Adsorption theory people see solid adsorption of adhesive as cementing main reason theory, called the adsorption theory of cementing.
Theory is that: the main source of sticky relay is molecular reaction bonding system, namely Fan Dehua gravitational force and hydrogen bond.
Adhesive and glued surfaces stick relay and adsorbability have some of the same nature.
Adhesive and glued surfaces molecules the role of the process, there are two processes: the first stage is the molecular liquid adhesives by Brownian motion to the glued surfaces spread, make the two polar groups of the interface or link close to each other, in the process, temperature, contact pressure and reduce the adhesive viscosity and so on all is conducive to the strengthening of Brownian motion.
The second stage is adsorption.
When the adhesive and glued intermolecular distance up to 10 -
Produces mutual attraction, interface between molecules, further shortened the distance between molecules in the largest stable state.
According to the calculation, due to the effect of van der Waals force, when two ideal plane distance of 10 & Aring;
When the gravitational strength can reach 10 - between them
When the distance is 3 -
When is 100 -
This value is much more than modern can achieve the best structure adhesives intensity.
As a result, some people think that as long as when two objects in contact with good, the adhesive for bonding interface fully wetting and reach the ideal state, only the effect of dispersion force, would be enough to produce high bonding strength.
But the actual difference in bonding strength and the theoretical calculation, this is because the mechanical strength of the solid is a kind of mechanical properties, rather than the molecular properties, its size depends on each of the local properties of materials, and is not equal to sum of molecular forces.
Assume that two values are closely contact plane, and ensure the interface layer on the damage at the same time, the function of intermolecular also there can be no guarantee the force between the molecules occur at the same time.
The polarity of the adhesive is too high, sometimes can seriously interfere with the wet process and reduce the stick relay.
Molecular inter-atomic forces is to provide stick relay factors, but it is not the only factor.
In some special cases, other factors can also play a leading role.
Chemical bonds to form chemical bonds theory think adhesive and glued thing except the interaction force between molecules, and sometimes chemical bonds, for example, vulcanized rubber and copper plating metal bonding interface, the action of coupling agent on bonding, isocyanate to metal and rubber adhesive interface etc, are evidence of the formation of chemical bonds.
The strength of the chemical bond is much taller than van der into force;
Chemical bond formed not only can improve the adhesion
strength, but also can overcome disadvantages of stripping the glue joint destruction.
But the formation of chemical bond is not normal, to form chemical bonds must satisfy certain quantization ` parts, it is not possible to make adhesive and glued all form chemical bonds between the contact.
Unit, the adhesive interface chemical bonds for much less than the number of molecular interaction, so adhesion strength from the intermolecular forces cannot be ignored.
When weak boundary layer theory cannot be glued very good infiltrating liquid adhesives body surface, air bubbles in space and form the weak area.
With impurity of, for example, can dissolve in the molten glue adhesion agent, and does not dissolve in the cured adhesive, the adhesive to form another phase after solidification, the gluing body produce weak interface layer between the whole and adhesives (
WBL in addition to the technological factors, in polymer network or melt into interaction of molding process, adhesive and surface adsorption thermodynamics phenomenon such as boundary layer is formed in the inhomogeneity of the structure.
WBL inhomogeneity interface layer will appear.
This WBL stress relaxation and the development of the cracks are different, thus greatly affecting the overall performance of materials and products.
Diffusion theory under the premise of two kinds of polymer with compatibility, when they close contact each other, because of the brown movement of molecules or segment produces mutual diffusion phenomenon.
This role is spread through glue adhesion agent, glued interface intertwined.
The spread of the results leads to the disappearance of the interface and the transition zone.
Adhesive system with diffusion theory can not explain the polymer material and metal, glass, or other hardware adhesive, because it is difficult to spread to this kind of material of polymer.
Electrostatic theory as adhesive and glued system is a kind of electron acceptor -
Supply body combination, electronic supply from the body (
Such as metal)
Transferred to the acceptor (
Such as polymers).
, formed in the interface area on both sides of the electric double layer, thus produced electrostatic attraction.
From the metal surface in the dry environment rapid stripping adhesive fillet, available instrument or macroscopic observation to discharge phenomenon of light, sound, confirmed the existence of electrostatic interactions.
But electrostatic interactions can only exist in the form of electric double layer bonding system, so there is no universal.
In addition, some scholars have pointed out that: in the electric double layer charge density must be 1021 electronic/cm 2, electrostatic attraction to the more obvious influence on bonding strength.
Habitat and electric double layer moving electric charge produce the maximum density is only 1019 cm/electronic 2 (
Some think that only 1010 -
Thus, even though the electrostatic force does exist in some special adhesive system, but is by no means dominant factors.
Theory of mechanical forces from the physical and chemical point of view, the mechanical action is not sticky relay, rather a way to increase the bonding effect.
Adhesive permeates the glued surfaces of cracks or concave and convex, after curing the meshing force in the interface area, these situations like nails and wood joint or roots into the soil.
Mechanical relay is the nature of friction.
In bonding porous materials, paper, fabric, such as institutions even relay is very important, but for some solid and smooth surface, the effect is not significant.
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