We usually use super glue to stick any two objects but I was wondering like why don't they stick inside their own bottle ?
Why doesn't glue stick to the tube?
Adhesives are designed to work when they leave the tube—and not before. Different adhesives achieve this in different ways. Some are dissolved in chemicals called solvents that keep them stable and non-sticky in the tube.
When you squeeze them out, the solvents quickly evaporate in the air or get absorbed by the surfaces you're sticking to, freeing the adhesives themselves to do their job.
Plastic modeling glue works like this. It contains molecules of polystyrene in an acetone solvent. When you squeeze the tube, the glue spurts out and you can usually smell the very strong acetone as it evaporates.
Once it's gone, the polystyrene molecules lock together to make strong chemical bonds. Glue doesn't smell when it's dry because all the solvent has vanished into the air.
Some glues (such as synthetic, epoxy resins) have to be mixed together before they work. They come in two different tubes, one containing the synthetic resin and the other containing a chemical that makes the resin harden. The two chemicals are useless by themselves but, mixed together, form a tough, permanent adhesive.
How super glue works
- The main ingredient in super glue is a chemical called cyanoacrylate, an acrylic resin that forms a bond (cures) almost instantly;
- The only trigger it requires are the hydroxide ions found in water;
- Traces of water are found on almost everything and in the surrounding air, which causes the glue to become sticky;
- It works best in moist conditions, although it is not advised to start gluing on a soaking wet surface.
Therefore the lack of water in the tube, or the chance of solvents evaporation, doesn't allow the glue to stick to the tube.
In other words: that strong smell that comes out when we open the tube's cap is due to the solvents evaporation, so once they're gone the glue sticks. If a superglue tube is left open for a long time (exposed to air, allowing the water to come in contact with the glue), it's impossible (or almost) to squeeze it out since it got stuck to the tube.