Question

What makes glue sticky ?

Answer 1

Glues like the ones used at school are made up of long chains called polymers, which are a bit like spaghetti strands. When you glue 2 pieces of paper together the polymers get into all the microscopic cracks and crevices in the paper, (a bit like ink soaking into the porous surface of paper). As it dries and the water evaporates the polymer molecules are left in the cracks to hold the paper together. But not all glues work like this. Sometimes the glue contains a substance that temporarily melts the 2 surfaces you're trying to stick together, effectively welding them together when the glue dries. Superglue contains cyanoacrylate. When this substance comes into contact with water it forms chains which bond to the ends of the 2 things you're trying to stick together. As the glue dries the chains harden until they can't move.