This critical review article gives an overview of efficiency, stability and durability of self-cleaning technology (SCT). The SCT includes so many widespread applications such as textiles / cotton-fabrics / garments, Construction of buildings / lavatories / domestic-automobiles windows / architectural heritage and photovoltaic / solar cells. Durability is a serious problem of SCT, so how the durability of SCT is significant in human life is also deliberating. Due to the SCT has broad categories of applications, there is a need for a deeper understanding of the durability and the preparation of self-cleaning surfaces?SCS?using a simple way of techniques of SHP surfaces of SCT are discussed in details with a separate section. The efficiency and durability studies are discussed with influence characteristics and importance of durability on SCT classified and summarized. In SCT, recent progress of the durability of SCT has been reviewed by for investigation at last decades, clinched that the research going on this field is increasing slowly from increasing a fraction of publication. We review the most current, and promising efforts in innovative applications of SCT to the understanding of efficiency, stability, and durability are studied. Present conclusions, future perspectives, and challenges on the field of the durability of SCT are also proposed.
Keywords: Materials, Surface, Self-cleaning, Durability, Superhydroscopic surface
1.1 Durability advances in SCT
1.2 Influence Parameters of Durability Studies of SCT
1.3 Why Efficiency and Durability essential for SCT
2. Fabrication of SCT
2.1 Sol-gel process
2.2 Dip-coating technique
2.3 Chemical deposition/Electrolysis
2.4 Layer by layer assembly
2.5 Miscellaneous techniques
3. Recent Applications in Durability of SCT
3.1 SC Building
3.1.1 SC Toilet
3.1.2 SC Mineral Paints for Architectural Heritage
3.2 SC Photovoltaic Devices/Solar Cell
3.3 SC Fabrics /Textile Industry
4. Summary and Future Perspectives
The most basic principle of the idea of self-cleaning technology (SCT) is the properties of spherical water droplets that can be removed dirt particles. The essential conditions for the formation of self-cleaning (SC) properties are the combination of surface hydrophobic epicuticular wax, and a hierarchical structure could contribute to a high water contact angle (CA), and a low sliding angle (SA) 1. Inspiration for nature will give an idea to develop a simple and low-cost method to construct and fabricated the SC surfaces with superhydrophobic (SHP) capable of advanced applications towards the SC. A review article was written by Ganesh et al. 2 on SC coatings of hydrophilic and hydrophobic surfaces, and also focused on their fabrication techniques and working mechanism. Biomimetic SC surfaces were studied by Xu et al. 3, they reported that SL studies with water and without water was discussed. Few of the researchers have been addressed their problems of SL-SHP surfaces represent a significant technological innovation in recent studies on durable surfaces. SCT used for daily application, SL surfaces were survived under harsh conditions, such as temperature, pressure, humidity, and chemical corrosion. Hereafter, designing and constructing durable and chemically stable SHP surfaces have become progressively meaningful and practical 4.
Durability enhancement of SHP surfaces was an essential issue for SCT, it would still necessary to develop a good SHP coatings achieved by the majority of methods hold limited abrasion resistance (AR), corrosion free, efficiency, non-hazardous chemicals, and stability. Researchers indorse that to use the alternative eco-friendly chemicals such as fluorine-containing chemicals, and organic chemicals, which are dangerous for human health and environmental conditions 5. Recently, there have been several studies have enunciated to the mechanical integrity of the SHP coatings, evaluating its outdoor stability and AR. The AR was resolute in assessing the change in a static CA, CA hysteresis, and the coefficient of surface friction 6.
Nowadays, seeking out low-cost materials and developing one-step methods has become gradually important to fabricating SC-SHP surfaces. For this reason, Sas et al. 7 reviewed article in a brief overview of the idea of SC-SHP surfaces and basic principles of the electrospinning process, considered into several groups and their results have been compared in SHP behaviors. An alternative approach is necessary for the minimizing a major problem facing to reduce the cost of preparation of SL surfaces and simultaneously, consider on the eco-friendly coatings for enhancement on environmental conditions for in a long period of durability and it will reduce time, energy, and laundry cost 8. The SCT is also useful in the various applications including the textile materials normally used in daily life. The SCT also developed various applications such as medical, textiles, athletic wear, outdoor fabrics, and military uniform. SCT fabrics are beneficial to human life as it effectively conserves water 9. Much of SCT has been already the presence of reflected in our daily life in different uses, such as clothes, shoes, waterproof umbrellas, and paints.
The main purpose of this article to overview of significant SCT durability studies initiated into the literature. The most relevant research investigations into durability of SCT results achieved from last decades. To summarize, compare and discuss the results from advances in durability of SCT, influencing characteristics of durability of SCT and also how efficiency and durability essential for SCT elaborated. The SCT of durability based materials fabrication method discussed in separate section. To delivery some general conclusions of the most suitable fabrication methods and their applications for studying the durability, and also recommend some future scenarios to develop them.
1.1 Advances of Durability in SCT
In a 21st century, there is major importance characteristics requirement of durability of materials 10, which involves the maintenance of SL behavior during their service era, intended at 5-10 years. The durability of SCT can be ruled by the applicable requirements of high-temperature stability for a SL-SHP surfaces leads to metals and ceramics as suitable candidates 11, for better use of parameters with lightweight, mechanical flexibility, corrosion resistance, chemical and mechanical stability are vital application requirements, than polymeric materials are more suitable candidates for SC surfaces. One of the main uses of these SHP surfaces is to grow the corrosion resistance of surfaces bare to harsh environments as well as their long-term chemical stability and maintaining the SCT 12. New synthesis techniques and surface modification methods need to be accepted, which can provide excellent adhesion and strength for the coatings on the substrates 13. We also focus on the SCT was strongly dependent on the availability and cost of fabrication techniques. SC materials (TiO2 and ZnO) have been identified, the choices of fabrication methods, once the fabrication processes finalized then these samples had been tested for SC-SHP. The highly optimized superior SCS are checked, their efficiency, stability and durability. From these comments, we can recognize the best efficiency and durability of SCT for our study.
Several researchers are reviewing for the SC coatings 2, 6-9, 14-16 such as, Sakhuja et al.17 systematically investigated the planar and nanostructure glass samples for the SC properties, and their durability test was studied over an open-air exposure period of 12 weeks, they obtained the SC and anti-reflective performance. Singh et al. 18 developed a super-repellent surfaces using zirconia particles of water-soluble siloxane emulsion on cotton fabric. They also studied that the stability of an coated cotton fabrics (CCF) was observed by the extents of water CA after the treatments of CCF with various tests such as chemical stability, UV irradiation stability, sandpaper abrasion test, and adhesive tape tear test with repetitions was presented in Fig. 1. The durability of the coating on CCF also measured by the repeated tear test of an adhesive tape. In their study, the cotton surface was paste onto an adhesive tape, and then it was peeled offed presented in Fig. 2. The developed material remained super-repellent with respect to all four test liquids, even after repetition of the tear test with an adhesive test for 20 cycles, with CA >150°. Thus the results of the study representing the excellent stability of the coating on cotton fabric 18. Quiroga et al.19 tested for long-term working conditions and performance of a commercial SC coating of water-based TiO2 sol has been coated on three building materials, it is significant in current and older European heritage such as concrete, Portland limestone, and Woodkirk sandstone.