As a rule, surfactants are organic compounds with amphiphilic structure, that is, their molecules contain a polar part, a hydrophilic component (functional groups -OH, -COOH, -SOOOH, -O-, etc., or, more often, their salts -ONa, -COONa, -SOOONa and etc.) and non-polar (hydrocarbon) part, hydrophobic component. An example of a surfactant is ordinary soap (a mixture of sodium salts of fatty carboxylic acids - oleate, sodium stearate, etc.) and SMS(synthetic detergents) as well as alcohols, carboxylic acids, amines, etc.

Surfactant classification

Anionic surfactants
- contain one or more polar groups in the molecule and dissociate in an aqueous solution with the formation of long-chain anions, which determine their surface activity. These are the groups: COOH (M), OSO 2 OH (M), SO 3 H (M), where M is metal (mono-, di- or trivalent). The hydrophobic part of the molecule is usually represented by saturated or unsaturated aliphatic chains or alkylaromatic radicals.

In anionic surfactants, the cation can be not only with a metal, but also with an organic base. This is often di- or triethanolamine. Surface activity begins to manifest itself at the length of the hydrocarbon hydrophobic chain C 8 and with an increase in the chain length, it increases up to a complete loss of surfactant solubility in water. Depending on the structure of the intermediate functional groups and the hydrophilicity of the polar part of the molecule, the length of the hydrocarbon part can reach C 18 .

Cationic surfactants
- dissociate in an aqueous solution to form a surface-active cation with a long hydrophobic chain and an anion (usually a halide, sometimes an anion of sulfuric or phosphoric acid).

Nitrogen-containing compounds predominate among cationic surfactants; also used substances that do not contain nitrogen: sulfonium compounds + X- and sulfoxonium + X-, phosphonium + X-, arsonium + X-, iodonium.

Cationic surfactants lower the surface tension less than anionic surfactants, but they chemically interact with the surface of the adsorbent, for example. with cellular proteins of bacteria, causing a bactericidal effect.

Ampholytic surfactants
- depending on the pH value, they exhibit the properties of cationic or anionic surfactants.

They contain in the molecule a hydrophilic radical and a hydrophobic moiety capable of being an acceptor or a proton donor, depending on the pH of the solution. Typically, these surfactants include one or more basic and acidic groups, and may also contain a nonionic polyglycolic group. At some pH values, called. isoelectric point, surfactants exist in the form of zwitterions. The ionization constants of acidic and basic groups of truly soluble amphoteric surfactants are very low, however, cation-oriented and anion-oriented zwitter ions are most often encountered. The cationic group is usually a primary, secondary or tertiary ammonium group, a pyridine or imidazoline residue. Instead of N m. atoms S, P, As, etc. Anionic groups are carboxyl, sulfonate, sulfoether or phosphate groups.

Nonionic PA
- high molecular weight compounds that do not form ions in an aqueous solution.

Their solubility is due to the presence in the molecules of hydrophilic ether and hydroxyl groups, most often a polyethylene glycol chain. When dissolved, hydrates are formed due to the formation of a hydrogen bond between the oxygen atoms of the polyethylene glycol residue and water molecules. Due to the rupture of the hydrogen bond with increasing temperature, the solubility of nonionic surfactants decreases, so for them the cloud point is the top. the temperature limit of micelle formation is an important indicator. Many compounds containing a mobile H atom (acids, alcohols, phenols, amines) react with ethylene oxide to form nonionic surfactants RO (C2H4O) nH. The polarity of one oxyethylene group is significantly less than the polarity of any acid group in anionic surfactants. Therefore, to give the molecule the required hydrophilicity and HLB value, depending on the hydrophobic radical, from 7 to 50 oxyethylene groups are required. A characteristic feature of nonionic surfactants is a liquid state and low foaming in aqueous solutions.

Nonionic surfactants combine well with other surfactants and are often included in formulations

Due to their detergent, wetting, emulsifying, dispersing and other valuable properties, surfactants are widely used in the production of detergents and cleaning products, cosmetics and pharmaceuticals. latex, rubber. polymers, plant protection chemicals, textiles, leather and paper, building materials, corrosion inhibitors, during the extraction, transportation and processing of oil, etc. Most of the surfactants are used for the production of synthetic detergents (CMC).

The use of surfactants (surfactants)

Surfactants are widely used in industry, agriculture, medicine and everyday life. The world production of surfactants is growing every year, and the share of non-ionic substances in the total output is constantly increasing. All types of surfactants are widely used in the preparation and use of synthetic polymers. The most important area of ​​consumption of micelle-forming surfactants is the production of polymers by emulsion polymerization. The type and concentration of the selected surfactants (emulsifiers) largely depend on the technological and physicochemical properties of the resulting latexes. Surfactants are also used in suspension polymerization. Usually used high-molecular surfactants - water-soluble polymers (volivinyl alcohol, cellulose derivatives, vegetable adhesives, etc.). By mixing varnishes or liquid oil-resin compositions with water in the presence of emulsifiers, emulsions are obtained that are used in the manufacture of plastics, imitation leather, nonwovens, impregnated fabrics, water-borne paints, etc. High-molecular water-soluble surfactants, in addition to being used in the above technological. processes are used as flocculants in various types of water treatment. With their help, suspended pollutants are removed from wastewater, as well as from drinking water..

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Or CMC), with the achievement of which, upon adding a surfactant to the solution, the concentration at the interface remains constant, but at the same time self-organization of surfactant molecules occurs in the bulk solution (micelle formation or aggregation). As a result of this aggregation, so-called micelles are formed. A distinctive feature of micelle formation is the turbidity of the surfactant solution. Aqueous solutions of surfactants, during micelle formation, also acquire a bluish tint (gelatinous hue) due to the refraction of light by micelles.

Methods for determining the CMC:

• Surface tension method
• Method for measuring the contact angle (contact angle) with TV. or liquid surface (Contact angle)
• Spindrop / Spinning drop method

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  As a rule, surfactants are organic compounds with amphiphilic structure, that is, their molecules contain a polar part, a hydrophilic component (functional groups -OH, -COOH, -SOOOH, -O-, etc., or, more often, their salts -ONa, -COONa, -SOOONa and etc.) and non-polar (hydrocarbon) part, hydrophobic component. An example of a surfactant is ordinary soap (a mixture of sodium salts of fatty carboxylic acids - oleate, sodium stearate, etc.) and CMC (synthetic detergents), as well as alcohols, carboxylic acids, amines, etc.

  Surfactant classification

  The use of higher fatty alcohols for the production of surfactants

  Surfactant class	Surfactant type		Chemical formula	Synthesis reagent	Synthesis scheme	Sources of
  Nonionic surfactants	Alkoxylates	ethoxylates	R − O− (CH 2 CH 2 O) n H	ethylene oxide	ROH + n (CH 2 CH 2) O → RO− (CH 2 CH 2 O) n H This reaction takes place in the presence of an alkali at a temperature up to 160 ° C and a pressure up to 0.55 MPa. Typically, C 9 -C 15 alcohols are used in combination with 6-7 moles of ethylene oxide.	: [p. 31, 35]: [p. 137-139]
  		propoxylates	R − O− (CH 2 CH (CH 3) O) n H	propylene oxide
  		butoxylates	R − O− (CH 2 CH (C 2 H 5) O) n H	butylene oxide
  	Alkyl glycosides		R− (O − C 6 H 10 O 5) n H	glucose	ROH + nC 6 C 12 O 6 → R− ​​(O − C 6 H 10 O 5) n H + nH 2 O This reaction takes place in the presence of sulfonic acids at a temperature of up to 140 ° C. Another option is the preliminary production of butyl ethers followed by transesterification. The number of glycosidic groups ranges from 1 to 3.	: [p. 38] : [p. 149]
  Anionic surfactants	Carboxyethoxylates		R − O− (CH 2 CH 2 O) n СH 2 COOH	chloroacetic acid	RO (CH 2 CH 2 O) n H + ClCH 2 COOH → RO (CH 2 CH 2 O) n СH 2 COOH + HCl The reaction proceeds in the presence of alkali, the acid is released by acidifying the aqueous solution and separating the water-salt phase.	: [p. 40] : [p. 126-127]
  	Phosphates and polyphosphates		ROP (OH) 2 O; (RO) 2 P (OH) O	phosphorus (V) oxide	3ROH + P 2 O 5 → ROP (OH) 2 O + (RO) 2 P (OH) O Adding powdered phosphorus oxide to anhydrous alcohols in an anhydrous medium at 50-70 ° C and vigorous stirring.	: [p. 54] : [p. 122-123]
  	Sulfosuccinates		ROC (O) CH 2 CH (SO 3 Na) COOH; ROC (O) CH 2 CH (SO 3 Na) COOR	maleic anhydride, sodium sulfite	ROH + (COCH = CHCO) O → ROC (O) CH = CHCOOH ROC (O) CH = CHCOOH + Na 2 SO 3 → ROC (O) CH 2 CH (SO 3 Na) COONa Esterification of alcohols with raspberry anhydride (T up to 100 ° C) and further addition to sodium sulfite ether on heating.	: [p. 52-53]
  	Alkyl sulfates		R − O − SO 3 H	sulfuric acid, sulfur (VI) oxide, chlorosulfonic acid	ROH + SO 3 → ROSO 3 H Direct sulfonation of alcohols with subsequent neutralization of the solution with alkali.	: [p. 55-56]
  	Alkyl ether sulfates		R− (CH 2 CH 2 O) n OSO 3 H

  Some other alcohols are also used in the production of surfactants: glycerin (esters with fatty acids - emulsifiers), sorbitol (sorbitans), monoethanolamine and diethanolamine (alkanolamides).

  Influence of surfactants on environmental components

  Surfactants are divided into those that are rapidly destroyed in the environment and those that are not destroyed and can accumulate in organisms in unacceptable concentrations. One of the main negative effects of surfactants in the environment is a decrease in surface tension. For example, in the ocean, a change in surface tension leads to a decrease in the retention of CO 2 and oxygen in the body of water. Only a few surfactants are considered safe (alkyl polyglucosides), since carbohydrates are the products of their degradation. However, when surfactants are adsorbed on the surface of earth / sand particles, the degree / rate of their degradation decreases many times. Since almost all surfactants used in industry and households have positive adsorption on particles of earth, sand, clay, under normal conditions they can release (desorb) heavy metal ions retained by these particles, and thereby increase the risk of these substances getting into human organism.

  Surfactants are compounds that affect the magnitude of the surface tension. In the process of interaction of liquid molecules, adhesion forces are formed between them. This force will be different in the surface and inner (deep) layers. Considering the state of the liquid, it is easy to establish that the particles that are directed into the system are surrounded from different sides by the same molecules that affect them. The resultant of all the forces that act on such a molecule is zero. Therefore, liquids have the smallest surface for a given volume. This is clearly manifested in the spherical shape of the droplets. The presence of impurities of various compounds in liquids determines the magnitude of the surface tension.

  The structure of surfactant molecules

  Particles of fatty acids and alcohols consist of two parts, which have different properties; therefore, these compounds are often called diphilic structures. One part of the molecule is represented by a hydrocarbon chain, while the other is represented by different functional groups (amino group, hydroxyl, carboxyl, sulfo group). The longer the hydrocarbon chain, the more pronounced the particles will be; they will interact weaker with water.

  Organic: proteins, soaps, alcohols, ketones, aldehydes, tannides, ketones, etc. Surfactants do not affect surface tension (starch, glucose, fructose).

  Nonionic surfactants (NSAS) are high molecular weight biocompounds that do not form ions in water. These substances enter the water bodies together with industrial (chemical, textile, household (the use of various synthetic detergents in everyday life) wastewater, as well as wastewater from agricultural land (herbicides, fungicides, insecticides, as well as folios as emulsifiers).

  Surfactants: harm and benefit

  Surface tension is of great importance for intestinal absorption processes. For example, fats and lipids enter the food tract as droplets. The latter are emulsified in the small intestine with the help of bile acids. Only then are these fats hydrolyzed by lipolytic enzymes. Very often, soap (surfactants) is added to insecticides to improve performance. The performed manipulation allows insecticides to better interact with the surface of the insect's body. However, surfactants have not only positive but also negative effects on the body. For example, the shampoo contains very harmful foaming agents (surfactants) such as sodium and ammonium lauryl sulfate, ammonium and sodium laureth sulfate. It is believed that these components have a carcinogenic effect.

  Disinfection of water occurs under the influence of ultraviolet radiation from the Sun. Other factors also adversely affect the processes of self-purification of water bodies. Chemical pollution of water bodies with industrial effluents, biogenic elements (nitrogen, phosphorus, etc.) inhibits natural oxidative processes, kills microorganisms. The rate of self-purification of a reservoir and the decomposition of carbon-containing compounds, including surfactants, depends on temperature, oxygen availability, nutritional regime of the aquatic environment, i.e. from those factors that determine its microbiological activity. In oxygen-depleted water, the decomposition of carbon-containing compounds is generally slowed down.

  Surfactants (surfactants) are chemical compounds that, concentrating on the water-air interface, cause a decrease in surface tension.

  According to their chemical structure, surfactants are organic compounds with a "diphilic structure", that is, their molecules contain a polar part, a hydrophilic component (functional groups - OH, - COOH, - O-, etc.) and non-polar (hydrocarbon ) part, hydrophobic component.

  A traditional example of surfactants can be ordinary soap (a mixture of sodium salts of fatty carboxylic acids - sodium oleate, stearate, etc.) and CMC (synthetic detergents), as well as alcohols, carboxylic acids, amines, etc. Surfactants may also contain bleaching agents, corrosion inhibitors, enzymes, and fragrances. The formed products of hydrolysis themselves do not pose a threat to humans and animals living in the water. However, one must take into account the effect of phosphorus on plants. An excess of phosphorus initiates the following chain: rapid plant growth - plant death - decay - depletion of oxygen in water bodies - deterioration of the life of organisms.

  In an aqueous solution, self-organization of surfactant molecules occurs into special associate structures called micelles. A distinctive feature of micelle formation is the turbidity of the surfactant solution. Aqueous solutions of surfactants, during micelle formation, also acquire a bluish tint (gelatinous hue) due to the refraction of light by micelles.

  Upon reaching the solubility limit, surfactants form conglomerates, or micelles - a kind of accumulation of molecules that have a spherical or plate-like structure

  In the world production of surfactants, anionic substances make up most of them. Among them, the following main groups can be distinguished: carboxylic acids, as well as their salts, alkyl sulfates (sulfoesters), alkyl sulfonates and alkyl aryl sulfonates, etc. products.

  The most common are sodium and potassium soaps of fatty and resin acids; neutralized products of sulfonation of higher fatty acids, olefins, alkylbenzenes. The second place in terms of industrial production is occupied by nonionic surfactants - polyethylene glycol ethers. Most non-ionic surfactants are obtained by the addition of ethylene oxide to aliphatic alcohols, alkyl phenols, carboxylic acids, amines, and other compounds with a reactive hydrogen atom.

  The range of surfactants is extremely large. Surfactant applications include:

  Detergents. The main use of surfactants is as an active component of detergents and cleaning agents, soaps, for the care of premises, dishes, clothes, things, cars, etc. In 2007, Russia produced more than 1 million tons of synthetic detergents, mainly washing powders ...

  Cosmetics. The main direction of the use of surfactants in cosmetics is the use in shampoos, where the surfactant content can reach tens of percent of the composition. Surfactants are also used in small amounts in toothpaste, lotions, tonics and other products.

  Textile industry. Surfactants are mainly used to remove static electricity on synthetic fibers.

  Leather industry. Protection of leather products from light damage and sticking.

  Paint and varnish industry. Surfactants are used to lower the surface tension so that the paint material can easily penetrate and fill small depressions on the surface of the workpiece, while displacing other material from the depression (eg water).

  Paper industry. Surfactants are used to separate ink and cooked cellulose when recycling used paper. Surfactant molecules are adsorbed on the ink pigment. The pigment becomes hydrophobic. Then the air is passed through a solution of pigment and cellulose. Air bubbles are adsorbed on the hydrophobic part of the surfactant and the ink pigment particles float to the surface. See flotation.

  Metallurgy. Surfactant emulsions are used to lubricate rolling mills. Reduces friction and is stable at high temperatures while the oil burns out.

  Plant protection. Surfactants are widely used in agronomy and agriculture to form emulsions. Surfactants are used to increase the efficiency of transporting nutrients into plants through membrane walls. Food industry. Surfactants are used in ice cream, chocolate, whipped cream and sauces for salads and other dishes.

  Oil production. Surfactants are used for hydrophobization of the bottomhole formation zone (BHZ) in order to increase oil recovery.

  Why are surfactants so terrible for the environment and humans? The fact is that surfactants can quickly degrade in the environment or, conversely, not degrade, but accumulate in organisms in unacceptable concentrations. One of the main negative effects of surfactants in the environment is a decrease in surface tension. For example, in the ocean, changes in surface tension reduce the retention of carbon dioxide CO2 in the body of water. According to some data, surfactant adsorbed on the surface of water in reservoirs increases the absorption of radar signal waves. In other words, radars and satellites pick up the signal from objects under water in water bodies with a certain concentration of surfactants worse.

  Only a few surfactants are considered safe (alkyl polyglucosides), since carbohydrates are the products of their degradation. However, after being adsorbed on the surface of earth / sand particles, the degree / rate of surfactant degradation decreases several times. Since almost all surfactants used in industry and households have positive adsorption on particles of earth, sand, clay, under normal conditions they can release (desorb) heavy metal ions retained by these particles, and thereby increase the risk of these substances getting into human organism.

  Most surfactants have an extremely wide range of negative effects both on the human body and aquatic ecosystems, and on water quality. First of all, they impart persistent specific odors and tastes to water, and some of them can stabilize unpleasant odors caused by other compounds. So, the content of surfactants in water in the amount of 0.4-3.0 mg / dm3 gives it a bitter taste, and 0.2-2.0 mg / dm3 gives it a soapy kerosene smell.

  One of the main physicochemical properties of surfactants is high foaming ability, and in relatively low concentrations (about 0.1-0.5 mg / dm3). The appearance of a layer of foam on the surface of the water makes it difficult for the heat and mass exchange of the reservoir with the atmosphere, reduces the flow of oxygen from the air into the water (by 15-20%), slowing down the sedimentation and decomposition of suspended matter, the processes of mineralization of organic substances, and thereby impairs the processes of self-purification. Some insoluble surfactants, when they hit the surface of water, form insoluble films, spreading with a sufficient spreading area into monolayers.

  A significant part of the anthropogenic load on surface water bodies is wastewater containing synthetic surfactants (SAS), which are part of all household and most industrial wastewater.

  95-98% of the total amount of detergents used in our country - synthetic detergents (CMC), produced by industry, are anionic and nonionic surfactants and detergents based on them, which, as a rule, are characterized by low biodegradability and, due to their chemical nature, have significant negative impact on water bodies.

  Once in water bodies, surfactants are actively involved in the processes of redistribution and transformation of other pollutants (such as chlorophos, aniline, zinc, iron, butyl acrylate, carcinogens, pesticides, oil products, heavy metals, etc.), activating their toxic effect. Surfactants are associated with 6-30% copper, 3-12% lead and 4-50% mercury in colloidal and dissolved form. An insignificant concentration of surfactants (0.05-0.10 mg / dm3) in water is sufficient to activate toxic substances.

  With a low content of surfactants in water, coagulation and sedimentation of impurities is often observed, due to a decrease or even removal of the electrokinetic potential of particles due to the sorption of oppositely charged organic ions of the surfactant.

  In addition, surfactants somewhat inhibit the decay of carcinogenic substances, inhibit the processes of biochemical oxygen consumption, ammonification and nitrification.

  During the hydrolysis of surfactants and detergents in the aquatic environment, a phosphate complex is formed, which leads to the eutrophication of water bodies. CMC supplies, on average, 20 to 40% of total phosphorus to natural waters.

  Surfactants can also contribute to an increase in the epidemiological hazard of water, and also contribute to the chemical pollution of water with substances of high biological activity.

  Most surfactants and their decay products are toxic for various groups of aquatic organisms: microorganisms (0.8-4.0 mg / dm3), algae (0.5-6.0 mg / dm3), invertebrates (0.01-0.9 mg / dm3) even in low concentrations, especially with chronic exposure. Surfactants can accumulate in the body and cause irreversible pathological changes.

  Many researchers have noted the dependence of the degree and nature of the effect of surfactants on aquatic organisms on the chemical structure of substances. The strongest negative effect is exerted by alkylaryl sulfonates, i.e. substances with a benzene ring in their molecule, and some non-ionic substances. The least toxic surfactants based on polymers are somewhat more toxic alkyl sulfates and alkyl sulfonates. Compounds with a straight side chain are more toxic than those with a highly branched carbon chain.

  The toxicity of surfactants in the aquatic environment is largely reduced due to their biodegradability. Surfactants, to one degree or another, are absorbed by the entire flora and fauna of water bodies.

  Among the main reasons for the pollution of water bodies with these substances is also often noted the ability of surfactants, emitted by the enterprises that release them into the air in significant quantities, to penetrate with atmospheric precipitation into open water bodies and seep into the near underground layers of groundwater. Surfactants also enter groundwater during wastewater treatment in filtration fields and, as a rule, carry along with them other contaminants. Surfactants from underground waters pass practically unhindered into surface water sources and through treatment facilities into drinking water. In addition, getting into natural waters, surfactants are sorbed by the particles of mineral and organic origin contained in them, settle to the bottom of reservoirs and thereby create centers of secondary pollution.

  The great difficulty in water purification from surfactants lies in the fact that various surfactants in water bodies are most often found in the form of a mixture of individual homologues and isomers, each of which exhibits individual properties when interacting with water and bottom sediments, and the mechanism of their biochemical decomposition is also different. Studies of the properties of surfactant mixtures have shown that in concentrations close to the threshold, these substances have the effect of summing up their harmful effects. Synergy is also observed in the interaction of the anionic substances included in the mixture; therefore, the total effect of N exerted by the surfactant mixture is determined as follows:

  body of water self-purification natural biological

  N = Q1P1 + Q2P2 +… + QnPn = 2% QiPi,

  where Qi is the influence exerted by each anion-active substance included in the mixture, taken at a concentration equal to the total concentration of the mixture; Pi is the relative proportion of each substance included in the mixture.

  Most of the newly synthesized surfactants entering water bodies and streams with wastewater are capable of accumulating in them for a long time, especially if they consist of a mixture of isomers with different cleavage rates. Based on this, the rationing of the presence of a mixture of surfactants in water bodies should be carried out according to the rules recommended for mixtures of chemicals.

  The maximum permissible concentration (MPC) of surfactants in the water of reservoirs is 0.5 mg / dm3, nonionic - 0.1 mg / dm3. The limiting indicator of the harmfulness of synthetic surfactants is their foaming ability, which must also be taken into account when reusing treated wastewater in the technical water supply of industrial enterprises.

  One of the distinguishing features of the impact of surfactants on the environment is that they can enhance the effects of other pollutants. This negative effect is obtained by improving the infiltration (penetration) of pollutants from the soil into water bodies that contain excess concentrations of surfactants. Surfactants are also able to wash off fixed pollutants from the surface and destroy the balance of pollutants in the environment, inhibiting the process of their natural processing.

  Therefore, the need for wastewater treatment from surfactants is obvious. Chemical enterprises annually dispose of more than 100 thousand tons of surfactants into water bodies. A stable foam forms on the surface of water containing surfactants, which prevents the flow of oxygen from the air into polluted water basins and, thereby, impairs self-purification processes and causes great harm to both flora and fauna.

  Surfactants have a polar (asymmetric) molecular structure, capable of being adsorbed at the interface between two media and lowering the free surface energy of the system. Quite insignificant additions of surfactants can change the properties of the particle surface and impart new qualities to the material. The effect of surfactants is based on the phenomenon of adsorption, which leads simultaneously to one or two opposite effects: a decrease in the interaction between particles and stabilization of the interface between them due to the formation of an interphase layer. Most surfactants are characterized by a linear structure of molecules, the length of which significantly exceeds the transverse dimensions (Fig. 15). The radicals of molecules consist of groups that are related in their properties to solvent molecules, and of functional groups with properties that are sharply different from them. These are polar hydrophilic groups, possessing pronounced valence bonds and having a certain effect on wetting, lubricating and other actions associated with the concept of surface activity . In this case, the supply of free energy decreases with the release of heat as a result of adsorption. Hydrophilic groups at the ends of non-polar hydrocarbon chains can be hydroxyl - OH, carboxyl - COOH, amino - NH 2, sulfo - SO and other strongly interacting groups. Functional groups are hydrophobic hydrocarbon radicals characterized by side valence bonds. Hydrophobic interactions exist independently of intermolecular forces, being an additional factor contributing to the convergence, "sticking" of non-polar groups or molecules. The adsorption monomolecular layer of surfactant molecules by the free ends of hydrocarbon chains is oriented from

  particle surface and makes it non-wettable, hydrophobic.

  The effectiveness of this or that surfactant additive depends on the physicochemical properties of the material. A surfactant that has an effect in one chemical system may have no effect or, clearly, the opposite, in another. In this case, the concentration of surfactants is very important, which determines the degree of saturation of the adsorption layer. Sometimes high molecular weight compounds exhibit an action similar to surfactants, although they do not change the surface tension of water, for example, polyvinyl alcohol, cellulose derivatives, starch, and even biopolymers (protein compounds). The action of surfactants can be exerted by electrolytes and substances insoluble in water. Therefore, it is very difficult to define the concept of "surfactant". In a broad sense, this concept refers to any substance that, in small quantities, noticeably changes the surface properties of a dispersed system.

  The classification of surfactants is very diverse and in some cases contradictory. Several attempts have been made to classify according to different criteria. According to Rebinder, all surfactants are divided into four groups according to the mechanism of action:

  - wetting agents, defoamers and foaming agents, i.e., active at the liquid-gas interface. They can reduce the surface tension of water from 0.07 to 0.03–0.05 J / m 2;

  - dispersants, peptizers;

  - stabilizers, adsorptive plasticizers and thinners (viscosity reducers);

  - detergents with all surfactant properties.

  Abroad, the classification of surfactants by functional purpose is widely used: thinners, wetting agents, dispersants, deflocculants, foaming agents and defoamers, emulsifiers, stabilizers of dispersed systems. Binders, plasticizers and lubricants are also released.

  According to the chemical structure, surfactants are classified depending on the nature of hydrophilic groups and hydrophobic radicals. Radicals are divided into two groups - ionic and nonionic, the first can be anionic and cationic.

  Nonionic surfactants contain non-ionizable end groups with high affinity for the dispersion medium (water), which usually include oxygen, nitrogen, and sulfur atoms. Anionic surfactants are compounds in which a long hydrocarbon chain of molecules with low affinity for the dispersion medium is part of the anion formed in an aqueous solution. For example, COOH is a carboxyl group, SO 3 H is a sulfo group, OSO 3 H is an ether group, H 2 SO 4, etc. Anionic surfactants include salts of carboxylic acids, alkyl sulfates, alkyl sulfonates, etc. Cationic substances form in aqueous solutions cations containing a long hydrocarbon radical. For example, 1-, 2-, 3- and 4-substituted ammonium, etc. Examples of such substances can be amine salts, ammonium bases, etc. Sometimes a third group of surfactants is isolated, which includes amphoteric electrolytes and ampholytic substances, which, depending by nature, the dispersed phase can exhibit both acidic and basic properties. Ampholytes are insoluble in water, but active in non-aqueous media, such as oleic acid in hydrocarbons.

  Japanese researchers propose a classification of surfactants according to their physicochemical properties: molecular weight, molecular structure, chemical activity, etc. The gel-like shells on solid particles formed by surfactants as a result of different orientations of polar and non-polar groups can cause various effects: liquefaction; stabilization; dispersion; defoaming; binding, plasticizing and lubricating actions.

  The surfactant has a positive effect only at a certain concentration. There are very diverse opinions on the optimal amount of surfactants to be introduced. P.A.Rebinder points out that for particles

  1–10 µm, the required amount of surfactant should be 0.1–0.5%. Other sources give values ​​of 0.05–1% and more for different dispersion. For ferrites, it was found that for the formation of a monomolecular layer during dry milling of a surfactant, it is necessary to take at the rate of 0.25 mg per 1 m 2 of the specific surface area of ​​the initial product; for wet grinding - 0.15–0.20 mg / m 2. Practice shows that the concentration of surfactants in each specific case should be selected experimentally.

  In the technology of ceramic SEM, four areas of surfactant application can be distinguished, which allow intensifying physicochemical changes and transformations in materials and controlling them during synthesis:

  - intensification of the processes of fine grinding of powders to increase the dispersion of the material and reduce the grinding time when a given dispersion is achieved;

  - regulation of the properties of physicochemical dispersed systems (suspensions, slips, pastes) in technological processes. Here, the processes of liquefaction (or a decrease in viscosity with an increase in fluidity without a decrease in moisture content), stabilization of rheological characteristics, defoaming in dispersed systems, etc., are important;

  - control of the processes of torch formation when spraying suspensions when obtaining a given size, shape and dispersion of the spray torch;

  - an increase in the plasticity of molding masses, especially those obtained when exposed to elevated temperatures, and the density of the manufactured blanks as a result of the introduction of a complex of binders, plasticizing and lubricating substances.

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