Nothing says “back to school” quite like a big bottle of white glue. Stick with us, folks, and you’ll learn something new today in Wonderopolis!

Have you ever wondered…

• Why doesn’t glue stick to the inside of the bottle?
• What are polymers?
• How does mechanical adhesion differ from chemical adhesion?

Did you know?

It’s one of the mysteries of life that has confounded many students throughout history. That pasty substance we all call “glue”… it sticks things together, but doesn’t stick to the inside of the bottle! Why not?

Is it magic? Nope! It’s science — and it’s all about water.

The regular white glue most students know so well is made up of a variety of chemicals called “polymers.” These polymers are long strands that are either sticky or stretchy.

Glue manufacturers have to find just the right combination of sticky and stretchy polymers to make the best glue.

White glue also contains water. Water acts as a solvent that keeps the glue liquid until you want it to stick.

When you put glue on a piece of paper, the solvent — water — is exposed to air. The water eventually evaporates (changes from a liquid to a gas).

As the water evaporates, the glue dries and hardens. All that’s left are the sticky polymers that hold things together. This process is called “mechanical adhesion.”

So why doesn’t white glue stick to the inside of the bottle? When white glue is inside a bottle, there’s not enough air inside the bottle to cause the water to evaporate to make the glue sticky.

Basically, the bottle protects the glue from the air and keeps the glue runny. If you’ve ever left the top off a glue bottle for a while, you may have noticed that, unfortunately, the glue dried up!

What about Super Glue®? You may have noticed that Super Glue tends to dry out in its container more quickly than white glue.

Super Glue works differently than white glue. Instead of the polymers in white glue, Super Glue is made of a chemical called “cyanoacrylate.”

This chemical bonds things together when it reacts with water vapor in the air. This process is called “chemical adhesion.”

No matter how dry the air may seem, there’s always some water vapor in the air. To keep Super Glue from drying out, its container must be kept tightly sealed to prevent water vapor from seeping in and reacting with the glue.

So whether you’re talking about white glue or Super Glue, water is the key. With white glue, you need the bottle to keep the water in the glue from drying up and becoming sticky. Super Glue containers, on the other hand, keep water out to prevent the chemical reaction that will make the glue harden.

Try it out!

Ready to have some fun with glue? If you don’t have any glue on hand, that’s fine.

We’re going to start by making our own homemade glue. Just follow the recipe and directions to make your very own all-natural glue.

When you’re finished, pick one or more of the fun crafts below to try. Don’t forget to clean up afterward!

• Decoupage in 5 Simple Steps
• Glue Ghosts
• I Love You! Poster
• Pasta Artwork
• Craft-Stick Picture Frame

Wonder words to know and use:

• polymer
• mechanical
• adhesion
• chemical
• confounded
• strand
• manufacturer
• solvent
• evaporate
• vapor

Still wondering?

Just like glue sticks to some things and not others, magnets attract some things and not others. Visit Science NetLinks’ Magnets 1: Magnetic Pick-ups lesson to learn which materials are attracted to magnets and which are not.

Wonder what’s next?

If you want to be prepared for tomorrow’s Wonder of the Day, you need to get a good night’s sleep. Time for bed!

• Tags: adhesion, chemical, evaporate, glue, mechanical, polymer, solvent, water