How does glue actually stick?
Quick Answer
Glue works through two forces. Adhesion makes it cling to each surface it touches, and cohesion holds the glue itself together once it sets. Super glue hardens when it meets traces of water.
The Full Story
Liquid glue flows into the tiny scratches, pores and fibres of a surface and gets extremely close to it. At that scale, attractive forces between molecules, such as van der Waals forces and sometimes chemical bonds, grip the surface; this is adhesion. Then the glue hardens, by drying, cooling or a chemical reaction, and its own molecules lock together to become strong; this is cohesion. A joint is only as good as its weakest part, so a bond can fail at the surface or inside the glue. Different glues harden in different ways. White PVA wood glue sets as the water in it evaporates or soaks into the wood. Super glue, made of cyanoacrylate, polymerises when it meets tiny amounts of moisture, which is why it bonds skin so fast. Two-part epoxies harden when a resin and a hardener react together.
Key Facts
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Suggested video title for this topic:
"The invisible forces that hold your world together"
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