For a long time, the optimized self-cleaning function has existed in nature, and the lotus leaf is the representative. The surface of lotus leaf is hydrophobic and actually non-wettable. It also produces sludge and is spotless. This is the result of long-term evolution to adapt to the environment. W bartblott, a professor of botany at Bonn University in Germany, studied the structure of lotus leaf and the mechanism of lotus leaf effect. It is found that the lotus leaf has the above properties because its surface is hydrophobic and has microstructure.

According to the mechanism of lotus leaf effect and the practical application results of silicone exterior wall coatings, ISPO Company, a subsidiary of German Sto listed company, successfully transplanted the lotus leaf effect into exterior wall latex paint after three years of research work, and developed microstructure silicone latex paint, namely lotus leaf effect latex paint. This kind of latex paint with lotus leaf effect uses some special substances such as silicone emulsion with less emulsifier and lasting hydrophobicity to form nano-scale microstructure, so that its coating film has a surface structure similar to lotus leaf, thus achieving the functions of water repellent and cleaning.

Most lotus leaf effect coatings or emulsions on the market are realized by reducing the surface tension. By reducing the surface tension, the ability to improve the contact angle with water is limited, which can be increased to about120. For example, the initial contact angle of silicone coatings on the market with water is about 93 ~ 1 15, and their contact area with dust remains basically unchanged. Therefore, the result of lotus leaf effect is limited, and it is difficult to keep the coating dry.

The contact angle with water should be at least 130. At this time, the surface has obvious hydrophobicity, and the rain falling from the beads has self-cleaning function. The properties of materials are determined by their composition and structure. Only by combining the reduction of surface tension with the formation of microstructure can a good lotus leaf effect be achieved. According to the influence of surface roughness on contact antenna in surface physical chemistry, when the contact angle is less than 90, if the surface roughness is larger, the contact angle can be further reduced. However, when the contact angle is greater than 90, the rough surface energy further increases the contact angle. The contact angle between lotus leaf effect latex paint film and water is greater than 90, and the rough microstructure can increase the contact angle to about 65438+040. On the other hand, the slightly rough surface can also reduce the contact area between dust and coating to below 1%, so that the adhesion between dust and water is greater than that between dust and coating. So when it rains, the rain drops on the wall and takes away the dust at the same time, keeping the wall dry and clean.