Adhesion needs molecular contact, so the adhesive must flow into every valley of the surface. Wetting is judged by the contact angle a droplet makes: low angles mean good spreading, while angles above 90 degrees mean the liquid beads. Contamination, low surface energy plastics and high-viscosity or partly gelled adhesive all reduce wetting.
Look at the bead on that part, it's not wetting at all, sitting up like water on a waxed car.
Also heard as
- wet-out
- spreading
Related terms
Surface energy
A measure of how strongly a solid surface attracts liquids, which decides whether an adhesive can wet it.
Wet-out
How fully a tape's adhesive has flowed into contact with a surface, often visible through clear parts.
LSE
Low surface energy, describing plastics and coatings that most adhesives cannot wet or bond without help.
Dyne pen
A marker filled with test fluid of known surface tension, used to check a surface's treatment level.