Curtain Wall Self-Cleaning Coatings: Principles of Hydrophobic Self-Cleaning Coatings

Curtain Wall Self-Cleaning Coatings: Principles of Hydrophobic Self-Cleaning Coatings

With the continuous increase of environmental pollution, more and more serious haze, oily smoke, exhaust gas, etc. Building exterior walls are subject to severe erosion that affects their aesthetics, functionality and durability. Poor stain resistance is a common shortcoming of traditional exterior wall coatings, which restricts its application to a certain extent. Therefore, in view of the problem of insufficient anti-fouling ability of exterior wall coatings, coatings with self-cleaning functions have become a hot spot of research and development.

Cleaning polluted building exterior walls not only requires high investment, but also the use of surfactants will affect the The environment has caused serious pollution, so functional coatings with self-cleaning effects have emerged as the times require. Self-cleaning coatings can use rainwater and other natural conditions to keep the surface of outdoor objects clean, which not only reduces maintenance costs and labor requirements, but also minimizes environmental pollution. It can be widely used in high-rise buildings, curtain walls, bridges and automobiles. , wind power and other fields.

 1 Foundation of Hydrophobic Self-Cleaning Paint

The phenomenon of self-cleaning by forming a hydrophobic surface is ubiquitous in nature, such as lotus leaves. The leaves and flowers of various plants, the legs and wings of insects, etc. all show low adhesion and self-cleaning ability. This phenomenon is called "lotus effect". The bionic principle of "lotus effect" is self-cleaning technology basis for development. In the 1970s, the botanists W. Barthlott and Neinhuis of the University of Bonn in Germany systematically studied the self-cleaning effect of the lotus leaf surface. Through electron microscope observation, it was found that there are countless micron papillae growing on the surface of the lotus leaf, and its surface is covered with nano-wax. quality crystals. In 2002, Jiang Lei and others from the Institute of Chemistry, Chinese Academy of Sciences found that nanostructures also existed on the surface of the lotus leaf. Nanostructures were also found between these papillae (Figure 1). A large number of studies have confirmed that the joint action of micro- and nano-scale micro-rough structures and waxy crystals with low surface energy makes the surface of lotus leaf have high water contact angle and low rolling angle, thus showing super-hydrophobic self-cleaning effect.

 The self-cleaning behavior of hydrophobic coatings comes from their high water contact angle and low roll angle. When water droplets drop on a hydrophobic surface, the droplets cannot expand automatically, maintaining their spherical state and reducing the contact area with the coating. When the surface has a small inclination angle, the droplets roll on the surface of the coating, and the contaminants adhere to the surface of the water droplets and are taken away, thus playing a self-cleaning role.

2 Preparation of Hydrophobic Self-Cleaning Surfaces

Appropriate surface roughness and wetting properties of low surface energy materials are closely related to the surface microstructure . The preparation of hydrophobic surfaces usually uses silanes or fluorocarbon chains to reduce the surface energy, but studies have shown that the purpose of superhydrophobic self-cleaning can not be fully achieved by chemically adjusting the surface energy on smooth surfaces. Therefore, the hydrophobic self-cleaning can be better achieved by constructing a suitable microscopic rough structure and introducing low surface energy substances. At present, there are many methods for preparing the hydrophobic self-cleaning surface imitating the lotus leaf effect (Table 1), and usually a combination of multiple methods can achieve a more ideal effect.

 3 Hydrophobic Self-Cleaning Paint

 Appropriate surface roughness and low surface energy substances are the keys to achieving hydrophobic self-cleaning. According to the principle of "lotus leaf effect" self-cleaning, there are two main ways to achieve hydrophobic self-cleaning: one is to modify low surface energy substances on rough surfaces. The low surface energy materials usually used to prepare hydrophobic surfaces mainly include polysiloxane Alkane, fluorocarbons and other organic compounds (such as polyethylene, polystyrene, etc.); the second is to build a rough structure similar to the surface of lotus leaves on the surface of hydrophobic materials, and the preparation method includes inorganic nanoparticles (such as TiO2, SiO2, ZnO, etc.) modification , laser/plasma/chemical etching, template method, electrospinning method, sol-gel, self-assembly, electrochemical deposition and chemical vapor deposition, etc.