Adhesive...!!!

Adhesive...!!!

An adhesive or stick on is a material, usually in a liquid or semi-liquid state, that adheres or bonds items together. Adhesives come from either natural or synthetic sources.... The types of materials that can be bonded are vast but they a
re especially useful for bonding thin materials.... Adhesives cure (harden) by either evaporating a solvent or by chemical reactions that occur between two or more constituents....
Adhesives are advantageous for joining thin or dissimilar materials, minimizing weight, and when a vibration-damping joint is needed.... A disadvantage of most adhesives is that most do not form an instantaneous joint, unlike many other joining processes, because the adhesive needs time to cure....
The earliest known date for a simple glue is 200,000 BC and for a compound glue 70,000 BC....

Mechanisms of adhesion:-
Adhesion, the attachment between adhesive and substrate may occur either by mechanical means, in which the adhesive works its way into small pores of the substrate, or by one of several chemical mechanisms. The strength of adhesion depends on many factors, including the means by which it occurs.
In some cases, an actual chemical bond occurs between adhesive and substrate. In others, electrostatic forces, as in static electricity, hold the substances together. A third mechanism involves the van der Waals forces that develop between molecules. A fourth means involves the moisture-aided diffusion of the glue into the substrate, followed by hardening....