Waterproof Sand - Cát không thấm nước
This “magic” sand is typical sand (silica grains) treated with the vapors of a silicon compound called trimethylhydroxysilane. While normal sand is hydrophilic (water-loving), this treatment causes the sand to become hydrophobic (water-hating) due to the non-polarity of silicone and the polarity of water.
Normal sand will quickly sink in water and will allow water to flow freely through its grains. Hydrophobic sand floats on top of the water—because of the strong surface tension—until the weight of the sand is enough to break the tension. The same tension that keeps the sand from sinking is also what keeps it dry when under water.
One of the original uses for this product was to soak up oil from oil spills in oceans. Both oil and silicone are non-polar and, because like attracts like, the sand and the oil combine and sink to the ocean floor for easy clean up.
The sand has been used to bury underground wires in cold climates. Because the sand will not absorb water, the ground will not freeze and digging is made easier. Mix the sand with other materials to change the way they interact with water.