71 Characterization and Application of Nanomaterials (2021) Volume 4 Issue 2 doi:10.24294/can.v4i2.1334 REVIEW ARTICLE Review of super-hydrophobic materials research Chengbao Liu1,2*, Minjia Li1, Xiaojie Liu1,2, Zhigang Chen1,2 1 School of Chemistry, Biology and Materials Engineering, Suzhou University of Science and Technology, Suzhou 215009, Jiangsu Province, China. E-mail: lcb@mail.usts.edu.cn 2 Jiangsu Key Laboratory for Environmental Functional Materials, Suzhou 215009, Jiangsu Province, China ABSTRACT We reviewed the research on super-hydrophobic materials. Firstly, we introduced the basic principles of super-hy- drophobic materials, including the Young equation, Wenzel model, and Cassie model. Then, we summarized the main preparation methods and research results of super-hydrophobic materials, such as the template method, soft etching method, electrospinning method, and sol-gel method. Among them, the electrospinning method that has developed in recent years is a new technology for preparing micro/nanofibers. Finally, the applications of super-hydrophobic materi- als in the field of coatings, fabric and filter material, anti-fogging, and antibacterial were introduced, and the problems existing in the preparation of super-hydrophobic materials were pointed out, such as unavailable industrialized produc- tion, high cost, and poor durability of the materials. Therefore, it is necessary to make a further study on the application of the materials in the selection, preparation, and post-treatment. Keywords: Super-hydrophobic Materials; Basic Principles; Preparation Method; Application ARTICLE INFO Received: 22 June 2021 Accepted: 14 August 2021 Available online: 21 August 2021 COPYRIGHT Copyright © 2021 Chengbao Liu, et al. EnPress Publisher LLC. This work is licensed under the Creative Commons Attribution- NonCommercial 4.0 International License (CC BY-NC 4.0). https://creativecommons.org/licenses/by- nc/4.0/ 1. Introduction Super-hydrophobic material refers to a material with a contact an- gle of the material surface and water greater than 150° and a rolling an- gle less than 10°[1,2]. In nature, many plant foliage and waterfowl feath- ers have super-hydrophobic water characteristics, such as dragonfly wing[3], water strider leg[4], lotus leaf[5], etc. (Figure 1), among which the most typical is the “lotus leaf effect”. The surfaces of these moving, plants contain special geometry with contact angles with water above 150°. In the lotus leaf[6–8], the lotus leaf surface (Figure 2) is composed of many papil- lae with an average diameter of 5 to 9 m, and the contact and rolling angles of water on that surface are (161.0 ± 2.7)° and 2°, respectively[6–8]. Each papilla is composed of a nanostructured branching with an average diameter of (124.3 ± 3.2) nm. These nanostructures on micromastoid especially, play an important role in super-hydrophobicity. Figure 1. Dragonfly wings (a), water strider legs (b), lotus leaf (c). 72 Through the research, people do not only find many super-hydrophobic phenomena in nature and their surface structures but also make artificial syn- thetic super-hydrophobic surfaces by various meth- ods. At present, there are two ways to prepare su- per-hydrophobic surfaces[9]: (1) modification of low surface energy material on a surface with micro-nano rough structure; and (2) construction of a micro-nano rough structure on the surface of the material with low surface energy. In recent years, the preparation of super-hydro- phobic surface materials with biological tissues and structures as bionic objects has become one of the hotspots in the field of material research. Jiang Lei research group is the first research group involved in this field in China. Their main preparation meth- ods are the template method, soft etching method, electrospinning method, and at present, its research focus is ultra-super-hydrophobic materials, name- ly ultra-hydrophobic ultra-hydrophobic oil. It will introduce the super-hydrophobic materials from the basic principles of super-hydrophobic water, its preparation method and its application. 2. The rationale of super-hydropho- bic water The wettability of the solid surface is mainly determined by the chemical composition of the solid surface and surface microstructure. The wettability of the solid liquid, that is, hydrophilic and hydro- phobicity is generally expressed by the contact angle θ of the liquid and solid phase. The shape formed when the droplet stays on a smooth solid surface by the droplet on its surface is determined by the in- terface tension of the three-phase contact surface of the solid, liquid and gas, whose contact angle can be described by the Young equation[10]: cosθ = (γSA – γSL)/γLA (1) γSA, γSL and γLA represent the interface tension of solid-gas, solid-liquid and liquid-gas individually. At this time, the three surface tension interactions are at equilibrium. But the Young equation is an idealized model suitable only for ideally smooth solid surfaces. If it is a solid surface with a certain roughness, there are some D-value between the apparent and intrinsic contact angles. The actual contact area of solid and liquid is more than the apparent contact area. The droplets fully enter the empty groove of the rough surface structure. Therefore, it must consider the im- pact of roughness on the hydrophobic performance. At present, Wenzel model[11] and Cassie model[12] are Figure 2. Microstructure of the surface of the lotus leaf. 73 relatively mature in the related basic theoretical re- search. The schematic diagram shows in Figure 3. 2.1 Wenzel model The Wenzel model considers that the droplets contact with the solid surface, and infiltrate into the surface groove. It increases the surface contact area, and the apparent geometrically observed contact area is less than the actual solid-liquid contact area when the apparent contact angle is greater than the intrin- sic contact angle: cosθw =r(γSA – γSL)/γLA = rcosθ (2) In the formula, r is the surface roughness factor, the ratio of the actual surface area to the project- ed area, and θw is the apparent contact angle of the rough surface. From Equation (2), increasing the value of the surface rough factor r can make the original hydro- phobic surface more hydrophobic. However, the Wenzel model also has its limitations, which do not apply in the case of solid surfaces composed of dif- ferent types of chemicals. 2.2 Cassie model The Cassie model suggests that water droplets are suspended on solid surface convex grooves and that liquid droplets fall on a composite phase com- posed of solid-liquid and solid-gas interfaces. There- fore, its equation is: cosθ′ = f1cosθ1 + f2cosθ2 (3) θ′ is the apparent contact angle in the Cassie model, f1 and f2 are the ratio of liquid contact to the solid surface and air, respectively, and 1 and 2 are the contact angles of liquid to solid surface and air, respectively. Where f1 + f2 = 1, 2 = 180°, the formula (3) can be written as: cosθ′ = f1cosθ1 – f2 = f1cosθ1 + f1–1 (4) From the above model, preparing a surface with a special structure can improve the contact angle of the surface. The Cassie model suggests that droplets are suspended on solid surface convex grooves and do not seep into the surface topography. In the Cassie model, droplets are usually scrollable on the surface. The Wenzel and Cassie models provide a strong theoretical basis for the preparation of super-hydro- phobic surfaces, and although they are currently un- der some controversy[14,15]. Moreover, the contact angles in the above three cases characterize the performance of water droplets on the horizontal surface and are more oblique in reality. The state of the droplet on the slope can be characterized by the rolling angle, the critical sur- face tilt angle of the drop when the droplet begins to roll on the solid surface. The smaller tilt angle if the droplet begins to roll indicates that the super-hydro- phobic water on this surface is better[16]. In conclusion, the contact and rolling angles jointly characterize the mutual permeability of the solid-liquid and the hydrophilic-hydrophobicity ex- hibited. The larger contact angle and the smaller roll- ing angle indicate the stronger hydrophobicity of the material surface[17–19]. 3. Preparation method of super-hy- drophobic materials Figure 3. Schematic diagram of the Wenzel and Cassie models[13]. 74 3.1 Template method The template method takes a substrate with a cavity structure as a template, and covers the casting film liquid on the template by dumping, casting and spin coating. The proposed method has the advantag- es of simplicity, effectiveness and large area replica- tion, and has good application prospects in practice. Zheng Jianyong et al. used calcium carbonate particles to form a polymer super-hydrophobic sur- face by thermal pressure and acid etching[20]. After the test, its droplet static contact angle reached 152.7° while its rolling angle was < 3°. Liu et al. coated a PDMS film with candle soot as a template, and calcination removed the template to form super-hydrophobic fiberglass cotton with a rough fiber mesh surface on the glass substrate[21]. After detection, the material has a contact angle with the water of up to 163° and can be used to optimize oil-water separation and air filtration, showing excel- lent thermal stability. Ke et al. took taro leaves as the parent plate, constructed the surface structure with subtle cavity by template method, and then modified by an im- pregnated coating method, which significantly im- proved the hydrophobic performance[22]. 3.2 Etching method Etching technology refers to the process of etch- ing the target surface into a micro rough appearance by physical or chemical methods. Laser etching, plasma, chemical and, photo etching are several commonly used micro etching methods. The etch- ing method can make more accurate operation and design of the surface structure to regulate surface hydrophobicity. While the cost is high, and it is not suitable for large-scale production. Qi et al.[23] used the chemical etching method as- sisted by metal ions (e. g., Ag+, Cu2+, Cr3+) to process Zinc substrate to get rough structure surface, and the water contact angle measured by fluoro silane modification is up to (161 ± 2)°. In addition, they explored the effects of different metal ions on the surface morphology and hydrophobic properties, and then they found that the addition of metal ions could enhance the strength and stability of the super-hy- drophobic surface. Sung-Woon et al.[24] took SF6 as a plasma source, obtained with the plasma etching method, and then C4F8 as a plasma source, and then a carbon-fluorine membrane was deposited on the silicon surface with a micron-grade rod structure. After testing, the con- tact angle with water is 165°. 3.3 Phase separation method The phase separation method is the membrane form in which the system produces two or multiple phases during the control conditions. This method is easy to regulate and simple to operate. It can prepare uniform and large areas of superhydrophobic films, which has great value in practical aspects. Liu et al.[25] put butyl methacrylate (BMA) and glycol dimethyl acrylic (EDMA) in a mixture of 1, 4-cis-butanediol (BDO) with N-methyl-pyrrolidone (NMP) to in situ polymerization. A super-hydropho- bic porous polymer surface with a micro-nano rough structure with a water contact angle of 159.5° and a rolling angle below 3.1°. Liu Jianfeng et al.[26] used butyl methyl acry- late (BMA) and ethylene glycol dimethyl acrylate (EDMA) as monomers and azo diisonitrile (AIBN) as an initiator for thermal polymerization on the glass substrate, thus forming a micro/nanocomposite roughness structure on the surface with a static water contact angle of up to 159.5°. 3.4 Chemical vaporous deposition Chemical vapor deposition is a simple, efficient, inexpensive, and effective method, which prepares rough structures without the limitation of substrate shape. Deng Tao et al. prepared aligned dense nanow- ire structures on silicon wafers by chemical vapor deposition[27]. They placed washed silicon wafers in inductively coupled plasma bins, deposited silicon nanowires while etching, and then modified them with fluoro silane to create a silicon nanowire sur- face structure with a line width of about 100 nm. 75 3.5 Electrospinning method Electrospinning is a new technology to prepare micro/nanoscale fibers. It places a polymer solution or melt in a high-pressure electrostatic field, and is stretched under the electric field Coulomb force to form a jet fine flow that falls on the substrate to form a micro/nanofiber membrane. Jiang Lei et al.[28] used electrospinning technolo- gy to build a rough surface and then used cheap low surface-energy silicon oil during calcination to pre- pare TiO2 super-hydrophobic surfaces with a contact angle greater than 150° and a rolling angle less than 5°. Huang et al.[29] constructed a coating with SiO2 nanoparticles and silicic acid solution. They adjusted the roughness of the coating by changing the ratio of SiO2 nanoparticles and silica acid. The coating was modified by perfluorooctyl trichlorosilane with a water contact angle of 160°, less than 10°. It also has high light transmittance, excellent thermal stability and mechanical stability. However, when the organic modifier of the coating surface contacts water for a long time, the turnover of its hydrophilic group results in poor hydrophobic stability, increasing the uncertainty in its practical application. Li Fang et al.[30] used polyvinylidene difluoride (PVDF) and N, N-dimethylformamide (DMF) as the test materials, and prepared the ultra hydropho- bic material with hollow microsphere structure by electrospinning. and the ultra hydrophobic material has super lipophilic properties. The contact angle be- tween the material and the water was 153.5°. 3.6 Layer upon layer assembly method Layer assembly technology refers to the tech- nology of membrane layer by layer deposition under the action of electrostatic action, hydrogen bonding, and coordination bonding. Zhang Qunbing, Wang Jun et al. of Ningbo University used layer by layer assembly method to prepare the superhydrophobic surface of sea urchin TiO2 with silicon sheet as the substrate[31]. The contact angle of the surface was 151.2° and a rolling angle of 4.5°. Shang et al.[32] used polypropylene dimethyl ammonium chloride (PDDA) and poly4-styrene sodium sulfonate (PSS) as the polyelectrolyte, and then dipped the glass in the polyelectrolyte solution. Then dipped it in polystyrene modified SiO2 particle suspension. Finally, a high transparent superhydro- phobic porous SiO2 glass coating made from perfluo- roctane by chemical gas deposition, measuring water contact angle greater than 150° and a rolling angle of less than 10°. 3.7 Sol-gel method The sol-gel method is a preparation method for condensing the solvent obtained after hydrolysis of high chemical activity compounds and drying the resulting gel to form a micro/nanopore structure to make it superhydrophobicity, but there are disadvan- tages such as long preparation process route, poor surface structure control, and solvent contamination. Sanjay et al.[33]. prepared a methyl triethox- ysilane (MTES) and porous silicon membrane into superhydrophobic surfaces with contact angles up to 160° on a glass substrate by solvent-gel method It is shown that the superhydrophobic films prepared by this method are transparent, adherent, good thermal stability and moisture resistant. Wei et al.[34] used potassium titanate and TEOS as precursors and used a solvent-gel method to pre- pare a perfect titanium-silicon mesh composite aero- sol structure, and the water contact angle of aerogel samples obtained after trimethylchlorosilane modifi- cation reached (145 ± 5)°. After Zheng Yansheng et al.[35] hybridized TFE with a SiO2 solvent modified by epoxy propoxy pro- pyl trimethoxysilane, the glass was coated with a hy- per-hydrophobic coating with a contact angle of up to 156°. 3.8 Electrochemical deposition method Su et al.[36] deposit a layer of nickel on the cop- per substrate, and then fluoro silane modification yields a superhydrophobic surface with a contact angle of 162°. The material is capable of maintaining superhydrophobic by moving 1 m on silicon carbide (SiC) sandpaper for 800 at a load pressure of 4.8 kPa, indicating that the surface has excellent micro 76 hardness and mechanical wear resistance. Ding, et al. used electrochemical method, and deposited a layer of micro/nanostructure copper ox- ide (Cu2O) membrane on the conductive glass (ITO) surface. It has a water contact angle up to about 170°, achieving a superhydrophobic effect. Mean- while, it could obtain the Cu2O films of different mi- cromorphology by regulating electrodeposition time. Xu et al.[38] electrochemical deposition of Tri- decafluoroctyl triethoxysilane (POTS) on a films of poly pyrene and SiO2 prepared a superhydrophobic complex coating of petal micronano layered struc- tures highly transparent, thermal and mechanical stability with a static water contact angle up to (163 ± 1)° and a rolling angle below 2° Hyper hydrophobic ZnO films were prepared on an aluminum alloy substrate after Huang et al.[39] functionally tionalized nanoZnO to 0. 01 mol·L–1 stearate ethanol solution, a mixture of isopropa- nol and butanol. It found that the roughness of the surface and the water contact angle of the surface gradually increased with the deposition temperature, and the film obtained at 50 ℃ had excellent super- hydrophobic properties, with a water contact angle reaching (1553)°. 3.9 Solution immersion method Li et al.[40] first impregnated the aluminum alloy plate in lanthanum nitrate aqueous solution for heat treatment to form a nano structure similar to Ginkgo biloba leaves on the surface, and then modified the super hydrophilic aluminum alloy surface with Do- decafluoroheptyl propyl trimethoxysilane. The water contact angle reached 160°, and the superhydropho- bic surface had a relatively good surface Strong ther- mal stability, corrosion resistance, wear resistance and other advantages. Yao Jiannian et al.[41] prepared superhydropho- bic materials by solution soaking. After first soaking the smooth copper sheet in a specific [Ag(NH3)2]OH solution for 6 h, a structure similar to the rose petals could appear on the surface of the copper sheet, and its contact angle reached 156°. 3.10 Other methods Yang and et al.[43]were prepared by microemul- sion, then heated on a glass plate to form porous rough structural films during the volatile process, and then modified with Xinji trimethoxysilane to make honeycomb-like superhydrophobic films with a contact angle of 156.3°, which is simple, fast and economical[42]. Furthermore, inspired by the micro- structure of plant leaf surfaces, researchers like Liu et al. prepared superhydrophobic surfaces with a high contact angle of around 170° and a rolling an- gle of about 6° on an aluminum alloy by a one-step anodized method. 4. Application of hytra hydrophobic materials Hyper hydrophobic materials have self-cleaning, pollution resistance and other characteristics, there- fore, superhydrophobic materials can be developed and applied, so that they have broad prospects in the fields of aerospace and military industry, agriculture, pipeline nondestructive transportation, housing con- struction, as well as the equipment working in vari- ous open-air environments. 4.1 Application of superhydrophobic materi- als in fabric and filter materials Various micronanostructural fibers with super- hydrophobic water are produced by electrophospin- ning or treatment of the material surface to obtain anti-polluting superhydrophobic fabrics. Such mate- rials can be used to make waterproof film, hydropho- bic filter film, etc., or make the fabric have new func- tions such as hydrowaterproof, pollution prevention and dust prevention due to hydrophobic properties. For example, Xue et al. creates a friction-resistant superhydrophobic fiber fabric coating with sodium hydroxide etched polyethylene terephthalate (PET) fiber fabric[44]. 4.2 Application of superhydrophobic materi- als in building coatings Due to their unique hydrophobic properties, superhydrophobic materials have wide application prospects in water resistance, snow prevention and pollution resistance. At present, the ultra-hydropho- 77 bic surface materials in building pollution prevention materials are mainly coating and protective fluid, for example, Ji Haiyan, Chen Gang et al.[45] using etch- ing glass also prepared ultra-hydrophobic glass sur- face. Yang et al.[46] developed a modified dodecthiol ZnO/PDMS complex with a water contact angle of 159.5° and 8.3° and excellent ice resistance at –10 and –5 ℃, showing great potential for application. 4.3 Application of superhydrophobic materi- als in fog prevention and self-cleaning Liquidation of water vapor in the air forms wa- ter mist covering the surface of transparent materials such as glass can cause reduced visibility of these materials[47]. Some bionic ultra-hydrophobic surface effectively reduce the condensation of water vapor, to achieve a certain anti-fog, self-cleaning effect. Af- ter alternating self-assembly of raspberry polystyrene and SiO2 particles on slides, a highly transparent po- rous SiO2 coating was obtained by high-temperature calcination. Finally, an ultra-hydrophobic transparent coating was obtained by chemical vapor deposition with a water contact angle of (1592)°. The coating improves the evaporation rate of water mist with ex- cellent anti-fog performance. 4.4 Application of superhydrophobic surface materials in metal anticorrosion protection Hyperhydrophobic materials have corrosion-re- sistant properties because a membrane of air occurs between solid and liquid, making it difficult for cor- rosive ions to contact the surface of the material[49,50]. Many people have researched in this regard, such as Guo Haifeng et al.[51] praying the inner surface of the natural gas pipeline to prepare super- hydrophobic films to further improve the corrosion resistance of the pipeline. The subject group, Lu Si et al., adhered the disordered carbon nanotubes to the surface of the substrate aluminum plate to form a composite structure surface and then modified with PTFE to form a hyper-hydrophobic PTFE. 4.5 Application of superhydrophobic surface materials in other aspects Mobina et al.[52] co-modified the trimonomomer copolymer with methanol and nano SiO2 and the wa- ter contact angle of the composite superhydrophobic coating was greater than 150° and could be applied to the surface of biomedical materials. Wang et al.[53] immersed aluminum alloy, silicon plates, polypropylene and other substrate in a buf- fer of dopamine-hydrochloride for a period, trans- ferred to different concentrations of silver ammonia solution, added formaldehyde solution, and finally modified the substrate into a mixture of ethanol and dodecyl thiol to make a superhydrophobic silver sub- strate with a water contact angle up to 170°. 5. Conclusion The application range of superhydrophobic materials is quite wide, which has had certain de- velopment in various aspects, and its application prospect is very broad. However, due to the current technology and development costs are limited, the actual industrialization and commercialization are not much[54,55]. First, from a theoretical perspective, the geometry of superhydrophobic, size, functional group influence of superhydrophobic surface struc- ture needs to be deepened. Secondly, in the prepara- tion process, the low surface energy substances used are more expensive, mostly fluoride or silane com- pounds. Finally, in terms of technology, it is mainly the durability and aging resistance of surface coating. Many superhydrophobic structures are prone to lose superhydrophobicicity due to infirmness. Therefore, in the selection of materials, preparation process and post-processing, further research and solution. Re- search on how to automatically recover or regenerate superhydrophobic surfaces after reduced or disrupted performance will be an important research direction in this field. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgements Fund Project: National Natural Science Foun- dation Grant Project (51478285); Natural Science Foundation of Jiangsu University Grant Project 78 (14KJA430004); Suzhou Science and Technology Development Plan Project (SYG201742); Jiangsu University Water Treatment Technology and Materi- al Collaborative Innovation Center Project. References 1. Manatunga DC, Silva RMD, Silva KMND. Double layer approach to create durable superhydrophobicity on cotton fabric using nano silica and auxiliary non fluorinated materials. Applied Surface Science 2016; 360: 777–788. 2. Brassard JD, Sarkar DK, Perron J. Studies of drag on the nanocomposite superhydrophobic surfaces. Applied Surface Science 2015; 324: 525–531. 3. Darvizeh M, Darvizehv A, Rajabi H, et al. Freevibra- tion analysis of dragon fly wings using finite element method. The International Journal of Multiphysics 2009; 3(1): 101–110. 4. Khila A, Abouheif E, Rowe L. Evolution of a novel appendage ground plan in water striders is driven by changes in the hox gene ultrabithorax. Plos Genetics 2009; 5(7): e1000583. 5. Barthlott W, Neinhuis C. Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta 1997; 202: 1–8. 6. Xiao, Tian J, Zhang B, et al. Research progress of su- perhydrophobic self-cleaning coatings. Modern Paint & Finishing 2017; 20(3): 32–35. 7. Minehide Y, Naoki N, Hiroyuki M, et al. Theoretical explanation of the lotus effect: superhydrophobic property changes by removal of nanostructures from the suface of a lotus leaf. Langmuir the Acs Journal of Surfaces & Colloids 2015; 31(26): 7355–7363. 8. Meng LY, Soo JP. Superhydrophobic carbon -based materials: a review of synthesis, structure, and appli- cations. Carbon Letters 2014; 15(2): 89–104. 9. Yang M, Zhang L, Jiang H, et al. Effect factors and fabrication of superhydrophobic surface. Science & Technology in Chemical Industry 2016; 24(4): 78–82. 10. Young RN. The bakerian lecture: experiments and calculations relative to physical optics. London: Philosophical Transactions of the Royal Society of London; 1804. p. 1–16. 11. Wenzel RN. Resistance of solid surfaces to wetting by water. Industrial and Engineering Chemistry 1936; 28: 988–994. 12. Cassie ABD, Baxter S. Wettability of porous surfac- es. Transactions of the Faraday Society 1944; 40: 546–551. 13. Chen J, Wang J, Wang W, et al. Preparation and Application of Hyperhydrophobic Surface Materials. China Materials Progress 2013; 32(7): 399–405. 14. Gao L, Mccaetgy TJ. How wenzel and cassie were wrong. Langmuir 2007; 23: 3762–3765. 15. Chen H, G T, Zhang X, et al. Research progress of superhydrophobic surface. Chemical Research 2013; 24 (4): 434–440. 16. Wang B, Nian J, Tie L, et al. Theoretical advances in stable hyper-hydrophobic surfaces. Physical Journal 2013; 62 (14): 1–15. 17. Yu M, Chen S, Zhang B, et al. Why a lotus-like supe- rhydrophobic surface is self-cleaning? An explana- tion from surface force measurements and analysis. Langmuir the Acs Journal of Surfaces & Colloids 2014; 30(45): 13615–13621. 18. Cao M, Guo D, Yu C, et al. Water-repellent prop- erties of superhydrophobic and lubricant-infused “slippery” surfaces: a brief study on the functions and applications. Acs Applied Materials & Interfaces 2016; 8(6): 3615–3623. 19. Spori DM, Drobek T, Zurcher S. et al. Beyond the lotus effect: roughness infuences on wetting over a wide surface-energy range. Langmuir the Acs Journal of Surfaces & Colloids 2008; 24(10): 5411–5417. 20. Zheng J. Feng J, Zhong M. Polymer superhydrophil- ic/superhydrophobic surfaces were prepared by the CaCO3 particle template method. Polymer Journal 2010; 1 (10): 1186–1192. 21. Liu X, Xu Y, Ben K, et al. Transparent, durable and thermally stable PDMS-derived superhydrophobic surfaces. Applied Surface Science 2015; 339(1): 94–101. 22. Peng P, Ke Q, Zhou G, et al. Fabrication of micro- cavity-array superhydrophobic surfaces using an improved template method. Journal of Colloid and Interface Science 2013; 395: 326–328. 23. Qi Y, Cui Z, Liang B, et al. A fast method to fabricate superhydrophobic suefaces on zinc substrate with ion 79 assisted chemical etching. Applied Surface Science 2014; 305(7): 716–724. 24. Cho SW, Kim JH, Lee HM, et al. Superhydrophobic Si surfaces having microscale rod structures prepared in a plasma etching system. Surface and Coatings Technology 2016; 306: 82–86. 25. Liu J, Xiao X, Shi WL, et al. Fabrication of a supe- rhydrophobic surface from porous polymer using phase separation. Applied Surface Science 2014; 297(4): 33–39. 26. Liu J, Xiao X, Cai X. Preparation of superhydro- phobic porous polymer coating via phase separation. Polymer Materials Science and Engineering 2013; 29 (10): 113–117. 27. Tao D, Varanasi KK, Ming H, et al. Nonwetting of impinging droplets on textured surfaces. Applied Physics Letters 2009; 94(13): 3109. 28. Jiang L, Wang L, Zhao Y, et al. Superhydrophobic TiO2 nanofiber mesh membranes were prepared by electrospinning (in Chinese). Journal of Higher Chemistry 2009; 30(4): 731–734. 29. Huang W, Lin CS. Robust superhydrophobic trans- parent coatings fabricated by a low-temperature sol- gel process. Applied Surface Science 2014; 305(3): 702–709. 30. Li F, Jia K, Li Q, et al. Farbrication of superhydro- phobic and superoleophilic PVDF nanofibers with hollow beads structure by electrospinng for the sep- aration of separation of oil and water. New chemical materials 2016; 44(3): 223–225. 31. Zhang Q. Preparation and characterization of su- per-hydrophobic surface of micro-nanocomposite (in Chinese). Ningbo: Ningbo University; 2012. 32. Shang Q, Zhou Y. Fabrication of transparent super- hydrophobic porous silica coating for self-cleaning and anti-fogging. Ceramics International 2016; 42: 8706–8712. 33. Sanjay S, Latthe IH. Porous superhydrophobic silica films by sol-gel process. Microporous and Meso- porous Materials 2010; 130(1-3): 115–121. 34. Wei W, Lu XM, Jiang D, et al. A novel route for syn- thesis of UV-resistant hydrophobic titania-containing silica aerogels by using potassiumtitanate as precur- sor. Dalton Transactions 2014; 43(25): 9456–9467. 35. Zheng Y, He Y, QingY, et al. Preparation of a SiO2/ polytetrafluoroethylene hybrid superhydrophobic coatings. Chemical Industry and Engineering Prog- ress 2012; 31(7): 1562–1566. 36. Su F, Yao K. Facile fabrication of superhydropho- bic surface with excellent mechanical abrasion and corrosion resistance on copper substrate by a novel method. ACS Applied Materials & Interfaces 2014; 6(11): 8762–8770. 37. Ding Y, Li Y, Yang L, et al. The fabrication of con- trolled coral-like Cu2O films and their hydrophobic property. Applied Surface Science 2013; 266: 395– 399. 38. Xu L, Tong F, Lu X, et al. Multifunctional poly- pyrene/silica hybrid coatings with stable excimer fluorescence and robust superhydrophobicity derived from electrodeposited polypyrene films. Journal of Materials Chemistry C 2015; 3(9): 2086–2092. 39. Huang Y, Sarker DK, Chen XG. Superhydrophobic nanostructured ZnO thin films on aluminum alloy substrates by electrophoretic deposition process. Applied Surface Science 2015; 327: 327–334. 40. Li L, Huang T, Jie J, et al. Robust biomimetic-struc- tural superhydrophobic surface on aluminum alloy. Acs Applied Materials & Interfaces 2015; 7(3): 1449–9457. 41. Cao Z, Xiao D, Kang L, et al. Superhydrophobic pure silver surface with flower-like structures by a facile galvanic exchange reaction with [Ag(NH3)2] OH. Chemical Communication 2008; 23(23): 2692– 2694. 42. Yang T, Tian H, Chen Y. Preparation of superhydro- phobic silica films with honeycomb like structure by emulsion method. Journal of Sol-Gel Science and Technology 2009; 49: 243–246. 43. Liu Y, Liu J, Li S, et al. One-step method for fabrica- tion of biomimetic superhydrophobic surface on alu- minum alloy. Colloids and Surfaces A: Physicochem- ical and Engineering Aspects 2015; 466: 125–131. 44. Xue C, Li Y, Zhang P, et al. Washable and wear-re- sistant superhydrophobic surfaces with self-cleaning property by chemical etching of fibers and hydropho- bization. ACS Applied Materials & Interfaces 2014; 2014(6): 10153–10161. 45. Ji H, Gang C, Hu J, et al. Preparation and proper- ties of monodisperse poly(ethyl methacrylate). New 80 Chemical Materials 2011; 39(8); 106–108. 46. Yang C, Wang F, Li W, et al. Anti-icing properties of superhydrophobic ZnO/PDMS composite coating. Applied Physics A 2015; 122(1): 1–10. 47. Shang Q, Zhou Y. Fabrication of transparent superhy- drophobic porous silica coating for self-cleaning and anti-fogging. Ceramics Inter-national 2016; 42(7): 8706–8712. 48. Hou L, Fang L. Preparation and application develop- ment of superhydrophobic surface. Chemistry 2016; 79(10): 897–904. 49. Zhou Y. Preparation and properties of artificial bionic superhydrophobic functional surfaces [PhD thesis]. Beijing: University of Science and Technology of China; 2012. 50. Li H, Gu X, Liu L, et al. Advances in studying hype- rhydrophobic surfaces (in Chinese). Applied Chemi- cal Industry 2016; 45(12): 2347–2350. 51. Guo H, Zhang, Z, Li G, et al. Super-hydrophobic molecular film on the inner wall surface of steel for natural gas pipelines and its corrosion resistance. Oil & Gas Storage and Transportation 2011; 30(10): 781–784. 52. Xue C, Li Y, Zhang P, et al. Super-hydrophobic mo- lecular film on the inner wall surface of steel for nat- ural gas pipelines and its corrosion resistance. Oil & Gas Storage and Transportation 2011; (10): 781–784, 717. 53. Wang Z, Ou J, Wang Y, et al. Anti-bacterial superhy- drophobic silver on diverse substrates based on the mussel-inspired polydopamine. Surface & Coatings Technology 2015; 280: 378–383. 54. Xu W, Song J, Sun J, et al. Progress in fabrication and application of superhydrophobic surfaces on metal substrates. Journal of Materials Engineering 2011; 1(5): 93–98. 55. Liang W, Zhang Y, Wang B, et al. Biological applica- tions of biomimetic superhydrophobic surfaces. Acta Chimica Sinica 2012; 70(23): 2393–2403.