Adhesives not only need to bond firmly but also require long - lasting stickiness. No matter how good the adhesive effect is, if it cannot last, it will fall off after a while or the stickiness will decrease due to certain reasons. Therefore, sometimes we need to find ways to ensure the long - term stickiness of the adhesive.
     Research work and experience have shown that adhesives can bond objects through intermolecular attraction. The adhesive force occurring at the interface is composed of a combination of secondary valence forces (physical forces, electrostatic forces), primary valence forces (chemical forces), and mechanical forces. Among them, secondary valence forces are the main forces generating the adhesive force.
       The realization of this adhesive force can be considered to occur in two stages:
The first stage is that the flowing adhesive molecules diffuse towards the surface of the object to be bonded with the help of Brownian motion and gradually approach it. The fluidity of the adhesive liquid during application (with a lower viscosity) and the application of curing pressure are conducive to this intermolecular contact and approach.
The second stage is the generation of intermolecular adsorption. When the distance between the adhesive molecules and the surface molecules of the object to be bonded approaches a certain value, the secondary valence forces begin to take effect and increase as the intermolecular distance between the adhesive and the surface decreases.
      These two processes cannot be completely separated and continue to occur before the adhesive cures. Thus, it can be seen that promoting full contact between the adhesive and the surface of the object to be bonded and bringing the molecules of the two closer is the key to obtaining adhesive force.
     Therefore, for the same adhesive, if the viscosity of the adhesive liquid itself is relatively high, or during construction, measures should be taken to make it thinner. Heating measures to promote Brownian motion, applying pressure during curing, and extending the curing time (especially for room - temperature - curing adhesive types), as well as ensuring the surface of the object to be bonded is flat, clean, and dry, are all conditions for obtaining the best adhesive force.
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