Wetting

In the bonding industry, attention must be paid to the wettability of a part to be bonded. Wetting is the formation of a contact surface between the adhesive and the part to be joined. The extent of wetting depends on the type of adhesive and the nature of the part surface, such as its chemical composition and roughness.

Many functional properties of the surfaces of the parts to be joined depend significantly on their wettability. Examples of such functional properties are the ability to self-clean, the prevention of contamination, ice formation and misting with moisture, as well as the usability for the purification of water, for the separation of water-oil mixtures and for water extraction by condensation of atmospheric moisture.

The extent of wetting is often determined by the contact angle. The following cases are distinguished:

• One speaks of non-wetting when the contact angle is greater than 90°. The liquid on the solid surface contracts into an almost spherical drop.
• Partial wetting is when the contact angle is greater than 0° and less than 90°. The liquid on the surface forms a round cap.
• We speak of complete wetting when the liquid spreads out on the solid surface in the form of a flat film. This scenario corresponds to a macroscopic contact angle of 0°.