Aggregative stability of disperse systems. Factors of aggregative stability Chapter xiv. structural and mechanical properties of disperse systems

There are thermodynamic and kinetic stability factors,

TO thermodynamic factors include electrostatic, adsorption-solvation and entropy factors.

Electrostatic factor is due to the existence of a dispersed double electric layer on the surface of particles. The main components of the electrostatic factor are the charge of the granules of all colloidal particles, the value of the electrokinetic potential, as well as a decrease in interfacial surface tension due to the adsorption of electrolytes (especially in cases where the electrolytes are ionic surfactants).

The identical electric charge of the granules leads to mutual repulsion of approaching colloidal particles. Moreover, at distances exceeding the diameter of the micelles, electrostatic repulsion is caused mainly by the charge of counterions in the diffuse layer. If fast moving particles collide with each other, then the counterions of the diffuse layer, being relatively weakly bound to the particles, can move, and as a result the granules come into contact. In this case, the electrokinetic potential plays the main role in the repulsive forces. Namely, if its value exceeds 70–80 mV, then particles colliding with each other as a result of Brownian motion will not be able to overcome the electrostatic barrier and, having collided, will disperse and aggregation will not occur. The role of surface tension as a thermodynamic stability factor was discussed in Chapter 1.

Adsorption-solvation factor associated with the hydration (solvation) of both the dispersed phase particles themselves and ions or uncharged surfactant molecules adsorbed on their surface. Hydration shells and adsorption layers are connected to the surface of particles by adhesion forces. Therefore, for direct contact of aggregates, the colliding particles must have the energy necessary not only to overcome the electrostatic barrier, but also exceed the work of adhesion.

Entropy factor consists in the tendency of the dispersed phase to uniformly distribute particles of the dispersed phase throughout the volume of the system as a result of diffusion. This factor manifests itself mainly in ultramicroheterogeneous systems, the particles of which participate in intense Brownian motion.

To kinetic factors stability include structural-mechanical and hydrodynamic factors.

Structural-mechanical factor This is due to the fact that the hydration (solvate) shells existing on the surface of the particles have increased viscosity and elasticity. This creates an additional repulsive force when particles collide - the so-called disjoining pressure. The elasticity of the adsorption layers themselves also contributes to the disjoining pressure. The doctrine of disjoining pressure was developed by B.V. Deryagin (1935).

Hydrodynamic factor associated with the viscosity of the dispersion medium. It reduces the rate of destruction of the system by slowing down the movement of particles in a medium with high viscosity. This factor is least pronounced in systems with a gaseous medium, and its greatest manifestation is observed in systems with a solid medium, where particles of the dispersed phase are generally devoid of mobility.

In real conditions, the stability of dispersed systems is usually ensured by several factors simultaneously. The highest stability is observed under the combined action of both thermodynamic and kinetic factors.

Each resistance factor has a specific method for its neutralization. For example, the effect of the structural-mechanical factor can be removed using substances that liquefy and dissolve elastic structured layers on the surface of particles. Solvation can be reduced or completely eliminated by lyophobization of particles of the dispersed phase during the adsorption of the corresponding substances. The effect of the electrostatic factor is significantly reduced when electrolytes are introduced into the system, compressing the DES. This last case is most important both in the stabilization and destruction of dispersed systems.

Coagulation

As mentioned above, coagulation is based on a violation of the aggregative stability of the system, leading to the sticking together of particles of the dispersed phase during their collisions. Externally, coagulation of colloidal solutions manifests itself in the form of turbidity, sometimes accompanied by a change in color, followed by precipitation.

In the aggregates formed during coagulation, the primary particles are connected to each other either through a layer of dispersion medium, or directly. Depending on this, the aggregates can be either loose, easily peptized, or quite strong, often irreversible, which are peptized with difficulty or not peptized at all. In systems with a liquid dispersion medium, especially with a high concentration of particles of the dispersed phase, the precipitation of the resulting aggregates is often accompanied by structure formation - the formation of a coagel or gel covering the entire volume of the system.

The first stage of coagulation of the sol when its stability is violated is hidden coagulation, which consists of combining only a small number of particles. Hidden coagulation is usually not visible to the naked eye and can only be noted with a special examination, for example, using an ultramicroscope. Following latent coagulation comes explicit, when such a significant number of particles combine that this leads to a clearly visible change in color, clouding of the sol and the loss of a loose precipitate from it ( coagulates). Coagulates arising as a result of the loss of aggregative stability are settling (or floating) formations of various structures - dense, curdled, flocculent, fibrous, crystal-like. The structure and strength of coagulates is largely determined by the degree of solvation (hydration) and the presence of adsorbed substances of various natures, including surfactants, on the particles.

P. A. Rebinder studied in detail the behavior of sols during coagulation with protective factors not completely removed and showed that in such cases coagulation structure formation is observed, leading to the appearance of gel-like systems (the structure of which will be discussed in Chapter 11).

The reverse process of coagulation is called peptization (see section 4.2.3). In ultramicroheterogeneous systems, in which the energy of Brownian motion is commensurate with the binding energy of particles in aggregates (floccules), a dynamic equilibrium can be established between coagulation and peptization. It must meet the condition

½ zE = kT ln( V s/ V To),

Where z – coordination number of a particle in the spatial structure of the coagulate (in other words, the number of contacts of one particle in the resulting aggregate with other particles included in it), E – binding energy between particles in contact, k – Boltzmann constant, T – absolute temperature, V h – volume per particle in a colloidal solution after the formation of a coagulate (if the particle concentration is equal to n particles/m3, then V z = 1/ n ,), V k is the effective volume per particle inside the coagulation structure (or the volume in which it fluctuates relative to the equilibrium position).

In lyophobic disperse systems after coagulation, the concentration of particles in the equilibrium ash is usually negligible compared to their concentration. Therefore, in accordance with the above equation, coagulation is, as a rule, irreversible. In lyophilic systems, the binding energies between particles are small and therefore

½ zE < kT ln( V s/ V To),

that is, coagulation is either impossible or highly reversible.

The reasons causing coagulation can be very different. These include mechanical influences (stirring, vibration, shaking), temperature influences (heating, boiling, cooling, freezing), and others, often difficult to explain and unpredictable.

But the most important in practical terms and at the same time the most well studied is coagulation under the influence of electrolytes or electrolyte coagulation.

There are thermodynamic and kinetic stability factors,

TO thermodynamic factors include electrostatic, adsorption-solvation and entropy factors.

To kinetic factors stability include structural-mechanical and hydrodynamic factors.

Based on Plato's discoveries, the Soviet scientist, academician P. A. Rebinder, together with his students, proposed and studied in detail the structural-mechanical theory of foam stability. According to this theory, the stability of adsorption layers (including in foams) is determined by both surface forces and the mechanical properties of foam films. If these properties are improved in any way, the stability of the foam will increase (sometimes many times).

It is the provision of the structural-mechanical factor of stability that can give the greatest stability to the foam. For example, all protein foaming agents, due to the special three-dimensional structure of protein surfactants, form mobile but very strong adsorption layers that form foam films. Due to the high stability of the foam, it is able to withstand significant mechanical influences from the outside - for example, when mixed with cement mortar. The traditional method of producing foam concrete is based on this fact: foam prepared in advance in a special foam generator is mixed with cement-sand mortar in a low-speed mixer.

The transition from considering two-component (solvent + surfactant) compositions to real multi-component (foam-cement mixture) allows, taking into account structural and mechanical factors, to explain the phenomenon of extremely high stability of some types of foams, in particular, those prepared from a mixture of resin and fatty acids (foaming agent SDO ).

This foaming agent consists of a mixture of saponified resin and fatty acids. The introduction of a stabilizer, lime, into its composition initiates exchange-substitution reactions for calcium. Resin soaps turn into calcium soaps, which have higher surface activity. Like sodium fatty acids, they lose their ability to dissolve in water.

As a result of these processes, a voluminous, strong and highly viscous structure of foam films is formed, which differs significantly from the rest of the solution. In addition, the smallest particles of calcium hydroxide and calcium soaps of fatty acids synthesized at the time of foam generation armor the surface of the foam bubbles and clog the Plateau channels. All together makes it possible to obtain such a stable low-expansion foam that it can even withstand a “meeting” with dry aggregates - cement and sand (this type of technological regulation for the production of foam concrete is called the dry mineralization method).

From the standpoint of the structural-mechanical factor of stability, it becomes possible to explain the fact that some foaming agents, in particular those based on saponins, provide an order of magnitude greater stability of the foam obtained from them if not freshly prepared, but aged solutions are used. As a result of hydrolysis during storage, more active components spontaneously accumulate in the foaming agent solution, capable of forming highly viscous adsorption layers of a spatial structure.

Foam block is one of the materials often used in the construction of houses. It has many advantages: light weight, convenient dimensions and low cost. At the same time, buildings made of foam blocks...

The composition depends on the place where the foam blocks are used, taking into account the climatic conditions of the area. The main elements in the composition (which must comply with GOST) are cement, sand, water and foaming additives. In pursuit of profit they can...

Foam blocks today are very popular building materials for the construction of modern structures and buildings. They are made from a cement mixture to which sand is added with a foaming agent and water. In some variants in…

Candidate of Chemical Sciences, Associate Professor

Topic 2. Properties of disperse systems,

their stability and coagulation

Lesson 2. Stability of disperse systems

Lectures

Saratov – 2010

If the AgCl precipitate is obtained in excess of AgNO3, then the colloidal micelle will have a different structure. Potential-determining Ag+ ions will be adsorbed on the AgCl aggregate, and NO3– ions will be the counterions.

For water-insoluble barium sulfate (obtained in excess of BaCl2), the structure of a colloidal particle can be represented by the formula:

BaCl2(g) + NaSO4 ® BaSO4(solid) + 2NaCl

In an electric field, a positively charged granule will move towards a negatively charged cathode.

2. PHYSICAL THEORY OF STABILITY AND COAGULATION

Colloidal stability – the ability of a dispersed system to maintain unchanged its composition (concentration of the dispersed phase and particle size distribution), as well as appearance: color, transparency, “uniformity”.

It should be pointed out that there is a sharp difference in stability between the two classes of colloids: lyophilic And lyophobic . Lyophilic colloids have a high affinity for the dispersion medium; they spontaneously disperse and form thermodynamically stable colloidal solutions. Lyophobic colloids have a much lower affinity for the solvent; their dispersions are thermodynamically unstable and are characterized by high surface tension at the interface. It is the stability and coagulation of lyophobic sols that we will study.

Colloidal stability is conventionally classified into sedimentation (kinetic) and aggregative .

Sedimentation stability determined by the system’s ability to resist particle settling. Sedimentation, or settling of particles, leads to the destruction of the dispersed system. The dispersed system is considered sedimentation resistant , if its dispersed particles do not settle, the system does not separate into phases, i.e., it is in stable diffusion-sedimentation equilibrium.

Sedimentation stability primarily depends on the particle size of the dispersed phase. If their size is less than 1000 nm, then the system usually has high sedimentation stability. In the case of larger particles, the system is unstable, i.e., it stratifies over time, and particles of the dispersed phase either float up or form a sediment.

Aggregative stability is determined by the ability of a dispersed system to resist the adhesion of particles, that is, to keep the particle sizes of the dispersed phase unchanged. But due to the desire of systems to “get rid” of free energy (in this case, surface energy), particles of the dispersed phase tend to become larger by merging or recrystallizing.

Under coagulation understand the loss of aggregative stability of a disperse system, which consists in the adhesion and fusion of particles.

If the particle sizes of the dispersed phase are constant and do not change over time, then colloidal disperse systems can maintain sedimentation stability indefinitely. The coarsening of particles in a disperse system (loss of aggregation stability) leads to a violation of sedimentation stability and sedimentation.

Quantitative relationships characterizing the stability of lyophobic sols in satisfactory agreement with experiment were obtained on the basis of the physical theory of stability and coagulation.

Physical theory of stability and coagulation (DPST)

In its most general form, this theory was developed by Soviet scientists in 2010, and somewhat later, independently of them, by the Dutch scientists Verwey and Overbeck. Based on the first letters of the names of these scientists, the theory is called the DLFO theory.

The theory of stability of colloidal systems should be based on the relationship between the forces of attraction and repulsion of particles. DLVO theory takes into account electrostatic repulsion between particles and intermolecular attraction.

Electrostatic repulsion between similarly charged particles occurs when they come close enough to each other, their electrical double layers overlap and repel.

a) there is no repulsion b) particles repel

(DES do not overlap) (DES overlap)

As a result of rather complex calculations (which we omit), expressions for the energy of electrostatic repulsion of particles are obtained. In accordance with this expression, the repulsive energy of particles increases with decreasing distance between them according to the exponential law

where Ue is the repulsion energy;

c is the potential on the particle surface;

h – distance between particles.

The second type of force that affects the stability of a sol is the force of attraction between particles. They are of the same nature as the forces acting between neutral molecules. Van der Waals explained the properties of real gases and liquids by the existence of these forces. The emergence of intermolecular forces is due to the interaction of dipoles (the Keeson effect), the polarization of one molecule by another (the Debye effect) and London dispersion forces, which are associated with the presence of instantaneous dipoles in neutral atoms and molecules.

The most universal component of molecular forces of attraction is the dispersion component. Calculations carried out by Hamaker led to the following expression for the energy of molecular attraction (for parallel plates located at small distances from each other).

Rice. 2. Potential curves

The shape of the curves of the total interaction energy of particles depends on the potential on their surface, on the value of the Hamaker constant, on the size of the particles and their shape. Therefore, depending on all these factors, three most characteristic types of potential curves are distinguished, corresponding to certain states of aggregative stability (Fig. 3).

Rice. 3. Potential curves for disperse systems

with different aggregative stability

Curve 1 corresponds to a state of the system in which, at any distance between particles, the attractive energy prevails over

repulsion energy. The system is unstable and quickly coagulates.

Curve 2 indicates the presence of a fairly high potential barrier and a secondary minimum. In this case, flocs are easily formed, in which the particles are separated by layers of the medium. This occurs at the secondary minimum. This state corresponds to the reversibility of coagulation. Under certain conditions, the potential barrier can be overcome and irreversible coagulation in the primary minimum occurs.

Curve 3 corresponds to the state of the system with a high potential barrier in the absence of a second minimum. Such systems have great aggregate stability.

3. BASIC REGULARITIES OF COAGULATION UNDER

ACTION OF ELECTROLYTES

The cause of coagulation can be the action of heat and cold, electromagnetic fields, hard radiation, mechanical influences, and chemical agents.

The most common cause of coagulation is the action of an electrolyte.

Electrolytes change the structure of the EDL, reducing the zeta potential (either due to the adsorption of electrolyte ions on particles, or due to compression of the diffuse part of the EDL), which leads to a decrease in the electrostatic repulsion between particles. According to the DLVO theory, as a result, particles can approach each other at distances at which attractive forces predominate, which can cause them to stick together and coagulate.

Coagulation threshold (denoted by Ck, g) is the minimum electrolyte concentration that causes a certain visible coagulation effect (color change, turbidity, appearance of sediment) over a certain period of time. The coagulation threshold is determined either visually by observing changes in the dispersed system when electrolyte solutions of different concentrations are introduced into it, or changes are recorded using appropriate instruments, most often by measuring the optical density or turbidity of the system.

Coagulation follows certain rules. Let's look at them.

Coagulation rules

– Coagulation is caused by any electrolytes, if their concentration

in the system will exceed a certain minimum called the coagulation threshold. The reason is the compression of the diesel engine. The coagulation threshold is different for different electrolytes and different disperse systems.

– Only the electrolyte ion whose charge is opposite to the charge of the colloidal particle has a coagulating effect, and its coagulating ability is expressed more strongly, the higher the valence of the counterion. This pattern is called the Schulze-Hardy rule. In accordance with this rule, the ratio of coagulation thresholds is one-; bi- and trivalent counterions looks like this:

For example, for arsenic sulfide sol As2S3, the particles of which have a negative charge, the coagulation thresholds of various electrolytes have the following values: LiCl – 58 mmol/l; MgCl2 – 0.71 mmol/l, AlCl3 – 0.043 mmol/l.

In the series of organic ions, the coagulating effect increases with increasing adsorption capacity, and therefore with charge neutralization.

– In a series of inorganic ions with the same charge, their coagulating activity increases with a decrease in their hydration (or with an increase in radius). For example, in the series of monovalent cations and anions, coagulating activity and hydration change as follows:

Aluminum" href="/text/category/alyuminij/" rel="bookmark">aluminum, silicon, iron).

3. Entropy factor , like the first two, they are thermodynamic. It operates in systems in which particles or their surface forces are involved in thermal motion. Its essence lies in the tendency of the dispersed phase to be uniformly distributed throughout the volume of the system, and this reduces the likelihood of particles colliding and sticking together.

Entropic repulsion can be explained based on the direct interaction of particles with surface layers in which there are mobile counterions or long and flexible radicals of surfactants (surfactants) and high molecular weight compounds (HMWs). Such radicals have many conformations. The approach of particles leads to a decrease in degrees of freedom or conformations, and this leads to a decrease in entropy, and, consequently, to an increase in free surface energy, which is a thermodynamically unfavorable process. Thus, this factor contributes to the repulsion of particles.

4. Structural-mechanical factor is kinetic. Its action is due to the fact that on the surface of the particles there are films that have elasticity, the destruction of which requires energy and time. Typically, such a film is obtained by introducing stabilizers into the system - surfactants and IUDs (colloidal protection). Surface layers acquire high strength characteristics due to the interweaving of navy chains and long-chain surfactants, and sometimes as a result of polymerization.

The action of structural-mechanical and other factors is manifested in such a phenomenon as colloidal protection

Colloidal protection is called an increase in the stability of colloidal systems due to the formation of an adsorption layer on the surface of particles when certain high-molecular substances are introduced into the sol .

Substances capable of providing colloidal protection are proteins, carbohydrates, pectins, and for systems with a non-aqueous dispersion medium - rubber. Protective substances are adsorbed on the surface of dispersed particles, which helps to reduce the surface energy of the system. This leads to an increase in its thermodynamic stability and ensures colloidal stability. Such systems are so stable that they acquire the ability to form spontaneously. For example, instant coffee is finely ground coffee powder treated with food-grade surfactants.

To assess the stabilizing effect of various substances, conditional characteristics have been introduced: “golden number”, “ruby number”, etc.

Golden number - this is the minimum mass (in mg) of a stabilizing substance that can protect 10 ml of red gold hydrosol (prevent color change) from the coagulating effect of 1 cm3 of 10% sodium chloride solution.

Ruby number - this is the minimum mass (in mg) of a stabilizing substance that is capable of protecting 10 cm3 of a solution of Congo red dye (Congo ruby) with a mass concentration of 0.1 kg/m3 from the coagulating effect of 1 cm3 of a 10% sodium chloride solution.

For example, the golden number of potato starch is 20. This means that 20 mg of starch, when introduced into a gold sol, prevents the coagulation of the sol when a coagulating electrolyte is added to the sol - 1 cm3 of a 10% sodium chloride solution. Without the addition of a stabilizing substance - starch, the gold sol under such conditions coagulates (destroys) instantly.

Table 1 shows the most common numbers for some protective substances.

The protective effect is of great industrial importance. It is taken into account in the manufacture of medicines, food products, technical emulsions, catalysts, etc.

Table 1. Values of the most common numbers for some protective substances

Protective substance	Golden number	Ruby number

Hemoglobin
Dextrin
Potato starch
Sodium caseinate

CONCLUSION

At today's lecture, we examined the structure of particles of the dispersed phase and the main factors influencing the stability and destruction of dispersed systems. These factors must be taken into account when obtaining stable colloidal systems, such as emulsions, aerosols, suspensions, as well as when destroying “harmful” disperse systems formed during industrial production.

Associate Professor of the Department of Physical Education

This section discusses phenomena and processes caused by aggregative stability dispersed systems.

First of all, we note that all dispersed systems, depending on the mechanism of their formation process, according to the classification of P.A. Rebinder, are divided into lyophilic, which are obtained by spontaneous dispersion of one of the phases (spontaneous formation of a heterogeneous freely dispersed system), and lyophobic, resulting from dispersion and condensation (forced formation of a heterogeneous free-dispersed system).

Lyophobic systems, by definition, must have an excess of surface energy, unless it is compensated by the introduction of stabilizers. Therefore, processes of particle enlargement spontaneously occur in them, i.e. There is a decrease in surface energy due to a decrease in specific surface area. Such systems are called aggregatively unstable.

The enlargement of particles can occur in different ways. One of them, called isothermal distillation , consists in the transfer of matter from small particles to large ones (Kelvin effect). As a result, small particles gradually dissolve (evaporate), and large ones grow.

The second way, the most characteristic and common for dispersed systems, is coagulation (from lat, coagulation, hardening), consisting in the sticking together of particles.

Coagulation in dilute systems also leads to loss of sedimentation stability and ultimately to phase separation.

The process of particle fusion is called coalescence .

In concentrated systems, coagulation can manifest itself in the formation of a volumetric structure in which the dispersion medium is evenly distributed. In accordance with the two different results of coagulation, the methods for observing this process also differ. The enlargement of particles leads, for example, to an increase in the turbidity of the solution and a decrease in osmotic pressure. Structure formation changes the rheological properties of the system, its viscosity increases, and flow slows down.

A stable free-dispersed system, in which the dispersed phase is uniformly distributed throughout the entire volume, can be formed as a result of condensation from a true solution. The loss of aggregative stability leads to coagulation, the first stage of which consists in bringing particles of the dispersed phase closer together and their mutual fixation at small distances from each other. A layer of medium remains between the particles.

The reverse process of the formation of a stable free-dispersed system from a sediment or gel (structured dispersed system) is called peptization.

A deeper coagulation process leads to the destruction of the layers of the medium and direct contact of particles. As a result, either rigid aggregates of solid particles are formed, or they completely merge in systems with a liquid or gaseous dispersed phase (coalescence). In concentrated systems, rigid volumetric solid-like structures are formed, which can again be converted into a freely dispersed system only through forced dispersion. Thus, the concept of coagulation includes several processes that occur with a decrease in the specific surface of the system.

Fig.33. Processes causing loss of stability of dispersed systems.

The aggregative stability of unstabilized lyophobic disperse systems is kinetic in nature, and can be judged by the rate of processes caused by excess surface energy.

The rate of coagulation determines the aggregative stability of the dispersed system, which is characterized by the process of adhesion (fusion) of particles.

Aggregate stability can also be thermodynamic in nature if the dispersed system does not have excess surface energy. Lyophilic systems are thermodynamically stable in aggregation; they form spontaneously and the coagulation process is not typical for them at all.

Lyophobic stabilized systems are thermodynamically resistant to coagulation; they can be removed from this state with the help of influences leading to excess surface energy (violation of stabilization).

In accordance with the above classification, thermodynamic and kinetic factors of aggregative stability of disperse systems are distinguished. Since the driving force of coagulation is excess surface energy, the main factors ensuring the stability of dispersed systems (while maintaining the surface size) will be those that reduce surface tension. These factors are classified as thermodynamic. They reduce the likelihood of effective collisions between particles and create potential barriers that slow down or even eliminate the coagulation process. The lower the surface tension, the closer the system is to thermodynamically stable.

The rate of coagulation, in addition, depends on kinetic factors.

Kinetic factors that reduce the coagulation rate are mainly associated with the hydrodynamic properties of the medium: slowing down the approach of particles, leakage and destruction of the layers of the medium between them.

The following thermodynamic and kinetic factors of stability of dispersed systems are distinguished.

1.Electrostatic factor consists in a decrease in interfacial tension due to the formation of a double electrical layer on the surface of particles, as well as in the Coulomb repulsion that occurs when they approach each other.

An electric double layer (EDL) is formed by the adsorption of ionic (dissociating into ions) surfactants. Adsorption of an ionic surfactant can occur at the interface of two immiscible liquids, for example water and benzene. The polar group of the surfactant molecule facing water dissociates, imparting to the surface of the benzene phase a charge corresponding to the organic part of the surfactant molecules (potential-determining ions). Counterions (inorganic ions) form a double layer on the side of the aqueous phase, since they interact with it more strongly.

There are other mechanisms for the formation of an electrical double layer. For example, DES is formed at the interface between water and poorly soluble silver iodide. If you add highly soluble silver nitrate to water, then the silver ions formed as a result of dissociation can complete the AgI crystal lattice, because they are part of it (specific adsorption of silver ions). As a result, the surface of the salt becomes positively charged (excess silver cations), and iodide ions will act as counterions.

It should also be mentioned the possibility of the formation of an electrical double layer as a result of the transition of ions or electrons from one phase to another (surface ionization).

The EDL formed as a result of the processes of spatial separation of charges described above has a diffuse (diffuse) character, which is due to the simultaneous influence on its structure of electrostatic (Coulomb) and van der Waals interactions, as well as the thermal motion of ions and molecules.

The so-called electrokinetic phenomena (electrophoresis, electroosmosis, etc.) are caused by the presence of a double electrical layer at the phase interface.

2. Adsorption-solvation factor consists in reducing the interfacial

tension when introducing surfactants (due to adsorption and solvation).

3. Entropy factor, like the first two, it is thermodynamic. It complements the first two factors and acts in systems in which particles participate in thermal motion. Entropic repulsion of particles can be represented as the presence of constant diffusion of particles from an area with a higher concentration to an area with a lower concentration, i.e. the system constantly strives to equalize the concentration of the dispersed phase throughout the entire volume.

4. Structural-mechanical factor is kinetic. Its effect is due to the fact that films with elasticity and mechanical strength can form on the surface of particles, the destruction of which requires energy and time.

5. Hydrodynamic factor reduces the coagulation rate due to changes in the viscosity and density of the dispersion medium in thin layers of liquid between the particles of the dispersed phase.

Typically, aggregative stability is ensured by several factors simultaneously. Particularly high stability is observed under the combined action of thermodynamic and kinetic factors.

The structural-mechanical barrier, first considered by P.A. Rebinder, is a strong stabilization factor associated with the formation of adsorption layers at the interfaces that lyophilize the surface. The structure and mechanical properties of such layers can ensure very high stability of the interlayers of the dispersion medium between the particles of the dispersed phase.

A structural-mechanical barrier arises during the adsorption of surfactant molecules that are capable of forming a gel-like structured layer at the interface, although they may not have high surface activity towards this phase boundary. Such substances include resins, cellulose derivatives, proteins and other so-called protective colloids, which are high-molecular substances.