Re: Why doesn't glue stick to the inside of the bottle?

Hi,

Excellent question!  I need to first assume you are asking about water-
based glues like Elmer's glue.  So based on this assumption I can answer 
the question.  Water based glues (or even solvent based glues) work 
because the water (or solvent) evaporates (for example, the thinner you 
spread the glue, the faster it will dry as you increase the surface area, 
hence speeding up the amount of water evaporating).  Since the water can 
not evaporate from a closed bottle, the glue remains "workable" so it can 
not stick to the sides.  If you leave the cap off a bottle of glue and all 
the water would evaporate (this would take a long time), the glue would 
harden, but would still not stick to the bottle.  The inside of the bottle 
is very smooth and the glue needs some roughness to grab causing the glue 
to stick.  This is why Elmer's glue works well on paper as paper on the 
microscopic level is actually porous and the glue can grab it.  Other 
glues that have a different solvent (that is not water, for instance an 
organic solvent) present may work better on some materials because the 
solvent present actually dissolves the piece you are interested in gluing.

So there are actually 2 factors preventing the glue from sticking: (1) 
lack of water evaporation (the more important reason) and (2) smooth 
surface.  As an experiment (if you'd like) put some Elmer's glue between 
two pieces of plastic wrap (like what you have in the kitchen, which is 
very similar to what a glue bottle is).  First off you will notice it will 
take longer to dry than if you had glued two pieces of paper together.  
Second you will find that the two pieces of plastic will not be glued 
together.  The dried glue should peel (rub it with your finger) leaving 
you with 3 pieces (2 pieces of plastic and 1 piece of dried glue, which is 
polyvinyl acetate).  This worked for me when I tried it! If it didn't 
work, you must have some rough plastic wrap!!

Now here's another question for you (and the answer is actually above hint 
see #2), how do non-stick surfaces (like Teflon) stick to the inside of a 
frying pan?

Hope this helps, if not send in some more questions for clarification.

KIP