How do sticky materials (like glue/tape etc) work?

Update:18-06-2021
Summary:

Ok this is a very deep topic and there is a trillion do […]

Ok this is a very deep topic and there is a trillion dollar industry (maybe more!) revolving around this question.

There are three major factors influencing sticky behavior.

1- Surface Area

2-Surface Energy

3-Chemical structure of a binding adhesive

Surface Area:

This is how gecko animal stick to every surface (not in Teflon! we will come to that). You see gecko can stick to even wet surfaces not because some adhesive secreted from its glands in its hands, but because the surface area of the skin.

This is an electron microscope picture 🙂 There are nano-meter scale fibrils there.

So surface area is a straightforward parameter. The more surface, the more strength you gain. The reason is simple. Van der Waals forces. No matter how incompatible your surfaces, every atom is made out of plus and minus charged particles therefore they will always pull each other to a degree. Now if you increase the number of these interractions by facing more and more surfaces, these weak Van der Waals forces will eventually stack up and becomes big enough to carry big bodies. This has an advantage over adhesives because it is simple and without an expiration date. It is also compatible with all surfaces (no teflon!) so you can bluntly go over any surface without hesitation.

Surface Energy

This is also a straightforward formula. The more surface energy you have, the better you stick. This is what we call the “ability to get wet”. Wet here is not a phrase only used for water. Any adhering material can wet a surface.

Now surfaces of polymers, especially polyolefins like polyethylene or PTFE (Teflon) have very low surface energy therefore you cannot wet the surface well. Remember gecko? The surface energy of Teflon is so low, the entire area cannot conjure up enough Van der Waals energy to carry that dude. This is due to the fluorine atoms. Fluorine is very very aggressive in getting its electron therefore it won’t share it with anybody.

Chemical Structure of the binding adhesive

This is not about secondary bonding of chemicals. This is about the ability of adhesives to break the bonds of surface atoms holding together and replacing them with its. This is the ability to chemically react. Adhesives like epoxy resin that you heard of regularly or cyanoacrylates are very very powerful due to their active groups. (Epoxy is the name of the active grup. that is why its name is epoxy resin).

Epoxy active group.

There are more to this topic than i explained but i have to catch a taxi 🙂

hope it helps.