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The durability studies of any materials can be influenced by many factors, the some major factors are effecting the on SCT durability, is classified and presented in the Fig.7. From figure 7, we can conclude that, these some major factors /characteristicses is influencing the durability of SC materials. First one, Metal corrosion (oxygen and moisture) was a serious problem in the performance of SCT. The SC-SHP has mainly used in aircraft, automobiles, pipelines and naval vessels these have broad categories of potential applications of SHP surfaces. There is a need for a deeper understanding of not only how to fabricate such surfaces using simple techniques, but also study how the specific surface properties (morphology, roughness, surface chemistry, surface wetting and stability) are significant 28. Vazirinasab et al. 29 reviewed the corrosion resistance of SHP coatings for metal surfaces such as aluminum, copper, magnesium, and steel can waste natural resources and degrade infrastructure. Improvement in the corrosion resistance of these metals is a remarkable application of SHP surfaces. Mohamed et al. 30 reviewed the corrosion behavior of SHP surfaces and significant attention was given to state of the art on corrosion performance of SHP coatings. Yao et al. 31 showed that the resulting SHP copper surface exhibits enhanced corrosion resistance and durability. SHP coatings can effectively enhance the anti-corrosion ability of the metal surface, which supports the possibility of using SHP film as a substitute for chromate-containing passivation coatings to protect metallic substrates was concluded from his review article by Zhan-Fang et al. 32. Aluminum has been generally used in many applications, it is disposed to pollution or damage under harsh working environmental condition. Zheng et al.33 developed a corrosion-resistant, SC and anti-icing application of a stable SHP coating on aluminum surface was studied. SHP multilayer coatings with layer number tuned swapping in surface wettability and redox catalytic anti-corrosion application, the corrosion resistance of the coating was remained steady even after 240?h of exposure, this enhancement is attributed to superhydrophobicity and anodic shift in corrosion potential 34.
Second, many researchers have been studied with the stability, and durability of SHP coatings on different metallic substrates in water and various organic. The stability of SHP surfaces over a wide pH-range was crucial, since they were used as engineering materials in several industrial applications 30. Isimjan et al. 35 reported that in the effect of water, chloroform and decane on the CAs of TiO2/SiO2 coated steel substrates measured after every 24 h for a period of eight days was tested. It is shown that the CAs remained constant, and the surfaces have steady even after 8 days. Influence of solution–immersion timed on surface morphology and the CA presented in Fig. 8. From the figure, 8a shows the surface has a sporadic flake structure of 5 min and after that surface covered by countless flake structures after 15 min (Fig. 8b). The time increased to 30 min, the surface uniformly and completely covered by flake structures (Fig. 8c). With further rising the time for 40 min, the surface still uniformly covered by flake structures, but the flake sizes increased (Fig. 8d). These SEM images showed that the flake structures were formed gradually as the solution-immersion time prolonging 36Third, the stability of SC SHP films against UV irradiation was extremely important, particularly for outdoor surfaces that would exposure to UV light. This is another one problem of the SC SHP surfaces for durability studies. We have been reviewed several papers, and they finally concluded that most of the SC SHP films remain constant and others strongly stable for UV, some were not good on UV irradiation, because they have lost their superhydrophobicity under UV illumination for 2 h and also the water CA released from 160° to 0° 30. Despite several excellent properties including good chemical, low shrinkage, resistance, cure at low temperatures and the absence of volatiles, epoxy resins subjected to UV damaged and their durability is reduced significantly, when exposed to outdoor environments, then to overcome this drawback, UV absorbers 37. However, Gao et al.38 reported the highly transparent and UV-resistant SHP arrays of SiO2-coated ZnO nano-rods for SHP.
Fourth, a recent studies have been showed that the high temperature typically decreases the durability of SHP coatings of surface. It leads to an irreversible changing from the hydrophobic character of a hydrophilic character 30. The stability and moisture of SHP wood explored for humidity and temperature aging conditions. Cracks in SHP coating were investigated after age with 20 cycles 39, 40. Some of the authors have been reported that there was no significant change in SHP after 60 or 90days, this showing a strong stability and durability against humidity 30.
1.3 Why efficiency and durability essential for SCT
Nowadays, if the consumers will buy an excellent SC-SHP product, it has a good quality of glass, low-cost, high efficiency, durability, and its stability will be more important, than only consumer demands/thinks of that product, therefore, the SC material efficiency and durability was the most important. An even lot of difficulties arise due to SC studies, they were resolved. A new era of SCT for the recent expansion of the field of fabrication and characterization of materials at the nano-scale create, it possible to design and realized new materials with special function parameters. The building materials strengthened made more flexible and greater electrical resistance.
Japanese scenario, ongoing research activities of SC-SHP material, study at Tokyo University of Science, Japan, researchers were considering the basic issue of SC properties includes durability and efficiency have been studied in details 27, 41-44. In the past, utmost of scientist has done work in the field of synthesis, formulation, and tasted of different types of SC materials and surfaces, as a result, they had published a number of research publications and several technologies were transferred to a private organization. Recently, SCT has been studied with different advanced application for many fields like medical, architecture, biology, and environmental engineering 45. The developed SCT is helpful in several applications including the textile materials, medical, athletic and military wear, and outdoor fabrics, which are basically used in daily life 8.
2. Fabrication of SC technology
This section covers a summary of the most essential results of the SCT of durability studies that reviewed for this effort. The reviewed results are collected rendering to the fabrication methods. A different types of material have been used to prepare a SC-SHP surfaces, several techniques for the preparation of SHP surfaces have been investigated and reported on recent year. Several fabrication techniques are used for preparation of rough surfaces such as such as mechanical stretching, sol-gel process, layer-by-layer assembly, chemical and electrochemical depositions, chemical vapor deposition, etching, and lithography, in detail of explanation and use of some of these important techniques are presented in the following.
2.1 Sol-gel process
An efficient, low-cost, low-temperature, low-pressure procedure and can produce rough surfaces on a variety of oxides as sol-gel process, have been investigated and studied. Sol-gel technique has a multi-step process and it has several advantages over other techniques. Sundaresan et al. 46 prepared a nano TiO2 cotton fabrics by sol-gel technique. They were tested the important functional properties viz. antimicrobial activity, UV protection, and SC activity. The durability test carried out in the range of 32–36 washes for antimicrobial activity. Kumar et al. 47 synthesized mechanically robust coatings based on TEOS and glycidoxypropyltriethoxysilane by using sol-gel method. They could maintain the required hydrophobicity even after the removal of the top surface by accelerating abrasion. These coatings show closed to 96% SC efficiency. The developing coating method was simple, low-cost, and easily scaled-up for large outdoor structures that required mechanically robust and durable SC functions. The SC and anti-fogging SHP coating from the Al surface was synthesized by employing chemical etching technique. The SHP with water CA (170?) and SA (4?) were achieved. The SHP surfaces recoiled from the high-speed water jet, signifying the excellent water-repellent nature of the coating surface. The coating supported SHP after undertaking 100 cycles of the adhesive tapes peeling to test. Their SHP behavior withstood 90? and 180? bending, and repetitive folding and de-folding are presented in Fig. 9, coating exhibits an excellent SC property 26.