By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Apr 16 2024Self-cleaning coatings and paints are designed with the capability to effectively remove contaminants such as dust, microbes, and toxins from surfaces. Inspired by natural phenomena observed in surfaces like rice and lotus leaves, butterfly and locust wings, and gecko legs, scientists have developed and applied these coatings to various materials such as metals, glass, fabric, and wood. Their practical applications span across domestic, industrial, medical, and agricultural sectors.1
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In response to escalating air pollution levels, contemporary construction demands materials equipped with self-cleaning capabilities. These innovative materials not only contribute to the improvement of air quality but also elevate the visual appeal of buildings, particularly in densely populated urban and industrial areas.2 This article explores self-cleaning coatings and paints and their applications and advantages in modern construction.
Production and Advantages
Self-cleaning properties can be imparted to a coating or paint by controlling its wettability (hydrophobic or hydrophilic) or photocatalytic activity. Wettability is determined by the balance between cohesion and adhesion forces. Both super-hydrophilic and super-hydrophobic materials can exhibit self-cleaning behavior. The former achieves this through slow sheeting of water (water-based self-cleaning), while the latter achieves it through the speedy rolling of water on the surface (waterless self-cleaning).1
Various methods are employed to create self-cleaning coatings and paints, including spin-coating, electrodeposition, dip-coating, plasma treatment, layer-by-layer assembly, electro-spinning, and chemical etching.2
Alternatively, photocatalysts like TiO2, SnO2, and ZnO can degrade surface contaminants upon exposure to light, effectively removing them from the coating/paint.1,2 In the presence of light, these materials produce strong oxidants like hydrogen peroxide and hydroxyl radicals, which can decompose organic contaminants on a surface into less toxic products like CO2 and water.2 The presence of microbes on building surfaces results in discoloration, corrosion, cracking, material disaggregation, weakening, and dissolution. Thus, coatings with antimicrobial elements like metal oxide nanoparticles exhibit superior self-cleaning.2
In addition to self-cleaning building exteriors, these coatings and paints can also be tailored to provide anti-fogging, anti-icing, anti-corrosion, and oil-water separation properties. Presently, building cleaning relies heavily on manual or mechanical methods, which consume significant labor, water, and electrical resources. Furthermore, the waste generated from manual cleaning often ends up in sewage, contributing to water pollution. However, by employing self-cleaning coatings and paints, infrastructure maintenance costs can be reduced by preventing deterioration and eliminating the need for extensive repainting.3
Applications of Self-Cleaning Coatings and Paints
Self-cleaning coatings offer versatile applications across multiple industries, ranging from infrastructure and textiles to automobiles, optics, aerospace, solar modules, and marine sectors. With the onset of the post-COVID-19 era, there's been a notable surge in demand for self-cleaning and antimicrobial paints and coatings. Consequently, beyond residential buildings, their utility extends to public infrastructure like hospitals, schools, and stores.1
One of the primary areas of application for these coatings lies in modern constructions, particularly in window glasses and exterior paints.1 The accumulation of pollutants, gases, dust, and aerosols in the atmosphere often results in deposits and patina on architectural surfaces, speeding up the degradation process. Thus, by integrating self-cleaning coatings and paints, not only can the air quality around buildings be improved, but maintenance efforts can also be streamlined.2
Additionally, self-cleaning coatings with hydrophobic properties act as a deterrent against unauthorized substances being applied to building walls, such as graffiti or advertisements. Similarly, in areas adjacent to industries or beaches, superoleophobic coatings can be used to efficiently remove oil-contaminated dust without the need for detergents. Photocatalytic coatings find diverse applications, from sound absorption along traffic routes and tunnel walls to disinfection in operating theaters and odor removal in bathroom tiles.2
Challenges in Self-Cleaning Coatings and Paints
Despite the advancements in self-cleaning coatings and paints, significant challenges remain that hinder their practical application and longevity.1 These products face issues related to aging and environmental decay, emphasizing the need for ongoing research and development. The interaction of these coatings with atmospheric charges and radicals can alter their surface properties, leading to decreased mechanical stability and impaired functionality. This degradation affects their effectiveness and reduces their useful life. It is therefore essential to evaluate the performance of these coatings in diverse real-world environments, such as urban, industrial, and rural settings.2
Moreover, the integration of these coatings with porous building materials like concrete presents additional challenges. Concrete's complex surface characteristics can result in poor adhesion, leading to damage or delamination of the coating. The performance of photocatalytic coatings is also dependent on several variables, including light intensity, the nature of the building surfaces (like roads and walls), and the presence of other chemical compounds. These factors, along with competing surface reactions, can significantly influence the effectiveness of these coatings.2
Another major barrier is the scalability and cost-effectiveness of these technologies. While some materials show promising results in laboratory settings, the high costs associated with scaling up production for commercial purposes make them less viable economically. Moreover, the development and deployment of self-cleaning coatings involve navigating complex issues related to intellectual property rights and regulatory compliance. Inconsistent IP protection laws across different countries and non-standardized regulations pose further challenges to the global adoption of these innovative solutions.1
Latest Developments
Recent research has prioritized enhancing the key properties of self-cleaning coatings, such as hardness, flexibility, scratch resistance, and transparency. These properties are crucial not only for maintaining the aesthetic appeal of buildings but also for their long-term durability and functionality in various environmental conditions.4
Application in Building Efficiency and Preservation
Recent material science advancements have led to the development of multifunctional coatings that are transforming modern construction. These coatings include transparent and heat-reflecting types specifically designed to improve building efficiency and aesthetic appeal. A key technological advancement is the use of magnetron sputtering, a method that allows for precise control over the creation of uniform multilayer structures at a commercial scale. This innovative production technique surpasses traditional methods in quality and efficiency, highlighting a significant advancement in the application of self-cleaning coatings for energy management and architectural preservation.4
Advancements in Cultural Heritage Conservation
In the field of cultural heritage conservation, self-cleaning coatings represent a groundbreaking advancement. These coatings are increasingly applied to a variety of historical materials—such as bricks, wood, and marble—to protect and preserve these surfaces with minimal intervention. By reducing the need for harsh chemical cleaners and frequent maintenance, these coatings offer a sustainable solution that preserves the integrity and aesthetics of cultural sites.
The ability to incorporate properties like UV resistance and moisture control further demonstrates the technological progress in making these coatings a viable option for conserving historic structures, ensuring their longevity, and reducing environmental impact.5
Conclusion and Future Prospects
In conclusion, the strategic advancement of self-cleaning coatings and paints is essential for maintaining competitiveness in the construction and materials industry. Emphasizing the development of resilient and effective products that can withstand various environmental conditions is paramount.5 Innovations such as machine learning and artificial intelligence are crucial for enhancing design processes, simulation accuracy, and manufacturing techniques to meet exacting industry standards.
The integration of functionalized nanomaterials can greatly improve the mechanical durability and ultraviolet resistance of coatings while self-healing properties could significantly boost commercial viability through lowered maintenance and replacement costs. Furthermore, addressing environmental concerns by avoiding harmful chemicals is essential for sustainable development.
As we look to the future, the pursuit of robust, multifunctional self-cleaning coatings will not only require novel, cost-effective synthesis and maintenance methods but will also benefit from the continued convergence of advances in material sciences and sophisticated computing technologies. Together, these efforts will propel the field towards achieving its ambitious objectives, supporting future architectural innovations and contributing to a more sustainable world.
References and Further Reading
1. Hosseini, S. (2020). Self-Cleaning surfaces for different purposes: Review of production methods and future prospects. In International Conference on Materials Engineering and Metallurgy. https://www.researchgate.net/publication/346027684_Self-Cleaning_surfaces_for_different_purposes_Review_of_production_methods_and_future_prospects
2. Rabajczyk, A., Zielecka, M., Klapsa, W., & Dziechciarz, A. (2021). Self-Cleaning Coatings and Surfaces of Modern Building Materials for the Removal of Some Air Pollutants. Materials, 14(9), 2161. https://doi.org/10.3390/ma14092161
3. Liu, G., Zhao, T., Fei, H., Li, F., Guo, W., Yao, Z., & Feng, Z. (2023). A review of various self-cleaning surfaces, durability and functional applications on building exteriors. Construction and Building Materials, 409, 134084–134084. https://doi.org/10.1016/j.conbuildmat.2023.134084
4. Wu, P., Xue, Z., Yu, T., & Penkov, O. V. (2023). Transparent Self-Cleaning Coatings: A Review. Coatings, 13(7), 1270–1270. https://doi.org/10.3390/coatings13071270
5. Bai, Y., Zhang, H., Shao, Y., Zhang, H., & Zhu, J. (2021). Recent Progresses of Superhydrophobic Coatings in Different Application Fields: An Overview. Coatings, 11(2), 116. https://doi.org/10.3390/coatings11020116
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