The relationship between surface energy and bonding?
Bonding is the surface where two materials are in contact with each other. There are two necessary conditions for bonding: one is wettability, and the other is adhesion.
What Is Wettability?
Wettability is the phenomenon of uniform spreading of liquids under the action of intermolecular forces on the surface of solids, that is, the affinity of liquids for solids. The wettability of liquids is caused by surface tension, while solids are called surface energy. The wettability is mainly determined by the surface energy of the adhesive and the adherend, and is also related to process conditions and environmental factors.
The Relationship Between Surface Energy and Wettability
- The surface energy of the solid determines its wettability. The basic condition for the liquid to spread on the solid surface is that the surface energy of the liquid is smaller than that of the solid. The lower the surface energy of the liquid (the higher the surface energy of the solid), the more conducive to spreading. On the contrary, it is not conducive to spreading.
- High surface energy liquids cannot wet low surface energy solids.
- The closer the surface energy of the liquid and the solid are, the worse the wettability.
- On the same solid, the higher the surface energy of the liquid, the worse the wettability.
- The same liquid has good wettability on solid surfaces with large surface energy.
Surface energy is an important factor affecting the bonding strength. Reducing the surface energy of the adhesive or increasing the surface energy of the adherend can enhance the wettability of the adhesive on the adherend, thereby improving the bonding strength.
How Do You Measure Surface Energy?
Swipe a certain value of the dyne pen on the tested film. If there are no bead points, it means that the surface dyne of the test film is higher than or equal to the dyne number on the dyne pen.
- If the scribe line of the test film shrinks slowly, it means that the surface dyne of the film is less than that of the dyne pen.
- If the scribe line shrinks immediately and appears spherical, it means that the dyne of the test film is very lower than that of the dyne pen.