Challenges and Opportunities in Fabrication of Transparent Superhydrophobic Surfaces

Background: Research in to transparent super-hydrophobic surfaces is of considerable interest in the present scenario, as it finds plenty of applications in both fundamental research and industry. An extensive scattering of propagated light may take place through super hydrophobic surfaces because of very high surface roughness. Transparency and super hydro-phobicity are general conflicting properties whereby; the main requirement to satisfy both these properties is the precise control of roughness. Further, the wettability of the surface is another important property of the material that depends on both the surface composition and its roughness. Methods: Approaches for fabrication of transparent super-hydrophobic surfaces may be categories as; bottom-up, top-down, and combination of bottom-up with top-down approaches. Bottom-up approaches encompass mostly self-assembly and self-organization such as chemical vapor deposition (CVD), layer-by-layer (LBL) deposition, hydrogen bonding and colloidal assemblies. Top-down approaches involve lithographic and template-based techniques, as well as surface plasma treatment. Methods combining bottom-up with top-down approaches include casting of polymer solution, phase separation, and electro-spinning. Results: Present work reviews the preparation of transparent superhydrophobic surfaces by following different techniques and the developments over the years. This paper deals with the detailed discussion regarding the origins of water-repellent surfaces, examining how the surface characteristics can be controlled by using the shape and size of surface features, in particular, how techniques have progressed to create multiscaled roughness to mimic the lotus leaf effect. Conclusion: With the availability of several methods to fabricate superhydrophobic surfaces and coatings, important applications for super-hydro-phobicity have been identified but the use of super-hydrophobic surfaces at the large scale is still lacking due to the poor wear resistance. Artificial superhydrophobic surfaces are not able to recover and heal the damages, due to abrasion. Further, the fabrication of robust surfaces is one of the major points to be focused with super- hydrophobic and other functional surfaces, which can withstand in wearing conditions. Long-term durability and wear resistance, which are the key issues with super-hydrophobic cotton clothes, is another major challenge with super-hydrophobic surfaces. However, the use of paper products in superhydrophobic coatings is quite different from cotton fabrics due to the difference in their quality and manufacturing. Therefore, the varied nature of the substrate materials, demands to seek new methods which are suitable for mass production of super- hydrophobic surfaces than to focus on the durability of surface. Keywords: Super hydrophobic, contact angle, surface energy, roughness.