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Research Progress of Self-cleaning Antireflection Membrane
From：CHANGZHOU ZHONGBO GLASS MACHINE AND EQUIPMENT CO.,LTD Date：2019-3-25 14:08:30
Antireflective coatings, also known as antireflective coatings, are widely used in daily life, electronics, industry, astronomy, military and other fields. The traditional cleaning method is surfactant cleaning, which not only aggravates environmental pollution, but also requires repeated, consuming a lot of manpower, financial and material resources. Therefore, in recent years, the research and development of self-cleaning antireflective coatings have attracted great attention. The preparation of self-cleaning and efficient antireflective coatings has become the need of technological development.
Principle introduction. (1) Anti-reflection principle, in order to reduce reflection and increase transmission light, a film with suitable thickness and refractive index can be coated on the surface of the substrate. Its anti-reflection effect is mainly achieved by means of cancelling interference, mainly by using the interference effect produced by the film system to eliminate reflection light and improve the transmittance of light. (2) In terms of self-cleaning principle and hydrophilicity, the contact angle of water droplets on the material surface tends to zero. When water contacts the material, it spreads rapidly to form a uniform water film on its surface and removes the stains by gravity falling of the water film, so as to achieve self-cleaning effect. In terms of hydrophobicity, the principle is based on the "lotus leaf effect". The self-cleaning effect of lotus leaves stems from the air layer on its surface. The fine structure composed of papillary protuberance and wax layer can improve the contact angle of water droplets on the surface of materials, and make the water droplets roll easily. When the water droplets roll on the surface of materials, they will take away dust and pollutants, so as to achieve self-cleaning effect.
Common materials for self-cleaning antireflective membranes. (1) Titanium dioxide is widely used as a self-cleaning antireflective film material because of its photocatalytic activity, photoinduced superhydrophilicity and low cost, especially the development of nano-powder and thin film, which promotes the application of titanium dioxide. However, because of the large defect of TiO2 thin film, the high refractive index, generally between 2.2~2.7, will increase the reflectivity of the transparent substrate surface. Therefore, scientific researchers have adopted different process methods to reduce the refractive index of TiO2 thin films. In 2011, Wang Jianwu et al. Used SiO2/TiO2 sol-gel method to prepare SiO2/TiO2 double layer antireflective film, and the transmittance in visible band was very high. 97.2%. The contact angle of the films irradiated by ultraviolet light is close to 0 degree, which has good self-cleaning property. (2) Silicon dioxide, with low refractive index (refractive index is about 1.3), low-cost electrical properties, high chemical stability, acid-base corrosion resistance and other excellent properties, is currently studied more, but also one of the widely used anti-reflection films. Nowadays, many scientists are exploring and constructing SiO 2 antireflective films with "lotus leaf effect". Wei-Lun Min and others have fabricated orderly micro-convex silica hexagonal column particle arrays by spin coating and etching technology, which enhance the visible light transmittance on the surface of materials, and control the contact angle by controlling the etching time to make them self-cleaning.
Research progress of self-cleaning antireflection membranes. In the research of self-cleaning antireflective membranes, many high-quality researchers have made outstanding contributions and made some achievements. In 2013, a thin film with broad wavelength antireflection and super-double sparsity was prepared on glass substrates by lamination technology (LBL), consisting of nanoparticles, hollow nanospheres and nanosheets. Although scientific researchers have adopted various means to construct self-cleaning anti-reflective films, most of the research knowledge is limited to the research stage of laboratory, and is not suitable for large-scale production. Therefore, there are still great opportunities and challenges for practical production applications: first, poor mechanics; secondly, high cost, small scale. Nowadays, most of the reported preparation processes with self-cleaning characteristics involve complex process, more stringent preparation environment, expensive reagents and equipment, etc. The cost is high, and they are only suitable for smaller or specific substrates with smaller scale.
The development trend of self-cleaning antireflective film. Such limited durability and high cost will hinder the application and development of self-cleaning antireflective membranes. In the future, the following research directions will attract more researchers'attention: firstly, using the advanced analytical tools and theoretical calculation level, more efforts will be made to reveal the relationship between the composition, structure and surface properties of thin films and the construction of film mechanism; secondly, the construction of self-cleaning anti-reflective film surface structure with high mechanical strength and durability will remain the focus of research work. Of course, environmental factors should also be taken into account. Third, the application of new materials and advanced coating technology can also broaden the application field of self-cleaning antireflective film.