When the pages of your book come off, you look for a glue stick. Have you wondered what makes it sticky? Why don’t we stick two small pieces of glass with the glue? Adhesives are substances capable of holding materials together by surface attachment. They are available in many forms as glue, tapes etc.
The stickiness of adhesives is the result of the chemical bonds that exist between the molecules of the substance it is made of. Adhesives are made of long chain of protein molecules (polymer). The molecules act as binders because of adhesion and cohesion. Adhesion is the binding force between two dissimilar molecules (molecules of adhesive and substrate) and cohesion is the binding force between two similar molecules (molecules of adhesive). The components of adhesive diffuse into the pores of the substrate material. Substrate material could be a paper. Stickiness is due to the combination of the molecular forces of the glue material sticking to itself as well as holding onto the substrate.
When a liquid is added to an adhesive, it becomes glue. Glue is an adhesive substance that binds two porous surfaces together. Modern glue is made from carbon based petrochemical derivatives. Tapes are made from mixing rubbery material with adhesives.
The adhesive bonding lets the adhesive to wet and spread on the adherends (surfaces being joined). The adhesion process is based on adsorption theory. Adhesion of atoms, ions, molecules of gas, liquid or dissolved solids to a surface is called adsorption. This process creates a film of the adsorbate – the molecules or atoms being accumulated, on the surface of the adsorbent. As per this theory, the substances stick primarily because of a close intermolecular contact force exerted due to adhesion and cohesion between the surface layers of the adhesive and adherend. When the glue dries, it hardens to make the molecules stick together.