Question

Почему одни твердые тела смачиваются водой а другие нет?

Answer 1

Why do some solids wet with water while others do not?

The ability of a solid to wet with water depends on its surface properties, specifically the interaction between the solid and the water molecules. This interaction is determined by the balance between adhesive forces (between the solid and the liquid) and cohesive forces (within the liquid itself).

Wetting occurs when the adhesive forces between the solid and the liquid are stronger than the cohesive forces within the liquid. This allows the liquid to spread and form a thin film on the surface of the solid.

On the other hand, non-wetting occurs when the cohesive forces within the liquid are stronger than the adhesive forces between the solid and the liquid. In this case, the liquid tends to form droplets on the surface of the solid, minimizing contact with it.

The wetting behavior of a solid is influenced by several factors, including the surface tension of the liquid, the surface energy of the solid, and the chemical nature of both the solid and the liquid.

Surface tension is a measure of the cohesive forces within a liquid. Liquids with high surface tension tend to form droplets on the surface of solids, while liquids with low surface tension tend to spread and wet the surface.

The surface energy of a solid is a measure of the energy required to create a unit area of the solid's surface. Solids with high surface energy tend to wet easily, while solids with low surface energy tend to be non-wetting.

The chemical nature of the solid and the liquid also plays a role in wetting behavior. For example, polar liquids like water tend to wet polar solids, while non-polar liquids tend to wet non-polar solids.

It's important to note that the wetting behavior of a solid can be modified by surface treatments or coatings. For example, a hydrophobic coating can make a solid non-wetting with water, even if it would normally wet without the coating.

In summary, the wetting or non-wetting behavior of a solid with water depends on the balance between adhesive and cohesive forces, as well as the surface tension and surface energy of the liquid and solid. The chemical nature of both the solid and the liquid also plays a role in determining wetting behavior.