Why water is wet
Many times it happens to us that the same out of habit or because it is obvious we affirm certain things. For example, water is a liquid and gets wet when you touch it. But if we stop to think for a moment, maybe what we thought was so obvious is not so obvious anymore. We know that water gets wet due to our experiences, such as that when it rains or we shower we get wet, that is, we cover ourselves with water, but could we really explain why this phenomenon?
Why does water get wet: simple explanation
The ability of water to wet or soak the surfaces it touches is due to its physical properties. A water molecule is made up of only three atoms, one of oxygen and two of hydrogen, linked by negative and positive charges. Consider the case of magnets, where the pole or negative charge joins the pole or positive charge. In the case of water, oxygen would be the negative pole of the magnet and hydrogen the positive one. But in water, molecules are also bound together, and they can form stronger or weaker bonds. Depending on the strength and number of these bonds and the position that the molecules have in space , water can be in a solid, liquid or gaseous state . Learn more about What are the physical states of water here.
Water also forms bonds with other substances, especially those that are polar like them, that is, they have positive and negative charges. Due to this, liquid water has different properties that give it the ability to wet and these properties are the cohesion and adhesion forces of water .
Cohesion is defined as the attractiveness of some molecules to other molecules of the same compound. In the case of water, the cohesion forces would be the forces that exist between the different water molecules, as explained before, and which are called hydrogen bonds.
We can easily see the cohesion forces of water , for example, by filling a glass of water to the top. If once it is full we add water droplets very slowly we can see how the surface bulges and the water remains above the edge of the glass.
In addition, this property or this attractive force can also be seen in the morning dew, when small water droplets remain on the leaves and flowers of plants. All this is due to the fact that the attraction between water molecules is stronger than that for other surfaces or materials.
On the other hand, the adhesion forces are those that occur between molecules of different types. In the case of water, they are those that appear between water molecules and other surfaces, especially if they are polar like water. When the adhesion forces are greater than the cohesion forces , the water is more attracted to the molecules of the other material and that is when the effect of being wet occurs .
The adhesion forces are closely related to capillarity. This phenomenon occurs when a capillary or a very fine glass tube is introduced into a glass of water, for example. Due to the attraction of the water by the walls of the glass, it begins to rise up the tube against gravity. Because the water that is in contact with the walls is more attracted, the water inside the capillary takes a u-shape, and that area where the water is lower is called the meniscus.
The wettability of a material is closely related to this concept and is the ability of a liquid to spread over the surface and wet it . This wettability or ability to wet the water depends on the molecular interactions of both substances. An interesting fact is that the fact that something gets more or less wet depends on the contact angle, which is the angle that is formed between the molecules of the water and those of the surface that is going to be wet. The smaller the contact angle, the greater the wettability.
Not everything gets wet
Recently, engineers at the University of Florida have been able to develop a flat surface that does not get wet or damp. On the contrary, the water droplets roll on its surface , so in this case the cohesion forces are greater than the adhesion forces.
To get this material they relied on the hairs that grow on the body of spiders that allow them to always stay dry.