My name is Sue Berk Koch. I am a children’s author. Welcome.

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Why does glue stick? Or Sue against Glue

After staring at the ugly wallpaper in our all purpose study/computer room for too long to admit, I decided it had to come down. The stuff, however, was stuck and I mean stuck.

It became Sue against Glue. Clearly, I needed an ally.

What kept this ugly crap on the wall, when a Band-Aid on one of the boys’ knees stayed in place for about thirty seconds? This has actually taxed greater minds than mine. There is no simple answer, just like there is not one type of glue. Super glue, wood glue, school glue, the glue on sticky notes, I could probably come up with two-dozen more.

This is actually a science question. (Aren’t they all?) But that means that I can do this. I will beat the scientists. They don’t know exactly what is going on, anyway, what with all the different surfaces and structures and combinations of factors. I only had to concentrate on the wall and the wallpaper. What they were made of and what type of glue would keep them in place.

Forces keep things in place. Cohesive and Adhesive.

Let’s start with adhesive forces. When you put a glue substance on another, one of the main factors keeping them together is adsorption. Remember Van Der Waals? This isn’t what keeps the individual molecules together, meaning the hydrogen and oxygen in water, but what keeps one type of molecule sticking to another type molecule, non-chemically/without any electrons changing hands. It is a lot of tiny attractive forces that add up, like millions of microscopic magnets.

For my science fiction novel, THE DARK SIDE OF AMBER, I researched geckos and why they can walk up walls. (So my characters could, too) Geckos have millions of hairs, called setae on their feet. Each hair is like a tiny hairbrush with bristles. We are talking small, as in electron microscope small. These hairs brush up against the surface the gecko wants to scale and tiny electrostatic forces (yup, Val der Waal) appear between the hairs and the surface. Every single hair provides a microscopic force that helps the gecko to stick. Imagine that? Molecular forces essentially defy gravity.

Gecko_foot_on_glassGecko foot on glass, as you probably guessed.

Scientists copied geckos too, and put, for example, microscopic glue bubbles inside the adhesive of a sticky note.

So, now we have millions of glue molecules sticking to millions of wall molecules AND wallpaper molecules. (They don’t care if the wallpaper is ugly)

It wasn’t enough for scientists. They made some glues stronger with chemical adhesion, which is a more specific intermolecular force. Now we’re getting to cohesive forces. Essentially, the substances are chemically bonded together. This means that the molecules share electrons via covalent, hydrogen or ionic bonds. (If you’re taking a quiz, covalent>hydrogen>ionic)

When you open that brand new bottle of glue, and the fancy chains of glue polymers come in contact with water in the air, on the wall and wallpaper– or in my case, the water on my fingers– a reaction takes place.

Then there are mechanical factors, like a surface full of holes so the glue can seep into the holes and grip. That’s pretty easy to understand.

Well, I’ve had about enough of adhesion and cohesion for one day, at least enough for a blog post.

How do I beat it? The same way that Band-Aids come off knees. I came back to water. Water is a brilliant beautiful molecule. Lots of organic molecules are soluble in water, meaning they form new bonds with the water itself. The oxygen in water is nucleophilic so it attacks other elements. Water breaks bonds.

I’ll confuse the glue by flooding it with water molecules. The higher the temperature of water, the more soluble the molecules are. (It’s a proven fact that heat breaks bonds more readily) Weaken the chemical bonds and the Van der Waals attractions with lots and lots of water.

My hero water will get into the wallpaper and push itself between those molecules. Guess what? It worked. The water needed about four times as long to break up the bonds than we needed to physically peel it from the wall.

Sue + H2O one: Glue zero.

Now. Is anyone up for a painting party?

Hideous wallpaper In progress

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