There are interface bonding issues between polymers, between polymers and non-metals or metals, between metals and metals, and between metals and non-metals, all of which involve the bonding between polymer base materials and different materials. Bonding is the result of the interaction between different materials after they come into contact at the interface. Therefore, the role of the interface layer is a fundamental issue studied in the science of adhesion. Factors such as the interfacial tension between the adherend and the adhesive, the surface free energy, the nature of the functional groups, and the reactions at the interface all affect the bonding. Bonding is a highly comprehensive technology with complex influencing factors. Since existing bonding theories all explain its principles from a certain aspect, there is still no comprehensive and unique theory up to now.

People call the theory that regards the adsorption of the adhesive by the solid as the main cause of bonding the adsorption theory of bonding.

The theory holds that the main source of the bonding force is the molecular force in the bonding system, that is, the van der Waals force and the hydrogen bond force.

The adhesive force between the adhesive and the surface of the adherend has a certain similarity in nature to the adsorption force. The interaction process between the adhesive molecules and the surface molecules of the adherend has two stages: In the first stage, the liquid adhesive molecules diffuse towards the surface of the adherend with the help of Brownian motion, bringing the polar groups or chain segments at the two interfaces closer to each other. During this process, increasing the temperature, applying contact pressure, and reducing the viscosity of the adhesive are all conducive to enhancing Brownian motion. The second stage is the generation of the adsorption force. When the distance between the adhesive and the adherend molecules reaches 10⁻⁵ Å, an attractive force will be generated between the interface molecules, further shortening the intermolecular distance to the state of maximum stability.

According to calculations, due to the action of the van der Waals force, when the distance between two ideal planes is 10 Å, the gravitational intensity between them can reach 10 - 1000 MPa; when the distance is 3 - 4 Å, it can reach 100 - 1000 MPa. This value far exceeds the strength that the best modern structural adhesives can achieve. Therefore, some people believe that as long as the two objects are in good contact, that is, when the adhesive fully wets the bonding interface and reaches an ideal state, the action of only the dispersive force is sufficient to produce a very high bonding strength. However, the actual bonding strength differs greatly from the theoretical calculation. This is because the mechanical strength of a solid is a mechanical property rather than a molecular property, and its magnitude depends on the properties of every part of the material, and is not equal to the sum of the molecular forces. The calculated value is based on the assumption that two ideal planes are in close contact, and it is guaranteed that the interactions between each pair of molecules in the interface layer are simultaneously destroyed. In reality, it is impossible to ensure that the forces between each pair of molecules occur simultaneously.

If the polarity of the adhesive is too high, it will sometimes seriously hinder the wetting process and reduce the bonding force. The intermolecular force is a factor that provides the bonding force, but it is not the only factor. In some special cases, other factors can also play a dominant role.