A disperse system in which. Dispersed medium. Appearance and disappearance of color characteristics

No. 6. For classification of disperse systems, see table. 3.

CLASSIFICATION OF DISPERSE SYSTEMS Table ACCORDING TO STATE OF AGREGATION

Dispersive medium	Dispersed	Examples of some natural and household disperse systems

	Liquid	Fog, associated gas with oil droplets, carburetor mixture in car engines (gasoline droplets in the air), aerosols
	Solid	Dust in the air, fumes, smog, simooms (dust and sand storms), solid aerosols
Liquid		Effervescent drinks, foams
	Liquid	Emulsions. Liquid media of the body (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,		Snow crust with air bubbles in it, soil, textile fabrics, brick and ceramics, foam rubber, aerated chocolate, powders
	Liquid	Moist soil, medical and cosmetic products (ointments, mascara, lipstick, etc.)
	Solid	Rocks, colored glasses, some alloys

§ 14. DISPERSE SYSTEMS

Pure substances are very common in naturerarely. Mixtures of various substances in different aggregatesstates can form heterogeneous and homogene systems – dispersed systems and solutions.

Dispersed called heterogeneous systems , in which one substance is in the form of very small particlesstits is evenly distributed in the volume of the other.

That substance (or several substances) thatpresent in the dispersed system in a smaller amountquality and distributed in volume is calleddispersenew phase . Present in greater quantitysubstance in the volume of which disperse is distributedthis phase is called dispersion medium . Betweendispersion medium and dispersed phase particlesthere is an interface, which is why dispersed systems are called heterogeneous, i.e. heterogeneous.
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 (Table 2).
table 2

Classification of disperse systems
by physical state

Dispersion- naya environment	Disperse nary phase	Examples of some natural and household dispersed systems
Gas	Liquid	Fog, associated gas with drops of oil, carburetor mixture in car engines biley (droplets of ben- zine in the air)
Gas	Solid substance	Dust in the air smoke, smog, smoums (dusty and sandy storms)
Liquid	Gas	Fizzy drinks, bubble bath
	Liquid	Organic liquid media nism (blood plasma, lymph, digestive body juices), liquid cell contents (cytoplasm, karyo- plasma)
	Solid substance	Jelly, jellies, glues, suspended in water river or sea silt, construction creations
Solid substance	Gas	Snow crust with pu- bubbles of air in germ, soil, textile fabrics, bricks and ceramics, foam rubber, porous chocolate, powders
	Liquid	Wet soil, copper Qing and cosmetic local remedies (ointments, mascara, lipstick, etc.)
	Solid substance	Rocks, color - new glasses, some alloys

Based on the size of the particles of the substance that make up the dispersed phase, dispersed systems are divided into coarse with particle sizes of more than 100 nm and finely dispersed with particle sizes from 1 to 100 nm. If the substance is fragmented into molecules or ions less 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 belong to disperse systems.

Getting to know dispersed systems and solutions shows how important they are in everyday life and nature. Judge for yourself: without the Nile silt the great civilization of Ancient Egypt would not have taken place (Fig. 15); without water, air, rocks, minerals, the living planet would not exist at all - our common home - the Earth; without cells there would be no living organisms.

Rice. 15. Nile floods and the history of civilization
The classification of disperse systems and solutions depending on the size of the phase particles is given in Scheme 1.
Scheme 1
Classification of disperse systems and solutions

Coarse dispersed systems. Coarsely dispersed systems are divided into three groups: emulsions, suspensions and aerosols.

Emulsions– these 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 a non-polar liquid in a polar medium (oil in water);
2) reverse (water in oil).
A change in the composition of emulsions or external influences can lead to the transformation of a direct emulsion into a reverse emulsion and vice versa. Examples of the most well-known natural emulsions are milk (direct emulsion) and oil (reverse emulsion). A typical biological emulsion is fat droplets in the lymph.
LABORATORY EXPERIMENT Pour whole milk into a plate. Place a few colorful drops of food coloring onto the surface. Soak a cotton swab in detergent and touch it to the center of the plate. The milk begins to move and the colors begin to mix. Why?
Among the emulsions known in human practice are cutting fluids, bituminous materials, pesticides, medicines and cosmetics, and food products. For example, in medical practice, fat emulsions are widely used to provide energy to a starving or weakened body through 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– these are coarse systems with a solid dispersed phase and a liquid dispersion medium.
Typically, the particles of the dispersed phase of a suspension are so large that they settle under the influence of gravity - sediment. Systems in which sedimentation occurs very slowly due to the small difference in density of the dispersed phase and the dispersion medium are also called suspensions. Practically significant construction suspensions
The gaps are whitewash (“lime milk”), enamel paints, various construction suspensions, for example those called “cement mortar.” Suspensions also include medications, for example liquid ointments - liniments.
A special group consists 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, hygiene, etc., that are well known to you from everyday life.
Aerosols– these are coarsely dispersed systems in which the dispersion medium is air, and the dispersed phase can be liquid droplets (clouds, rainbows, hairspray or deodorant released from a can) or particles of a solid substance (dust cloud, tornado) (Fig. 16).

Rice. 16. Examples of coarse systems with solid

Dispersed phase: a – suspension – mortar;
b – aerosol – dust storm
Colloidal systems. Colloidal systems occupy an intermediate position between coarse systems and true solutions. They are widespread in nature. Soil, clay, natural waters, many minerals, including some precious stones, are all colloidal systems.
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 body as a whole is a complex collection 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 primarily due to the fact that a substance in a colloidal state has a large interface between phases, which contributes to better metabolic reactions.
LABORATORY EXPERIMENTS: Pour a tablespoon of starch into a plastic glass. Gradually add warm water and thoroughly rub the mixture with a spoon. You cannot overfill the water; the mixture must be thick. Pour a tablespoon of the resulting colloidal solution into your palm and touch it with the finger of your other hand. The mixture hardens. If you remove your finger, the mixture becomes liquid again.
Colloids under pressure can change their state. As a result of finger pressure on the prepared colloid, the starch particles combine with each other, and the mixture becomes solid. When the pressure is released, the mixture returns to its original liquid state.

Colloidal systems are divided into sols (colloidal solutions) and gels (jellies).
Most biological fluids of the cell (the already mentioned cytoplasm, nuclear juice - karyoplasm, contents of vacuoles) and the living organism as a whole are colloidal solutions (sols).
Sols are characterized by the phenomenon of coagulation, i.e. adhesion of colloidal particles and their precipitation. In this case, the colloidal solution turns into a suspension or gel. Some organic colloids coagulate when heated (egg whites, adhesives) or when the acid-base environment changes (digestive juices).
Gels are colloidal systems in which particles of the dispersed phase form a spatial structure.
Gels are dispersed systems that you encounter in everyday life (Scheme 2).
Scheme 2
Classification of gels

Over time, the structure of the gels is disrupted and liquid is released from them. Syneresis occurs - a spontaneous decrease in the volume of the gel, accompanied by the separation of liquid. Syneresis determines the shelf life of food, medical and cosmetic gels. Biological syneresis is very important when making cheese and cottage cheese. Warm-blooded animals have a process called blood coagulation: under the influence of specific factors, the soluble blood protein fibrinogen is converted into fibrin, the clot of which, during the process of syneresis, thickens and clogs the wound. If blood clotting is difficult, then the person may have hemophilia. As you know from your biology course, women are carriers of the hemophilia gene, and men get it. A well-known historical dynastic example: the Russian Romanov dynasty, which reigned for more than 300 years, suffered from this disease.
In appearance, true and colloidal solutions are difficult to distinguish from each other. To do this, they use the Tyndall effect - the formation of a cone of a “luminous path” when a beam of light is passed through a colloidal solution (Fig. 17). Particles of the dispersed phase of the sol reflect light with their surface, but particles of the true solution do not. You can observe a similar effect, but only for an aerosol rather than a liquid colloid, in a cinema when a beam of light from a movie camera passes through the dusty air of the auditorium.

Rice. 17. The Tyndall effect allows you to visually distinguish
true solution (in the right glass) from colloidal
(in the left glass)

? 1. What are disperse systems? Dispersive medium? Dispersed phase?
2. How are disperse systems classified according to the state of aggregation of the medium and phase? Give examples.
3. Why are air, natural gas and true solutions not classified as dispersed systems?
4. How are coarse systems divided? Name the representatives of each group and indicate their significance.
5. How are finely dispersed systems divided? Name the representatives of each group and indicate their significance.
6. What subgroups can gels be divided into? How is the shelf life of cosmetic, medical and food gels determined?
7. What is coagulation? What could be causing it?
8. What is syneresis? What can cause it?
9. Why did nature choose colloidal systems as a carrier of evolution?
10. Prepare a message on the topic “The aesthetic, biological and cultural role of colloidal systems in human life” using Internet resources.
11. What disperse systems are discussed in the short poem by M. Tsvetaeva?
Take away the pearls - tears will remain,
Take away the gold - leaves remain
Autumn maple, take away the purple -
There will be blood left.

Dispersion scale.

Specific surface area. Degree of dispersion. Classification

dispersed systems. Concepts: dispersed phase and dispersive

Wednesday. Methods for obtaining dispersed systems

Dispersed call a system in which one substance is distributed in the medium of another, and there is a phase boundary between the particles and the dispersion medium. Dispersed systems consist of a dispersed phase and a dispersion medium.

Dispersed phase - These are particles distributed in the medium. Its signs: dispersion And intermittency(Fig. 1.1.1.1).

Dispersive medium - material environment in which the dispersed phase is located. Its sign is continuity .

The phase interface is characterized by fragmentation And heterogeneity. Fragmentation is characterized by:

1)degree of dispersion :

, [cm -1 ; m -1 ], where S- the total interfacial surface or the surface of all particles of the dispersed phase; V- volume of dispersed phase particles.

2)dispersion- the reciprocal of the minimum size:

; ];

3)specific surface :

, [m 2 /kg; cm 2 /g];

where m- mass of dispersed phase particles.

4) surface curvature :

. For an irregularly shaped particle,

Where r 1 and r 2 - radii of circles when passing through the surface and the normal to it at a given point of two perpendicular planes.

1. Based on dispersion, they are distinguished:

A) coarse systems for them D < 10 3 (рис. 1.1.1.3);

b) microheterogeneous systems for them D = 10 3 - 10 5 ;

V) ultramicroheterogeneous systems for them D = 10 5 - 10 7 .

2. By state of aggregation dispersed phase and dispersion medium. This classification was proposed by Ostwald (see Table 1.1.1.1).

3. According to their structure, dispersed systems are distinguished:

1) free dispersed systems, when particles of both components of the system can move freely relative to each other (sol);

2) related dispersed systems, when one of the components of the system is a structured system, i.e. phase particles are rigidly interconnected (jelly, composites).

Table 1.1.1.1

Classification according to the state of aggregation of phases

Aggregate state of the dispersed phase	Aggregate state of the dispersion medium	Symbol phase/medium	System name	Examples
G	G	g/g w/g tv/g	Aerosols	Earth's atmosphere
and	G			fog, stratus clouds
TV	G			smoke, dust, cirrus clouds
G	and	g/f	Gas emulsions, foams	sparkling water, soap and beer foam
and	and	w/w	Emulsions	milk, butter, creams, etc.
TV	and	TV/W	Lyosols, suspensions	lyophobic colloidal solutions, suspensions, pastes, paints, etc.
G	TV	g/tv	Solid foams	pumice, polystyrene foam, activated carbon, bread, foam concrete, etc.
and	TV	g TV	Solid emulsions	water in paraffin, minerals with liquid inclusions, porous bodies in liquid
TV	TV	tv/tv	Solid sols	steel, cast iron, colored glass, precious stones

4. According to interphase interaction - lyophilic And lyophobic systems (proposed by G. Freundlich). The classification is only suitable for systems with a liquid dispersion medium.

Lyophilic systems– in them the dispersed phase interacts with the dispersion medium and, under certain conditions, is capable of dissolving in it – solutions of colloidal surfactants, solutions of Naval Forces. Free energy of system D F < 0.

D F=D U – TdS ; D S mixing > 0;

D U = W when - W solv,

Where W cog - cohesion work;

W solv - work of solvation.

At D U> 0, D U < 0 ÞTdS>D U. This group is characterized by a low surface tension at the interface.

Lyophobic systems– in them the dispersed phase is not able to interact with the dispersion medium and dissolve in it. For them D F> 0. Dispersion in this case occurs either due to external work or due to other processes occurring spontaneously in the system (chemical reaction) and is characterized by a high surface tension at the phase boundary, which corresponds to a low value of solvation energy.

There are two groups of methods receiving dispersed systems:

1. Methods dispersing consist in crushing the body to a colloidal state (flour milling).

2. Methods condensation consist in the enlargement of particles, atoms, molecules to particles of colloidal sizes (a chemical reaction with the formation of a precipitate).

Molecular-kinetic properties of disperse systems

All molecular kinetic properties are caused by the chaotic thermal motion of the molecules of the dispersion medium, which consists of translational, rotational and vibrational motion of the molecules.

The molecules of a liquid and gaseous dispersion medium are in constant motion and collide with each other. The average distance traveled by a molecule before colliding with a neighboring one is called the mean free path. Molecules have different kinetic energies. At a given temperature, the average value of the kinetic energy of molecules remains constant, amounting to one molecule and one mole:

;

Where m– mass of one molecule;

M – mass of one mole;

v– speed of movement of molecules;

k– Boltzmann constant;

R– universal gas constant.

Fluctuation in the values of the kinetic energy of the molecules of the dispersion medium (i.e., deviation from the average) is the cause of the molecular kinetic properties.

The study of molecular kinetic properties is possible as a result of the use of statistical research methods valid for systems consisting of many elements (molecules). Based on the assumption that the movement of individual molecules is random, the theory determines the most likely combination for systems of many objects. Molecular kinetic properties manifest themselves in liquid and gaseous media, the molecules of which are definitely mobile.

Brownian motion

Brownian motion is the continuous, chaotic, equally probable in all directions movement of small particles suspended in liquids or gases due to the influence of molecules of a dispersion medium.

The smallest particles of insignificant mass experience unequal impacts from the molecules of the dispersion medium, a force arises that moves the particle, the direction and impulse of the force continuously changes, so the particle makes chaotic movements.

These changes were identified and associated with the molecular kinetic properties of the environment in 1907 by A. Einstein and M. Smoluchowski. The calculation is based not on the true path of the dispersed phase particle, but on the displacement of the particles. If the particle path is determined by a broken line, then the shift X characterizes the change in the coordinates of a particle over a certain period of time. The mean shift determines the root-mean-square displacement of the particle:

Where X 1 , X 2 , X i– particle displacement over a certain time.

The theory of Brownian motion is based on the idea of the interaction of a random force f(t), characterizing the impacts of molecules, force F t, depending on time, and the friction force when particles of the dispersed phase move in a dispersion medium with speed v. The equation of Brouer motion (Langevin equation) has the form:

, where m is the particle mass; h is the viscosity coefficient of the dispersion medium. For large periods of time (t>> m/h) particle inertia ( m (dv / d t) can be neglected. After integrating Eq.

provided that the average product of random force impulses is zero, the average fluctuation value (average shift) is equal to:

, where t is time; r is the radius of dispersed phase particles; N A is the Avogadro number of particles.

There are no elements in nature that are pure. Basically, they are all different mixtures. They, in turn, can be heterogeneous or homogeneous. They are formed from substances in an aggregate state, creating a specific dispersion system in which various phases are present. In addition, mixtures usually contain a dispersion medium. Its essence lies in the fact that it is considered an element with a large volume in which a substance is distributed. In a dispersed system, the phase and medium are located in such a way that there are interface particles between them. Therefore, it is called heterogeneous or heterogeneous. In view of this, the action of the surface, and not the particles as a whole, is of great importance.

Classification of dispersed system

A phase, as is known, is represented by substances having different states. And these elements are divided into several types. The aggregate state of the dispersed phase depends on the combination of the medium in it, resulting in 9 types of systems:

Gas. Liquid, solid and element in question. Homogeneous mixture, fog, dust, aerosols.
Liquid dispersed phase. Gas, solid, water. Foams, emulsions, sols.
Solid dispersed phase. Liquid, gas and the substance considered in this case. Soil, medicine or cosmetics, rocks.

As a rule, the dimensions of a disperse system are determined by the size of the phase particles. There is the following classification:

coarse (suspensions);
subtle and true).

Dispersion system particles

By examining coarse mixtures, one can observe that the particles of these compounds in the structure can be visible to the naked eye, due to the fact that their size is more than 100 nm. Suspensions generally refer to a system in which the dispersed phase is separable from the medium. This is because they are considered opaque. Suspensions are divided into emulsions (insoluble liquids), aerosols (small particles and solids), and suspensions (solids in water).

A colloidal substance is any substance that has the quality of having another element dispersed evenly throughout it. That is, it is present, or rather, it is part of the dispersed phase. This is a state when one material is completely distributed in another, or rather in its volume. In the milk example, liquid fat disperses into an aqueous solution. In this case, the smaller molecule is within 1 nanometer and 1 micrometer, making it invisible to the optical microscope once the mixture becomes homogeneous.

That is, no part of the solution has a higher or lower concentration of the dispersed phase than any other. It can be said to be colloidal in nature. The larger one is called a continuous phase or dispersion medium. Because its size and distribution do not change, and the element in question spreads across it. Types of colloids include aerosols, emulsions, foams, dispersions, and mixtures called hydrosols. Each such system has two phases: dispersed and continuous phase.

Colloids in history

Intense interest in such substances was present throughout the sciences at the beginning of the 20th century. Einstein and other scientists carefully studied their characteristics and applications. At the time, this new field of science was a leading area of research for theorists, researchers and manufacturers. After a peak of interest before 1950, research on colloids declined significantly. It is interesting to note that with the recent advent of higher power microscopes and "nanotechnology" (the study of objects on a specific tiny scale), there is a renewed scientific interest in the study of new materials.

Preparation of colloidal mixtures

By enlarging small molecules to the 1 to 1 micrometer range, or by reducing large particles to the same size. Colloidal substances can be obtained. Further production depends on the type of elements used in dispersed and continuous phases. Colloids behave differently than ordinary liquids. And this is observed in transport and physicochemical properties. For example, a membrane may allow a true solution with solid molecules attached to liquid molecules to pass through it. While a colloidal substance, which has a solid dispersed through a liquid, will be stretched by the membrane. The parity of the distribution is uniform to the point of microscopic equality in the gap throughout the second element.

True solutions

A colloidal dispersion is presented in the form of a homogeneous mixture. The element consists of two systems: continuous and dispersed phase. This indicates that this case is related to for they are directly related to the above mixture consisting of several substances. In a colloid, the second has a structure of tiny particles or droplets that are evenly distributed in the first. From 1 nm to 100 nm is the size constituting the dispersed phase, or more precisely particles, in at least one dimension. In this range, the dispersed phase with the indicated dimensions can be called approximate elements that fit the description: colloidal aerosols, emulsions, foams, hydrosols. The particles or droplets present in the compositions in question are largely affected by the chemical composition of the surface.

Colloidal solutions and systems

One should take into account the fact that the size of the dispersed phase is a difficult to measure variable in the system. Solutions are sometimes characterized by their own properties. To make it easier to perceive the indicators of the compositions, colloids resemble them and look almost the same. For example, if it has a solid form dispersed in a liquid. As a result, particles will not pass through the membrane. While other components such as dissolved ions or molecules are able to pass through it. If we analyze it more simply, it turns out that the dissolved components pass through the membrane, but colloidal particles cannot with the phase under consideration.

Appearance and disappearance of color characteristics

Due to the Tyndall effect, some such substances are translucent. In the structure of the element it is the scattering of light. Other systems and compositions come with some kind of tint or are completely opaque, with a certain color, even if some are dim. Many familiar substances, including butter, milk, cream, aerosols (fog, smog, smoke), asphalt, paints, paints, glue, and sea foam, are colloids. This field of study was introduced in 1861 by Scottish scientist Thomas Graham. In some cases, a colloid can be considered a homogeneous (not heterogeneous) mixture. This is because the distinction between "dissolved" and "granular" matter can sometimes be a matter of approach.

Hydrocolloid types of substances

This component is defined as a colloidal system in which particles are dispersed in water. Hydrocolloid elements, depending on the amount of liquid, can take on different states, for example, gel or sol. They can be irreversible (one-part) or reversible. For example, agar, the second type of hydrocolloid. Can exist in gel and sol states, and alternate between states with the addition or removal of heat.

Many hydrocolloids are obtained from natural sources. For example, carrageen is extracted from algae, gelatin is derived from bovine fat, and pectin is derived from citrus peels and apple pomace. Hydrocolloids are used in foods primarily to affect texture or viscosity (sauce). Also used for skin care or as a healing agent after injury.

Essential characteristics of colloidal systems

From this information it is clear that colloidal systems are a subsection of the dispersed sphere. They, in turn, can be solutions (sols) or gels (jelly). The former, in most cases, are created on the basis of living chemistry. The latter are formed under sediments that arise during the coagulation of sols. Solutions can be aqueous with organic substances, with weak or strong electrolytes. The particle sizes of the dispersed phase of colloids range from 100 to 1 nm. They cannot be seen with the naked eye. As a result of settling, the phase and medium are difficult to separate.

Classification by types of dispersed phase particles

Multimolecular colloids. When, upon dissolution, atoms or smaller molecules of substances (having a diameter less than 1 nm) combine together to form particles of similar sizes. In these sols, the dispersed phase is a structure that consists of aggregates of atoms or molecules with a molecular size of less than 1 nm. For example, gold and sulfur. These are held together by van der Waals forces. They are usually lyophilic in nature. This means significant particle interaction.

High molecular weight colloids. These are substances that have large molecules (so-called macromolecules), which, when dissolved, form a certain diameter. Such substances are called macromolecular colloids. These elements forming the dispersed phase are usually polymers having very high molecular weights. Natural macromolecules are starch, cellulose, proteins, enzymes, gelatin, etc. Artificial ones include synthetic polymers such as nylon, polyethylene, plastics, polystyrene, etc. They are usually lyophobic, which means in this case weak interaction particles.

Bound colloids. These are substances that, when dissolved in a medium, behave like normal electrolytes at low concentrations. But they are colloidal particles with a larger enzymatic component of components due to the formation of aggregated elements. The aggregate particles thus formed are called micelles. Their molecules contain both lyophilic and lyophobic groups.

Micelles. They are clustered or aggregated particles formed by the association of a colloid in solution. Common examples are soaps and detergents. Formation occurs above a certain Kraft temperature, and above a certain critical micellization concentration. They are capable of forming ions. Micelles can contain up to 100 molecules or more, with sodium stearate being a typical example. When it dissolves in water, it produces ions.

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, the chemical composition and physical properties of which are the same in all parts 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, while studying the properties of 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.

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 word 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

A professor at Kyiv University objected to such a strict separation of chemicals 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 and so on.

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 an electric charge and solvation-ion shells, they remain in a suspended state 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 speak about structure true solutions, then their homogeneity will be relative. The structural units of true solutions (molecules or ions) are much smaller than the particles of 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 back, the properties of dispersed systems will change accordingly. Wherein 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 aggregative states 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 can 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,
On the image G depicted fiber-dispersed system
On the image d depicted film-dispersed system

- solid. 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- coagulum with a loose “arched” structure
In the pictures g, d depicted capillary-dispersed systems

Powders (pastes), foams– examples of cohesively dispersed systems.

The 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 a 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 of a 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 interface of a liquid or solid with its vapor. Or, in the boundary layer, molecules of a substance interact with molecules of a different 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 bulk of the 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 sediment 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.