Transparent Self-Cleaning Coatings: A Review

Abstract

Advanced coatings are essential to modern technologies as they optimise surface characteristics for different application scenarios. Transparent and self-cleaning coatings are increasingly used as protective coatings for various applications, such as foldable touchscreens, windows, and solar panels. Moreover, incorporating other functionalities such as high hardness, wear resistance, and flexibility into transparent and self-cleaning coatings is important for broadening the use cases. Although many kinds of multifunctional coatings have been developed, it is still difficult to embody several properties in one coating adequately as some properties, such as hardness and flexibility, are inherently contrastive. This review first describes basic principles, including wettability, photocatalytic reactions, photo-induced hydrophilic phenomena, and the implication of self-cleaning. The desired properties of multifunctional coatings are then listed and the methods for evaluating different properties are used. Recent progress in various preparation methods for multifunctional coatings, including the sol–gel, dip/spin, and chemical vapour deposition (CVD) methods, are also presented. Magnetron sputtering (MS) technology is widely used in coating preparation. Compared with chemosynthesis and CVD, MS is time-saving, suitable for industrial production, and environmentally friendly. Coatings prepared by MS usually possess excellent mechanical properties. Thus, we highlight the current research status of MS technology in multifunctional coating preparation. Moreover, according to the multilayer design structure of coatings, their optical and mechanical properties and self-cleaning ability can be controlled by combining the characteristics of different materials. Finally, combining photocatalytic materials such as TiO2 with other materials through a multilayer structure to obtain a multifunctional coating with excellent overall properties is discussed.

Hardness and Wettability Characteristics of Electrolytically Produced Copper Composite Coatings Reinforced with Layered Double Oxide (Fe/Al LDO) Nanoparticles

“…The surface roughness, the preferred orientation, a distribution of the grain size (height), and the size of crystallites have effects on the hardness values, while only roughness has an impact on the wettability properties of coatings [66,67]. In our case, all listed factors are additionally affected by the change in the coating thickness and by the addition of Fe/Al LDO nanoparticles in the electrolyte.…”

Solvent-Free and UV-Cured Epoxy Silicone Coating with Excellent Wear Resistance and Antismudge Properties

“…Coatings are important for many products by changing their surface conditions and appearance, and in particular the color, gloss, transparency, sense of touch, hardness, and other surface functionalities which are directly related to applied coatings. − In recent years, foldable smart devices such as foldable phones, tablets, and e-readers have become increasingly popular, putting an increased demand for transparent, hard, flexible coatings to protect their screens. − High hardness will increase scratch resistance, and high flexibility will increase tolerance to bending; however, they are mutual exclusion in most cases . In general, inorganic materials such as metals and ceramics are extremely hard but opaque, while glass is very hard but brittle .…”