Because of their repellent, corrosion-mitigating, anti-icing, and self-cleaning properties, superhydrophobic coatings have numerous applications from windshields to textiles. A superhydrophobic coating is defined as one having a water contact angle (WCA) greater than 150° with a surface sliding angle less than 10°, and very low hysteresis between the advancing and receding angles. Its surface exhibits the so-called “lotus leaf effect,” whereby water bounces and balls up on contact. Here, water droplets run off readily, taking along dirt and dust for a self-cleaning effect that keeps the surface dry. The chemical composition of a surface affects the WCA, which can rise to 120°, but to achieve a WCA greater than 150°, which is considered superhydrophobic, an additional micro- and nanostructural component is needed. This functional hierarchical micro- and nanomorphology is exhibited in nature by plants and insects. A superhydrophobic coating on metallic substrates promises to provide corrosion mitigation by blocking oxygen and electrolytes, which are needed for the initiation of corrosion at the surface and interface. The methods used for preparing functional superhydrophobic coatings include sol-gel processing, layer-by-layer assembly, etching, lithography, chemical and electrochemical depositions, chemical vapor deposition, electrospinning, hydrothermal synthesis, and one-pot reactions. In this work, some research studies conducted to develop robust and durable superhydrophobic coatings are discussed in detail and analyzed for possible corrosion mitigation on the surfaces of metals and alloys. Scientists, engineers, students, and other participants in automotive, aircraft, energy, defense, electronics, and other industries will benefit greatly from this work.

1. [1] A. Otten and S. Herminghaus, “How Plants Keep Dry: A Physicist’s Point of View,” Langmuir, Vol.20, No.6, pp. 2405-2408, 2004.
2. [2] C. Neinhuis and W. Barthlott, “Characterization and Distribution of Water-Repellent, Self-cleaning Plant Surfaces,” Annals of Botany, Vol.79, No.6, pp. 667-677, 1997.
3. [3] M. N. Uddin, F. J. Desai, and E. Asmatulu, “Biomimetic Electrospun Nanocomposite Fibers from Recycled Polystyrene Foams Exhibiting Superhydrophobicity,” Energy, Ecology, and Environment, Vol.5, No.1, pp. 1-11, doi: 10.1007/s40974-019-00140-7, 2019.
4. [4] J. T. Woodward, H. Gwin, and D. K. Schwartz, “Contact Angles on Surfaces with Mesoscopic Chemical Heterogeneity,” Langmuir, Vol.16, No.6, pp. 2957-2961, 2000.
5. [5] R. N. Wenzel, “Resistance of Solid Surfaces to Wetting by Water,” Industrial and Engineering Chemistry, Vol.28, No.8, pp. 988-994, 1936.
6. [6] R. N. Wenzel, “Surface Roughness and Contact Angle,” The J. of Physical and Colloid Chemistry, Vol.53, No.9, pp. 1466-1467, 1949.
7. [7] A. B. D. Cassie and S. Baxter, “Wettability of Porous Surfaces,” Transactions of the Faraday Society, Vol.40, pp. 546-551, 1944.
8. [8] M. N. Uddin, M. Alamir, H. Muppalla, M. M. Rahman, and R. Asmatulu, “Nanomembranes for Sustainable Fresh Water Production,” The 5th Int. Conf. on Mechanical Industrial and Energy Engineering, Khulna, Bangladesh, 2018.
9. [9] T. T. Isimjan, T. Wang, and S. Rohani, “A Novel Method to Prepare Superhydrophobic, UV Resistance and Anti-Corrosion Steel Surface,” Chemical Engineering J., Vol.210, pp. 182-187, 2012.
10. [10] A. J. B. Milne and A. Amirfazli, “The Cassie Equation: How It is Meant to be Used,” Advances in Colloid and Interface Science, Vol.170, No.1-2, pp. 48-55, 2012.
11. [11] K. M. Hay, M. I. Dragilab, and J. Liburdy, “Theoretical Model for the Wetting of a Rough Surface,” J. of Colloid and Interface Science, Vol.325, No.2, pp. 472-477, 2008.
12. [12] W. Choi, A. Tuteja, J. M. Mabry, R. E. Cohen, and G. H. McKinley, “A Modified Cassie–Baxter Relationship to Explain Contact Angle Hysteresis and Anisotropy on Non-Wetting Textured Surfaces,” J. of Colloid and Interface Science, Vol.339, No.1, pp. 208-216, 2009.
13. [13] P. Varshney, S. S. Mohapatra, and A. Kumar, “Superhydrophobic Coatings for Aluminium Surfaces Synthesized by Chemical Etching Process,” Int. J. of Smart and Nano Materials, Vol.7, No.4, pp. 248-264, 2016.
14. [14] S. Zheng, C. Li, Q. Fu, W. Hu, T. Xiang, Q. Wang, M. Du, X. Liu, and Z. Chen, “Development of Stable Superhydrophobic Coatings on Aluminum Surface for Corrosion-Resistant, Self-Cleaning, and Anti-Icing Applications,” Materials & Design, Vol.93, pp. 261-270, 2016.
15. [15] S. Pana, N. Wang, D. Xionga, Y. Dengb, and Y. Shi, “Fabrication of Superhydrophobic Coating via Spraying Method and Its Applications in Anti-Icing and Anti-Corrosion,” Applied Surface Science, Vol.389, pp. 547-553, 2016.
16. [16] L. B. Boinovich, S. V. Gnedenkov, D. A. Alpysbaeva, V. S. Egorkin, A. M. Emelyanenko, S. L. Sinebryukhov, and A. K. Zaretskaya, “Corrosion Resistance of Composite Coatings on Low-Carbon Steel Containing Hydrophobic and Superhydrophobic Layers in Combination with Oxide Sublayers,” Corrosion Science, Vol.55, pp. 238-245, 2012.
17. [17] A. B. Radwan, A. M. A. Mohamed, A. M. Abdullah, and M. A. Al-Maadeed, “Corrosion Protection of Electrospun PVDF–ZnO Superhydrophobic Coating,” Surface & Coatings Technology, Vol.289, pp. 136-143, 2016.
18. [18] R. Blossey, “Self-cleaning Surfaces – Virtual Realities,” Nature Materials, Vol.2, No.5, pp. 301-306, 2003.
19. [19] Y. Hao, D. M. Soolaman, and H.-Z. Yu, “Controlled Wetting on Electrodeposited Oxide Thin Films: From Hydrophilic to Superhydrophobic,” The J. of Physical Chemistry C, Vol.117, No.15, pp. 7736-7743, 2013.
20. [20] C. Zhang, S. Zhang, P. Gao, H. Ma, and Q. Wei, “Superhydrophobic Hybrid Films Prepared from Silica Nanoparticles and Ionic Liquids Via Layer-by-Layer Self-Assembly,” Thin Solid Films, Vol.570, Part A, pp. 27-32, 2014.
21. [21] H. Li and S. Yu, “Three-Level Hierarchical Superhydrophobic Cu-Zn Coating on a Steel Substrate without Chemical Modification for Self-cleaning Property,” New J. of Chemistry, Vol.41, No.13, pp. 5436-5444, 2017.
22. [22] Q. Liu, D. Chen, and Z. Kang, “One-step electrodeposition process to fabricate corrosion resistant superhydrophobic surface on magnesium alloy,” ACS Appl. Mater. Interfaces, Vol.7, No.3, pp. 1859-1867, 2015.
23. [23] A. Khadak, M. N. Uddin, M. M. Rahman, and R. Asmatulu, “Enhancing the De-Icing Capabilities of Carbon Fiber-reinforced Composite Aircraft via Super-hydrophobic Coatings,” The Composites and Advanced Materials Expo (CAMX), Dallas, TX, 2018.
24. [24] N. Nuraje, W. S. Khan, Y. Lei, M. Ceylan, and R. Asmatulu, “Superhydrophobic Electrospun Nanofibers,” J. of Materials Chemistry A, Vol.1, No.6, pp. 1929-1946, 2013.
25. [25] R. Asmatulu, M. Ceylan, and N. Nuraje, “Study of Superhydrophobic Electrospun Nanocomposite Fibers for Energy Systems,” Langmuir, Vol.27, No.2, pp. 504-507, 2011.
26. [26] M. Salahuddin, M. N. Uddin, G. Hwang, and R. Asmatulu, “Superhydrophobic PAN Nanofibers for Gas Diffusion Layers of Proton Exchange Membrane Fuel Cells for Cathodic Water Management,” Int. J. of Hydrogen Energy, Vol.43, No.25, pp. 11530-11538, 2018.
27. [27] S. S. S. Kumar, M. N. Uddin, M. M. Rahman, and R. Asmatulu, “Introducing Graphene Thin Films into Carbon Fiber Composite Structures for Lightning Strike Protection,” Polym. Compos., Vol.40, No.S1, pp. E517-E525, 2019.
28. [28] Q. F. Xu, J. N. Wang, and K. D. Sanderson, “A General Approach for Superhydrophobic Coating with Strong Adhesion Strength,” J. of Materials Chemistry, Vol.20, No.28, pp. 5961-5966, 2010.
29. [29] S. A. Mahadik, D. B. Mahadik, M. S. Kavale, V. G. Parale, P. B. Wagh, H. C. Barshilia, S. C. Gupta, N. D. Hegde, and A. V. Rao, “Thermally Stable and Transparent Superhydrophobic Sol–Gel coatings by Spray Method,” J. of Sol-Gel Science and Technology, Vol.63, No.3, pp. 580-586, 2012.
30. [30] A. V. Rao, S. S. Latthe, S. A. Mahadik, and C. Kappenstein, “Mechanically Stable and Corrosion Resistant Superhydrophobic Sol–Gel Coatings on Copper Substrate,” Applied Surface Science, Vol.257, No.13, pp. 5772-5776, 2011.
31. [31] A. Roig, E. Molins, E. Rodríguez, S. Martínez, M. Moreno-Manãs, and A. Vallribera, “Superhydrophobic Silica Aerogels by Fluorination at the Gel Stage,” Chemical Communications, No.20, pp. 2316-2317, 2004.
32. [32] R. Taurino, E. Fabbri, D. Pospiech, A. Synytska, and M. Messori, “Preparation of Scratch Resistant Superhydrophobic Hybrid Coatings by Sol-Gel Process,” Progress in Organic Coatings, Vol.77, No.11, pp. 1635-1641, 2014.
33. [33] G. Momen and M. Farzaneh, “Simple Process to Fabricate a Superhydrophobic Coating,” Micro & Nano Letters, Vol.6, No.6, pp. 405-407, 2011.
34. [34] K. Wang, N.-X. Hu, G. Xu, and Y. Qi, “Stable Superhydrophobic Composite Coatings Made from an Aqueous Dispersion of Carbon Nanotubes and a Fluoropolymer,” Carbon, Vol.49, No.5, pp. 1769-1774, 2011.
35. [35] Y. Si, F. Yang, and Z. Guo, “Bio-Inspired One-Pot Route to Prepare Robust and Repairable Micro-Nanoscale Superhydrophobic Coatings,” J. of Colloid and Interface Science, Vol.498, pp. 182-193, 2017.
36. [36] A. M. Escobar and N. Llorca-Isern, “Superhydrophobic Coating Deposited Directly on Aluminum,” Applied Surface Science, Vol.305, pp. 774-782, 2014.
37. [37] F. Zhang, S. Chen, L. Dong, Y. Lei, T. Liu, and Y. Yin, “Preparation of Superhydrophobic Films on Titanium as Effective Corrosion Barriers,” Applied Surface Science, Vol.257, No.7, pp. 2587-2591, 2011.
38. [38] R. Asmatulu, G. A. Mahmud, C. Hille, and H. E. Misak, “Effects of UV Degradation on Surface Hydrophobicity, Crack, and Thickness of MWCNT-Based Nanocomposite Coatings,” Progress in Organic Coatings, Vol.72, No.3, pp. 553-561, 2011.
39. [39] M. N. Uddin, L. Le, R. Nair, and R. Asmatulu, “Effects of Graphene Oxide Thin Films and Nanocomposite Coatings on Fire Retardancy and Thermal Stability of Aircraft Composites: A Comparative Study,” J. of Engineering Materials and Technology, Vol.141, No.3, 031004, 2019.
40. [40] R. Asmatulu, D. Diouf, M. Moniruddin, and N. Nuraje, “Enhanced Anti-Weathering of Nanocomposite Coatings with Silanized Graphene Nanomaterials,” Int. J. of Engineering Research and Application, Vol.6, No.6, pp. 23-36, 2016.
41. [41] M. N. Uddin, J. M. George, and R. Asmatulu, “Investigating the Effects of UV Light and Moisture Ingression on the Low-Impact Resistance of Three Different Carbon Fiber–Reinforced Composites,” Advanced Composites and Hybrid Materials, Vol.2, No.4, pp. 701-710, doi: 10.1007/s42114-019-00117-4, 2019.
42. [42] T. Ishizaki, Y. Masuda, and M. Sakamoto, “Corrosion Resistance and Durability of Superhydrophobic Surface Formed on Magnesium Alloy Coated with Nanostructured Cerium Oxide Film and Fluoroalkylsilane Molecules in Corrosive NaCl Aqueous Solution,” Langmuir, Vol.27, No.8, pp. 4780-4788, 2011.
43. [43] D. Lai, G. Kong, and C. Che, “Synthesis and Corrosion Behavior of ZnO/SiO₂ Nanorod-Sub Microtube Superhydrophobic Coating on Zinc Substrate,” Surface & Coatings Technology, Vol.315, pp. 509-518, 2017.
44. [44] Z. Zheng, M. Schenderlein, X. Huang, N. J. Brownbill, F. Blanc, and D. Shchukin, “Influence of Functionalization of Nanocontainers on Self-Healing Anticorrosive Coatings,” ACS Applied Materials & Interfaces, Vol.7, No.41, pp. 22756-22766, 2015.
45. [45] M. N. Uddin, H. T. N. Gandy, M. M. Rahman, and R. Asmatulu, “Adhesiveless Honeycomb Sandwich Structures of Pre-preg Carbon Fiber Composites for Primary Structural Applications,” Advanced Composites and Hybrid Materials, Vol.2, No.2, pp. 339-350, doi: 10.1007/s42114-019-00096-6, 2019.
46. [46] N. Nuraje, R. Asmatulu, and G. Mul, “Green Photo-Active Nanomaterials: Sustainable Energy and Environmental Remediation,” RSC Publishing, 2015.