Today, many of us hear about self-cleaning surfaces, which are also used in various industries. The discovery of this property started with the effect of the water lily. It has been observed for a long time that the lotus is a flower that does not get dirty in any way (even though it lives in swamps and muddy waters). The water on this flower simply slips; As if its surface is completely greasy.

Later, it became clear that the cause of this incident is the small bumps on the surface of the lotus. These protrusions make water droplets not absorbed by the surface and it can be said that these flowers are “hydrophobic”. This property is also called “water repellency” . Hydrophobicity means that water is not absorbed by the surface and its adhesion to the surface is very low. This is how the water drops easily pass over it and on their way, they also take surface pollution with them. It is like this that flowers like lotus are simply cleaned by a rain.

Of course, self-cleaning has three main mechanisms, which are explained below:

Super hydrophobic

Superhydrophobic surfaces can be created using many methods such as using plasma or ions, crystal growth on the surface of a material and nanolithography or other methods. All these processes cause the formation of surfaces with small protrusions that cause superhydrophobic properties . The reason for the hydrophobic property of these surfaces is their ability to prevent water from spreading on the surface when water comes in contact with the surface. In hydrophobic surfaces, the water drop is usually placed at a large angle to the surface. Usually, superhydrophobic surfaces, having a very small angle to the ground, water easily slides over them and falls to the ground.

Water repellency on self-cleaning surfaces

In this process, by sliding the water over these surfaces, the water easily washes away the pollution on the surface.

Hydrophilicity

Super hydrophilic surfaces also have good self-cleaning properties. In these surfaces, the water droplets are completely spread over the surface and placed at a very small angle to the surface. When water is placed on this surface, dust particles and pollution are placed on the water (in fact, water is placed between the surface and the pollution). As a result, they are easily washed with water and cleaned without contact with the surface.

The water droplet spreads completely on the surface and is placed between the surface and the dust particles. After that, it is simply run over the surface with water and the surface is cleaned.

Photocatalytic

One of the materials used in self-cleaning surfaces, especially glasses, is titanium oxide. This material has a different mechanism than the previous two methods. In this mechanism, titanium oxide is coated on the desired surface and releases electrons by irradiating it with ultraviolet (UV) rays. Electrons released from titanium oxide react with surrounding water or air and produce free radicals. These free radicals react with organic materials on the surface and cause them to break and destroy. Also, the coating of titanium oxide can transform the surface of the glass, which is normally a relatively hydrophobic surface, into a super hydrophilic surface, and as a result of this transformation, when it rains, the water drops will spread completely on the surface instead of being lumped, which makes it easier The surface can also be cleaned.

Most of the self-cleaning surfaces use these mechanisms for cleaning, and even today, mechanisms such as super-hydrophobicity are used a lot. One of the industries that use the superhydrophobic method a lot is the automobile industry. By covering the car windows, they become super-hydrophobic, which makes these windows not need to be washed for a long time. Other mechanisms are also used for these cases.