Re: Adhesives/glue

Dear User,

Your question is very broad, and an answer to it would require the volume
of several large books if not more. 

In short, things "stick" due to the forces of molecular attraction. 
Polished glass pieces for instance actually mold together if the polished
surfaces are allowed to stay in contact for some time, due to the fact that
a lot of intermolecular contacts are made since the interface is very 
smooth. Glues and adhesives work on a similar basis, filling the microscopic
 cavities of the contacting  surfaces and creating lots of contacts between
glue and the surface. Viscosity-based glues simply provide an intermediate
between the two surfaces, with a high fill ratio combined with high viscosity
and elasticity of the glue itself. Many glues, however, change their molecular
structure upon "setting" - either reversibly or irreversibly. Common 
driving forces of the change are dehydration and polymerization. In many
cases, actual chemical bonds are formed between the glue and the surface
molecules of the objects which are glued. Thermal glues are liquid at high 
temperatures which allows good pore-filling and penetration of the liquid glue
but when the glue cools, it looses plasticity and a strong bond is created.

This is but a short and incomplete review of the many possible processes
which are responsible for things "sticking" together. 

HiH.