Hydrophobic sand

Sand that doesn’t get wet in water!

Difficulty:
Danger:
Duration:
10 minutes
Hydrophobic sand

Safety

  • Perform the experiment on the protective underlay.
  • Carefully review the general safety advice in the instruction book before starting the experiment.

Step-by-step instructions

Use the waterproof underlay to keep your table dry. You’ll be using the large square cups for this experiment.

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A crumbly substance like sand can also be made hydrophobic! While regular sand gladly allows water into the gaps between its grains, hydrophobic sand doesn’t absorb water. Water’s presence in sand changes its properties.

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Your special sand remains dry and crumbly even when immersed in a glass of water—it retains some air within its mass and on its surface!

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Some water can permeate even into materials with very weak wetting properties. Still, water evaporates from hydrophobic sand much faster than from regular sand.

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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

If you’ve ever built a sandcastle, you know quite well that dry and wet sand have drastically different properties. Dry sand crumbles easily and is completely unsuitable for building lofty towers. Wet sand, meanwhile, is perfect for sophisticated architectural designs. It feels denser and isn’t as prone to breaking down.

Sand  consists of many small separate particles that we call “grains.” There are no forces binding dry grains; they move separately from one another, and the wind  can easily blow them away one by one. However, regular sand can be wetted with water . Water fills in the voids between the grains, expelling the tiny amount of air that was there. Moreover, as water  and sand  particles are attracted to each other, a small force arises that does not allow the water-melded grains to crumble away that easily.

Hydrophobic sand  consists of the same grains of regular sand, but they’re coated with a special substance  that keeps water out. A drop of water  on the surface of this sand behaves similarly to a droplet on hydrophobic fabric. When you pour your hydrophobic sand into a glass of water, the grains hold some air bubbles  on their surfaces.

But even though the water can’t permeate between the separate grains, the sand doesn’t scatter underwater. In fact, it behaves quite similarly to wet sand in an airy atmosphere. The difference is that now it is the air between the grains creating that small force that binds the grains underwater. It’s even more exciting when you lift the sand out of the water – it emerges completely dry!

That’s interesting!

Hydrophobic surfaces aren’t exactly a secret technology available exclusively to scientists in laboratories. The leaves of some plants have a super-hydrophobic surface, too! This explains why drops of water sometimes instantly turn into small balls and roll off of the leaves they’ve fallen on, cleaning away any dirt.