Droplet labyrinth

Soak in or flee? Depends on nature!

Difficulty:
Danger:
Duration:
20 minutes
Droplet labyrinth

Safety

  • Perform the experiment on the underlay and use protective gloves to avoid staining your hands.
  • Carefully review the general safety advice in the instruction book before starting the experiment.

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

Everything around us is made up of tiny particles known as molecules. They act on each other by forces of attraction and repulsion. These forces  define certain physical properties of the material: whether it is liquid or solid, how easy it is to shape and pour, and so on.

Also, these forces determine how the molecules of different substances physically interact upon contact with each other. For instance, a drop of water  will adopt a rounded shape on any flat surface. However, this drop will occupy different areas on different materials.

The stronger the attraction between the water  molecules and the molecules of the supporting material , the wider the drop will spread . Conversely, the weaker the attraction, the more the drop of water retains its original round shape. This ultimately reduces its contact area with the surface —the drop  can even form a tall dome  over the material.

Here, we say that water doesn’t wet the material well, and we call the latter hydrophobic (from the Greek “afraid of water”). However, if water can bind more strongly to a material, we say that the material has stronger wettability and call it hydrophilic (meaning “water-loving”).

Ordinary felt is made of fibers that can be easily wetted with water. When you dripped water on the rectangular piece of felt , the droplets spread along the fibers, filling in the gaps and promptly soaking into the fabric. Meanwhile, when you applied water to the square piece of hydrophobic fabric , the water didn’t soak into the material—it remained on the surface as a multitude of spherical droplets.