Adhesion. Basic terms and definitions. We study the adhesive properties of materials: adhesion - what it is and how it affects paint and concrete Adhesive coating

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This is the adhesion of materials that are different in composition and structure, due to their physical and chemical properties. The term adhesion comes from the Latin word adhesion - sticking. In construction, they give a more narrowly focused and specific designation to what adhesion is - this is the ability of decorative and finishing coatings (coatings, plasters), sealing or adhesive mixtures to a strong and reliable connection with the outer surface of the base material.

Impressive demonstration of the adhesion effect of modern adhesives

Important! It is necessary to distinguish between the concepts of adhesion and cohesion. Adhesion connects materials of different types, affecting only the surface layer. For example, paint on a metal surface. Cohesion is a combination of materials of the same type, as a result of which intermolecular interactions are formed.

Adhesion is one of the key properties of materials in the following areas:

1. Metallurgy - anti-corrosion coatings.
2. Mechanics - a layer of lubricant on the surface of the elements of machines and mechanisms.
3. Medicine - dentistry.
4. Construction. In this industry, adhesion is one of the main indicators of the quality of work and the reliability of structures.

At almost all stages of construction, adhesion indicators for the following compounds are controlled:

• paints and varnishes;
• plaster mixtures, screeds and fills;
• adhesives, masonry mortars, sealants, etc.

Example of Chemical Adhesion - Bonding Reaction silicone sealant with glass

There are three main principles of adhesive bonding of materials. In construction and technology, they manifest themselves as follows:

1. Mechanical- adhesion occurs by sticking the applied material to the base. The mechanism of such a connection is the penetration of the applied substance into the pores of the outer layer or the connection with a rough surface. An example is the coloring of the surface of concrete or metal.
2. Chemical— the relationship between materials, including different density takes place at the atomic level. The presence of a catalyst is necessary for the formation of such a bond. An example of this type of adhesion is soldering or welding.
3. Physical- on the mating surfaces there is an electromagnetic intermolecular bond. May be formed as a result of the occurrence of a static charge or under the influence of a constant magnetic or electromagnetic field. Technology Use Case - Coloring various surfaces in an electromagnetic field.

Adhesive properties of building and finishing materials

Adhesion of construction and finishing materials carried out mainly on the principle of mechanical and chemical connection. Used in construction a large number of various substances performance characteristics and the specifics of interaction which are fundamentally different. We divide them into three main groups and describe them in more detail.

paints and varnishes

The adhesion of coatings to the surface of the base is carried out according to the mechanical principle. At the same time, the maximum strength indicators are achieved if the working surface of the material is rough or porous. In the first case, the contact area increases significantly, in the second, the paint penetrates into the surface layer of the base. In addition, the adhesion properties of paintwork materials increase due to various modifying additives:

• organosilanes and polyorganosiloxanes have an additional hydrophobic and anticorrosive effect;
• polyamide and polyester resins;
• organometallic catalysts for chemical processes of paint and varnish hardening;
• ballast fine fillers (for example, talc).

Talc-filled paint - non-intumescent flame retardant

Building plasters and dry adhesive mixtures

Until recently, building and Finishing work were carried out using various solutions based on gypsum, cement and lime. Often, they were mixed in a certain proportion, which gave a limited change in their basic properties. Modern ready-made dry building mixtures: starting, finishing and multi-finishing plasters and putties have a much more complex composition. Supplements of various origins are widely used:

• mineral- magnesium catalysts, liquid glass, aluminous, acid-resistant or non-shrinking cement, microsilica, etc.
• polymeric- dispersible polymers (PVA, polyacrylates, vinyl acetates, etc.).

Such modifiers significantly change the following main characteristics of building mixtures:

• plastic;
• water-retaining properties;
• thixotropy.

Important! The use of polymer modifiers gives a more pronounced effect of adhesion enhancement. However, the formation of stable compounds of polymer films at the boundary of different types of materials (the base is hardening plaster) is possible only at a certain temperature. This term is called minimum temperature film formation - MTP. For different plasters, it can be different from + 5 ° С to + 10 ° С. To avoid delamination, the manufacturer's temperature recommendations must be strictly adhered to, as environment, as well as the foundations.

Sealants

Sealants used in construction come in three different types, each of which requires specific conditions for high-strength adhesion to the substrate material. Let's consider each type in more detail.

• Drying sealants. The composition includes various polymers and organic solvents: styrene-butadiene or nitrile, chloroprene rubber, etc. As a rule, they have a pasty consistency with a viscosity of 300-550 Pa. Depending on the viscosity, they are applied either with a spatula or with a brush. After their application to the surface, a certain time is required for drying (evaporation of the solvent) and the formation of a polymer film.

• Non-drying sealants. They usually consist of rubber, bitumen and various plasticizers. They have limited resistance to high temperatures, not more than 70 0 C-80 0 C, after which they begin to deform.

• curing sealants. After their application, under the influence of various factors: moisture, heat, chemical reagents, an irreversible polymerization reaction occurs.

Of all the listed varieties, curing sealants provide the maximum reliability of adhesion to the micro-roughness of the substrate surface. In addition, they are resistant to high temperatures, mechanical and chemical influences. They have an optimal combination of stiffness and viscosity, allowing them to maintain their original shape. However, they are the most expensive and difficult to use.

How is adhesion measured?

Adhesion measurement technology, testing methods, as well as all indicators of the strength of the connection of materials are specified in the following standards:

• GOST 31356-2013 - putties and plasters;
• GOST 31149-2014 - paints and varnishes;
• GOST 27325 - Paintwork for wood, etc.

Information! Adhesion is measured in kgf / cm 2 , MPa (megapascals) or kN (kilonewtons) - this is an indicator of the force that must be applied to separate the base and coating materials.

Whereas in the past the adhesive properties of materials could only be measured in the laboratory, today there are many instruments that can be used directly on the construction site. Most methods for measuring adhesion, both "field" and laboratory, are associated with the destruction of the outer, covering, layer. But there are several devices whose principle of operation is based on ultrasound.

• Knife adhesion gauge. It is used to determine the adhesion parameters by the method of lattice and or parallel cuts. It is applied to paint and varnish and film coverings up to 200 microns thick.

• Pulsar 21. The device determines the density of materials. It is used to detect cracks and delaminations in concrete, both piece and monolithic. There are special firmware and subprograms that, by the density of fit, allow you to determine the adhesion strength of plasters various types to concrete surfaces.

• SM-1U. It is used to determine the adhesion of polymer and bituminous insulating coatings by the method of partial destruction - shear. The measurement principle is based on the detection of linear deformations of the insulating material. As a rule, it is used to determine the strength of the insulating coating of pipelines. It is allowed to use for quality control the application of bituminous waterproofing on building structures: basement walls and ground floors, flat roofs and so on.

Factors that reduce the adhesion of materials

Various physical and chemical factors influence the decrease in adhesion. The physical ones include the temperature and humidity of the environment at the time of applying decorative and finishing or protective materials. Various contaminants also reduce adhesive interactions, in particular, dust covering the surface of the base. During operation, the strength of the connection of paints and varnishes can be affected by ultraviolet radiation.

Chemical factors that reduce adhesion are represented by various materials that pollute the surface: gasoline and oils, fats, acid and alkaline solutions, etc.

Also, the adhesion of finishing materials can be reduced by various processes that occur in building structures:

• shrinkage;
• tensile and compressive stresses.

Information! A substance applied to a surface to increase the adhesive force between the base and the finishing material is called an adhesive. The base on which the adhesive is applied is called the substrate.

Adhesion enhancement methods

In construction, there are several universal ways to increase the adhesion of decorative finishing materials to the base surface:

1. Mechanical- the base surface is roughened to increase the contact area. To do this, it is treated with various abrasive materials, notches are applied, etc.
2. Chemical- various substances are added to the composition of the applied protective and finishing materials. These are, as a rule, polymers that form stronger bonds and give the material additional elasticity.
3. Physico-chemical- the base surface is treated with a primer that changes the basic chemical parameters of the material and affects certain physical properties. For example, reducing moisture absorption in porous materials, fixing a loose outer layer, etc.

Ways to increase adhesion to various materials

Let us dwell in more detail on the methods of increasing adhesion for various materials used in construction.

Concrete

Concrete building materials and structures are widely used in construction. Due to the high density and smoothness of the surface, their potential adhesive performance is rather low. To increase the strength of the connection finishing compositions the following parameters must be taken into account:

• dry or wet surface. As a rule, adhesion to a dry surface is higher. However, many adhesive mixtures have been developed that require pre-wetting of the substrate surface. In this case, it is necessary to pay attention to the requirements of the manufacturer;
• ambient and ground temperature. Most finishing materials are applied to concrete surfaces at an air temperature of at least +5°С...+7°С. In this case, the concrete should not be frozen;
• primer. Used without fail. For dense concretes, these are compositions with quartz sand filler (concrete contact), for porous concretes (foam, aerated concrete), these are deep penetration primers based on acrylic dispersions;
• adding modifiers. Ready-made dry plaster mixtures already contain various adhesive additives. If the plaster is mixed on its own, then it is recommended to add to it: PVA, an acrylic primer, instead of the same amount of water, silicate glue, which gives the finishing material additional water-repellent properties.

Metal

The method and quality of surface preparation plays a key role in the strength of the connection of paints and varnishes with a metal surface. At home, it is recommended to do the following:

• degreasing– metal processing with various solvents: 650, 646, R-4, white spirit, acetone, kerosene. In extreme cases, the surface is wiped with gasoline;
• matting- treatment of the base with abrasive materials;
• padding- the use of special primer paints. They are sold in a set with decorative coatings of a certain type.

Important! The adhesion of lead, aluminum and zinc is much lower than that of cast iron and steel. The reason is that these metals form oxide films on their surface. Therefore, peeling of paint coatings occurs along the oxide layer. It is recommended to color these materials immediately after removing the film by mechanical or chemical means.

Wood and wood composites

Wood is a porous surface with a large number of irregularities and does not experience any problems with the strength of the connection of finishing materials. But there is no limit to perfection, so various technologies have been developed to improve adhesion in combination with maintaining the protective and decorative properties of the finish itself. Their use, for example, in combination with acrylic paints, significantly improves weather resistance, resistance to ultraviolet fading, and gives biological protection to the material. The surface of the wood is treated with a wide variety of primers, most often based on boron compounds and nitrocellulose.

Adhesion during welding

Welding is one of the most durable joining methods. metal structures. This is the adhesion of the molecules of two elements without the use of intermediate or auxiliary substances - glue or solder. going on this process under the influence of thermal activation. The outer layer of the elements to be joined is heated above the melting point, after which the intermolecular approach and joining of the materials takes place.

The following factors can serve as an obstacle to high-quality adhesion during welding:

• the presence of oxide films. They are removed mechanically or chemically during surface preparation or disappear directly during the welding process under the influence of high temperature or fluxes;
• discrepancy between the chemical composition of materials and electrodes. Special attention attention should be paid to the presence and amount of silicon and carbon in the parts to be joined. For joining steel different brands it is recommended to use electrodes with a low content of diffusible hydrogen;
• insufficient penetration depth, which directly depends on the current strength and the speed of movement of the electrode.

16291 0

First, let's assume that the first condition for adhesion is to have close contact at the molecular level between the adhesive and the substrate. Now let's imagine what will happen after the materials come into contact, and how they will interact. The adhesive bond can be mechanical, physical, or chemical, but is usually a combination of these types of bond.

Mechanical adhesion

The simplest type of adhesion is the mechanical adhesion of the adhesive components to the surface of the substrate. This adhesion is formed due to the presence of such surface irregularities as depressions, cracks, gaps, during the development of which microscopic undercuts are formed.

The main condition for the formation of mechanical adhesion is the ability of the adhesive to easily penetrate into the recesses on the surface of the substrate, and then harden. This condition depends on the wetting of the substrate surface by the adhesive, which, in turn, is related to the ratio of the surface energies of the materials in contact, which determines the value of the contact wetting angle. The ideal situation is that the substrate is completely wetted by the adhesive. To improve contact, the air or steam present in the recesses must be removed before applying the adhesive. If the adhesive is able to fill in the undercuts and then cure, then naturally it is blocked by the undercuts (Fig. 1.10.7).

Rice. 1.10.7. Mechanical engagement between adhesive and substrate at the microscopic level

The degree of penetration of the adhesive into the undercuts depends both on the pressure that was applied during its application and on the properties of the adhesive itself. If you try to tear the adhesive from the substrate, then this can only be done by tearing it, since the adhesive cannot be removed from the undercuts. The concept of mechanical adhesion does not conflict with the conditions for attachment or retention of fixed dentures used in their fixation, except for those phenomena that occur at the microscopic level. An important difference between these concepts is that good wettability is not necessary condition macroretention, while it plays a decisive role in creating mechanical engagement at the microscopic level.

In general, undercuts often increase the mechanical strength of a joint, but this is usually not sufficient to trigger the (specific) adhesion mechanism itself. There are a number of additional adhesion mechanisms caused by physical and chemical causes. The term true or specific adhesion is usually used to distinguish physical and chemical adhesion from mechanical adhesion, but such terms are best discarded as they are not entirely accurate.

The concept of true adhesion implies that, in addition to it, there is false adhesion, but in reality adhesion either exists or it does not exist. Physical and chemical adhesion differ from mechanical adhesion in that the former involve the adhesive and substrate in molecular interaction with each other, while mechanical adhesion does not require such interaction at the interface between two phases.

Physical adhesion

When two planes are in close contact, secondary bonds are formed due to the dipole-dipole interaction between polarized molecules. The magnitude of the resulting attractive forces is very small, even if they have a high value of the dipole moment or increased polarity.

The value of the binding energy depends on the relative orientation of the dipoles in two planes, but usually this value is not more than 0.2 electron volts. This value is much less than that of primary bonds, such as ionic or covalent bonds, in which the bond energy typically ranges from 2.0 to 6.0 electron volts.

Secondary bonds due to the dipole-dipole interaction arise very quickly (since no activation energy is needed for their formation) and are reversible (since the molecules on the surface of the substance remain chemically unaffected). This weak adsorption physical attraction is easily destroyed by rising temperatures, and is not suitable for applications where a permanent connection is required. However, bonds such as hydrogen bonds can be an essential prerequisite for the formation of a chemical bond.

It follows that the connection of non-polar liquids with polar solids is difficult, and vice versa, since there will be no interaction at the molecular level between these two substances, even if they are in close contact. This behavior is observed in liquid silicone polymers, which are non-polar and therefore do not form secondary bonds with solid surfaces. Connections with them are possible only through the passage of a chemical crosslinking reaction, which will create junctions between the liquid and the solid.

Chemical adhesion

If, after adsorption on the surface, the molecule dissociates, and then its functional groups, each separately, can be combined by covalent or

ionic bonds with the surface, then a strong adhesive bond is formed as a result. This form of adhesion is called chemisorption and can be either ionic or covalent in nature.

A chemical bond differs from a physical bond in that two neighboring atoms share the same electrons. The surface of the adhesive must be firmly bonded to the surface of the substrate through chemical bonds, so the presence of reactive groups on both surfaces is necessary. In particular, this applies to the formation of covalent bonds, which occurs, for example, when reactive isocyanates are bonded to polymer surfaces containing hydroxyl and amine groups (Fig. 1.10.8).

Rice. 1.10.8. Formation of a covalent bond between isocyanate and hydroxyl and amine groups on the substrate surface

Unlike non-metallic compounds, a metallic bond is easily formed between solid and liquid metals - this mechanism underlies soldering. The metallic bond arises from free electrons and does not depend on the presence of reactive groups. However, this relationship is only possible if metal surfaces will be perfectly clean. In practice, this means that fluxes must be used to remove oxide films, otherwise these films will prevent contact between metal atoms.

The only way to separate the adhesive from the substrate is the mechanical breaking of chemical bonds, however, this does not mean that these, and not other valence bonds, will be broken in the first place. This places limits on the strength that can be achieved in a joint. If the strength of the bond or adhesive bond is greater than the tensile strength of the adhesive or substrate materials, then the cohesive adhesive or substrate will fail before the adhesive bond fails.

Adhesion by entanglement of molecules (Diffusion mechanism of adhesion)

So far, we have assumed that there is a clearly defined interface between the adhesive and the substrate. Typically, the adhesive is adsorbed to the surface of the substrate and can be considered as a surfactant that accumulates on the surface but does not penetrate deep. In some cases, the adhesive or one of its components is able to penetrate into the surface of the substrate, and not accumulate on it. It should be emphasized that the absorption of molecules occurs as a result of good wetting of the surface, and is not its cause.

If the absorbed component is a long chain molecule, or forms a long chain molecule after being absorbed by the substrate, the result can be entanglement or interdiffusion of the adhesive and substrate molecules, resulting in very high adhesive strength (Fig. 1.10.9).

Rice. 1.10.9. Diffusion transition layer formed by mutual intertwining of molecular fragments of adhesive and substrate

This equality is called the Dupree equation. It means that the work of adhesion (W) is the sum of the free surface energies of the solid (y) and liquid (y|v) minus the energy at the interface between the liquid and solid (ysl).

From Young's equation,

Ysv Ysi = Ysi cose

Adhesion will be maximum at full (ideal) wetting, i.e. in the case when cosq = 1, therefore, the energy of the glued surfaces and the energies of each of these surfaces separately (Fig. 1.10.10).

Rice. 1.10.10. Separation of a liquid from a solid surface to form two new surfaces

The surface tension of a liquid hydrocarbon is approximately 30 mJ/m. Assuming that the attractive forces decrease to zero at a distance of 3 x 10~ meters, then the force required to separate a liquid from a solid surface is equal to the work of adhesion divided by the distance, and is equal to 200 MPa.

In fact, this value is much higher.

Thus, adhesives must be strongly chemically attracted to the surface of the substrates to ensure high adhesive strength.

Clinical Significance

The clinician needs to know what kind of bond they are trying to achieve, and this requires an understanding of the steps involved in creating an adhesive bond. This will help you avoid mistakes in your work.

Fundamentals of Dental Materials Science
Richard van Noort

Thanks to the development of new technologies in dentistry, today we have the opportunity to restore the integrity and functionality of damaged and decayed teeth quickly, efficiently and for a long time. Adhesive systems provide reliable fixation of fillings and artificial prosthetic structures.

In this article, we will look at what adhesion is in dentistry and how it works in the service of a beautiful and healthy smile.

Adhesion - what is it

In general, the word "adhesive" in translation from in English means "adhesive substance, sticking". This "glue" is used in dentistry in order to connect materials of different composition with the tooth tissue (do not confuse adhesion and cohesion - this is a physical term).

By itself, the filling material does not have chemical adhesion, that is, the ability to adhere to naturally moist dentin, so a “mediator” is needed here, which will take care of the reliable adhesion of two dissimilar tissues. During polymerization, the composite material shrinks, so if adhesive systems are not used, the desired adhesion quality cannot be achieved. And this is a direct road to the development of repeated caries or even under a filling.

“I have been worried about my diastema since childhood, . About 5 years ago, I heard that there is such a technique as adhesive reconstruction of teeth, in which no painful grinding is needed and the material literally “sticks” to the teeth. The doctor simply polished the enamel of the front teeth and covered the unattractive gap in layers with a composite. The enamel remained intact, and the smile became open.

Elena Salnikova, review on the website of one of the Moscow dentistry

Innovative light-curing adhesive systems are used for filling teeth with composites, for fixing bridges, as well as for installing braces, veneers, skyces.

Classification of adhesive systems

In essence, the composition of the adhesive system is represented by a group of liquids from the etching component, the bond, and the primer. Together they provide micromechanical links between artificial materials and dental tissues.

Since the structure of enamel and dentin is heterogeneous, the adhesive systems used for them are also different. In the classification of adhesive systems, options are distinguished separately for enamel and separately for dentin.

Modern adhesive systems differ in the following characteristics:

• the number of components that are included in their composition (1, 2 and more),
• filler content: if acid is present, it is a self-etching adhesive system,
• curing method: self-curing, light-curing, and dual-curing.

So, in the composition of enamel adhesives - low-viscosity monomers of composite materials. Important point is that enamel adhesives do not work on dentin. Therefore, it is important either to put insulating pads for the hard part of the tooth, or to use a special dentin adhesive - a primer.

What are the types of adhesion

There are several types of adhesion: mechanical, chemical, and combinations thereof. The simplest is mechanical. The essence of the system is to create micromechanical bonds between the components of the material and the rough surface of the tooth. To ensure high quality adhesion, the natural micropits on the surface of the dental tissues are thoroughly dried before applying the adhesive.

Interesting! Dr. Buoncore found out 63 years ago that phosphoric acid roughens tooth enamel. This helps to enhance the adhesion of the composite to the tooth tissues. Appeared more than half a century ago, the technique of etching tooth enamel with acid became the foundation for modern adhesive restorative methods.

The chemical bonding option is based on the chemical bonding of the composite material with enamel and dentine. Only glass ionomer cements have this type of adhesion. Other materials used by dentists have only mechanical adhesion.

How does the composite “stick” to the enamel surface?

As noted above, in dentistry, the mechanisms of adhesion to enamel and dentin differ. The protective outer shell of the teeth is transformed under the influence of acids. If we examine the enamel after acid etching under a microscope, it will resemble a honeycomb. The acid in this case works to strengthen the bond with the composite. As a result, viscous hydrophobic adhesives penetrate deeper layers of enamel more easily and ensure its strong adhesion to the composite.

Interesting! Enamel is considered the hardest tissue in our body. It contains the largest amount of inorganic substances - approximately 97%. The remaining 2% is water, 1% is organic matter.

How enamel is etched

This treatment method involves removing a portion of the 10 micronewton (µN) layer from the enamel. As a result, pores with a depth of 5–50 μN appear on its surface. Often, enamel is lubricated with phosphoric acid for etching, but organic acids can be used for dentin, but in a low concentration.

The etching process lasts from 30 to 60 seconds. Of decisive importance are individual characteristics structure of the enamel surface, in particular its initial porosity. If the acid is overexposed, it will inevitably affect the structure of the enamel and weaken the adhesion. So if the patient's dental tissues are rather weak, then the etching should last no longer than 15 seconds. The acid is removed with a jet of water, and for the same amount of time as it is kept on the enamel.

How does the composite adhere to the dentine surface?

The properties of dentin are such that its outer layer is moist. The fluid in this part of the tooth is updated quickly, so it is very difficult to dry it. And so that moisture does not affect the quality of adhesion of dentin to the composite, special water-compatible (scientifically - hydrophilic) systems are used. Also, the bond strength is directly affected by the so-called “smear layer”, which occurs as a result of instrumental processing of dentin. There are 2 approaches to using linking mechanisms:

• the smear layer is impregnated with water-compatible substances,
• the smeared layer is artificially dissolved and scraped off.

It is worth noting that the latter method, which involves the removal of excess microparticles from the surface of the enamel, is now used much more often than the first.

How dentine is poisoned

Japanese dentist Fuzayama 39 years ago was the first in history to apply the dentine etching technique. Today, before the procedure, special conditioners are applied to the tissues of the teeth - they help hydrophilic substances to penetrate deeper into the dentinal tissues and adhere to the water-repellent composite. At the same time, the smeared layer partly leaves, the dentinal tubules open, and mineral salts come out of the upper layer. After that, the conditioners are washed off with water. Next comes the drying stage, and the main thing is not to overdo it, otherwise it will affect the grip.

Next, a primer is applied, which helps the hydrophilic substances to pass into the tubules and adhere to the collagen fibers. As a result, a kind of hybrid layer is formed, which contributes to the effective bonding of the composite to the dentin. It also serves as a barrier against seepage of chemicals and microbes into the internal structures of the tooth.

Adhesive systems for enamel

If we are talking about enamel, then adhesion here is provided on the basis of micromechanical coupling. For this, hydrophobic liquids are used, however, they will not give the necessary “sticking” to wet dentin, therefore a primer is also used. The handling of enamel adhesives having a one-component composition is based on the following steps:

1. etching the enamel with phosphoric acid - about half a minute,
2. removing the etching gel with a water jet,
3. enamel drying,
4. connection in the same proportion of the substances of the adhesive system,
5. introduction of an adhesive into the tooth cavity with an applicator,
6. leveling it with an air jet.

Only after performing all of the above manipulations, the doctor introduces the composite material.

Adhesive systems of different generations in clinical dentistry

To date, 7 generations of adhesive systems are known. Today, dentists use systems, starting from the 4th generation, that help us keep our teeth whole and healthy throughout our lives. They contain 3 components: conditioner + primer + adhesive. But the innovative 6th and 7th generations with single-stage drugs, alas, have not yet become widespread.

Interestingly, many experts talk about the primary role of enamel adhesion, but dentine adhesion comes second. Conducted laboratory research also indicate that today maximum efficiency demonstrates alcohol protocol of adhesion. Ethanol helps to eliminate pain and sensitivity after the procedure. In addition, when using this type of adhesion protocol, there is less leakage of dentinal fluid. However, in each individual situation, the doctor himself decides which protocol and which adhesive system to give preference to in the existing clinical conditions.

1 Protocols for the use of adhesives Popova A.O., Ignatova V.A. - 4th year students of the Faculty of Dentistry.

From Wikipedia, the free encyclopedia

The most well-known adhesion effects are capillarity, wettability / non-wetting, surface tension, liquid meniscus in a narrow capillary, static friction of two absolutely smooth surfaces. The criterion for adhesion in some cases may be the time of detachment of a layer of material of a certain size from another material in a laminar fluid flow.

Adhesion takes place in the processes of gluing, soldering, welding, coating. The adhesion of the matrix and filler of composites (composite materials) is also one of the most important factors affecting their strength.

Theories of adhesion

Adhesion is an extremely complex phenomenon, which is the reason for the existence of many theories that interpret this phenomenon from different positions. The following theories of adhesion are currently known:

• adsorption theory, according to which the phenomenon is carried out as a result of the adsorption of the adhesive on the pores and cracks of the surface of the substrate.
• mechanical theory considers adhesion as a result of the manifestation of the forces of intermolecular interaction between the contacting molecules of the adhesive and the substrate.
• electrical theory identifies the "adhesive-substrate" system with a capacitor, and the double electric layer, which occurs when two dissimilar surfaces come into contact, with the capacitor lining.
• Electronic theory considers adhesion as a result of the molecular interaction of surfaces that are different in nature.
• diffusion theory reduces the phenomenon to mutual or one-sided diffusion of adhesive and substrate molecules.
• chemical theory explains adhesion not by physical, but by chemical interaction.

Physical Description

Adhesion is a reversible thermodynamic work of forces aimed at separating two dissimilar (heterogeneous) phases brought into contact. Described by the Dupre equation:

$(Wa\; =\; \backslash sigma\_(13)\; +\; \backslash sigma\_(23)\; -\; \backslash sigma\_(12))$

$(Wa\; =\; -\backslash Delta\; G^o)$

A negative value of ΔG° indicates a decrease in the work of adhesion as a result of the formation of interfacial tension.

Changes in the Gibbs energy of the system during the adhesion process:

$(\backslash Delta\; G^o\_1\; =\; \backslash sigma\_(13)\; +\; \backslash sigma\_(23))$

$(\backslash Delta\; G^o\_2\; =\; \backslash sigma\_(12))$

$(\backslash Delta\; G^o\; =\; \backslash Delta\; G^o\_2\; -\; \backslash Delta\; G^o\_1)$

$(\backslash sigma\_(12)\; -\; \backslash sigma\_(13)\; -\; \backslash sigma\_(23)\; =\; \backslash Delta\; G^o)$.

Adhesion is inextricably linked to many surface phenomena such as wetting. If adhesion causes a bond between a solid body and a liquid in contact with it, then wetting is the result of such a bond. The Dupre-Young equation shows the relationship between adhesion and wetting:

$(Wa\; =\; \backslash sigma\_(12)(1\; +\; cos\backslash theta))$

where σ 12 is the surface tension at the interface between two phases (liquid-gas), cosθ is the wetting angle, Wa is the reversible work of adhesion.

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Literature

• Deryagin B. V., Krotova N. A., Smilga V. P. Adhesion of solids. - M .: Nauka, 1973.
• Freidin AS Properties and calculation of adhesive joints. - M .: Chemistry, 1990.
• Berlin A. A., Basin V. E. Fundamentals of polymer adhesion. - M .: Chemistry, 1974.
• Trizno M.S., Moskalev E.V. Adhesives and gluing. - L .: Chemistry, 1980.

Notes

Links

• Adhesion- article from the Great Soviet Encyclopedia.

see also

An excerpt characterizing Adhesion

“Yes, yes, yes,” Natasha said happily.
Natasha told him her affair with Prince Andrei, his arrival in Otradnoye, and showed him his last letter.
- What are you happy about? Natasha asked. - I'm so calm now, happy.
“I am very glad,” Nikolai replied. - He's a great person. What are you so in love with?
- How can I tell you, - Natasha answered, - I was in love with Boris, with a teacher, with Denisov, but this is not at all the same. I am calm, firm. I know that there are no people better than him, and I feel so calm, good now. Not at all like before...
Nikolai expressed his displeasure to Natasha that the wedding had been postponed for a year; but Natasha attacked her brother with bitterness, proving to him that it could not be otherwise, that it would be bad to enter the family against the will of her father, that she herself wanted it.
“You don’t understand at all,” she said. Nicholas fell silent and agreed with her.
Her brother was often surprised looking at her. It was not at all like she was a bride in love separated from her fiancé. She was even, calm, cheerful, completely as before. This surprised Nikolai and even made him look incredulously at Bolkonsky's matchmaking. He did not believe that her fate had already been decided, especially since he had not seen Prince Andrei with her. It always seemed to him that something was not right in this proposed marriage.
"Why the delay? Why didn't you get engaged?" he thought. Having talked once with his mother about his sister, he, to his surprise and partly to his pleasure, found that his mother, in the depths of her soul, sometimes looked with distrust at this marriage.
“Here he writes,” she said, showing her son a letter from Prince Andrei with that hidden feeling of hostility that a mother always has against her daughter’s future marital happiness, “writes that she will not arrive before December. What kind of business could hold him back? That's right, a disease! Health is very weak. Don't tell Natasha. Don't look at how cheerful she is: this is the last girl's time, and I know what happens to her every time we receive his letters. But God willing, everything will be fine, - she concluded every time: - he is an excellent person.

The first time of his arrival, Nikolai was serious and even boring. He was tormented by the imminent need to intervene in these stupid household affairs for which his mother had called him. In order to get this burden off his shoulders as soon as possible, on the third day of his arrival, he angrily, without answering the question where he was going, went with frowning eyebrows to Mitenka's wing and demanded from him the accounts of everything. What these accounts of everything were, Nikolai knew even less than Mitenka, who had come in fear and bewilderment. The conversation and accounting of Mitenka did not last long. The headman, the elector and the zemstvo, who were waiting in the ante-room of the wing, heard with fear and pleasure at first how the young count’s voice, which seemed to rise ever higher, hummed and crackled, heard abusive and terrible words, pouring out one after another.
- Rogue! Ungrateful creature! ... I will chop up a dog ... not with my father ... robbed ... - etc.
Then, with no less pleasure and fear, these people saw how the young count, all red, with bloodshot eyes, pulled Mitenka by the collar, with great dexterity, with great dexterity, between his words, pushed him in the behind and shouted: “Get out! so that your spirit, bastard, is not here!
Mitenka flew headlong down the six steps and ran into the flower bed. (This flowerbed was a well-known area for saving criminals in Otradnoye. Mitenka himself, when he arrived drunk from the city, hid in this flowerbed, and many residents of Otradnoye, hiding from Mitenka, knew the saving power of this flowerbed.)
Mitenka's wife and sisters-in-law, with frightened faces, leaned out into the hallway from the door of the room, where a clean samovar was boiling and the clerk's high bed stood under a quilted blanket sewn from short pieces.
The young count, panting, paying no attention to them, walked past them with resolute steps and went into the house.
The countess, who immediately learned through the girls about what had happened in the wing, on the one hand, calmed down in the sense that now their condition should get better, on the other hand, she was worried about how her son would endure this. She tiptoed to his door several times, listening to him smoke pipe after pipe.
The next day the old count called his son aside and said to him with a timid smile:
- Do you know, you, my soul, got excited in vain! Mitenka told me everything.
"I knew, thought Nikolai, that I would never understand anything here in this stupid world."
- You were angry that he did not enter these 700 rubles. After all, he wrote them in transport, and you didn’t look at the other page.
- Daddy, he's a scoundrel and a thief, I know. And what he did, he did. And if you don't want me, I won't tell him anything.
- No, my soul (the count was also embarrassed. He felt that he was a bad manager of his wife's estate and was guilty before his children, but did not know how to fix it) - No, I ask you to take care of business, I'm old, I ...
- No, papa, you will forgive me if I did something unpleasant for you; I can do less than you.
“To hell with them, with these men and money, and transports along the page,” he thought. Even from a corner of six kush, I once understood, but from the page of transport - I don’t understand anything, ”he said to himself, and since then he has no longer intervened in business. Only once did the countess call her son to her, inform him that she had Anna Mikhailovna's bill for two thousand and asked Nikolai what he was thinking of doing with him.
“But how,” Nikolai answered. – You told me that it depends on me; I do not love Anna Mikhailovna and I do not love Boris, but they were friendly with us and poor. So that's how! - and he tore the bill, and with this act, with tears of joy, he made the old countess sob. After that, young Rostov, no longer intervening in any business, with passionate enthusiasm, took up the still new for him cases of dog hunting, which in large sizes was instituted by the old count.

There were already winters, morning frosts shackled the ground moistened with autumn rains, already the greenery had become narrower and brightly green separated from the stripes of turning brown, knocked out by cattle, winter and light yellow spring stubble with red stripes of buckwheat. The peaks and forests, which at the end of August were still green islands between the black fields of winter and stubble, became golden and bright red islands in the midst of bright green winters. The Rusak was already halfway lost (molted), the fox broods began to disperse, and the young wolves were more dog. It was the best hunting time. The dogs of the hot, young hunter Rostov not only entered the hunting body, but also knocked out so that in the general council of hunters it was decided to give the dogs a rest for three days and go on departure on September 16, starting from the oak forest, where there was an untouched wolf brood.

The term "adhesion" is often found in documents in various scientific disciplines. It is used in physics, chemistry, and biology. However, each science has its own approach to what adhesion is, the definition of which, taking into account all the facets of the phenomenon, cannot yet be given by any scientist. True, everyone agrees on one thing: it is a connection, an interaction of various particles.

If we consider it as a process, we can say that adhesion is a phenomenon that consists in the appearance of interaction between some condensed phases. When their molecular contact occurs, this interaction leads to the emergence of a new heterogeneous entity.

If this phenomenon is understood as a property, then adhesion is (in the case of liquids) the interaction between the liquid and solid phases at their interface.

Physics

From the standpoint of physics, adhesion is the adhesion of surfaces of various substances when they come into contact. Moreover, substances can be both in the same and in different state of aggregation. Thus, the effect may concern two solids, two liquids, or a liquid and a solid.

Substances adhere under the influence of the following factors:

• chemical bonds between the molecules of two substances
• diffusion occurs when the molecules of the first substance penetrate the boundary of the surface of the second,
• van der Waals forces act, which arise when polarization of molecules occurs.

There are still special cases when adhesion can occur. They are often confused. These are autohesion and cohesion.

Autohesion occurs as a result of the adhesion of homogeneous bodies, however, the phase boundary is preserved.

Cohesion can occur when molecules of the same body interact.

IN natural conditions there are cases when adhesion due to various external causes becomes cohesion. Such a situation arises during diffusion if the phase boundaries become blurred. In some cases, the strength of the adhesive bond between the phases may be greater than the cohesive one. Then, depending on the strength of the substance, when a force is applied to the connection of substances, the interface is preserved or the cohesive bonds are broken.

Chemistry

Chemistry has a vision of the adhesion process similar to physics. Many technological processes in the chemical industry have adopted practical use of this phenomenon. It is this that underlies the technology for the manufacture of composite materials, and the production of paints and varnishes is also based on it. The concept of adhesion in chemical science is used when talking about the process of gluing surfaces in the solid state with an adhesive (substrates are glued together with an adhesive).

Biology

In biological science, the term is used not in relation to molecules, but in relation to relatively large biological particles - cells. Adhesion is such a connection of cells that allows the formation of histological structures correctly, and the type of these structures is determined by the specifics of the cells involved in the interaction. The result of the interaction depends on the presence of certain proteins on the surface of the connecting cells.

Effect on material properties

Adhesion has the ability to significantly change the characteristics of the surfaces that come into contact. It can help surfaces acquire a low coefficient of friction. If the substances have a solid crystal structure, then their further use as antifriction lubricants becomes possible. Effects such as capillarity and wettability also occur due to this phenomenon.

Unit

When adhesion occurs, the energy of the body on some part of the surface instantly becomes less. For this reason, it is customary to measure it by the work or force required to tear the surfaces apart on a certain unit area.

Application of adhesion in construction

Such physical phenomenon, as adhesion, contributed to the improvement technological process manufacturing of steel plates and blocks having thin and thick walls. Possession of information about the mechanisms of the phenomenon made it possible to increase the productivity of the lines for the manufacture of these building products and significantly reduce the weight of structures.

Only this phenomenon makes it possible to paint and varnish the surfaces of building materials, apply galvanic and anodic coatings. These operations contribute to the creation of anti-corrosion protection of the metal, giving the material a marketable appearance.

Knowledge of the nature of the phenomenon is of great help in high-quality gluing of various materials and their strong welding. With the participation of adhesion, metals are coated with oxide films that perform protective functions. The effect is used in the production of concrete works - in situations where it is not possible to immediately achieve a complete pouring of the object with concrete. When refilling, two concrete bases form between themselves the so-called cold joint, which negatively affects the strength characteristics of the joint. Adhesion is also recommended for applications where it is necessary to separate concrete from steel moulds. In other ways, this operation is simply impossible to perform. The use of adhesion makes it possible to successfully deal with surface defects of finished concrete products.

cement mortars

The division of adhesive mortars with the participation of cement into classes C1 and C2 is based on an assessment of the degree of adhesion of the mortar to the base after hardening. The adhesion of class C1 adhesive solution to the base according to the requirements of European quality standards should be more than 0.5 MPa, while for class C2 cement adhesive mortar its value is not less than 1.0 MPa. Thus, the difference between the two classes of solutions determines the adhesion strength.

Methods for determining adhesion

Methods by which adhesion is determined (GOST 15140-78):

• flaking;
• lattice cuts;
• lattice cuts with reverse impact;
• parallel cuts.

Adhesion in metallurgy

During adhesion, the phase boundary between the bodies is preserved. The adhesion of metals finds its manifestation when non-metallic inclusions are coagulated in the composition of liquid metals and alloys. Adhesion contributes to the enlargement of non-metallic inclusions, which subsequently leads to their removal from the metal into the slag.

The effect of adhesion or wetting of non-metallic inclusions with liquid metal can:

• interfere with the extraction of inclusions from the metal if the metal melt wets the non-metallic inclusions well (in this case, good adhesion takes place);
• create conditions for the removal of non-metallic inclusions from the metal in a situation where these inclusions are not sufficiently wetted by the metal melt (in this case, the adhesion value is small).

During cold welding, almost all hard metals that are in a plastic state are joined under pressure. Adhesion underlies the adhesion of galvanic, oxide, sulfide coatings to metal, which are applied to the metal surface in order to protect products from corrosion. The adhesion of the coating ensures its reliable adhesion of such compositions to the surface of metals. It has found its application in powder metallurgy, when products are formed and sintered from metal powders.

Adhesion of materials is widely used in cases where it is necessary to solder, tin, zinc, apply a variety of paint and varnish coatings. Without it, the creation of various composite materials is not complete. In the manufacture of such materials, particles of a substance come into contact with the base of the alloy. The effect increases in the presence of an electric charge on the surfaces of the bodies, which makes it possible to form a donor-acceptor bond upon connection. Adhesion is also enhanced during chemical cleaning of the surfaces to be joined. For these purposes, degreasing, vacuuming, ion bombardment, and exposure to electromagnetic radiation are used.

Adhesion activator

When a car is in operation, the smallest pores on the surface of the paint layer and polymer parts become clogged with residues of dust, tar, auto chemicals. As a result, an attempt to glue something on the parts often ends in failure due to poor adhesion of the surface. Degreasing does not eliminate all contaminants. Adhesion activator is designed for use in preparing surfaces before applying decorative films, stickers, nameplates, double-sided tape. The activator significantly increases the adhesive properties of surfaces due to a specially developed composition. Its use ensures that the bonding is reliable and allows the materials to be joined to be used for a long time. The high adhesion provided by the activator is the reason for the high demand for it.