Knowledge of adhesive theory

Application theory
between polymers, polymers and non-metallic or metal, metal and non-metallic glue between the interface between the polymer base and different materials glue problems. Glue is a kind of technology with strong comprehensiveness and complex influence factors, and the existing glue theory is based on a certain aspect to explain its principle, so the only theory so far is not comprehensive.
theory of adsorption
People regard the adsorption of solids to adhesives as the main cause of glue, called the adsorption theory of glue
in
. The theory holds that the main source of bonding is the molecular force of the bonding system, i.e. the van dering gravity and hydrogen bond force. When the distance between the adhesive and the adherent molecule reaches 10-5-Aring;, the interface molecules become mutually attractive, further reducing the distance between the molecules to the maximum stable state.
it is calculated that, due to the effects of Van der Worrest, the gravitational intensity between the two ideal planes can be up to 10-1000MPa when the difference is 10-1000MPa, and 100-1000MPa when the distance is 3-4-Aring; This value far exceeds the strength achieved by the best structural adhesives of modern times. Therefore, some people think that as long as the two objects contact very well, that is, the adhesive to the bonding interface fully wet, the calculated value is to assume that the two ideal planes close contact, and ensure that the role of the two pairs of molecules on the interface layer is destroyed at the same time, it is impossible to ensure that the forces between the molecules occur at the same time.
the polarity of the adhesive is too high, sometimes seriously hindering the wetting process and reducing the adhesion. Inter-molecular force is the factor that provides the bonding, but it is not the only factor. In some exceptional cases, other factors can also play a leading role.the basic rationale of
glued leather shoes shows that
chemical bond theory
chemical bond theory holds that in addition to the interaction force between the adhesive and the adhesive molecule, there are sometimes chemical bonds produced, such as vulcanized rubber and copper-plated metal bonding interface, the effect of the coupled agent on the glue, isocyanate on the metal and rubber bonding interface, etc. However, the formation of chemical bonds is not ordinary, to form chemical bonds must meet a certain degree of quantum' parts, so it is not possible to make the adhesive and the bonded contact point between the formation of chemical bonds. Moreover, the number of chemical bonds on the unit adhesion interface is much smaller than the number of inter-molecular effects, so the adhesion strength comes from the inter-molecular force can not be ignored.
weak boundary layer theory
when the liquid adhesive does not well immerse the surface of the viscous body, the air bubble remains in the void and forms a weak area. For example, when impurities are soluble in the molten adhesive and not in the cured adhesive, another phase is formed in the solidified adhesive, creating a weak interface layer (WBL) between the adhesive and the adhesive as a whole. In addition to the process factors, in the forming process of polymer meshing or melt interaction, the impermanity of boundary layer structure is produced in the thermodynamic phenomena such as adhesive and surface adsorption. The uneven interface layer will have a WBL. This WBL stress relaxation and crack development will be different, thus greatly affecting the overall performance of materials and products.
diffusion theory
the two polymers, under the premise of compatible, when they come into close contact with each other, due to the brown movement of molecules or the pendulum of the chain segments produce mutual diffusion phenomenon. This diffusion is carried out through the interface of adhesive and adhesive. The result of diffusion is the disappearance of the interface and the generation of transition zones. Bonding systems cannot explain the adhesion of polymer materials to metals, glass or other hard bodies by diffusion theory, as polymers are difficult to spread to such materials.
Stectrectronic Theory
When adhesives and adhesive systems are a combination of electron receptors-suppliers, electrons are transferred from the supply body (e.g. metals) to receptors (e.g. polymers), creating a double electron layer on both sides of the interface area, resulting in electrostational gravity.
the rapid stripping of the bonding layer from the metal surface in a dry environment, the discharge of light and sound phenomena can be observed by instruments or the naked eye, confirming the existence of electrostitive action. However, static electricity only exists in the bonding system that can form a double layer, so it is not universal. In addition, some scholars have pointed out that the charge density in the dual-electric layer must reach 10
21
electrons/cm
2
, the electrostectronic attraction can have a more obvious impact on the strength of the glue. The maximum density of the perch charge generation in the double-layer is only 10
19
electrons/cm
2
(some think only 10
10
-10
11
electrons/cm2). Therefore, although static power does exist in some special bonding systems, it is by no means a leading factor.
mechanical force
from a physical and chemical point of view, mechanical action is not a factor in the production of adhesion, but a way to increase the bonding effect. The adhesive penetrates into gaps or bumps on the surface of the viscous, curing and producing a meshing force in the interface area, similar to the bonding of nails to wood or the implantation of roots into soil. The essence of mechanical connection is friction. Mechanical connectivity is important when bonding porous materials, paper, fabrics, etc., but is not significant on certain solid, smooth surfaces.
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