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

Disperse system

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

Classification of disperse systems

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

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

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

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

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

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

General ideas about disperse systems

Chemical interaction in homogeneous reactions occurs during effective collisions of active particles, and in heterogeneous ones - at the interface between the phases when the reactants come into contact, moreover, the rate and mechanism of the reaction depend on the surface area, which is the greater, the more developed the surface. From this point of view, dispersed systems with a high specific surface area are of particular interest.

A dispersed system is a mixture consisting of at least two substances that do not chemically react with each other and have almost complete mutual insolubility. Disperse system - This is a system in which very fine particles of one substance are evenly distributed in the volume of another.

Considering disperse systems, two concepts are distinguished: the dispersed phase and the dispersion medium (Fig. 10.1).

Dispersed phase - This is a collection of particles of a substance dispersed to small sizes, evenly distributed in the volume of another substance. Signs of the dispersed phase are fragmentation and discontinuity.

Dispersion mediumis a substance in which the particles of the dispersed phase are evenly distributed. A sign of a dispersion medium is its continuity.

The dispersed phase can be separated from the dispersion medium by a physical method (centrifugation, separation, settling, etc.).

Figure 10.1 - Dispersed system: particles of the dispersed phase s (in the form of small solid particles, crystals, liquid drops, gas bubbles, associates of molecules or ions), having an adsorption layer d, are distributed in a homogeneous continuous dispersion medium f.

Disperse systems are classified according to various distinguishing features: dispersion, state of aggregation of the dispersed phase and dispersion medium, the intensity of interaction between them, the absence or formation of structures in disperse systems.

Classification according to the degree of dispersion

Depending on the particle size of the dispersed phase, all disperse systems are conditionally divided into three groups (Fig. 10.2).

Figure 10.2 - Classification of dispersed systems by particle size (for comparison, particle sizes in true solutions are given)

1. Coarsely dispersed systems , in which the particle size is more than 1 µm (10 –5 m). This group of dispersed systems is characterized by the following features: particles of the dispersed phase settle (or float) in the field of gravitational forces, do not pass through paper filters; they can be viewed with a conventional microscope. Coarse systems include suspensions, emulsions, dust, foam, aerosols, etc.

Suspension - is a dispersed system in which the dispersedphase is solid, and the dispersion medium is a liquid.

An example of a suspension can be a system formed by shaking clay or chalk in water, paint, paste.

Emulsion - this is a dispersed system in which the liquid dispersed phase is uniformly distributed in the volume of the liquid dispersion medium, i.e. An emulsion consists of two mutually insoluble liquids.

Examples of emulsions include milk (drops of liquid fat act as the dispersed phase, and water is the dispersion medium), cream, mayonnaise, margarine, ice cream.

When settling, suspensions and emulsions are separated (separated) into their constituent parts: the dispersed phase and the dispersion medium. So, if benzene is vigorously shaken with water, an emulsion is formed, which after some time is divided into two layers: the upper benzene and the lower water. To prevent separation of emulsions, they are added emulsifiers- substances that impart aggregate stability to emulsions.

Foam - a cellular coarse-dispersed system in which the dispersed phase is a set of gas (or vapor) bubbles, and the dispersion medium is a liquid.

In foams, the total volume of the gas in the bubbles can be hundreds of times greater than the volume of the liquid dispersion medium contained in the interlayers between the gas bubbles.

2. Microheterogeneous (orfinely dispersed ) intermediate systems in which the particle size ranges from 10 – 5 –10 –7 m. These include fine suspensions, fumes, porous solids.

3. Ultramicroheterogeneous (orcolloid-dispersed ) systems in which particles with a size of 1–100 nm (10–9 –10 –7 m) consist of 10 3_ 10 9 atoms and are separated from the solvent by an interface. Colloidal solutions are characterized by a limiting highly dispersed state, they are usually called ash, or often lyosolsto emphasize that the dispersion medium is a liquid. If water is taken as the dispersion medium, then such sols are calledhydrosols, and if the organic liquid -organosols.

For most finely dispersed systems, certain features are inherent:

low diffusion rate;

particles of the dispersed phase (i.e. colloidal particles) can only be examined using an ultramicroscope or an electron microscope;

scattering of light by colloidal particles, as a result of which they take the form of light spots in an ultramicroscope - the Tyndall effect (Fig. 10.3);

Figure 10.3 - Ultramicroheterogeneous (finely dispersed) system: a) colloidal solution; b) scheme of deflection of a narrow beam of light when passing through a colloidal solution; c) scattering of light by a colloidal solution (Tyndall effect)

on the phase interface in the presence of stabilizers (electrolyte ions), an ionic layer or a solvate shell is formed, which contributes to the existence of particles in a suspended form;
the dispersed phase is either completely insoluble or slightly soluble in the dispersion medium.

Examples of colloidal particles include starch, proteins, polymers, rubber, soaps, Aluminum and Ferum (III) hydroxides.

Classification of dispersed systems according to the ratio of aggregate states of the dispersed phase and the dispersion medium

This classification was proposed by Ostavld (Table 10.1). When schematically recording the state of aggregation of dispersed systems, the first is indicated by the letters G (gas), F (liquid) or T (solid) state of aggregation dispersed phase, and then put a dash (or a fraction sign) and record the state of aggregation of the dispersion medium.

Table 10.1 - Classification of dispersed systems

Classification of dispersed systems according to the intensity of molecular interaction

This classification was proposed by G. Freindlich and is used exclusively for systems with a liquid dispersion medium.

Lyophilic systems , in which the dispersed phase interacts with the dispersion medium and under certain conditions is able to dissolve in it - these are solutions of colloidal surfactants (surfactants), solutions of macromolecular compounds (HMCs). Among the various lyophilic systems, the most important in practical terms are surfactants, which can be both in a molecularly dissolved state and in the form of aggregates (micelles) consisting of tens, hundreds or more molecules.
Lyophobic systems , in which the dispersed phase is not able to interact with the dispersion medium and dissolve in it. In lyophobic systems, the interaction between molecules of different phases is much weaker than in the case of lyophilic systems; interfacial surface tension is high, as a result of which the system tends to spontaneous coarsening of the particles of the dispersed phase.

Classification of dispersed systems by physical state

The author of the classification is P. Rebinder. According to this classification, a disperse system is denoted by a fraction, in which the dispersed phase is placed in the numerator, and the dispersion medium is in the denominator. For example: T 1 /W 2 denotes a dispersed system with a solid phase (index 1) and a liquid dispersion medium (index 2). The Rehbinder classification divides disperse systems into two classes:

1. Freely dispersed systems – sols in which the dispersed phase does not form continuous rigid structures (grids, trusses or frames), has fluidity, and the particles of the dispersed phase do not contact each other, participating in random thermal motion and moving freely under the action of gravity. These include aerosols, lyosols, diluted suspensions and emulsions.

Examples of free-dispersed systems:

Dispersed systems in gases with colloidal dispersity (T 1 /G 2 - dust in the upper layers of the atmosphere, aerosols), with coarse dispersion (T 1 /G 2 - smoke and Zh 1 /G 2 - fogs);
Dispersed systems in liquids with colloidal dispersion (T 1 / W 2 - lyosols, dispersed dyes in water, latexes of synthetic polymers), with coarse dispersion (T 1 / W 2 - suspensions; W 1 / W 2 - liquid emulsions; G 1 / Zh 2 - gas emulsions);
Dispersed systems in solids ax: T 1 /T 2 - solid sols, for example, yellow metal sol in glass, pigmented fibers, filled polymers.

2. Cohesive-dispersed (or continuous) systems . In continuous (coherently dispersed) systems, particles of the dispersed phase form rigid spatial structures. Such systems resist shear deformation. Cohesive-dispersed systems are solid; they arise when the particles of the dispersed phase come into contact, leading to the formation of a structure in the form of a skeleton or network, which limits the fluidity of the dispersed system and gives it the ability to retain its shape. Such structured colloidal systems are called gels.

Examples of connected disperse systems:

Dispersed systems with a liquid interface (G 1 / Zh 2 - foam; Zh1 / Zh 2 - foamy emulsions);
Dispersed systems with a solid phase interface (G 1 /T 2 - porous bodies, natural fibers, pumice, sponge, charcoal; W 1 /T 2 - moisture in granite; T 1 /T 2 - interpenetrating networks of polymers).

Preparation and purification of colloidal solutions

Obtaining colloidal solutions

Colloidal solutions can be obtaineddispersive or to condensation methods.

1. Dispersion methods- these are methods for obtaining lyophobic sols by crushing large pieces to aggregates of colloidal sizes.

mechanical crushing of coarse-dispersed systems is carried out by: crushing, impact, abrasion, splitting. The grinding of particles to sizes of several tens of microns is carried out using ball mills.Very fine crushing (up to 0.1-1 micron) is achieved on specialcolloid millswith a narrow gap between a rapidly rotating rotor (10-20 thousand rpm) and a fixed body, and the particles are torn or abraded in the gap.The works of P. A. Rebinder established the phenomenon of a decrease in the resistance of solids to elastic and plastic deformations, as well as mechanical destruction under the influence of adsorption of surfactants. Surfactants facilitate dispersion and contribute to a significant increase in the degree of dispersion.

2. Condensation methods- these are methods for obtaining colloidal solutions by combining (condensing) molecules and ions into aggregates of colloidal sizes. The system transforms from homogeneous into heterogeneous, i.e., a new phase appears (dispersed phase). The prerequisite is supersaturation original system.

Condensation methods are classified according to the nature of the forces causing condensation into physical condensation and chemical condensation.

physical condensation can be carried out from vapors or by changing the solvent.

vapor condensation. The starting material is in pairs. As the temperature decreases, the vapor becomes supersaturated and partially condenses, forming a dispersed phase. Hydrosols of mercury and some other metals are obtained in this way.

Solvent replacement method. The method is based on changing the composition and properties of the dispersion medium. For example, an alcohol solution of sulfur, phosphorus or rosin is poured into water, due to a decrease in the solubility of the substance in the new solvent, the solution becomes supersaturated and part of the substance condenses, forming particles of the dispersed phase.

Chemical condensation consists in the fact that the substance that forms the dispersed phase is obtained as a result of chemical reaction. In order for the reaction to form a colloidal solution, and not a true solution or precipitate, at least three conditions must be met:

the substance of the dispersed phase is insoluble in the dispersion medium;
the rate of formation of nuclei of crystals of the dispersed phase is much greater than the rate of crystal growth; this condition is usually met when a concentrated solution of one component is poured into a highly dilute solution of another component with vigorous stirring;
one of the starting materials is taken in excess, it is it that is the stabilizer.

Methods for purification of colloidal solutions.

Colloidal solutions obtained in one way or another are usually purified from low-molecular impurities (molecules and ions). Removal of these impurities is carried out by methods of dialysis, (electrodialysis), ultrafiltration.

Dialysis– cleaning method using a semi-permeable membrane that separates the colloidal solution from a pure dispersion medium. As a semi-permeable (i.e., permeable to molecules and ions, but impermeable to particles of the dispersed phase) membranes, parchment, cellophane, collodion, ceramic filters and other finely porous materials are used. As a result of diffusion, low-molecular impurities pass into the external solution.

Ultrafiltration called dialysis, carried out under pressure in the inner chamber. Essentially, ultrafiltration is not a method for purifying sols, but only a method for concentrating them.

Optical properties of colloidal solutions

When light falls on a disperse system, the following phenomena can be observed:

the passage of light through the system;
refraction of light by particles of the dispersed phase (if these particles are transparent);
reflection of light by particles of the dispersed phase (if the particles are opaque);
scattering of light;
absorption ( absorption) of light by the dispersed phase.

light scattering observed for systems in which the particles of the dispersed phase are smaller or commensurate with the wavelength of the incident light. Recall that the particle size of the dispersed phase in colloidal solutions is 10 -7 -10 -9 m. Consequently, light scattering is a characteristic phenomenon for the colloidal systems we study.

Rayleigh created the theory of light scattering. He derived an equation that relates the scattered light intensity I to the incident light intensity I 0 . fair, provided that:

the particles are spherical;
particles do not conduct electricity(i.e. are non-metallic);
the particles do not absorb light, that is, they are colorless;
the colloidal solution is diluted to such an extent that the distance between the particles is greater than the wavelength of the incident light.

Rayleigh equation:

where V is the volume of one particle,
λ - wavelength;
n 1 is the refractive index of the particle;
n o is the refractive index of the medium.

The following conclusions follow from the Rayleigh equation:

The intensity of the scattered light is the greater, the more the refractive indices of the particle and the medium differ (n 1 - P 0 ).
If the refractive indices P 1 and n 0 are the same, then light scattering will be absent in an inhomogeneous medium.
The intensity of the scattered light is the greater, the greater the partial concentration v. Mass concentration c, g / dm 3, which is usually used in the preparation of solutions, is associated with a partial concentration by the expression:

where ρ is the particle density.

It should be noted that this dependence is preserved only in the region of small particle sizes. For the visible part of the spectrum, this condition corresponds to the values 2 10 -6 cm< r < 4 10 -6 см. С увеличением r рост I slows down, and for r > λ, scattering is replaced by reflection. The intensity of the scattered light is directly proportional to the concentration.

4. The intensity of scattered light is inversely proportional to the wavelength to the fourth power.

This means that when a white light beam passes through a colloidal solution, short waves - the blue and violet parts of the spectrum - are predominantly scattered. Therefore, a colorless sol has a bluish color in scattered light, and a reddish color in transmitted light. The blue color of the sky is also due to the scattering of light by tiny water droplets in the atmosphere. The orange or red color of the sky at sunrise or sunset is due to the fact that in the morning or evening there is mainly light that has passed through the atmosphere.

light absorption. The Rayleigh equation was derived for uncolored sols, i.e., not absorbing light. However, many colloidal solutions have a certain color, i.e. absorb light in the corresponding region of the spectrum - the sol is always colored in a color complementary to that absorbed. So, absorbing the blue part of the spectrum (435-480 nm), the sol turns yellow; upon absorption of the bluish-green part (490-500 nm), it takes on a red color.If the rays of the entire visible spectrum pass through a transparent body or are reflected from an opaque body, then the transparent body appears colorless, and the opaque body appears white. If a body absorbs radiation from the entire visible spectrum, it appears black.The optical properties of colloidal solutions capable of absorbing light can be characterized by the change in light intensity as it passes through the system. To do this, use the Bouguer-Lambert-Beer law:

where I 0 is the intensity of the incident light ; I etc is the intensity of the light transmitted through the sol; k - absorption coefficient; l- thickness of the sol layer; With- sol concentration.

If we take the logarithm of the expression, we get:

The value is called optical density solution . When working with monochromatic light, they always indicate at what wavelength the optical density was determined, denoting it D λ .

Micellar theory of the structure of colloidal systems

Let us consider the structure of a hydrophobic colloidal particle using the example of the formation of an AgI sol by the exchange reaction

AgNO 3 + KI → AgI + KNO 3.

If the substances are taken in equivalent quantities, then a crystalline precipitate of AgI precipitates. But, if one of the initial substances is in excess, for example, KI, the AgI crystallization process leads to the formation of a colloidal solution - AgI micelles.

The structure diagram of AgI hydrosol micelles is shown in Fig. 10.4.

Figure 10.4 - Scheme of an AgI hydrosol micelle formed with an excess of KI

An aggregate of molecules [ mAgI ] of 100-1000 (microcrystals) - the core, is the embryo of a new phase, on the surface of which the adsorption of electrolyte ions in the dispersion medium takes place. According to the Panet-Fajans rule, ions are better adsorbed, the same as the ions that enter the crystal lattice of the nucleus and complete this lattice. Ions that adsorb directly to the nucleus are called potential-determining, since they determine the magnitude of the potential and the sign of the surface charge, as well as the sign of the charge of the entire particle. Potential-determining ions in this system are I - ions, which are in excess, are part of crystal lattice AgI nuclei act as stabilizers and form the inner shell in the hard part of the electric double layer (EDL) of the micelle. The aggregate with adsorbed ions I - forms the core of a micelle.

To the negatively charged surface of AgI particles at a distance close to the radius of the hydrated ion, ions opposite sign(counterions) - positively charged ions K +. The layer of counterions - the outer shell of the double electric layer (EDL), is held both by electrostatic forces and by the forces of adsorption attraction. An aggregate of molecules together with a solid double layer is called a colloidal particle - a granule.

Part of the counterions due to thermal motion is located diffusely around the granule, and is associated with it only due to electrostatic forces. Colloidal particles, together with the diffuse layer surrounding it, are called micelles. The micelle is electrically neutral, since the charge of the nucleus is equal to the charge of all counterions, and the granule usually has a charge, which is called electrokinetic or ξ - zeta - potential. In an abbreviated form, the micelle structure scheme for this example can be written as follows:

One of the main provisions of the theory of the structure of colloidal particles is the concept of the structure of a double electric layer (EDL). According to modern ideas, double electrical layer DELconsists of adsorption and diffusion layers. The adsorption layer consists of:

the charged surface of the micelle core as a result of the adsorption of potential-determining ions on it, which determine the magnitude of the surface potential and its sign;
a layer of ions of the opposite sign - counterions, which are attracted from the solution to the charged surface. Adsorption layer of counterions located at a distance of a molecular radius from the charged surface. Both electrostatic and adsorption forces exist between this surface and the counterions of the adsorption layer, and therefore these counterions are bonded especially strongly to the core. The adsorption layer is very dense, its thickness is constant and does not depend on changes external conditions(electrolyte concentration, temperature).

Due to thermal motion, part of the counterions penetrate deep into the dispersion medium, and their attraction to the charged surface of the granule is carried out only due to electrostatic forces. These counterions make up the diffuse layer, which is less strongly bonded to the surface. The diffuse layer has a variable thickness, which depends on the concentration of electrolytes in the dispersion medium.

When the solid and liquid phases move relative to each other, a DEL break occurs in the diffuse part and a potential jump occurs at the phase interface, which is called electrokinetic ξ - potential(zeta - potential). Its value is determined by the difference between total charges (φ) of potential-determining ions and the number of counterion charges (ε) contained in the adsorption layer, i.e. ξ = φ - ε. The drop in the interfacial potential with distance from the solid phase deep into the solution is shown in Fig. 10.5.

Figure 10.5 DPP structure

The presence of a potential difference around the particles of a hydrophobic sol prevents them from sticking together during a collision, that is, they are a factor in the aggregate stability of the sol. If the number of diffuse ions decreases or tends to zero, then the granule becomes electrically neutral (isoelectric state) and has the least stability.

Thus, the magnitude of the electrokinetic potential determines the repulsive forces, and hence the aggregate stability of the colloidal solution. Sufficient stability of the colloidal solution is ensured at the value of the electrokinetic potential ξ = 0.07V, at values less than ξ = 0.03V, the repulsive forces are too weak to resist aggregation, and therefore coagulation occurs, which inevitably ends with sedimentation.

The magnitude of the electrokinetic potential can be determined using an electrophoresis device using the formula (10.5):

where η is the viscosity; ϑ - speed of movement of particles; l is the distance between the electrodes along the solution; E - electromotive force, D - dielectric constant.

Factors affecting ξ - potential:

The presence in the solution of an indifferent electrolyte - an electrolyte that does not contain a potential-determining ion.

The indifferent electrolyte contains a counterion. In this case, the diffusion layer is compressed and ξ falls and, as a consequence, coagulation occurs.
An indifferent electrolyte contains an ion of the same sign as a counterion, but not the counterion itself. In this case, ion exchange occurs: the counterion is replaced by ions of an indifferent electrolyte. A drop in ξ is observed, but the degree of drop will depend on the nature of the substituent ion, its valence, and the degree of hydration. Lyotropic series of cations and anions - series in which ions are arranged according to their ability to compress the diffuse layer and cause a drop in the ξ potential.

Li + - Na + - NH 4 + - K + - Rb + - Cs + - Mg 2+ - Ca 2+ - Ba 2+ ...

CH 3 COO - - F - - NO 3 - - Cl - - I - - Br - - SCN - - OH - - SO 4 2 -

2. Adding solution stabilizer electrolyte- an electrolyte containing a potential-determined ion causes an increase in ξ - potential, and therefore contributes to the stability of the colloidal system, but up to a certain limit.

Stability and coagulation of colloidal systems

The modern theory of stability and coagulation of colloidal systems was created by several well-known scientists: Deryagina, Landau, Verwey, Overbeck, and therefore it is abbreviated as DLVO theory . According to this theory, the stability of a disperse system is determined by the balance of attractive and repulsive forces that arise between particles as they approach each other as a result of Brownian motion. There are kinetic and aggregate stability of colloidal systems.

Kinetic (sedimentation) stability- the ability of dispersed particles to be in suspension and not settle (not sediment). In dispersed systems, as in natural solutions, there is Brownian motion. Brownian motion depends on particle size, dispersion medium viscosity, temperature, etc. Finely dispersed systems (sols), whose particles practically do not settle under the action of gravity, are kinetically (sedimentation) stable. They also include hydrophilic sols - solutions of polymers, proteins, etc. Hydrophobic sols, coarse systems (suspensions, emulsions) are kinetically unstable. In them, the separation of the phase and the medium takes place quite quickly.
Aggregate stability- the ability of the particles of the dispersed phase to keep a certain degree of dispersion unchanged. In aggregate-stable systems, particles of the dispersed phase do not stick together during collisions and do not form aggregates. But if the aggregate stability is violated, the colloidal particles form large aggregates, followed by the precipitation of the dispersed phase. Such a process is called coagulation, and it proceeds spontaneously, since it decreases free energy systems (ΔG<0) .

Factors that affect the stability of colloidal systems include:

The presence of an electric charge of dispersed particles. Dispersed particles of lyophobic sols have the same charge, and therefore, upon collision, they will repel each other the stronger, the higher the zeta potential. However, the electrical factor is not always decisive.
The ability to solvate (hydrate) stabilizing ions. The more hydrated (solvated) counterions in the diffuse layer, the larger the total hydrated (solvate) shell around the granules and the more stable the dispersed system.

According to the theory, during Brownian motion, colloidal particles freely approach each other at a distance of up to 10 -5 see. The nature of the change in the van der Waals forces of attraction (1) and electrostatic repulsive forces (2) between colloidal particles is shown in fig. 10.6. The resulting curve (3) was obtained by geometric addition of the corresponding ordinates. At minimum and large distances, the attraction energy prevails between the particles (I and II energy minima). In the second energy minimum, the particle cohesion energy is insufficient to keep them in an aggregated state. At medium distances corresponding to the thickness of the electrical double layer, the repulsive energy prevails with a potential barrier AB preventing particles from sticking together. Practice shows that at a zeta potential ξ = 70 mV, colloidal systems are characterized by a high potential barrier and high aggregative stability. To destabilize the colloidal system, i.e. implementation of the coagulation process, it is necessary to reduce -potential up to values 0 - 3 mV.

Figure 10.6. Potential curves of interaction of colloidal particles

Coagulation of dispersed systems

Coagulation - the process of adhesion of colloidal particles. This process proceeds relatively easily under the influence of a variety of factors: the introduction of electrolytes, non-electrolytes, freezing, boiling, mixing, exposure to sunlight, etc.. In the process electrolytic coagulation (under the influence of electrolytes) ion-exchange adsorption is often observed: coagulant ions with a higher valence or a higher adsorption potential displace the counterions first of the diffuse layer and then of the adsorption layer. The exchange takes place in an equivalent amount, but the replacement of counterions leads to the fact that, at a sufficient concentration of electrolytes in a dispersed medium, the particles lose their stability and stick together upon collision.

A number of experimental general rules have been established for electrolytic coagulation:

1. Coagulation of lyophobic sols is caused by any electrolytes, but it is observed at a noticeable rate when a certain electrolyte concentration is reached. Coagulation threshold(C to) is the minimum electrolyte concentration required to start coagulation of the sol. In this case, external changes are observed, such as cloudiness of the solution, a change in its color, etc.

where Sal is the molar concentration of the electrolyte, mmol/l;
Vel - volume of electrolyte solution, l;
Vz is the volume of the sol, l.

The reciprocal of the coagulation threshold is called the coagulating ability () of the electrolyte:

where Ck is the coagulation threshold.

2. Schultz–Hurdy rule:

the coagulating effect is exhibited by that ion, the charge of which is opposite in sign to the charge of the surface of colloidal particles (the charge of the granule), and this effect increases with increasing valency of the ion;
the coagulating effect of ions increases many times with an increase in the valency of the ions. For one - two and trivalent ions, the coagulating effect is roughly related as 1: 50: 500.

This is explained by the fact that multivalent highly charged ions of coagulants are much stronger attracted by the charged surface of a colloidal particle than monovalent ones, and much easier to displace counterions from the diffuse and even adsorption layer.

3. The coagulating effect of organic ions is much higher than that of inorganic ones. This is due to their high adsorption capacity, the ability to be adsorbed in a superequivalent amount, and also to cause recharging of the surface of colloidal particles.

4. In a number of inorganic ions with the same charges, the coagulating ability depends on the radius of the ion - coagulant: the larger the radius, the greater the coagulating ability (see. lyotropic series). This is explained by the fact that the degree of ion hydration decreases, for example, from L + to Cs + , and this facilitates its incorporation into the double ionic layer.

5. Electrically neutral particles of lyophobic colloidal sols coagulate with the highest speed.

6. The phenomenon of sol addiction. If a coagulant is quickly added to the sol, then coagulation occurs, if slowly, there is no coagulation. This can be explained by the fact that a reaction occurs between the electrolyte and the sol, as a result of which peptizers are formed that stabilize the dispersed system:

Fe (OH) 3 + HCl → FeOCl + 2H 2 O,

FeOCl → FeO + + Cl - ,

where FeO + is a peptizer for the Fe (OH) 3 sol.

The coagulating effect of a mixture of electrolytes manifests itself differently depending on the nature of the ion - coagulator. In a mixture of electrolytes, the action can be added to the coagulating action of each electrolyte. This phenomenon is called additivity ions (NaCl, KCl). If the coagulating effect of electrolyte ions decreases with the introduction of ions of another electrolyte, antagonism of ions (LiCl, MgCl 2 ). In the case when the coagulating effect of electrolyte ions increases with the introduction of ions of another electrolyte, this phenomenon is called synergy ions.

The introduction, for example, of 10 ml of a 10% NaCl solution in 10 ml of Fe (OH) 3 sol leads to coagulation of this sol. But this can be avoided if one of the protective substances is added to the sol solution: 5 ml of gelatin, 15 ml of egg albumin, 20 ml of dextrin.

Protection of colloidal particles

Colloidal protection- increasing the aggregate stability of the sol by introducing a macromolecular compound (HMC) into it. For hydrophobic sols, proteins, carbohydrates, pectins are usually used as IUDs; for non-aqueous sols - rubbers.

The protective effect of the IUD is associated with the formation of a certain adsorption layer on the surface of colloidal particles (Figure 10.7). The reverse of coagulation is called peptization.

Figure 10.7 Mechanism of peptization

To characterize the protective effect of various naval forces, Zsigmondy proposed using the golden number.golden numberis the number of milligrams of IUD to be added to 10 cm 3 0.0006% red gold sol to prevent it from turning blue (coagulation) when 1 cm is added to it 3 10% NaCl solution. Sometimes, instead of gold sol, colloidal solutions of silver (silver number), iron hydroxide (iron number), etc. are used to characterize the protective effect of the IUD.Table 10.2 shows the meaning of these numbers for some IUDs.

Table 10.2 Protective action of the IUD

Chemistry lesson in grade 11: "Dispersed systems and solutions"

The goal is to give the concept of dispersed systems, their classification. To reveal the importance of colloidal systems in the life of nature and society. Show the relativity of dividing solutions into true and colloidal.

Equipment and materials:

Technological maps: diagram-table, laboratory work, instructions.

Equipment for laboratory work:

Reagents: sugar solution, iron (III) chloride solution, a mixture of water and river sand, gelatin, paste, oil, aluminum chloride solution, sodium chloride solution, a mixture of water and vegetable oil.

Chemical beakers

Paper filters.

Black paper.

Flashlights

The course of the lesson in chemistry in grade 11:

Lesson stage	Stage features	Teacher actions	Student actions
Organizational (2 min.)	Preparing for the lesson	Greets students.	Getting ready for the lesson. Greet the teacher.
Introduction (5 min.)	Introduction to a new topic.	Leads to the topic of the lesson, tasks and “questions for yourself” Introduces the topic of the lesson. Displays the tasks of today's lesson.	Take part in the discussion of the topic. Get acquainted with the topic of the lesson and tasks (APPENDIX No. 1) Write down three questions on the topic that you would like to have answered.
Theoretical part (15 minutes.)	Explanation of the new topic.	Gives tasks for working in groups to search for new material (APPENDIX No. 3,4)	Having united in groups, they perform tasks in accordance with the technological map provided by the scheme (APPENDIX No. 4) and the requirements of the teacher.
Summing up the theoretical part (8 min.)	Conclusions based on the obtained theoretical knowledge.	In advance, he hangs out empty diagrams (A3 format) on the board for visual filling by students. (APPENDIX №4) Together with students formulates the main theoretical conclusions.	The markers fill in the schemes corresponding to the one they worked on, report on the work done in groups Write down the main conclusions in technological maps.
Practical part (10 min.)	Performing laboratory work, consolidating the experience gained.	Offers to perform laboratory work on the topic "Dispersed systems" (APPENDIX No. 2)	Perform laboratory work (APPENDIX No. 2), fill out the forms, in accordance with the instructions for laboratory work and the requirements of the teacher.
Summary and conclusions (5 min.)	Summing up the lesson. Homework.	Together with the students makes a conclusion about the topic. Suggests to correlate the questions that were written at the beginning of the lesson with those received at the end of the lesson.	Summing up, writing down homework.

Forms and methods of control:

Technological schemes for filling (APPENDIX No. 4).

Laboratory work (APPENDIX No. 2)

Control is carried out frontally in oral and written form. Based on the results of the laboratory work, the cards with laboratory work are handed over to the teacher for verification.

1. Introduction:

What is the difference between marble and granite? What about mineral and distilled water?

(answer: marble is a pure substance, granite is a mixture of substances, distilled water is a pure substance, mineral water is a mixture of substances).

Good. What about milk? Is it a pure substance or a mixture? And the air?

The state of any pure substance is described very simply - solid, liquid, gaseous.

But absolutely pure substances do not exist in nature. Even a small amount of impurities can significantly affect the properties of substances: boiling point, electrical and thermal conductivity, reactivity, etc.

Obtaining absolutely pure substances is one of the most important tasks of modern chemistry, because it is the purity of a substance that determines the possibility of manifestation of its individual means (demonstration of labeled reagents).

Consequently, in nature and the practical life of man, there are not individual substances, but their systems.

Mixtures of different substances in different states of aggregation can form heterogeneous and homogeneous systems. Homogeneous systems are the solutions that we got acquainted with in the last lesson.

Today we will get acquainted with heterogeneous systems.

2. The topic of today's lesson is DISPERSIVE SYSTEMS.

After studying the topic of the lesson, you will learn:

the importance of dispersed systems.

This, as you understand, is our main task. They are written in your technological maps. But to make our work more productive and motivated, I suggest that you write at least three questions next to the main tasks that you would like to find an answer to in the course of this lesson.

3. Theoretical part.

Dispersed systems - what is it?

Let's try together to derive a definition based on the construction of words.

1) System (from other Greek “system” - a whole made up of parts; connection) - a set of elements that are in relationships and connections with each other, which forms a certain integrity, unity.

2) Dispersion - (from lat. dispersio - dispersion) scatter of something, crushing.

Disperse systems are heterogeneous (heterogeneous) systems in which one substance in the form of very small particles is evenly distributed in the volume of another.

If we go back to the review and the previous lesson, we can remember that: Solutions are made up of two components: a solute and a solvent.

Dispersed systems, as mixtures of substances, have a similar structure: they consist of small particles that are evenly distributed in the volume of another substance.

Take a look at your technological maps and try to make two similar schemes from disparate parts: for a solution and for a dispersed system.

Check the results by comparing them with the image on the screen.

So, the dispersion medium in the disperse system plays the role of a solvent, and is the so-called. continuous phase, and the dispersed phase - the role of the solute.

Since the dispersion system is a heterogeneous mixture, there is an interface between the dispersion medium and the dispersion phase.

Classification of dispersed systems.

You can study each disperse system separately, but it is better to classify them, highlight the common, typical, and remember it. To do this, you need to determine on what grounds to do this. You are united in groups, each of which is given a task and a flowchart attached to it.

Guided by the literature offered to you, find in the text the sign of classification proposed for you to study, study it.

Create a cluster (block diagram), indicating the signs and properties of disperse systems, give examples to it. To help you with this, you have already been provided with a blank flowchart for you to complete.

4. Conclusion on the theoretical task.

Let's summarize.

From each team, I ask one person to come out and fill in the diagrams posted on the board.

(students come up and fill in each of the schemes with a marker, after which they report on the work done)

Well done, now let's fix:

What is the basis for the classification of disperse systems?

What are the types of disperse systems?

What features of colloidal solutions do you know?

What is another name for gels? What value do they have? What is their feature?

5. Practical part.

Now that you are familiar with the features of disperse systems and their classification, and also determined by what principle disperse systems are classified, I suggest that you consolidate this knowledge in practice by completing the appropriate laboratory work offered to you on a separate form.

You are in groups of 2 people. For each group, you have an appropriate form with laboratory work, as well as a specific set of reagents that you need to study.

You have been given a sample of the disperse system.

Your task: using the instructions, determine which dispersion system you were given, fill in the table and draw a conclusion about the features of the dispersion system.

6. Generalization and conclusions.

So, in this lesson, we studied in more depth the classification of dispersed systems, their importance in nature and human life.

However, it should be noted that there is no sharp boundary between the types of disperse systems. The classification should be considered relative.

And now back to the tasks set for today's lesson:

what are dispersed systems?

What are the properties of dispersed systems?

the importance of dispersed systems.

Pay attention to the questions you wrote down for yourself. In the reflection box, mark the usefulness of this lesson.

7. Homework.

We are constantly faced with dispersed systems in nature and everyday life, even in our body there are dispersed systems. In order to consolidate knowledge about the significance of disperse systems, you are invited to do your homework in the form of an essay /

Choose a disperse system that you constantly encounter in your life. Write an essay on 1-2 pages: “What is the significance of this dispersed system in human life? What similar disperse systems with similar functions are still known?

Thank you for the lesson.

The classification of dispersed systems can be carried out on the basis of various properties: by dispersion, by the state of aggregation of phases, by the interaction of a dispersed phase and a dispersed medium, by interparticle interaction.

Classification by dispersion

The dependence of the specific surface area on the dispersion Ssp = f(d) is graphically expressed by an equilateral hyperbola (Fig.).

It can be seen from the graph that with a decrease in the transverse dimensions of the particles, the specific surface area increases significantly. If a cube with an edge size of 1 cm is crushed to cubic particles with dimensions d = 10 -6 cm, the value of the total interfacial surface will increase from 6 cm 2 to 600 m 2.

At d ≤ 10 -7 cm, the hyperbola breaks off, since the particles are reduced to the size of individual molecules, and the heterogeneous system becomes homogeneous, in which there is no interfacial surface. According to the degree of dispersion, disperse systems are divided into:

coarse systems, d ≥ 10 -3 cm;
microheterogeneous systems, 10 -5 ≤ d ≤ 10 -3 cm;
colloidal-dispersed systems or colloidal solutions, 10 -7 ≤ d ≤ 10 -5 cm;
true solutions, d ≤ 10 -7 cm.

It should be emphasized that the particles of the dispersed phase in colloidal solutions have the largest specific surface area.

Classification according to the state of aggregation of phases

The classification according to the state of aggregation of the phases was proposed by Wolfgang Ostwald. In principle, 9 combinations are possible. Let's put them in the form of a table.

Aggregate state of the dispersed phase	Aggregate state of a dispersed medium	Legend	System name	Examples
G	G	y/y	aerosols	Earth's atmosphere
and	G	w/g		fog, stratus clouds
tv	G	tv/g		smoke, dust, cirrus clouds
G	and	g/f	gas emulsions, foams	carbonated water, soap foam, therapeutic oxygen cocktail, beer foam
and	and	w/w	emulsions	milk, butter, margarine, creams, etc.
tv	and	tv/w	lyosols, suspensions	lyophobic colloidal solutions, suspensions, pastes, paints, etc. d.
G	tv	g/tv	hard foam	pumice, hard foams, polystyrene, foam concrete, bread, porous bodies in gas, etc. d.
and	tv	g TV	solid emulsions	water in paraffin, natural minerals with liquid inclusions, porous bodies in liquid
tv	tv	tv/tv	solid sols	steel, cast iron, colored glasses, precious stones: Au sol in glass - ruby glass (0.0001%) (1 t of glass - 1 g of Au)

Classification according to the interaction of the dispersed phase and the dispersed medium (according to interfacial interaction).

This classification is only suitable for systems with a liquid dispersion medium. G. Freindlich proposed to subdivide dispersed systems into two types:

lyophobic, in which the dispersed phase is not able to interact with the dispersion medium and, consequently, dissolve in it; these include colloidal solutions, microheterogeneous systems;
lyophilic, in which the dispersed phase interacts with the dispersion medium and under certain conditions is able to dissolve in it, these include solutions of colloidal surfactants and solutions of IUDs.

Classification by interparticle interaction

According to this classification, disperse systems are divided into:

freely dispersed (structureless);
connected dispersed (structured).

In freely dispersed systems, the particles of the dispersed phase are not bound to each other and are able to move independently in the dispersion medium.

In coherently dispersed systems, the particles of the dispersed phase are connected to each other due to intermolecular forces, forming peculiar spatial networks or frameworks (structures) in the dispersion medium. The particles that form the structure are not capable of mutual displacement and can only perform oscillatory motions.

List of used literature

Gelfman M. I., Kovalevich O. V., Yustratov V. P. colloidal chemistry. 2nd ed., ster. - St. Petersburg: Publishing house "Lan", 2004. - 336 p.: ill. ISBN 5-8114-0478-6 [p. 8-10]

Systems in which one substance, which is in a dispersed (crushed or crushed) state, is evenly distributed in the volume of the second substance, are called dispersed.(The concept of "dispersed" comes from the Latin dispersus - scattered, scattered).

Dispersed systems, as a rule, are heterogeneous and consist of two or more phases. The continuous continuous phase in them is called differently dispersion medium, and discrete or discontinuous particles of another substance located in this medium - dispersed phase.

The measure of fragmentation of dispersed systems is either the transverse particle size of the dispersed phase a, or its reciprocal, degree of dispersionD, which has the dimension 1/m or m –1:

The degree of dispersion is a value that shows how many particles can be closely packed on a segment 1 m long.

The concept of transverse size has a clearly defined meaning for spherical particles ( a equal to the diameter d of these particles) and for particles having the shape of a cube ( a equal to the length of the edge l Cuba). For particles of a different shape (filamentous, lamellar, etc.), the value a depends on the direction in which the measurements are taken. In such cases, very often a different shape of particles is equated with a spherical one with a certain value d, considering that these conditional particles behave in systems in exactly the same way as real ones.

Sometimes another characteristic of the degree of dispersion is used - the so-called specific surface areaS beats ,which corresponds to the total surface (m 2 ) all particles of the dispersed phase having a total mass of 1 kg or a total volume of 1 m 3 . In the first case S beats has dimension m 2 /kg, in the second - 1/m or m –1 .

Thus, the specific surface area can be defined as follows:

whereS– total area (m 2 ) surfaces of particles of the dispersed phase;

mis the total mass (kg) of these particles;

V– total volume (m 3 ) of these particles.

There is a directly proportional relationship between S beats. and D:

wherek- coefficient of proportionality.

In dispersed systems, the particles of the dispersed phase are rarely of the same size. They can only be obtained artificially, using special techniques. In this case, the resulting systems are called monodisperse. Real systems are often polydisperse and the particle sizes of the dispersed phase in them lie in a certain range.

All disperse systems according to the size of the particles of the dispersed phase can be conditionally divided into 3 groups (Table 14).

Table 14. Classification of dispersed systems according to the particle size of the dispersed phase

The boundary between these types of systems cannot be established precisely. For individual systems, it can be shifted in one direction or another, depending on the chemical nature of the substance of the dispersed phase and the dispersion medium, and the physicochemical properties of the system itself.

A distinctive feature of true solutions is that the particles of the dispersed phase in them are separate molecules or ions. As a result, in these systems there is no interfacial surface and therefore, unlike other dispersed systems, they are homogeneous.

In colloid-dispersed systems (or sols), particles of the dispersed phase are formed by several tens or hundreds of molecules, ions, or atoms connected to each other by various bonds.

The transverse dimensions of such particles range from 1 nm to 300–400 nm (1 10–9 ÷ 4 10–7 m). Due to their small size, they cannot be visually detected with a light microscope. A characteristic feature of colloidal systems is their significant specific surface (Table 15), as a result of which they are often called ultramicroheterogeneous.

Table 15 Change in surface area during crushing of 1 cm 3 of a substance

This leads to the fact that most of all molecules or atoms of the substance of the dispersed phase are located on the surface of its particles, i.e. at the phase boundary. As a result, colloidal systems acquire special properties that sharply distinguish them from other types of disperse systems.

The physicochemical properties of colloidal systems, the processes occurring on the surface of their particles, are studied in the section of physical chemistry, which has become an independent field of science -colloid chemistry.

Name " colloid chemistry"comes from the Greek word kola- glue and eidos- view. It was proposed by the English scientist Thomas Graham, who studied diffusion from solutions of various substances through plant and animal membranes in the second half of the 19th century.

Thomas Graham (1805 - 1869) Scottish chemist. Graham's works are devoted to diffusion in gases and liquids, colloid chemistry, and the chemistry of polybasic acids. Graham came up with the idea of separating all substances into crystalloids and colloids. The former form stable solutions and crystallize, the latter give unstable solutions and easily coagulate, forming a gelatinous precipitate. These works laid the foundations of colloid chemistry. Continuing the study of gases, Graham in the late 1860s discovered the phenomenon of occlusion - the absorption of gases by microscopic cavities in metals.

At the same time, substances that quickly diffuse in solution and pass well through the membrane were named by him. crystalloids, because when planted, they form dense precipitates having a crystalline structure.

Substances that have little ability to diffuse in solution and do not pass through dialysis membranes are called colloids, i.e. glue-like. The emergence of this name is due to the fact that the first objects of this type, studied by the scientist T. Graham, were solutions of various high-molecular compounds: polysaccharides, proteins, which, when precipitated, usually form sticky precipitates with an amorphous structure.

Further work in this area by other scientists: I.G. Borschova, P.P. Weimarn, D.I. Mendeleev - showed that the same substance, depending on the type of dispersion medium, can exhibit both the properties of colloids and the properties of crystalloids in solutions. So, for example, soap dissolved in H 2 O, has the properties of a colloid, and a solution of soap in alcohol - a crystalloid; table salt dissolved in H 2 O, forms a true solution, and in benzene - colloidal.

Thus, there is no reason to subdivide chemical compounds into two separate classes, but we can only talk about the crystalloid and colloidal state of a substance in solution.

In the crystalloid state, the substance is present in solutions in the form of individual molecules or ions, and in the colloidal state, in the form of crushed (dispersed) small particles consisting of a certain number of molecules, ions or atoms, evenly distributed throughout the volume of the system.

Solutions of macromolecular compounds, despite the fact that in most cases they are true, also belong to the subject of research in colloidal chemistry, because in many respects similar in properties to colloidal systems.

Colloidal chemistry also studies dispersed systems with larger particles of the dispersed phase compared to sols. Their transverse dimensions lie, as a rule, in the range of 10–7 m ÷ 10–5 m. In most cases, such particles are visible in an optical microscope, their specific surface is hundreds of times smaller than in sols (Table 15). These systems are called microheterogeneous or coarsely dispersed.

Disperse systems are widespread in nature and play an important practical role, which determines not only the scientific but also the national economic significance of colloidal chemistry.

Many precious stones, various minerals in the bowels of the Earth, food products, smoke, clouds, dust, muddy water in natural reservoirs, soil, clay, oil, etc. are colloidal or coarsely dispersed systems.

Colloidal systems play an important role in biochemistry and medicine. The most important biological fluids: blood, plasma, lymph, cell cytoplasm, cerebrospinal fluid - are dispersed systems in which a number of substances (proteins, cholesterol and many others (Table 16)) are in a colloidal state. From a chemical point of view, the human body as a whole is a complex set of dispersed systems of various types. In this regard, the various aspects of the phenomena occurring in a living organism, their cause-and-effect relationships, the possibility of influencing them and adjusting them from the outside can only be understood as the nature of the colloidal state of matter is known.

Table 16 Sizes of some dispersed particles

Many physical and chemical properties of a substance in the form of dispersed particles differ significantly from similar properties of its larger formations. These differences are called size or scale effects. They are more pronounced, the smaller the size of dispersed particles, and therefore are especially characteristic of particles in the nanometer range (1 10 –9 m ÷ 9 10 –9 m), the so-called nanoparticles.

The special qualities of nanoparticles (including their quantum properties) open up fundamentally new practical applications in chemistry, physics, biology, and medicine. Recently, the study of methods for obtaining, structure, physical and chemical properties of dispersed particles and dispersed systems (the development of so-called nanotechnologies) is one of the urgent problems not only of colloid chemistry, but also of a number of other scientific disciplines.