Droplet labyrinth

Soak in or flee? Depends on nature!

Difficulty:
Danger:
Duration:
20 minutes

Safety

  • Carefully review the general safety advice on the back of the box cover before starting the experiment.
  • Perform the experiment on the safety tray and use protective gloves to avoid staining your hands.
  • Never eat or drink any of the substances provided. Do not use for culinary purposes.

Step-by-step instructions

Wear protective gloves and use the waterproof underlay to keep your table clean. To open a bottle, push the cap down and turn it. Use a paper clip to pierce the bottle nozzle.

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The two pieces of felt in this set have different wetting properties: one is hydrophilic, which means it tends to absorb water, and the other is hydrophobic, so water will be repelled from its surface.

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The hydrophobic powder’s attraction to water molecules is very weak, so drops of water will slide off of it easily. Let’s prepare a card with both hydrophobic and hydrophilic areas.

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The areas of the card that didn't retain the hydrophobic powder will absorb water. Try to lead a single drop from the start to the finish by tilting the card.

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Repeat steps 3 and 4 with the other card, and try to navigate a more challenging labyrinth!

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Disposal

  • Dispose of solid waste together with household garbage.
  • Pour liquids down the sink. Wash with an excess of water.

Scientific description

In the first experiment, you observed that a droplet spreads differently on different surfaces. On hydrophilic surfaces , a water drop  adopts the widest possible shape  or is completely absorbed, sinking into the material’s pores. On hydrophobic surfaces , conversely, it tends to touch the surface as little as possible .

Once coated with a hydrophobic powder , the card attracts water molecules  weakly. In each drop, the outer layer of water molecules holds  the remaining molecules inside, keeping the drop in a spherical form . Since the water droplets  are weakly attracted to the surface of the card, they can easily roll along the surface just as a ball rolls across a floor.