispersed with a particle radius of more than 100 nm
Colloidal dispersed (sols) with a particle size of 100 nm to 1 nm.
Molecular or ionic solutions with particle sizes less than 1 nm.
Coarse dispersed systems.
Emulsions (both the medium and the phase are liquids insoluble in each other, in which one of the liquids is suspended in the other in the form of droplets). This is milk, lymph, water-based paints, sour cream, mayonnaise, ice cream, etc.;
Suspensions (the medium is a liquid, and the phase is a solid insoluble in it). These are construction solutions (for example, “lime milk” for whitewashing), river and sea silt suspended in water, and pureed soup.
Aerosols - dispersed systems, the dispersion medium of which is a gas, and the dispersed phase can be solid particles or liquid droplets. Distinguish between dust, smoke, and fog. The first two types of aerosols are suspensions of solid particles in gas (larger particles in dust), the latter is a suspension of small droplets of liquid in gas. Bioaerosols are pollen and plant spores.
Foams - highly concentrated coarse systems in which the dispersion medium is liquid and the dispersed phase is gas.
Powders – the dispersed phase is a solid, and the dispersion medium is a gas.
Coarsely dispersed systems are unstable.
Colloidal systems
Colloidal systems - these are dispersed systems in which the phase particle size is from 100 to 1 nm. These particles are not visible to the naked eye, and the dispersed phase and the dispersion medium in such systems are difficult to separate by settling. They are divided intosols (colloidal solutions) andgels(jellies). 1. Colloidal solutions, orsols . This is the majority of the fluids of a living cell (cytoplasm, nuclear juice, contents of organelles and vacuoles) and the living organism as a whole (blood, lymph, tissue fluid, digestive juices). Such systems form adhesives, starch, proteins, and some polymers. Colloidal solutions are similar in appearance to true solutions. They are distinguished from the latter by the “luminous path” that is formed - a cone when a beam of light is passed through them.
This phenomenon is called the Tyndall effect. The particles of the dispersed phase of the sol, larger than in the true solution, reflect light from their surface, and the observer sees a luminous cone in the vessel with the colloidal solution. It is not formed in a true solution. You can observe a similar effect, but only for an aerosol rather than a liquid colloid, in cinemas when a beam of light from a movie camera passes through the air of the cinema hall. Particles of the dispersed phase of colloidal solutions often do not settle even during long-term storage due to continuous collisions with solvent molecules due to thermal movement. They do not stick together when approaching each other due to the presence of like electric charges on their surface. But under certain conditions, a coagulation process can occur.Coagulation
- the phenomenon of colloidal particles sticking together and precipitating - is observed when the charges of these particles are neutralized when an electrolyte is added to the colloidal solution. In this case, the solution turns into a suspension or gel. Some organic colloids coagulate when heated (glue, egg white) or when the acid-base environment of the solution changes. 2.
Gels,
or jellies, which are gelatinous sediments formed during the coagulation of sols. These include a large number of polymer gels, so well known to you confectionery, cosmetic and medical gels (gelatin, jellied meat, jelly, marmalade, Bird's Milk cake) and of course an endless variety of natural gels: minerals (opal), jellyfish bodies, cartilage , tendons, hair, muscle and nervous tissue, etc. Over time, the structure of the gels is disrupted - water is released from them. This phenomenon is calledsyneresis.
Solutions
Solution is a homogeneous (homogeneous) system consisting of particles of a dissolved substance, a solvent and the products of their interactionSolutions are always single-phase, that is, they are a homogeneous gas, liquid or solid. This is due to the fact that one of the substances is distributed in the mass of the other in the form of molecules, atoms or ions (particle size less than 1 nm). Solutions are called true if it is necessary to emphasize their difference from colloidal solutions.Table
Examples of dispersed systems
Dispersive medium
Self-test questions
- What is called a disperse system, phase, medium? How to relate dispersity to particle size? What disperse systems are classified as colloidal? What is coagulation and what factors cause it? What's it like practical significance coagulation? What is a suspension? What are the main properties of suspensions? What is an emulsion and how can it be broken? Where are aerosols used? What methods exist for destroying aerosols?
Safety precautions when working with alcohol lamps
When working with alcohol lamps, you must follow safety regulations.
It is necessary to use the alcohol lamp only for the intended purpose specified in its technical data sheet.
Do not refuel the alcohol lamp near open flame devices.
Do not fill the alcohol lamp with fuel more than half the capacity of the tank.
Do not move or carry a spirit lamp with a burning wick.
Fill the alcohol lamp only with ethyl alcohol.
Extinguish the flame of the alcohol lamp only with the cap.
Do not keep flammable substances and materials that can ignite from short-term exposure to an ignition source with low thermal energy (match flame, alcohol lamp) on the workbench where an alcohol lamp is used.
When working, do not tilt the spirit lamp, and if such a need arises, use spirit lamps that operate in an inclined position (faceted spirit lamps).
If the spirit lamp tips over and burning alcohol spills on the table, immediately cover the spirit lamp. thick fabric, and if necessary, use a fire extinguisher to extinguish the flame.
The room in which work with alcohol lamp(s) is carried out must be equipped with primary fire extinguishing means, for example, an OP-1 or OP-2 powder fire extinguisher.
Literature
- HELL. Zimon “Entertaining colloidal chemistry”, Moscow, “Agar”, 2008 N.A. Zharkikh “Chemistry for economic colleges”, Rostov-on-Don, “Phoenix”, 2008 Physical and colloidal chemistry in catering, Moscow, Alpha - M 2010. E.A. Arustamov “Nature Management”, Moscow, “Dashkov and K”, 2008. http://ru.wikipedia.org http://festival.1september.ru/articles/575855/
Dispersed systems. Definition. Classification.
Solutions
In the previous paragraph we talked about solutions. Let us briefly recall this concept here.
Solutions are called homogeneous (homogeneous) systems consisting of two or more components.
Homogeneous system is a homogeneous system, chemical composition And physical properties in which all parts are the same or change continuously, without jumps (there are no interfaces between parts of the system).
This definition of a solution is not entirely correct. It rather refers to true solutions.
At the same time, there are also colloidal solutions, which are not homogeneous, but heterogeneous, i.e. consist of different phases separated by an interface.
In order to achieve greater clarity in definitions, another term is used - dispersed systems.
Before considering dispersed systems, let’s talk a little about the history of their study and the appearance of such a term as colloidal solutions.
Background
Back in 1845, the chemist Francesco Selmi, exploring the properties various solutions, noticed that biological fluids - serum and blood plasma, lymph and others - differ sharply in their properties from ordinary true solutions, and therefore such liquids were called pseudo-solutions by him.
Colloids and crystalloids
Further research in this direction, carried out since 1861 by the English scientist Thomas Graham, showed that some substances that quickly diffuse and pass through plant and animal membranes easily crystallize, while others have a low ability to diffusion, do not pass through membranes and do not crystallize , but form amorphous precipitates.
Graham named the first crystalloids, and the second – colloids(from the Greek words kolla - glue and eidos - kind) or glue-like substances.
In particular, it was found that substances capable of forming amorphous sediments, such as albumin, gelatin, gum arabic, iron and aluminum hydroxides and some other substances, diffuse in water slowly compared to the diffusion rate of crystalline substances such as table salt , magnesium sulfate, cane sugar, etc.
The table below shows the diffusion coefficients D for some crystalloids and colloids at 18°C.
The table shows that there is an inverse relationship between molecular weight and diffusion coefficient.
In addition, crystalloids were found to have the ability not only to diffuse quickly, but also dialyze, i.e. pass through membranes, as opposed to colloids, which have larger molecular sizes and therefore diffuse slowly and do not penetrate membranes.
The walls of a bull's bladder, cellophane, films of ferrous-cyanide copper, etc. are used as membranes.
Based on his observations, Graham established that all substances can be divided into crystalloids and colloids.
Russians disagree
Against such strict division chemicals a professor at Kyiv University objected I.G. Borschev(1869). Borshchev's opinion was later confirmed by the research of another Russian scientist Weimarn, who proved that the same substance, depending on conditions, can exhibit the properties of colloids or crystalloids.
For example, a solution of soap in water has the properties colloid, and soap dissolved in alcohol exhibits properties true solutions.
In the same way, crystalline salts, for example, table salt, dissolved in water, give true solution, and in benzene – colloidal solution etc.
Hemoglobin or egg albumin, which has the properties of colloids, can be obtained in a crystalline state.
DI. Mendeleev believed that any substance, depending on the conditions and nature of the environment, can exhibit properties colloid. Currently, any substance can be obtained in a colloidal state.
Thus, there is no reason to divide substances into two separate classes - crystalloids and colloids, but we can talk about the colloidal and crystalloid states of the substance.
The colloidal state of a substance means a certain degree of its fragmentation or dispersion and the presence of colloidal particles in suspension in a solvent.
The science that studies the physicochemical properties of heterogeneous highly dispersed and high-molecular systems is called colloid chemistry.
Dispersed systems
If one substance, which is in a crushed (dispersed) state, is evenly distributed in the mass of another substance, then such a system is called dispersed.
In such systems, the fragmented substance is usually called dispersed phase, and the environment in which it is distributed is dispersion medium.
So, for example, a system representing agitated clay in water consists of suspended small particles of clay - the dispersed phase and water - the dispersion medium.
Dispersed(fragmented) systems are heterogeneous.
Dispersed systems, in contrast to heterogeneous ones with relatively large, continuous phases, are called microheterogeneous, and colloidal dispersed systems are called ultramicroheterogeneous.
Classification of disperse systems
Classification of dispersed systems is most often made based on degree of dispersion or state of aggregation dispersed phase and dispersion medium.
Classification by degree of dispersion
All dispersed systems Based on the size of dispersed phase particles, they can be divided into the following groups:
For reference, here are the units of size in the SI system:
1 m (meter) = 102 cm (centimeter) = 103 mm (millimeters) = 106 microns (micrometers) = 109 nm (nanometers).
Sometimes other units are used - mk (micron) or mmk (millimicron), and:
1 nm = 10 -9 m = 10 -7 cm = 1 mmk;
1 µm = 10 -6 m = 10 -4 cm = 1 µm.
Coarse dispersed systems.
These systems contain as a dispersed phase the largest particles with a diameter of 0.1 microns and above. These systems include suspensions And emulsions.
Suspensions are systems in which a solid substance is in a liquid dispersion medium, for example, a suspension of starch, clay, etc. in water.
Emulsions are called dispersion systems of two immiscible liquids, where droplets of one liquid are suspended in the volume of another liquid. For example, oil, benzene, toluene in water or droplets of fat (diameter from 0.1 to 22 microns) in milk, etc.
Colloidal systems.
They have the particle size of the dispersed phase from 0.1 µm to 1 µm(or from 10 -5 to 10 -7 cm). Such particles can pass through the pores of filter paper, but do not penetrate the pores of animal and plant membranes.
Colloidal particles if they have electric charge and solvation-ion shells remain in suspension and, without changing conditions, may not precipitate for a very long time.
Examples of colloidal systems include solutions of albumin, gelatin, gum arabic, colloidal solutions of gold, silver, arsenic sulfide, etc.
Molecular dispersed systems.
Such systems have particle sizes not exceeding 1 mm. Molecular dispersed systems include true solutions of non-electrolytes.
Ion-dispersed systems.
These are solutions of various electrolytes, such as salts, bases, etc., which disintegrate into corresponding ions, the sizes of which are very small and go far beyond
10 -8 cm.
Clarification on the representation of true solutions as dispersed systems.
From the classification given here it is clear that any solution (both true and colloidal) can be represented as a dispersed medium. True and colloidal solutions will differ in the particle sizes of the dispersed phases. But above we wrote about the homogeneity of true solutions, and dispersion systems are heterogeneous. How to resolve this contradiction?
If we talk about structure true solutions, then their homogeneity will be relative. The structural units of true solutions (molecules or ions) are significantly fewer particles colloidal solutions. Therefore, we can say that compared to colloidal solutions and suspensions, true solutions are homogeneous.
If we talk about properties true solutions, then they cannot be fully called dispersed systems, since the mandatory existence of dispersed systems is the mutual insolubility of the dispersed substance and the dispersion medium.
In colloidal solutions and coarse suspensions, the dispersed phase and the dispersion medium practically do not mix and do not react chemically with each other. This cannot be said at all about true solutions. In them, when dissolved, substances mix and even interact with each other. For this reason, colloidal solutions differ sharply in properties from true solutions.
The sizes of some molecules, particles, cells.
As the particle sizes change from the largest to the smallest and vice versa, the properties of disperse systems will change accordingly. At the same time colloidal systems occupy as it were intermediate position between coarse suspensions and molecular disperse systems.
Classification according to the state of aggregation of the dispersed phase and dispersion medium.
Foam is a dispersion of gas in a liquid, and in foams the liquid degenerates into thin films separating individual gas bubbles.
Emulsions are dispersed systems in which one liquid is crushed by another liquid that does not dissolve it (for example, water in fat).
Suspensions are called low-disperse systems of solid particles in liquids.
Combinations of three types of state of aggregation make it possible to distinguish nine types of dispersed systems:
Dispersed phase | Dispersive medium | Title and example |
|---|---|---|
Gaseous | Gaseous | No disperse system is formed |
Gaseous | Gas emulsions and foams |
|
Gaseous | Porous bodies: foam pumice |
|
Gaseous | Aerosols: fogs, clouds |
|
Emulsions: oil, cream, milk, margarine, butter |
||
Capillary systems: Liquid in porous bodies, soil, soil |
||
Gaseous | Aerosols (dusts, fumes), powders |
|
Suspensions: pulp, sludge, suspension, paste |
||
Solid systems: alloys, concrete |
Sols are another name for colloidal solutions.
Colloidal solutions are also called sols(from Latin solutus - dissolved).
Dispersed systems with a gaseous dispersion medium are called aerosols. Fogs are aerosols with a liquid dispersed phase, and dust and smoke are aerosols with a solid dispersed phase. Smoke is a more highly dispersed system than dust.
Dispersed systems with a liquid dispersion medium are called Lysols(from the Greek “lios” - liquid).
Depending on the solvent (dispersion medium), i.e. water, benzene alcohol or ether, etc., there are hydrosols, alcosols, benzols, etherosols, etc.
Cohesively dispersed systems. Gels.
Dispersed systems there may be freely dispersed And cohesively dispersed depending on the absence or presence of interaction between particles of the dispersed phase.
TO freely dispersed systems include aerosols, lysols, diluted suspensions and emulsions. They are fluid. In these systems, particles of the dispersed phase have no contacts, participate in random thermal motion, and move freely under the influence of gravity.
The pictures above show free-dispersed systems:
In the pictures a, b, c depicted corpuscular-dispersed systems:
a, b- monodisperse systems,
V- polydisperse system,
In the picture G depicted fiber-dispersed system
In the picture d depicted film-dispersed system
– solid-like. They arise when particles of the dispersed phase come into contact, leading to the formation of a structure in the form of a framework or network.
This structure limits the fluidity of the dispersed system and gives it the ability to retain its shape. Such structured colloidal systems are called gels.
The transition of a sol to a gel, which occurs as a result of a decrease in the stability of the sol, is called gelation(or gelatinization).
In the pictures a, b, c depicted cohesive dispersed systems:
A- gel,
b- coagulum with a dense structure,
V- coagulate with a loose “arched” structure
In the pictures g, d depicted capillary-dispersed systems
Powders (pastes), foams– examples of cohesively dispersed systems.
Soil, formed as a result of contact and compaction of dispersed particles of soil minerals and humus (organic) substances, is also a coherently dispersed system.
A continuous mass of substance can be penetrated by pores and capillaries, forming capillary-dispersed systems. These include, for example, wood, leather, paper, cardboard, fabrics.
Lyophilicity and lyophobicity
A general characteristic of colloidal solutions is the property of their dispersed phase to interact with the dispersion medium. In this regard, two types of sols are distinguished:
1. Lyophobic(from Greek phobia - hatred) And
2.Lyophilic(from Greek philia – love).
U lyophobic In sols, the particles have no affinity for the solvent, interact weakly with it, and form around themselves a thin shell of solvent molecules.
In particular, if the dispersion medium is water, then such systems are called hydrophobic, for example, sols of metals iron, gold, arsenic sulfide, silver chloride, etc.
IN lyophilic systems there is an affinity between the dispersed substance and the solvent. The particles of the dispersed phase, in this case, acquire a more voluminous shell of solvent molecules.
In the case of an aqueous dispersion medium, such systems are called hydrophilic, such as solutions of protein, starch, agar-agar, gum arabic, etc.
Coagulation of colloids. Stabilizers.
Substance at the interface.
All liquids and solids are limited by an outer surface at which they come into contact with phases of a different composition and structure, for example, vapor, another liquid or solid.
Properties of matter in this interfacial surface, with a thickness of several diameters of atoms or molecules, differ from the properties inside the volume of the phase.
Inside the volume pure substance in a solid, liquid or gaseous state, any molecule is surrounded by similar molecules.
In the boundary layer, molecules are in interaction with another number of molecules (different in comparison with the interaction inside the volume of the substance).
This occurs, for example, at the boundary of a liquid or solid with their steam. Or, in the boundary layer, molecules of a substance interact with molecules of another chemical nature, for example, at the boundary of two mutually poorly soluble liquids.
As a result, differences in the nature of the interaction inside the volume of phases and at the phase boundary arise force fields associated with this unevenness. (More on this in the section Surface tension of a liquid.)
The greater the difference in the intensity of intermolecular forces acting in each of the phases, the greater the potential energy of the interphase surface, briefly called surface energy.
Surface tension
To estimate surface energy, a quantity such as specific free surface energy is used. It is equal to the work spent on the formation of a unit area of a new phase interface (assuming a constant temperature).
In the case of a boundary between two condensed phases, this quantity is called boundary tension.
When talking about the boundary of a liquid with its vapors, this quantity is called surface tension.
Coagulation of colloids
All spontaneous processes occur in the direction of decreasing the energy of the system (isobaric potential).
Similarly, processes spontaneously occur at the phase interface in the direction of decreasing free surface energy.
The smaller the interphase surface, the smaller the free energy.
And the phase interface, in turn, is related to the degree of dispersion of the dissolved substance. The higher the dispersion (smaller particles of the dispersed phase), the larger the interface between the phases.
Thus, in dispersed systems there are always forces leading to a decrease in the total interphase surface, i.e. to particle enlargement. Therefore, the merging of small droplets in fogs, rain clouds and emulsions occurs - the aggregation of highly dispersed particles into larger formations.
All this leads to the destruction of dispersed systems: fogs and rain clouds rain, emulsions separate, colloidal solutions coagulate, i.e. are separated into a precipitate of the dispersed phase (coagulate) and a dispersion medium or, in the case of elongated particles of the dispersed phase, turn into a gel.
The ability of fragmented systems to maintain their inherent degree of dispersion is called aggregative stability.
Stabilizers for dispersed systems
As stated earlier, dispersed systems are fundamentally thermodynamically unstable. The higher the dispersion, the greater the free surface energy, the greater the tendency to spontaneously reduce dispersion.
Therefore, to obtain stable, i.e. long-lasting suspensions, emulsions, colloidal solutions, it is necessary not only to achieve the desired dispersion, but also to create conditions for its stabilization.
In view of this, stable disperse systems consist of at least three components: a dispersed phase, a dispersion medium and a third component - disperse system stabilizer.
The stabilizer can be either ionic or molecular, often high-molecular, in nature.
Ionic stabilization of sols of lyophobic colloids is associated with the presence of low concentrations of electrolytes, creating ionic boundary layers between the dispersed phase and the dispersion medium.
High-molecular compounds (proteins, polypeptides, polyvinyl alcohol and others) added to stabilize dispersed systems are called protective colloids.
Adsorbed at the phase interface, they form mesh and gel-like structures in the surface layer, creating a structural-mechanical barrier that prevents the integration of particles of the dispersed phase.
Structural-mechanical stabilization is crucial for the stabilization of suspensions, pastes, foams, and concentrated emulsions.
Dispersion systems can be divided according to the particle size of the dispersion phase. If the particle size is less than one nm, these are molecular ionic systems, from one to one hundred nm are colloidal, and more than one hundred nm are coarse. The group of molecularly dispersed systems is represented by solutions. These are homogeneous systems that consist of two or more substances and are single-phase. These include gas, solid or solutions. In turn, these systems can be divided into subgroups:
- Molecular. When organic matter, such as glucose, combine with non-electrolytes. Such solutions were called true so that they could be distinguished from colloidal ones. These include solutions of glucose, sucrose, alcohol and others.
- Molecular-ionic. In case of interaction between weak electrolytes. This group includes acidic solutions, nitrogenous, hydrogen sulfide and others.
- Ionic. Compound strong electrolytes. Prominent representatives are solutions of alkalis, salts and some acids.
Colloidal systems
Colloidal systems are microheterogeneous systems in which the sizes of colloidal particles vary from 100 to 1 nm. They long time may not precipitate due to the solvation ionic shell and electric charge. When distributed in a medium, colloidal solutions uniformly fill the entire volume and are divided into sols and gels, which in turn are precipitates in the form of jelly. These include albumin solution, gelatin, colloidal silver solutions. Jellied meat, soufflé, puddings are bright colloidal systems found in everyday life.
Coarse systems
Opaque systems or suspensions in which fine particle ingredients are visible to the naked eye. During the settling process, the dispersed phase is easily separated from the dispersed medium. They are divided into suspensions, emulsions, and aerosols. Systems in which a solid with larger particles are placed in a liquid dispersion medium are called suspensions. These include aqueous solutions starch and clay. Unlike suspensions, emulsions are obtained by mixing two liquids, in which one is distributed in droplets into the other. An example of an emulsion is a mixture of oil and water, droplets of fat in milk. If small solid or liquid particles are distributed in a gas, these are aerosols. Essentially, an aerosol is a suspension in gas. One of the representatives of a liquid-based aerosol is fog - this is a large number of small water droplets suspended in the air. Solid aerosol - smoke or dust - a multiple accumulation of small solid particles also suspended in the air.
Dispersed systems and colloidal chemical processes take place both in the food industry and in public catering. Colloidal chemical processes, such as swelling, dissolution, gelation, aggregation, coagulation, precipitation, peptization, adsorption, underlie the production of many food products: broths, ice cream, various confectionery products, dairy products, as well as the basis for baking, winemaking, and brewing. Butter, margarine, mayonnaise, sour cream, cream, milk are complex colloidal systems. To carry out control technological processes food production, economic engineers need knowledge of the characteristics of dispersed systems and their basic properties.
Dispersed systems are systems consisting of a substance, crushed into particles of larger or smaller size, and distributed in another substance. The same substance can be in varying degrees of fragmentation: macroscopically visible particles (>0.2-0.1 mm, eye resolution), microscopically visible particles (from 0.2-0.1 mm to 400-300 nm* , the resolving power of the microscope when illuminated with white light) and in the molecular (or ionic) state. Between the world of molecules and microscopically visible particles there is a region of fragmentation of matter with a complex of new properties inherent in this form of organization of matter. Such particles, invisible under an optical microscope, are called colloidal, and the crushed (dispersed) state of substances with particle sizes from 400-300 nm to 1 nm - colloidal state of the substance.
Dispersed systems consist of a continuous continuous phase - dispersion medium, in which crushed particles are distributed, and the crushed particles themselves of one size or another shape located in this environment - dispersed phase. Dispersed systems are heterogeneous, i.e. they are characterized by the existence of real physical phase interfaces between the dispersion phase and the dispersed medium.
A prerequisite for obtaining dispersed systems is the mutual insolubility of the dispersible substance and the dispersion medium. For example, it is impossible to obtain colloidal solutions of sugar or table salt in water, but they can be obtained in kerosene or benzene, in which these substances are practically insoluble.
A quantitative characteristic of the dispersion (fragmentation) of a substance is the degree of dispersion (degree of fragmentation, D) - the reciprocal of the size (a) of dispersed particles:
Here a is equal to either the diameter of spherical or fibrous particles, or the length of the edge of cubic particles, or the thickness of the films (Fig. 1). The smaller the particle sizes, the greater the dispersion, and vice versa.
*1 nm (nanometer) = 10 –6 mm.
), which are completely or practically immiscible and do not react chemically with each other. The first of the substances ( dispersed phase) finely distributed in the second ( dispersion medium). If there are several phases, they can be separated from each other physically (centrifuge, separate, etc.).
Typically dispersed systems are colloidal solutions, sols. Dispersed systems also include the case of a solid dispersed medium in which the dispersed phase is located.
Systems with dispersed phase particles of equal size are called monodisperse, and systems with particles of unequal size are called polydisperse. As a rule, the real systems around us are polydisperse.
Based on particle size, freely dispersed systems are divided into:
Ultramicroheterogeneous systems are also called colloidal or sols. Depending on the nature of the dispersion medium, sols are divided into solid sols, aerosols (sols with a gaseous dispersion medium) and lyosols (sols with a liquid dispersion medium). Microheterogeneous systems include suspensions, emulsions, foams and powders. The most common coarse systems are solid-gas systems, such as sand.
According to the classification of M. M. Dubinin, coherently dispersed systems (porous bodies) are divided into:
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