Why is Blu-Tack sticky?

What makes Blu-Tack so sticky?
24 September 2018
Presented by Adam Murphy
Production by Adam Murphy.


Gum on Shoe


Tom asked us "Why is Blu-Tack sticky?". Adam Murphy spoke to Jennifer Gaughran, researcher at Dublin City University, to see if she could help with a question that had us stuck...

In this episode

Gum on Shoe

Why is blu tack sticky?

It’s time for Question of the week. Adam Murphy has been stuck on this question from Tom.

Adam - Blu tack is everywhere, probably in every home and office, holding up our posters and our notices. But figuring out what’s in this adhesive puts us in something of a sticky situation. To learn more, I spoke to Jennifer Gaughran, a researcher in Dublin City University.

Jennifer - We don’t know exactly what Blu-Tack is made of because it’s a trade secret, but we do know that it contains something called hydrocarbon polymers. Hydrocarbon polymers are included in most glues and hat turns Blu-Tack into an adhesive. Polymers which are molecules that form these long chains, do tend to be quite sticky because, from chemical point of view, they have a lot of hydrogen on their surface which likes to form very strong physical bonds with anything they touch.

Adam - So that’s part of it, but is that the whole sticky story?

Jennifer - It’s actually the squishy nature of the Blu-Tack that’s the real trick though. Blu-Tack is a putty-like substance that’s moveable and able to deform. Blu-Tack seeps into any little indents on the surface that it’s sticking to and this makes it even stickier.

Adam - That might be why there’s still blu tack on the walls from the posters that covered my childhood bedroom.

Jennifer - When you press hard enough, it forms a very smooth flat surface against your surface and pushes all the air out. This creates a vacuum, which is a very difficult thing to break. It’s like when you stack two wet glasses together. The water pushes all the air out and it very difficult to pull them apart again. You have to twist them apart or disrupt the water somehow.

Adam - Or just like a plunger!

Jennifer - This also explains why Blu-Tack doesn’t feel sticky at first in your hand but does get stickier the more you handle it. It’s because it’s starting to fill all those nooks and crannies, getting you into a sticky situation!

Adam - Thank you Jennifer. I’m sure everyone was glued to their speakers. Next week, we’ll be tackling this muddy question from Daniel.

Daniel - If I stand in the shallow end of a swimming pool, I don't feel the pressure of the water around my legs. But if I put my wellies on and stand in a deep puddle, I do feel the pressure of the water on my lower legs. Why is this?


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