There are many different ways of interaction between physical bodies. One of them is surface adhesion. Let's look at what this phenomenon is and what properties it has.
What is adhesion
The definition of the term becomes clearer if you find out how the given word was formed. From Latin adhaesio is translated as "attraction, adhesion, sticking." Thus, adhesion is nothing but the connection of condensed dissimilar bodies that occurs when they come into contact. When homogeneous surfaces come into contact, a special case of this interaction arises. It's called autohesion. In both cases, it is possible to draw a clear line of phase separation between these objects. In contrast, they distinguish cohesion, in which the adhesion of molecules occurs within the substance itself. To make it clearer, consider an example from life. Take PVA glue and plain water. Then we apply them to different parts of the same glass surface. In our example, water is a substance that has poor adhesion. This is easy to check by turning the glass upside down. Cohesion characterizes the strength of a substance. If you glue two pieces of glassglue, then the connection will be quite reliable, but if you connect them with plasticine, the latter will tear in the middle. From which we can conclude that its cohesion for a strong bond will not be enough. We can say that both these forces complement each other.
Types of adhesion and factors affecting its strength
Depending on which bodies interact with each other, certain features of sticking appear. The highest value is the adhesion that occurs when interacting with a solid surface. This property is of practical value in the manufacture of all kinds of adhesives. In addition, the adhesion of solids and liquids is also distinguished. There are several key factors that directly determine the strength with which adhesion will occur. This is the contact area, the nature of the contacting bodies and the properties of their surfaces. In addition, if at least one of the pair of objects carries an electric charge, then during the interaction a donor-acceptor bond will appear, which will increase the adhesion force. A significant role is played by capillary condensation of water vapor on surfaces. Due to this phenomenon, chemical reactions can occur between the substrate and the adhesive, which also increases the strength of the bond. And if a solid body is dipped into a liquid, then one can notice a consequence that also causes adhesion - this is wetting. This phenomenon is often used in painting, gluing, soldering, lubricating, rock dressing, etc. To eliminate adhesion, a lubricant is used that prevents direct contact of the surfaces, andto enhance it, on the contrary, the surface is activated by mechanical or chemical cleaning, exposure to electromagnetic radiation or the addition of various functional impurities.
Quantitatively, the degree of such interaction is determined by the force that must be applied in order to separate the contact surfaces. And in order to measure the adhesion force, special devices are used, which are called adhesion meters. The very set of methods for its determination is called adhesionometry.