When considering adhesives, the bonding surface is a critical factor. Unlike processes such as welding that alter and fuse surfaces, adhesive bonding joins two surfaces without changing their individual characteristics. Therefore, the selected adhesive must be compatible with the surfaces involved in the application.

What is Surface Energy and Why is it Important in the Bonding Process?

When considering adhesives, the bonding surface is a critical factor. Unlike processes such as welding that alter and fuse surfaces, adhesive bonding joins two surfaces without changing their individual characteristics. Therefore, the selected adhesive must be compatible with the surfaces involved in the application.

When considering adhesives, the bonding surface is a critical factor. Unlike processes such as welding that alter and fuse surfaces, adhesive bonding joins two surfaces without changing their individual characteristics. Therefore, the selected adhesive must be compatible with the surfaces involved in the application.

Surface Energy is a term used to describe the nature of a substrate's surface—it can vary from high to low. The molecular attraction between different materials determines how well they adhere to one another. The strength of this attraction depends on the surface energy of the substrate. High surface energy implies stronger molecular attraction, whereas low surface energy results in weaker bonding forces.

To better understand surface energy, imagine water on the hood of a car. An unpolished (bare) hood has high surface energy, so water spreads across its surface. In contrast, a polished hood has low surface energy, causing water to bead up and roll off. Similarly, on high surface energy materials, adhesives flow and “wet” the surface—wetting is essential to create a strong bond.

Wetting

• For physical interactions to develop, the adhesive and the surface to be bonded must come within 1 nanometer of each other—this is achieved through proper wetting. Wetting is the ability of a liquid to maintain contact with a solid surface.

Surface Tension

• Water molecules inside a droplet attract each other equally from all directions. However, molecules at the surface are pulled inward more strongly, as they have fewer adjacent molecules to interact with on the outer side (facing air).
• This net inward force creates surface tension, which attempts to minimize the surface area. The stronger the internal forces, the higher the surface tension of the liquid.

Good Wetting:

• Occurs when the surface energy of the substrate is higher than the surface tension of the liquid (adhesive).
• The contact angle α is less than 90°.

Poor Wetting: 

• Occurs when the surface energy of the substrate is lower than the surface tension of the adhesive.
• The contact angle α is greater than 90°.

Updated on 2024-10-02 23:29:01