The Magic Paper Towel: Exploring Water Repellent

The Magic Paper Towel

We all know paper towels like to absorb water. What if we make paper towels waterproof? 

Watch the video to see what it looks like.

Directions

Spray the top side of a paper towel with 2 coats of water repellent.  Let it dry.

Lesson

Place a piece of regular paper towel in each group.

Pour about 250ml of water slowly on each group’s regular paper towel.  Try to keep it on the paper towel.  Students will notice it absorbs the water and some most likely spreads.

Have students clean up their area.

Place a piece of waterproof paper towel in each group.
Pour about 250ml of water slowly on each group’s waterproof paper towel.  Try to keep it on the paper towel.  Students will be amazed to notice the water does not soak in.  It stays on top.  Even the bottom does not get wet.

Have the groups discuss what happened.  They need to try and figure out how the teacher did this.

Then show them the waterproof spray.
Have extra waterproof paper towels to give students an opportunity to explore.

Why is this possible?

The paper towel was sprayed with silicone-based water repellent.  Silicone is a hydrophobic substance.  That means it does not absorb water.  Paper towel is naturally hydrophilic (water-loving).  Which means it absorbs water.  The water repellent creates a barrier keeping the water out.  Water forms curved drops on the paper towel because it has polar bonds.  Water molecules have a positive and negative end.  This means water molecules are attracted to each other.  The drops attract to each other forming raised droplets on the waterproof paper towel. This attraction creates surface tension.

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