Disperse systems and solutions. Dispersed systems Dispersed phase of carburetor mixture

dispersed called heterogeneous systems in which one substance in the form of very small particles is evenly distributed in the volume of another.

The substance that is present in a smaller amount and distributed in the volume of another is called dispersed phase. It may consist of several substances.

A substance that is present in a larger amount, in the volume of which the dispersed phase is distributed, is called dispersion medium. There is an interface between it and the particles of the dispersed phase; therefore, disperse systems are called heterogeneous (non-uniform).

Both the dispersion medium and the dispersed phase can be represented by substances in various states of aggregation - solid, liquid and gaseous.

Depending on the combination of the state of aggregation of the dispersion medium and the dispersed phase, 8 types of such systems can be distinguished.

According to the particle size of the substances that make up the dispersed phase, dispersed systems are divided into coarse(suspend) with particle sizes over 100 nm and finely dispersed(colloidal solutions or colloidal systems) with particle sizes from 100 to 1 nm. If the substance is fragmented to molecules or ions with a size of less than 1 nm, a homogeneous system is formed − solution. It is homogeneous (homogeneous), there is no interface between the particles of the dispersed phase and the medium.

Even a cursory acquaintance with dispersed systems and solutions shows how important they are in everyday life and in nature (see table).

Table. Examples of disperse systems

Dispersion medium	Dispersed phase	Examples of some natural and domestic disperse systems
Gas	Liquid	Fog, associated gas with oil droplets, carburetor mixture in car engines (gasoline droplets in the air), aerosols
Solid	Dust in the air, smoke, smog, simums (dust and sand storms), aerosols
Liquid	Gas	Effervescent drinks, foam
Liquid	emulsions. Body fluids (blood plasma, lymph, digestive juices), liquid contents of cells (cytoplasm, karyoplasm)
Solid	Sols, gels, pastes (jelly, jellies, glues). River and sea silt suspended in water; mortars
Solid	Gas	Snow crust with air bubbles in it, soil, textile fabrics, bricks and ceramics, foam rubber, aerated chocolate, powders
Liquid	Wet soil, medical and cosmetic products (ointments, mascara, lipstick, etc.)
Solid	Rocks, colored glasses, some alloys

Judge for yourself: without the Nile silt, the great civilization of Ancient Egypt would not have taken place; without water, air, rocks and minerals, there would be no living planet at all - our common home - the Earth; without cells there would be no living organisms, etc.

If all particles of the dispersed phase have the same size, then such systems are called monodisperse (Fig. 1, a and b). Particles of the dispersed phase of unequal size form polydisperse systems (Fig. 1, c).

Rice. 1. Freely dispersed systems: corpuscular - (a-c), fibrous - (d) and film-dispersed - (e); a, b - monodisperse; c - polydisperse system.

Dispersed systems can be freely dispersed(Fig. 1) and coherently dispersed(Fig. 2, a - c) depending on the absence or presence of interaction between the particles of the dispersed phase. Freely dispersed systems include aerosols, dilute suspensions and emulsions. They are fluid, in these systems the particles of the dispersed phase do not have contacts, participate in random thermal motion, move freely under the action of gravity. Cohesive-dispersed systems are solid-like; they arise when the particles of the dispersed phase come into contact, leading to the formation of a structure in the form of a framework or network. Such a structure limits the fluidity of the dispersed system and gives it the ability to retain its shape. Powders, concentrated emulsions and suspensions (pastes), foams, gels are examples of cohesively dispersed systems. A solid mass of a substance can be penetrated by pores and capillaries, which form capillary-dispersed systems (leather, cardboard, fabrics, wood).

Rice. 3. Cohesive-dispersed (a-c) and capillary-dispersed (d, e) systems: gel (a), coagulant with a dense (b) and loose - arched (c) structure.

Disperse systems, in accordance with their intermediate position between the world of molecules and large bodies, can be obtained in two ways: by dispersion methods, i.e., grinding large bodies, and by methods of condensation of molecular or ionic substances.

Under the interaction of the phases of dispersed systems, solvation processes (hydration in the case of aqueous systems) are meant, i.e., the formation of solvate (hydrate) shells from the molecules of the dispersion medium around the particles of the dispersed phase. Accordingly, according to the intensity of interaction between the substances of the dispersed phase and the dispersion medium (only for systems with a liquid dispersion medium), at the suggestion of G. Freindlich, the following disperse systems are distinguished:

− Lyophilic (hydrophilic, if DS is water): micellar solutions of surfactants, critical emulsions, aqueous solutions of some natural HMS, for example, proteins (gelatin, egg white), polysaccharides (starch). They are characterized by a strong interaction of DF particles with DS molecules. In the limiting case, complete dissolution is observed. Lyophilic disperse systems are formed spontaneously due to the solvation process. Thermodynamically aggregatively stable.

− Lyophobic (hydrophobic, if DS is water): emulsions, suspensions, sols. They are characterized by a weak interaction of DF particles with DS molecules. They do not form spontaneously, for their formation it is necessary to expend work. Thermodynamically aggregatively unstable (i.e., they tend to spontaneous aggregation of particles of the dispersed phase), their relative stability (the so-called metastability) is due to kinetic factors (i.e., low aggregation rate).

3. Weigh.

suspension are dispersed systems in which the particle size of the phase is more than 100 nm. These are opaque systems, individual particles of which can be seen with the naked eye. The dispersed phase and the dispersed medium are easily separated by settling, filtering. Such systems are divided into:

1. emulsions ( both the medium and the phase are liquids insoluble in each other). From water and oil, you can prepare an emulsion by shaking the mixture for a long time. These are milk, lymph, water-based paints, etc., well known to you.

2. Suspensions (the medium is a liquid, the phase is a solid insoluble in it). To prepare a suspension, the substance must be ground to a fine powder, poured into a liquid and shaken well. Over time, the particle will fall to the bottom of the vessel. Obviously, the smaller the particles, the longer the suspension will last. These are building solutions, river and sea silt suspended in water, a living suspension of microscopic living organisms in sea water - plankton, which feed on giants - whales, etc.

3. Aerosols suspensions in a gas (for example, in air) of small particles of liquids or solids. Dusts, smokes, fogs differ. The first two types of aerosols are suspensions of solid particles in a gas (larger particles in dusts), the last one is a suspension of liquid droplets in a gas. For example: fog, thunderclouds - a suspension of water droplets in the air, smoke - small solid particles. And the smog hanging over the largest cities of the world is also an aerosol with a solid and liquid dispersed phase. Residents of settlements near cement plants suffer from the finest cement dust always hanging in the air, which is formed during the grinding of cement raw materials and the product of its firing - clinker. The smoke of factory pipes, smog, the smallest droplets of saliva flying out of the mouth of a flu patient are also harmful aerosols. Aerosols play an important role in nature, everyday life and human production activities. Cloud accumulation, chemical treatment of fields, paint spraying, respiratory treatment (inhalation) are examples of phenomena and processes where aerosols are beneficial. Aerosols - fogs over the sea surf, near waterfalls and fountains, the rainbow that arises in them gives a person joy, aesthetic pleasure.

For chemistry, the most important are dispersed systems in which the medium is water and liquid solutions.

Natural water always contains dissolved substances. Natural aqueous solutions are involved in the processes of soil formation and supply plants with nutrients. The complex life processes that occur in human and animal organisms also occur in solutions. Many technological processes in the chemical and other industries, such as the production of acids, metals, paper, soda, fertilizers, proceed in solutions.

4. Colloidal systems.

colloid systems (translated from the Greek "cola" - glue, "eidos" kind of glue-like) – these are dispersed systems in which the particle size of the phase is from 100 to 1 nm. These particles are not visible to the naked eye, and the dispersed phase and the dispersed medium in such systems are separated by settling with difficulty.

You know from your general biology course that particles of this size can be detected using an ultramicroscope, which uses the principle of light scattering. Due to this, the colloidal particle in it appears as a bright dot on a dark background.

They are divided into sols (colloidal solutions) and gels (jelly).

1. Colloidal solutions, or sols. This is the majority of fluids of a living cell (cytoplasm, nuclear juice - karyoplasm, the contents of organelles and vacuoles). And the living organism as a whole (blood, lymph, tissue fluid, digestive juices, etc.) Such systems form adhesives, starch, proteins, and some polymers.

Colloidal solutions can be obtained as a result of chemical reactions; for example, when solutions of potassium or sodium silicates (“soluble glass”) interact with acid solutions, a colloidal solution of silicic acid is formed. The sol is also formed during the hydrolysis of iron (III) chloride in hot water.

A characteristic property of colloidal solutions is their transparency. Colloidal solutions are outwardly similar to true solutions. They are distinguished from the latter by the resulting “luminous path” - a cone when a beam of light passes through them. This phenomenon is called the Tyndall effect. Larger than in a true solution, the particles of the dispersed phase of the sol reflect light from their surface, and the observer sees a luminous cone in a vessel with a colloidal solution. It does not form in true solution. A similar effect, but only for an aerosol rather than a liquid colloid, can be observed in the forest and in cinemas when a beam of light from a movie camera passes through the air of the cinema hall.

Passing a beam of light through solutions:

a - a true solution of sodium chloride;

b – colloidal solution of iron (III) hydroxide.

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 motion. They do not stick together when approaching each other due to the presence of similar electric charges on their surface. This is explained by the fact that substances in a colloidal, i.e., in a finely divided state, have a large surface. Either positively or negatively charged ions are adsorbed on this surface. For example, silicic acid adsorbs negative SiO 3 2- ions, which are abundant in solution due to the dissociation of sodium silicate:

Particles with like charges repel each other and therefore do not stick together.

But under certain conditions, the process of coagulation can occur. When boiling some colloidal solutions, desorption of charged ions occurs, i.e. colloidal particles lose their charge. They start to thicken and settle down. The same is observed when adding any electrolyte. In this case, the colloidal particle attracts an oppositely charged ion and its charge is neutralized.

Coagulation - the phenomenon of adhesion of colloidal particles and their precipitation - 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 are gelatinous precipitates formed during the coagulation of sols. These include a large number of polymer gels, confectionery, cosmetic and medical gels so well known to you (gelatin, jelly, marmalade, bread, meat, jam, jelly, marmalade, jelly, cheese, cottage cheese, curdled milk, Bird's Milk cake) and of course, an infinite number of natural gels: minerals (opal), jellyfish bodies, cartilage, tendons, hair, muscle and nerve tissue, etc. The history of development on Earth can be simultaneously considered the history of the evolution of the colloidal state of matter. Over time, the structure of the gels is broken (peeled off) - water is released from them. This phenomenon is called syneresis .

jelly are structured systems with properties of elastic solids. The gelatinous state of matter can be considered as intermediate between liquid and solid state.

Jellies of macromolecular substances can be obtained mainly in two ways: by the method of formation of jellies from polymer solutions and by the method of swelling of dry macromolecular substances in the corresponding liquids.

The process of transition of a polymer solution or sol into a jelly is called jelly formation . Gelation is associated with an increase in viscosity and a slowdown in Brownian motion and consists in combining particles of the dispersed phase in the form of a grid or cells and binding the entire solvent.

The process of gelation is significantly influenced by the nature of dissolved substances, the shape of their particles, concentration, temperature, process time and impurities of other substances, especially electrolytes. .

Based on their properties, jellies are divided into two large groups:

a) elastic, or reversible, obtained from macromolecular substances;

b) fragile, or irreversible, obtained from inorganic hydrophobic sols.

As already mentioned, jellies of macromolecular substances can be obtained not only by the method of gelation of solutions, but also by the method of swelling of dry substances. Limited swelling ends with the formation of jelly and does not turn into dissolution, and with unlimited swelling, jelly is an intermediate stage on the way to dissolution.

Jelly is characterized by a number of properties of solids: they retain their shape, have elastic properties and elasticity. However, their mechanical properties are determined by concentration and temperature.

When heated, the jellies pass into a viscous state. This process is called melting. It is reversible, because when cooled, the solution again forms a jelly.

Many jellies are able to liquefy and go into solutions under mechanical action (stirring, shaking). This process is reversible, since at rest, after a while, the solution forms a jelly. The property of jelly to liquefy repeatedly isothermally under mechanical influences and form jelly at rest is called thixotropy . For example, chocolate mass, margarine, dough are capable of thixotropic changes.

Having in its composition a huge amount of water, jellies, in addition to the properties of solid bodies, also have the properties of a liquid body. Various physical and chemical processes can take place in them: diffusion, chemical reactions between substances.

Freshly made jelly is subject to change over time as the structuring process in the jelly continues. At the same time, droplets of liquid begin to appear on the surface of the jelly, which, merging, form a liquid medium. The resulting dispersion medium is a dilute polymer solution, and the dispersed phase is a gelatinous fraction. Such a spontaneous process of dividing the jelly into phases, accompanied by a change in volume, is called by the studio. syneresis ( soaking).

Syneresis is considered as a continuation of the processes that cause the formation of jelly. The speed of syneresis of different jellies is different and depends mainly on temperature and concentration.

Syneresis in jellies formed by polymers is partially reversible. Sometimes heating is enough to return the jelly that has undergone syneresis to its original state. In culinary practice, this method is used, for example, to refresh cereals, mashed potatoes, and stale bread. If during the storage of jelly chemical processes occur, then syneresis becomes more complicated and its reversibility is lost, aging of the jelly occurs. In this case, the jelly loses its ability to retain bound water (staleness of bread). The practical significance of syneresis is quite large. Most often, syneresis in everyday life and industry is undesirable. This is the staleness of bread, the soaking of marmalade, jelly, caramel, fruit jams.

5. Solutions of macromolecular substances.

Polymers, like low molecular weight substances, depending on the conditions for obtaining a solution (the nature of the polymer and solvent, temperature, etc.), can form both colloidal and true solutions. In this regard, it is customary to talk about the colloidal or true state of a substance in solution. We will not touch upon colloid-type "polymer-solvent" systems. Let us consider only solutions of polymers of the molecular type. It should be noted that due to the large size of the molecules and the peculiarities of their structure, HMS solutions have a number of specific properties:

1. Equilibrium processes in HMS solutions are established slowly.

2. The process of dissolution of the IUD, as a rule, is preceded by the process of swelling.

3. Polymer solutions do not obey the laws of ideal solutions, i.e. the laws of Raoult and van't Hoff.

4. During the flow of polymer solutions, anisotropy of properties arises (different physical properties of the solution in different directions) due to the orientation of molecules in the direction of flow.

5. High viscosity of IUD solutions.

6. Due to their large size, polymer molecules tend to associate in solutions. The lifetime of polymer associates is longer than that of associates of low molecular weight substances.

The process of HMC dissolution proceeds spontaneously, but for a long time, and it is often preceded by swelling of the polymer in the solvent. Polymers whose macromolecules have a symmetrical shape can pass into solution without preliminary swelling. For example, hemoglobin, liver starch - glycogen almost do not swell when dissolved, and solutions of these substances do not have a high viscosity even at relatively high concentrations. While substances with highly asymmetric elongated molecules swell very strongly when dissolved (gelatin, cellulose, natural and synthetic rubbers).

Swelling is an increase in the mass and volume of the polymer due to the penetration of solvent molecules into the spatial structure of the IUD.

There are two types of swelling: unlimited, ending with the complete dissolution of the IUD (for example, swelling of gelatin in water, rubber in benzene, nitrocellulose in acetone) and limited, leading to the formation of a swollen polymer - jelly (for example, swelling of cellulose in water, gelatin in cold water, vulcanized rubber in benzene).

In the world around us, pure substances are extremely rare; basically, most substances on earth and in the atmosphere are various mixtures containing more than two components. Particles ranging in size from about 1 nm (several molecular sizes) to 10 µm are called dispersed(lat. dispergo - to scatter, spray). A variety of systems (inorganic, organic, polymeric, protein), in which at least one of the substances is in the form of such particles, are called dispersed. dispersed - these are heterogeneous systems consisting of two or more phases with a highly developed interface between them or a mixture consisting of at least two substances that are completely or practically not miscible with each other and do not chemically react with each other. One of the phases, the dispersed phase, consists of very fine particles distributed in the other phase, the dispersion medium.

Dispersion system

According to the state of aggregation, dispersed particles can be solid, liquid, gaseous, and in many cases have a complex structure. Dispersion media can also be gaseous, liquid and solid. Most of the real bodies of the world around us exist in the form of dispersed systems: sea water, soils and soils, tissues of living organisms, many technical materials, food products, etc.

Classification of dispersed systems

Despite numerous attempts to propose a unified classification of these systems, it is still missing. The reason lies in the fact that in any classification not all properties of disperse systems are taken as a criterion, but only one of them. Consider the most common classifications of colloidal and microheterogeneous systems.

In any field of knowledge, when one has to deal with complex objects and phenomena, in order to facilitate and establish certain patterns, it is advisable to classify them according to one or another feature. This also applies to the field of disperse systems; at different times, various principles of classification were proposed for them. According to the intensity of interaction between the substances of the dispersion medium and the dispersed phase, lyophilic and lyophobic colloids are distinguished. Other methods for classifying disperse systems are briefly outlined below.

Classification by the presence or absence of interactionbetween the particles of the dispersed phase. According to this classification, dispersed systems are divided into freely dispersed and coherently dispersed; the classification is applicable to colloidal solutions and to solutions of macromolecular compounds.

Svobodnodispersnye systems include typical colloidal solutions, suspensions, suspensions, various solutions of macromolecular compounds that have fluidity, like ordinary liquids and solutions.

The so-called structured systems, in which, as a result of the interaction between particles, a spatial openwork mesh-framework arises, and the system as a whole acquires the property of a semi-solid body, are classified as connected-dispersed ones. For example, sols of certain substances and solutions of macromolecular compounds with a decrease in temperature or with an increase in concentration above a known limit, without undergoing any external changes, lose their fluidity - gelatinize (gelify), go into a gel (jelly) state. This also includes concentrated pastes, amorphous precipitates.

Classification by dispersion. The physical properties of the substance do not depend on the size of the body, but at a high degree of grinding they become a function of dispersion. For example, metal sols have different colors depending on the degree of grinding. So, colloidal solutions of gold of extremely high dispersion are purple, less dispersed - blue, even less - green. There is reason to believe that other properties of the sols of the same substance change with grinding: This suggests a natural criterion for classifying colloidal systems according to dispersion, i.e., the separation of the area of ​​the colloidal state (10 -5 -10 -7 cm) to a number of narrower intervals. Such a classification was once proposed, but it turned out to be useless, since colloidal systems are almost always polydisperse; monodisperse are very rare. In addition, the degree of dispersity can change over time, i.e., it depends on the age of the system.

In nature, it is quite difficult to find a pure substance. In different states, they can form mixtures, homogeneous and heterogeneous - dispersed systems and solutions. What are these connections? What types are they? Let's consider these questions in more detail.

Terminology

First you need to understand what disperse systems are. This definition is understood as heterogeneous structures, where one substance as the smallest particles is distributed evenly in the volume of another. The component that is present in a smaller amount is called the dispersed phase. It may contain more than one substance. The component present in the larger volume is called the medium. There is an interface between the particles of the phase and it. In this regard, disperse systems are called heterogeneous - heterogeneous. Both the medium and the phase can be represented by substances in various states of aggregation: liquid, gaseous or solid.

Disperse systems and their classification

In accordance with the size of the particles entering the phase of substances, suspensions and colloidal structures are distinguished. For the former, the value of the elements is more than 100 nm, and for the latter, from 100 to 1 nm. When a substance is broken down into ions or molecules whose size is less than 1 nm, a solution is formed - a homogeneous system. It differs from others by its uniformity and the absence of an interface between the medium and particles. Colloidal disperse systems are presented in the form of gels and sols. In turn, suspensions are divided into suspensions, emulsions, aerosols. Solutions are ionic, molecular-ionic and molecular.

suspension

These dispersed systems include substances with a particle size greater than 100 nm. These structures are opaque: their individual components can be seen with the naked eye. The medium and phase are easily separated during settling. What are suspensions? They can be liquid or gaseous. The former are divided into suspensions and emulsions. The latter are structures in which the medium and phase are liquids that are insoluble in each other. These include, for example, lymph, milk, water-based paint and others. A suspension is a structure where the medium is a liquid, and the phase is a solid, insoluble substance in it. Such disperse systems are well known to many. These include, in particular, "milk of lime", sea or river silt suspended in water, microscopic living organisms common in the ocean (plankton), and others.

Aerosols

These suspensions are distributed small particles of a liquid or solid in a gas. There are fogs, smokes, dusts. The first type is the distribution of small liquid droplets in a gas. Dusts and fumes are suspensions of solid components. At the same time, the first particles are somewhat larger. Thunderclouds, fog itself, are natural aerosols. Smog hangs over large industrial cities, consisting of solid and liquid components distributed in gas. It should be noted that aerosols as dispersed systems are of great practical importance, they perform important tasks in industrial and household activities. Examples of a positive result from their use include treatment of the respiratory system (inhalation), treatment of fields with chemicals, spraying paint with a spray gun.

colloid structures

These are disperse systems in which the phase consists of particles ranging in size from 100 to 1 nm. These components are not visible to the naked eye. The phase and medium in these structures are separated with difficulty by settling. Sols (colloidal solutions) are found in a living cell and in the body as a whole. These fluids include nuclear juice, cytoplasm, lymph, blood, and others. These dispersed systems form starch, adhesives, some polymers, and proteins. These structures can be obtained through chemical reactions. For example, during the interaction of sodium or potassium silicate solutions with acidic compounds, a silicic acid compound is formed. Externally, the colloidal structure is similar to the true one. However, the former differ from the latter by the presence of a "luminous path" - a cone when a beam of light passes through them. The sols contain larger particles of the phase than in true solutions. Their surface reflects light - and in the vessel the observer can see a luminous cone. There is no such phenomenon in a true solution. A similar effect can also be observed in the cinema. In this case, the beam of light does not pass through a liquid, but an aerosol colloid - the air of the hall.

Precipitation of particles

In colloidal solutions, phase particles often do not settle even during prolonged storage, which is associated with continuous collisions with solvent molecules under the influence of thermal motion. When approaching each other, they do not stick together, since on their surfaces there are electric charges of the same name. However, under certain circumstances, a coagulation process can occur. It is the effect of sticking and precipitation of colloidal particles. This process is observed during the neutralization of charges on the surface of microscopic elements when an electrolyte is added. In this case, the solution turns into a gel or suspension. In some cases, the coagulation process is noted when heated or in the event of a change in the acid-base balance.

Gels

These colloidal disperse systems are gelatinous sediments. They are formed during the coagulation of sols. These structures include numerous polymer gels, cosmetic, confectionery, medical substances (Bird's Milk cake, marmalade, jelly, jelly, gelatin). They also include natural structures: opal, bodies of jellyfish, hair, tendons, nervous and muscle tissue, cartilage. The process of development of life on planet Earth can, in fact, be considered the history of the evolution of a colloidal system. Over time, a violation of the gel structure occurs, and water begins to be released from it. This phenomenon is called syneresis.

homogeneous systems

Solutions include two or more substances. They are always single-phase, that is, they are a solid, gaseous substance or liquid. But in any case, their structure is homogeneous. This effect is explained by the fact that in one substance another is distributed in the form of ions, atoms or molecules, the size of which is less than 1 nm. In the case when it is necessary to emphasize the difference between the solution and the colloidal structure, it is called true. In the process of crystallization of a liquid alloy of gold and silver, solid structures of various compositions are obtained.

Classification

Ionic mixtures are structures with strong electrolytes (acids, salts, alkalis - NaOH, HC104 and others). Another type are molecular-ionic disperse systems. They contain a strong electrolyte (hydrosulfide, nitrous acid and others). The last type are molecular solutions. These structures include non-electrolytes - organic substances (sucrose, glucose, alcohol, and others). A solvent is a component whose state of aggregation does not change during the formation of a solution. Such an element may, for example, be water. In a solution of salt, carbon dioxide, sugar, it acts as a solvent. In the case of mixing gases, liquids or solids, the solvent will be the component that is greater in the compound.

), which are completely or practically immiscible and do not chemically react with each other. The first of the substances dispersed phase) is finely distributed in the second ( dispersion medium). If there are several phases, they can be physically separated from each other (by centrifugation, separation, etc.).

Usually 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 particles of the dispersed phase of the same size are called monodisperse, and systems with particles of different sizes are called polydisperse. As a rule, the real systems surrounding us are polydisperse.

According to particle size, free-disperse 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.

Cohesive-dispersed systems (porous bodies), according to the classification of M. M. Dubinin, are divided into:

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See what the "Disperse System" is in other dictionaries:

dispersed system- dispersed system: A system consisting of two or more phases (bodies) with a highly developed interface between them. [GOST R 51109 97, article 5.6] Source ... Dictionary-reference book of terms of normative and technical documentation

dispersed system- A system consisting of two or more phases (bodies) with a highly developed interface between them. [GOST R 51109 97] [GOST R 12.4.233 2007] Topics industrial cleanliness personal protective equipment ... Technical Translator's Handbook

dispersed system- - a heterogeneous system consisting of two phases or more, characterized by a highly developed interface between them. General chemistry: textbook / A. V. Zholnin ... Chemical terms

dispersed system- ▲ mechanical mixture fine dispersed system heterogeneous system in which particles of one phase (dispersed) are distributed in another homogeneous phase (dispersion medium). foam (shreds of foam). foam. foam, sya. foam up. foamy. foamy… … Ideographic Dictionary of the Russian Language

dispersed system- dispersinė sistema statusas T sritis chemija apibrėžtis Sistema, subsidedanti iš dispersinės fazės ir dispersinės terpės (aplinkos). atitikmenys: engl. dispersion system; dispersion rus. dispersion; dispersed system ryšiai: sinonimas - dispersija ... Chemijos terminų aiskinamasis žodynas

dispersed system- dispersinė sistema statusas T sritis fizika atitikmenys: angl. dispersion system vok. disperses System, n rus. dispersed system, n pranc. système disperse, m … Fizikos terminų žodynas

dispersed system- a heterogeneous system of two or more phases with a highly developed interface between them. In a dispersed system, at least one of the phases (it is called dispersed) is included in the form of small particles in another ... ... Encyclopedic Dictionary of Metallurgy

Physico-mechanical system consisting of a dispersed phase and a dispersion medium. Distinguish between coarse and highly dispersed (colloidal) systems.

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Disperse systems

For chemistry, the most important are dispersion systems in which the medium is water and liquid solutions.

Pure substances are very rare in nature. Mixtures of various substances in different states of aggregation can form heterogeneous and homogeneous systems - dispersed systems and solutions. Familiarity with disperse systems and solutions shows how important they are in everyday life and nature. The civilization of Ancient Egypt would not have taken place without the Nile silt; without water, air, rocks, minerals, there would be no living planet at all - our common home - the Earth; Without cells, there would be no living organisms.

As you know, the chemical basis for the existence of a living organism is the exchange of proteins in it. On average, the concentration of proteins in the body is from 18 to 21%. Most proteins dissolve in water (the concentration of which in humans and animals is approximately 65%) and form colloidal solutions.

Dispersed systems are heterogeneous systems consisting of two or more phases with a highly developed interface between them.

The special properties of dispersed systems are due precisely to the small particle size and the presence of a large interfacial surface. In this regard, the properties of the surface, and not of the particles as a whole, are decisive. Processes occurring on the surface, and not inside the phase, are characteristic. Hence it becomes clear why colloid chemistry is called the physical chemistry of surface phenomena and dispersed systems.

Dispersed phase and dispersed medium. That substance (or several substances), which is present in a dispersed system in a smaller amount and is distributed in volume, is called the dispersed phase. The substance present in a larger amount, in the volume of which the dispersed phase is distributed, is called the dispersion medium. There is an interface between the dispersion medium and the particles of the dispersed phase, which is why disperse systems are called heterogeneous, i.e. heterogeneous.

Classification of dispersed systems

Both the dispersion medium and the dispersed phase can be composed of substances in different states of aggregation. Depending on the combination of states of the dispersion medium and the dispersed phase, eight types of such systems can be distinguished

Classification of disperse systems according to their state of aggregation

Dispersion medium	Dispersed phase	Examples of some natural and domestic disperse systems
	Liquid	Fog, associated gas with oil droplets, carburetor mixture in car engines (gasoline droplets in the air)
	Solid	Dust in the air, smoke, smog, simums (dust and sand storms)
Liquid		Fizzy drinks, bath foam
	Liquid	Body fluids (blood plasma, lymph, digestive juices), liquid contents of cells (cytoplasm, karyoplasm)
	Solid	Kissels, jellies, glues, river or sea silt suspended in water, mortars
Solid		Snow crust with air bubbles in it, soil, textile fabrics, bricks and ceramics, foam rubber, aerated chocolate, powders
	Liquid	Wet soil, medical and cosmetic products (ointments, mascara, lipstick, etc.)
	Solid	Rocks, colored glasses, some alloys

Also, as a classification feature, one can single out such a concept as the particle size of a dispersed system:

Coarse (> 10 microns): sugar, soil, fog, raindrops, volcanic ash, magma, etc.

Medium-dispersed (0.1-10 microns): human blood erythrocytes, E. coli, etc.

dispersed emulsion suspension gel

Highly dispersed (1-100 nm): influenza virus, smoke, turbidity in natural waters, artificially obtained sols of various substances, aqueous solutions of natural polymers (albumin, gelatin, etc.), etc.

Nanoscale (1-10 nm): glycogen molecule, fine pores of coal, metal sols obtained in the presence of organic molecules that limit the growth of particles, carbon nanotubes, magnetic nanowires made of iron, nickel, etc.

Coarse systems: emulsions, suspensions, aerosols

According to the size of the particles of the substance that make up the dispersed phase, dispersed systems are divided into coarse ones with particle sizes of more than 100 nm and finely dispersed ones with particle sizes from 1 to 100 nm. If the substance is fragmented to molecules or ions smaller than 1 nm in size, a homogeneous system is formed - a solution. The solution is homogeneous, there is no interface between the particles and the medium, and therefore it does not apply to dispersed systems. Coarsely dispersed systems are divided into three groups: emulsions, suspensions and aerosols.

Emulsions are dispersed systems with a liquid dispersion medium and a liquid dispersed phase.

They can also be divided into two groups: 1) direct - drops of non-polar liquid in a polar medium (oil in water); 2) reverse (water in oil). Changes in the composition of emulsions or external influences can lead to the transformation of a direct emulsion into an inverse one and vice versa. Examples of the best-known natural emulsions are milk (forward emulsion) and oil (inverse emulsion). A typical biological emulsion is fat droplets in the lymph.

Of the emulsions known in human practice, one can name cutting fluids, bituminous materials, pesticide preparations, medicines and cosmetics, and food products. For example, in medical practice, fat emulsions are widely used to provide energy to a starving or weakened organism by intravenous infusion. To obtain such emulsions, olive, cottonseed and soybean oils are used. In chemical technology, emulsion polymerization is widely used as the main method for producing rubbers, polystyrene, polyvinyl acetate, etc. Suspensions are coarsely dispersed systems with a solid dispersed phase and a liquid dispersion medium.

Typically, the particles of the dispersed phase of the suspension are so large that they settle under the action of gravity - sediment. Systems in which sedimentation proceeds very slowly due to the small difference in the density of the dispersed phase and the dispersion medium are also called suspensions. Practically significant building suspensions are whitewash (“milk of lime”), enamel paints, various building suspensions, for example, those that are called “cement mortar”. Suspensions also include medications, such as liquid ointments - liniments. A special group is made up of coarsely dispersed systems, in which the concentration of the dispersed phase is relatively high compared to its low concentration in suspensions. Such dispersed systems are called pastes. For example, dental, cosmetic, hygienic, etc. well-known to you from everyday life.

Aerosols are coarsely dispersed systems in which the dispersion medium is air, and the dispersed phase can be liquid droplets (clouds, a rainbow, hairspray or deodorant released from a spray can) or solid particles (dust cloud, tornado)

Colloidal systems - in them, the sizes of colloidal particles reach up to 100 nm. Such particles easily penetrate through the pores of paper filters, but do not penetrate through the pores of biological membranes of plants and animals. Since colloidal particles (micelles) have an electric charge and solvate ionic shells, due to which they remain in a suspended state, they may not precipitate for a sufficiently long time. A striking example of a colloidal system are solutions of gelatin, albumin, gum arabic, colloidal solutions of gold and silver.

Colloidal systems occupy an intermediate position between coarse systems and true solutions. They are widely distributed in nature. Soil, clay, natural waters, many minerals, including some precious stones, are all colloidal systems.

There are two groups of colloidal solutions: liquid (colloidal solutions - sols) and gel-like (jelly - gels).

Most of the biological fluids of the cell (the already mentioned cytoplasm, nuclear juice - karyoplasm, the contents of vacuoles) and the living organism as a whole are colloidal solutions (sols). All vital processes that occur in living organisms are associated with the colloidal state of matter. In every living cell, biopolymers (nucleic acids, proteins, glycosaminoglycans, glycogen) are in the form of dispersed systems.

Gels are colloidal systems in which the particles of the dispersed phase form a spatial structure.

Gels can be: food - marmalade, marshmallow, jellied meat, jelly; biological - cartilage, tendons, hair, muscle and nerve tissue, bodies of jellyfish; cosmetic - shower gels, creams; medical medicines, ointments; mineral - pearls, opal, carnelian, chalcedony.

Colloidal systems are of great importance for biology and medicine. The composition of any living organism includes solid, liquid and gaseous substances that are in a complex relationship with the environment. From a chemical point of view, the organism as a whole is a complex set of many colloidal systems.

Biological fluids (blood, plasma, lymph, cerebrospinal fluid, etc.) are colloidal systems in which organic compounds such as proteins, cholesterol, glycogen, and many others are in a colloidal state. Why does nature give such preference to him? This feature is connected, first of all, with the fact that the substance in the colloidal state has a large interface between the phases, which contributes to a better flow of metabolic reactions.

Examples of natural and artificial disperse systems. Minerals and rocks as natural mixtures

All the nature around us - the organisms of animals and plants, the hydrosphere and atmosphere, the earth's crust and bowels are a complex set of many diverse and diverse coarse and colloidal systems. The clouds of our planet are the same living entities as all the nature that surrounds us. They are of great importance for the Earth, as they are information channels. After all, clouds consist of the capillary substance of water, and water, as you know, is a very good store of information. The water cycle in nature leads to the fact that information about the state of the planet and the mood of people accumulates in the atmosphere, and together with clouds moves throughout the space of the Earth. An amazing creation of nature is a cloud that gives a person joy, aesthetic pleasure and just a desire to sometimes look at the sky.

Fog can also be an example of a natural dispersed system, the accumulation of water in the air, when the smallest condensation products of water vapor are formed (at air temperatures above? 10 ° - the smallest droplets of water, at? 10 ..? 15 ° - a mixture of water droplets and crystals ice, at temperatures below? 15 ° - ice crystals sparkling in the sun's rays or in the light of the moon and lanterns). Relative humidity during fogs is usually close to 100% (at least exceeds 85-90%). However, in severe frosts (? 30 ° and below) in settlements, at railway stations and airfields, fogs can be observed at any relative humidity of the air (even less than 50%) - due to the condensation of water vapor formed during the combustion of fuel (in engines, furnaces, etc.) and emitted into the atmosphere through exhaust pipes and chimneys.

The continuous duration of fogs usually ranges from several hours (and sometimes half an hour or an hour) to several days, especially during the cold period of the year.

Fogs impede the normal operation of all types of transport (especially aviation), so fog forecasts are of great national economic importance.

An example of a complex dispersed system is milk, the main components of which (not counting water) are fat, casein and milk sugar. Fat is in the form of an emulsion and when the milk is standing, it gradually rises to the top (cream). Casein is contained in the form of a colloidal solution and is not released spontaneously, but can easily be precipitated (in the form of cottage cheese) when milk is acidified, for example, with vinegar. Under natural conditions, the release of casein occurs during the souring of milk. Finally, milk sugar is in the form of a molecular solution and is released only when water evaporates.

Many gases, liquids and solids dissolve in water. Sugar and table salt dissolve easily in water; carbon dioxide, ammonia and many other substances, colliding with water, go into solution and lose their previous state of aggregation. A solute can be separated from a solution in a certain way. If a solution of table salt is evaporated, the salt remains in the form of solid crystals.

When substances are dissolved in water (or other solvent), a homogeneous (homogeneous) system is formed. Thus, a solution is a homogeneous system consisting of two or more components. Solutions can be liquid, solid or gaseous. Liquid solutions include, for example, a solution of sugar or common salt in water, alcohol in water, and the like. Solid solutions of one metal in another include alloys: brass is an alloy of copper and zinc, bronze is an alloy of copper and tin, and the like. A gaseous substance is air or in general any mixture of gases.

Minerals and rocks as natural mixtures.

It is generally accepted to understand rocks as natural mineral aggregates of a certain composition and structure, formed as a result of geological processes and occurring in the earth's crust in the form of independent bodies. In accordance with the main geological processes leading to the formation of rocks, three genetic classes are distinguished among them by origin: sedimentary, igneous and metamorphic.

In nature, there are simply no rocks, but these are either solid dispersed phases of suspensions, or dispersion media of porous bodies, or hardened emulsions.

Geologists say that clay accumulates at the bottom of the sea. In reality, the deposited clay sediment is a loose finely dispersed mineral mass saturated with sea water. The initial porosity of clayey silts ranges from 70 to 90%, or 1 m 3 of silt contains 700-900 liters of sea water. As you know, a vessel with a volume of 1 m 3 holds 1000 liters of water. Such a formation practically from one water (dispersion medium), in which clay particles are isolated from each other in a small amount, cannot be called a rock. It is a physico-chemical suspension type system.

With immersion in the bowels of the lithosphere and overlapping with new layers, water begins to be squeezed out of the suspension, clay minerals contact, squeeze each other, which leads to a decrease in the distance of atoms in their crystal lattices. The substance of the dispersed phase of the suspension begins to recrystallize with an increase in the size of the crystals. Loose mineral clay mass is cemented by emerging crystals, transitions into a cemented clay mass - mudstone.

The increasing lithostatic load (mass) of the layers accumulating from above causes a strong one-sided pressure. According to Rikke's principle (law), minerals begin to dissolve in the direction of this pressure. With continued removal of part of the dispersion medium of the suspension, which is accompanied by a decrease in the density of the system, the minerals crystallize in the direction perpendicular to the static pressure. With an increase in the size of the crystals, the physicochemical system from the suspension passes into the porous body system from the crystalline dispersion medium and the heated liquid dispersed phase. In a crystalline dispersion medium, a schistous (crystal schist) and parallel-banded (gneiss) texture appears.

Below, a water-silicate solution of basalt composition is removed from the porous body. The remaining dispersion medium of granite crystals has a density lower than clay particles. The decrease in density is fixed by the formation of granite with a chaotic texture.

During the recrystallization of the clay dispersed phase of the suspension into the crystalline dispersion medium of the porous body with an increase in the size of the crystals, it is accompanied by the release of potential free surface, internal energy (accumulated during the hypergenesis of solar energy) in the form of kinetic heat from clay minerals. Recrystallization of a substance with the removal of impurities from silicate minerals (eventually all cations) leads to a decrease in the density of the substance with depth, which contributes to a change in the coordination number of aluminum in clays from 4 to 6 in gneiss and granite feldspars, which is accompanied by the release of geochemical energy in the form of heat .

The removed heated water-silicate solution of basalt composition is an emulsion of solutions of electrolytes, non-electrolytes, and its silicate part is a colloidal solution.

Coagulation - the phenomenon of sticking together of colloidal particles and their precipitation - 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.

Syneresis. Over time, the structure of the gels is broken - liquid is released from them. Syneresis occurs - a spontaneous decrease in the volume of the gel, accompanied by the separation of the liquid. Syneresis determines the shelf life of food, medical and cosmetic gels. Biological syneresis is very important in the preparation of cheese, cottage cheese. Warm-blooded animals have a process called blood coagulation: under the influence of specific factors, the soluble blood protein fibrinogen turns into fibrin, the clot of which thickens and clogs the wound during syneresis. If blood clotting is difficult, then they talk about the possibility of human disease with hemophilia. The carriers of the hemophilia gene are women, and men get sick with it. A historical dynastic example is well known: the Russian Romanov dynasty, which reigned for more than 300 years, suffered from this disease.

Conclusion

In dispersed systems, the specific surface of the dispersed phase is very large. One of the most important consequences of the large surface of the dispersed phase is that lyophobic disperse systems have excess surface energy and, therefore, are thermodynamically unstable. Therefore, various spontaneous processes occur in disperse systems, which lead to a decrease in excess energy. The most common are the processes of reducing the specific surface due to coarsening of the particles. As a result, such processes lead to the destruction of the system. Thus, the key property that characterizes the very existence of dispersed systems is their stability, or, conversely, instability.

The global role of colloids lies in the fact that they are the main components of such biological formations as living organisms. All substances of the human body are colloidal systems.

Colloids enter the body in the form of nutrients and in the process of digestion are converted into specific colloids characteristic of the given organism. Protein-rich colloids make up the skin, muscles, nails, hair, blood vessels, and so on. We can say that the entire human body is a complex colloidal system.

List of information sources

1. Official website of the Russian Academy of Natural Sciences

2. Wikipedia, the free encyclopedia

3. Rebinder P. A. Dispersed systems

4. Site about chemistry "Chemist"

5. Official website of the journal "Chemistry and Life"

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