4.1.3 Wetting and Polarity

4.1.3 Wetting and Polarity

Surface energy is the degree of attraction or repulsion exerted by the surface of one material to another (measured in mN/m or outdated dyn/cm). Surface tension is a liquid’s resistance to surface penetration, which allows the liquid to behave like a thin elastic film. The wetting theory states that adhesion results from the surface forces of molecular contact. In the ideal bonding condition, a substrate has high surface energy, i.e. the surface has the capacity to attract, and the adhesive has a low surface tension, i.e. low resistance to deformation or breakage. This results in the adhesive properly wetting the substrate and forming a strong bond.12 Surface preparation for bonding frequently increases the surface energy of a substrate to improve bond strength.

Figure 76 High surface energy substrate
Figure 76 High surface energy substrate
Figure 77 Medium surface energy substrate
Figure 77 Medium surface energy substrate
Figure 78 Low surface energy substrate
Figure 78 Low surface energy substrate

12) S. Ebnesajjad, Handbook of adhesives and surface preparation, Technology, Applications and Manufacturing (2011).

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