Basic conditions for obtaining dispersed systems. Preparation, stabilization and purification of dispersed systems

Acquisition Methods colloidal solutions can also be divided into two groups: condensation and dispersion methods (a separate group is the peptization method, which will be discussed later). Another necessary condition for obtaining sols, in addition to bringing the particle size to colloidal, is the presence of stabilizers in the system - substances that prevent the process of spontaneous enlargement of colloidal particles.

Rice. Classification of methods of obtaining dispersed systems(the type of systems is indicated in brackets)

Dispersion methods

Dispersion methods are based on the crushing of solids to particles of colloidal size and thus the formation of colloidal solutions. The dispersion process is carried out various methods: mechanical grinding of the substance in the so-called. colloid mills, electric arc spraying of metals, crushing of matter using ultrasound.

Dispersion can be spontaneous and non-spontaneous. Spontaneous dispersion is characteristic of lyophilic systems and is associated with an increase in the disorder of the system (when many small particles are formed from one large piece). When dispersing at a constant temperature, the increase in entropy must exceed the change in enthalpy.

ΔН > TΔS; ∆G > 0.

The dispersion process in this case is typically non-spontaneous and is carried out at the expense of external energy.

Dispersion is characterized by the degree of dispersion. It is determined by the ratio of the sizes of the initial product and the particles of the dispersed phase of the resulting system. The degree of dispersion can be expressed as follows:

α 1 \u003d d n / d to; α 2 \u003d B n / B to; α 3 \u003d V n / V to,

where d n; d to; B n; B to; V n; V to - respectively, the diameter, surface area, volume of particles before and after dispersion.

Thus, the degree of dispersion can be expressed in units of size (α 1), surface area (α 2) or volume (α 3) of the particles of the dispersed phase, i.e. can be linear, superficial or volumetric.

The work W required to disperse a solid or liquid is expended on the deformation of the body W d and the formation of a new interface W a, which is measured by the work of adhesion. Deformation is a necessary prerequisite for the destruction of the body. According to P.A. Rebinder, the work of dispersion is determined by the formula

W \u003d W a + W d \u003d σ * ΔB + kV,

where σ* is a value proportional to or equal to the surface tension at the interface between the dispersed phase and the dispersion medium; ΔB is the increase in the phase interface as a result of dispersion; V is the volume of the original body before dispersion; k is a coefficient equivalent to the work of deformation of a unit volume of the body.

Condensation methods

Condensation methods for obtaining disperse systems include condensation, desublimation and crystallization. They are based on the formation of a new phase under conditions of a supersaturated state of matter in a gaseous or liquid medium. In this case, the system changes from homogeneous to heterogeneous. Condensation and desublimation are characteristic of a gas medium, while crystallization is characteristic of a liquid medium.

A necessary condition for condensation and crystallization is supersaturation and uneven distribution of the substance in the dispersion medium (concentration fluctuation), as well as the formation of condensation centers or nuclei.

The degree of supersaturation β for solution and vapor can be expressed as follows:

β w = s / s s , β P = p / p s ,

where p, c are the supersaturated vapor pressure and the concentration of the substance in the supersaturated solution; p s is the equilibrium pressure of saturated vapor over a flat surface; c s is the equilibrium concentration corresponding to the formation of a new phase.

To carry out crystallization, the solution or gas mixture is cooled.

The condensation methods for obtaining dispersed systems are based on the processes of crystallization, desublimation and condensation, which are caused by a decrease in the Gibbs energy (ΔG< 0) и протекают самопроизвольно.

During the nucleation and formation of particles from a supersaturated solution or gaseous medium, the chemical potential µ changes, a phase interface appears, which becomes a carrier of excess free surface energy.

The work spent on the formation of particles is determined by the surface tension σ and is equal to:

W 1 \u003d 4πr 2 σ,

where 4πr 2 is the surface of spherical particles of radius r.

The chemical potential changes as follows:

Δμ = μ i // - μ i /< 0; μ i // >μ i / ,

where μ i / and μ i // are the chemical potentials of homo and heterogeneous systems (in the transition from small drops to large ones).

The change in the chemical potential characterizes the transfer of a certain number of moles of a substance from one phase to another; this number n moles is equal to the particle volume 4πr 3 /3 divided by the molar volume Vm:

The work of formation of a new surface in the process of condensation W to is equal to:

where W 1 and W 2 are, respectively, the work expended on the formation of the surface of particles, and the work on the transfer of matter from a homogeneous medium to a heterogeneous one.

The formation of dispersed systems can occur as a result of physical and chemical condensation, as well as during the replacement of the solvent.

Physical condensation is carried out by lowering the temperature of the gaseous medium containing vapors of various substances. When the necessary conditions are met, particles or drops of the dispersed phase are formed. A similar process takes place not only in the volume of gas, but also on a cooled solid surface, which is placed in a warmer gaseous environment.

Condensation is determined by the difference in chemical potentials (μ i // - μ i /)< 0, которая изменяется в результате замены растворителя. В отличие от обычной физической конденсации при solvent change the composition and properties of the dispersion medium do not remain constant. If alcohol or acetone solutions of sulfur, phosphorus, rosin and some others organic matter pour into water, the solution becomes supersaturated, condensation occurs and particles of the dispersed phase are formed. The solvent exchange method is one of the few methods by which sols can be obtained.

At chemical condensation a substance is formed with its simultaneous supersaturation and condensation.

A dispersed system is 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.

The dispersed phase is the particles distributed in the medium. Its features are dispersion and discontinuity.

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

dispersion method. It consists in mechanical crushing of solids to a given dispersion; dispersion by ultrasonic vibrations; electrical dispersion under the action of alternating and direct current. To obtain dispersed systems by the dispersion method, mechanical devices are widely used: crushers, mills, mortars, rollers, paint grinders, shakers. Liquids are atomized and sprayed using nozzles, tops, rotating discs, centrifuges. The dispersion of gases is carried out mainly by bubbling them through a liquid. In foam polymers, foam concrete, foam gypsum, gases are obtained using substances that release gas at elevated temperatures or in chemical reactions.

Despite the widespread use of dispersion methods, they cannot be used to obtain dispersed systems with a particle size of -100 nm. Such systems are obtained by condensation methods.

Condensation methods are based on the process of formation of a dispersed phase from substances that are in a molecular or ionic state. A necessary requirement for this method is the creation of a supersaturated solution from which a colloidal system must be obtained. This can be achieved under certain physical or chemical conditions.

Physical condensation methods:

1) cooling of vapors of liquids or solids during adiabatic expansion or mixing them with a large volume of air;

2) gradual removal (evaporation) of the solvent from the solution or its replacement with another solvent, in which the dispersed substance dissolves worse.

So, physical condensation refers to the condensation of water vapor on the surface of solid or liquid particles, ions or charged molecules (fog, smog) in the air.

Solvent replacement results in the formation of a sol when another liquid is added to the original solution that mixes well with the original solvent but is a poor solvent for the solute.

Chemical methods of condensation are based on the performance various reactions, as a result of which an undissolved substance precipitates from a supersaturated solution.

Chemical condensation can be based not only on exchange, but also on redox reactions, hydrolysis, etc.

Dispersed systems can also be obtained by peptization, which consists in transferring precipitates into a colloidal “solution”, the particles of which already have colloidal sizes. There are the following types of peptization: peptization by washing the precipitate; surface peptization - active substances; chemical peptization.

From the point of view of thermodynamics, the dispersion method is the most advantageous.

Cleaning Methods:

1. Dialysis - purification of sols from impurities using semi-permeable membranes washed with a pure solvent.

2. Electrodialysis - dialysis accelerated by an electric field.

3. Ultrafiltration - purification by forcing the dispersion medium together with low molecular weight impurities through a semi-permeable membrane (ultrafilter).

Molecular-kinetic and optical properties of dispersed systems: Brownian motion, osmotic pressure, diffusion, sedimentation equilibrium, sedimentation analysis, optical properties of dispersed systems.

All molecular-kinetic properties are due to the spontaneous movement of molecules and are manifested in Brownian motion, diffusion, osmosis, and sedimentation-ionic equilibrium.

Brownian movement is called continuous, chaotic, equally probable for all directions, the movement of small particles suspended in a liquid or gases, due to the action of molecules of a dispersion medium. The theory of Brownian motion proceeds from the concept of the interaction of a random force that characterizes the impacts of molecules, a time-dependent force, and a friction force when particles of a dispersed phase move in a dispersion medium at a certain speed.

Except forward movement possible and rotational, characteristic of two-dimensional particles irregular shape(threads, fibers, flakes). Brownian motion is most pronounced in highly dispersed systems, and its intensity depends on the dispersion.

Diffusion is the spontaneous spread of a substance from an area of ​​higher concentration to an area of ​​lower concentration. There are the following types:

1.) molecular

3) colloidal particles.

The diffusion rate in gases is the highest, and in solids it is the lowest.

Osmotic pressure is the excess pressure above the solution that is necessary to prevent the transfer of the solvent through the membrane. OD occurs when a pure solvent moves towards a solution or from a more dilute solution towards a more concentrated one, and therefore is associated with the difference in the concentration of the solute and solvent. The osmotic pressure is equal to the pressure that the dispersed phase (solute) would produce if it, in the form of a gas at the same temperature, occupied the same volume as the colloidal system (solution).

Sedimentation is the stratification of disperse systems under the action of gravity with the separation of the dispersed phase in the form of sediment. The ability of dispersed systems to sedimentation is an indicator of their sedimentation stability. Stratification processes are used when it is required to isolate one or another component from some component from some natural or artificially prepared product, which is a heterogeneous liquid system. In some cases, a valuable component is removed from the system, in others, unwanted impurities are removed. In public catering, the processes of stratification of dispersed systems are necessary when it is required to obtain transparent drinks, illuminate the broth, and free it from meat particles.

The behavior of a light beam that encounters particles of a dispersed phase on its way depends on the ratio of the light wavelength and particle size. If the particles are larger than the wavelength of light, then light is reflected from the surface of the particles at a certain angle. This phenomenon is observed in suspensions. If the particles are smaller than the wavelength of light, then the light is scattered.

Methods for obtaining dispersed systems are divided into two fundamentally different groups: dispersive and condensation.

dispersion

Obtaining dispersed systems by the method of dispersion is associated with crushing and grinding of substances. Dispersion can be carried out by mechanical, electrical, chemical (peptization) and ultrasonic methods.

Mechanical dispersion of substances constantly occurs in nature - the weathering of rocks, the formation of glaciers and other processes. Great importance mechanical dispersion has in industrial processes - ore dressing, metallurgical production in the formation of slag, in oil refining, construction, medicine, pharmaceuticals. At the same time, they use Various types and mill designs that provide the desired degree of grinding. Thus, ball mills provide coarse grinding particles (~ 10 4 m); in colloidal mills, particles of finer grinding are obtained, for example, when crushing sugar, coffee, starch, graphite, chemical reagents, colloidal mills are used to obtain a high degree of dispersion of the substance.

Dispersion starts with crushing, grinding of the substance is the next stage. Job W, spent on the dispersion of the substance, according to the Rehbinder equation, consists of two terms:

Where W^- work spent on crushing; - the work spent on grinding the substance; A K and As- change in the volume of the system and the surface of dispersed particles in it; and - coefficients of proportionality.

If the volume of a body is proportional to the cube of the linear size, and the area is proportional to its square, then the Rebinder equation can be rewritten as the ratio

where / Г and - coefficients of proportionality.

For the first stage of dispersion, the first term is important K.a*,

since the work expended on deformation and crushing is related to the size of the initial pieces of matter (as a rule, large and with a small surface) and their mechanical strength. At the second stage of dispersion, the work is proportional to the size of the resulting surface. At large particle sizes, the work of surface formation can be neglected and, conversely, at small sizes, the work of volumetric deformation.

If in general the coefficients of proportionality K^ And TO 2 depend

on the nature of the substance, medium, crushing method, then in the second term the coefficient /C, takes on the function of the energy of formation of a surface unit, that is surface tension: k^ = K^ c5.

During crushing and grinding, the destruction of bodies occurs in places of strength defects - micro cracks, which are present in weak points crystal lattice, while the strength of the particles increases, which is used to obtain more durable materials.

To facilitate the dispersion of materials and reduce energy costs, special additives called strength reducers are usually used. Typically, the addition of strength reducers in the amount of -0.1% by weight of the crushed substances reduces the energy consumption for obtaining dispersed systems by about half. The effect of reducing the strength of solids in the presence of strength reducers is called the effect

Rebinder. It is based on the fact that the development of microcracks under the action of force is easier when various substances are adsorbed from the medium, that is, the medium itself does not destroy the surface of bodies, but only helps destruction. The effect of additives, which are most often surfactants, is primarily to reduce surface tension and reduce the grinding work. In addition, additives, by wetting the material, help the medium to penetrate into the places of defects in the solid and, with the help of capillary forces, facilitate its destruction. The Rebinder effect is widely used in industry. For example, the grinding of ore is always carried out in aquatic environment in the presence of surfactants; the quality of machining parts on machine tools in the presence of a surfactant emulsion increases dramatically, the service life of the metal-cutting tool increases and the energy consumption for the process is reduced.

Dispersion is widely used in the production of emulsions - dispersed systems in which one liquid is dispersed in another liquid, that is, both phases are liquid (L/L). A necessary condition for the formation of emulsions is the complete or partial insolubility of the dispersed phase in the dispersion medium. Therefore, liquid substances that form an emulsion must differ in polarity. Usually water (polar phase) is a constituent part of emulsions. The second phase should be a non-polar or slightly soluble liquid, called an oil regardless of its composition (benzene, toluene, vegetable and mineral oils).

Emulsions are divided into two types: O/W emulsions are called direct (the dispersed phase is oil, the dispersion medium is water); reverse (invert) - W/O emulsions (water-in-oil dispersions). An example of type I emulsions are emulsions formed during the condensation of exhaust steam in an engine, food emulsions (milk, cream); a typical type II emulsion is crude oil containing up to 50% brine. Crude oil is a W/O emulsion stabilized with oil-soluble surfactants (paraffins, asphaltenes). Examples of food inverse emulsions include margarines or butter. The type of emulsion is determined by the volume ratio of the phases: the dispersed phase is the liquid that is in the smallest amount. The type can be determined by the ability to mix with polar and non-polar solvents or dissolve polar or non-polar dyes, as well as electrical conductivity (for an aqueous dispersion medium, the electrical conductivity is several orders of magnitude higher than for a non-aqueous one).

Emulsions are widely distributed in nature and various technological processes. Emulsions play an important role in human life, for example, blood is an emulsion in which erythrocytes are the dispersed phase.

The uniformity of the state of aggregation of two adjacent phases determines the stability of emulsions. The sedimentation stability of emulsions is quite high and the greater, the smaller the difference in the densities of the dispersed phase and the dispersion medium. The process of sedimentation in emulsions can be superimposed by the process of flocculation (aggregation), leading to coarsening of particles and, consequently, to an increase in the rate of their settling (or floating).

The aggregative stability of emulsions, like all dispersed systems, is determined by their lyophilicity or lyophobicity. Most emulsions are classified as lyophobic systems. They are thermodynamically unstable and cannot form spontaneously due to the presence of excess free energy at the interface. This instability manifests itself in spontaneous coalescence of liquid drops with each other (coalescence), which can lead to complete destruction of the emulsion and its separation into two layers. The aggregative stability of such emulsions is possible only in the presence of a stabilizer that prevents particles from coalescing. The stabilizer can be a component of the system that is in excess in it, or a substance specially introduced into the system, in which case the stabilizer is called an emulsifier. As emulsifiers, surfactants or macromolecular substances are usually used. Emulsifiers can be hydrophilic and hydrophobic. The most common hydrophilic emulsifiers are sodium (potassium) salts of fatty acids, which are more soluble in water than in hydrocarbons. They are capable of stabilizing O/W type direct emulsion. The orientation of the surfactant adsorption layer occurs in accordance with the Rehbinder rule: the nonpolar radical faces the nonpolar liquid, and the polar group faces the polar one. In direct type emulsions, the polar parts of the emulsifier are located on the outer side of the oil droplets and prevent them from approaching. The same substances in reverse type emulsions are adsorbed by polar groups on the inner surface of water droplets and do not interfere with their merging (Fig. 1.3).

Rice. 1.3. Location of hydrophilic emulsifier in straight lines (A) and reverse ( 6 ) emulsions

Under certain conditions, a phenomenon called inversion is possible - the inversion of the phases of the emulsion (or simply the inversion of the emulsion), when, when conditions change or the introduction of any reagents, an emulsion of a given type turns into an emulsion of the opposite type.

Obtaining dispersed systems is associated primarily with obtaining dispersed particles. It is necessary to solve the following tasks:

• 1) distribute dispersed particles in a dispersion medium to the required concentration;
• 2) to stabilize the dispersed system in order to preserve its structure and properties for a sufficiently long time;
• 3) to clean the dispersed system from various impurities.

These problems are solved depending on the specifics (type) of a particular disperse system.

Obtaining dispersed systems

emulsions. Since emulsions are coarsely dispersed systems, they are usually obtained by the dispersion method. The liquids to be emulsified are stirred vigorously or subjected to mechanical vibrations or ultrasound. In order to obtain drops of the same size (i.e., a monodisperse system), homogenization is carried out. This process consists in forcing the liquid of the dispersed phase into the dispersion medium through small holes of the required diameter under high pressure. This technique is used, for example, in the processing of milk. As a result of homogenization the average size drops of fat decreases from about 1-3 to 0.1-0.2 microns.

Emulsions are also obtained by condensation methods (usually by replacing the solvent).

An independent task is to obtain highly concentrated emulsions. These include emulsions with a dispersed phase concentration of more than 74 vol. %, up to 99 vol. %. Drops of the dispersed phase in such emulsions, having the shape of polyhedral prisms, are separated by thin films of a liquid dispersion medium.

Concentrated emulsins may have mechanical properties solids - strength and elasticity.

The specificity of the preparation of concentrated emulsions lies in the fact that the dispersed phase is introduced into the dispersion liquid medium in small portions with vigorous stirring.

Foam. Like emulsions, foams are coarse systems. Therefore, in many technological processes, foams are obtained by the same dispersion methods that are used to obtain gas bubbles.

Condensation methods for producing foams are based on the supersaturation of a gas solution in a given liquid with a corresponding change in temperature or pressure. Chemical reactions with evolution of gas are also used. As an example, here is the reaction underlying the preparation of foam in fire extinguishers:

NaHCO 3 + HCl > NaCl + H 2 O+ CO 2 ^

Another condensation method for producing foams is based on the use of microbiological processes.

colloidal solutions. Colloidal solutions (sols) are obtained by various condensation methods. To obtain highly dispersed sols, it is necessary to ensure the fulfillment of the following condition: the rate of formation of solid particles must be many times higher than the rate of their growth. To fulfill this condition, when obtaining dispersed particles using chemical reactions, the following method is often used: a concentrated solution of one component is poured in a small amount into a highly diluted solution of another component with very vigorous stirring.

Gels. The above systems are freely dispersed. Obtaining connected-dispersed systems has a certain specificity. Consider, as an example, the preparation of gels. Usually they are obtained from colloidal solutions (sols). Under certain conditions, dispersed particles stick together with each other - the process of coagulation occurs.

If the particles have an anisodiametric shape (rods, ellipsoids), then they are connected mainly by their ends and form a spatial structure (network), in the cells of which there is a liquid dispersion medium. The process of converting sols to gels is called sol-gel transition. He has importance in nanotechnology. Thus, gels, like concentrated emulsions, can sometimes be bicontinuous disperse systems.

The properties of gels are very effectively controlled by changing the concentration of the dispersed phase and the shape of the dispersed particles. Another important factor is temperature: its increase hinders the formation of contacts between dispersed particles and, therefore, the strength of gels decreases.

Condensation methods are based on the processes of the emergence of a new phase by combining molecules, ions or atoms in a homogeneous medium. These methods can be divided into physical and chemical.

physical condensation. The most important physical methods for obtaining dispersed systems are condensation from vapors and solvent replacement. Most good example condensation from vapor is the formation of fog. When the parameters of the system change, in particular, when the temperature decreases, the vapor pressure can become higher than the equilibrium vapor pressure over the liquid (or over the solid) and a new liquid (solid) phase appears in the gas phase. As a result, the system becomes heterogeneous - fog (smoke) begins to form. In this way, for example, camouflage aerosols are obtained, which are formed by cooling the vapors of P2O5, ZnO and other substances. Lyosols are obtained in the process of joint condensation of vapors of substances that form a dispersed phase and a dispersion medium on a cooled surface.

The method of replacing the solvent is widely used, based, like the previous one, on such a change in the parameters of the system, in which the chemical potential of the component in the dispersion medium becomes higher than the equilibrium one and the tendency to transition to an equilibrium state leads to the formation of a new phase. In contrast to the vapor condensation method (temperature change), in the solvent replacement method, the composition of the medium is changed. So, if a saturated molecular solution of sulfur in ethyl alcohol is poured into a large volume of water, then the resulting solution in an alcohol-water mixture is already supersaturated. Supersaturation will lead to the aggregation of sulfur molecules with the formation of particles of a new phase - dispersed.

The solvent replacement method produces sols of sulfur, phosphorus, arsenic, rosin, cellulose acetate and many organic substances by pouring alcohol or acetone solutions of these substances into water.

chemical condensation. These methods are also based on the condensation separation of a new phase from a supersaturated solution. However, unlike physical methods, the substance that forms the dispersed phase, appears as a result of a chemical reaction. Thus, any chemical reaction proceeding with the formation of a new phase can be a source of obtaining a colloidal system. The following chemical processes are given as examples.

• 1. Recovery. A classic example of this method is the preparation of a gold sol by the reduction of chloroauric acid. Hydrogen peroxide can be used as a reducing agent (Zigmondy method):
• 2HauCl2+3H2O22Au+8HCl+3O2

Other reducing agents are also known: phosphorus (M. Faraday), tannin (W. Oswald), formaldehyde (R. Zhigmondy). For example,

• 2KauO2+3HCHO+K2CO3=2Au+3HCOOK+KHCO3+H2O
• 2. Oxidation. Oxidative reactions are widespread in nature. This is due to the fact that during the rise of magmatic melts and gases separated from them, fluid phases and groundwater, all mobile phases pass from the zone recovery processes at great depths to zones of oxidative reactions near the surface. An illustration of such processes is the formation of a sulfur sol in hydrothermal waters, with oxidizing agents (sulfur dioxide or oxygen):
• 2H2S+O2=2S+2H2O

Another example is the process of oxidation and hydrolysis of iron bicarbonate:

4Fe(HCO3)2+O2+2H2O4Fe(OH)3+8CO2

The resulting iron hydroxide sol imparts a red-brown color to natural waters and is the source of rusty-brown sediment zones in the lower soil layers.

• 3. Hydrolysis. The formation of hydrosols in the processes of hydrolysis of salts is widespread in nature and of great importance in technology. Salt hydrolysis processes are used for wastewater treatment (aluminum hydroxide obtained by hydrolysis of aluminum sulfate). The high specific surface of the colloidal hydroxides formed during hydrolysis makes it possible to effectively adsorb impurities - surfactant molecules and heavy metal ions.
• 4. Exchange reactions. This method is the most common in practice. For example, obtaining an arsenic sulfide sol:
• 2H3AsO3+3H2SAs2S3+6H2O,

obtaining silver iodide sol:

AgNO3+KIAgI+KNO3

Interestingly, exchange reactions make it possible to obtain sols in organic solvents. In particular, the reaction

Hg(CN)2+H2SHgS+2HCN

It is carried out by dissolving Hg (CN) 2 in methyl, ethyl or propyl alcohol and passing hydrogen sulfide through the solution.

Well-known reactions in analytical chemistry, such as the production of precipitates of barium sulfate or silver chloride

Na2SO4 + BaCl2 BaSO4 + 2NaCl

AgNO3 + NaCl AgCl + NaNO3

under certain conditions lead to the production of almost transparent, slightly cloudy sols, from which precipitation may subsequently occur.

Thus, for the condensation preparation of sols, it is necessary that the concentration of the substance in the solution exceed the solubility, i.e. the solution must be supersaturated. These conditions are common both for the formation of a fine sol and for a normal solid phase deposit. However, in the first case, compliance special conditions, which, according to the theory developed by Weimarn, consists in the simultaneous appearance of a huge number of nuclei of the dispersed phase. The nucleus should be understood as the minimum accumulation of a new phase, which is in equilibrium with environment. To obtain a highly dispersed system, it is necessary that the rate of nucleation be much higher than the rate of crystal growth. In practice, this is achieved by pouring a concentrated solution of one component into a very dilute solution of the other with vigorous stirring.

Sols are formed more easily if special compounds, called protective substances, or stabilizers, are introduced into solutions in the process of their preparation. Soaps, proteins and other compounds are used as protective substances in the preparation of hydrosols. Stabilizers are also used in the preparation of organosols.