A facile process for fabrication of environmentally safe superhydrophobic surfaces Tanu Mittal, Sangeeta Tiwari, S. K. Tiwari Ó American Coatings Association 2017 Abstract Superhydrophobic coatings have opened new vistas in the field of self-cleaning surfaces by having improved performance, robustness and preser- vation of cleaning agents including water. Presently, fluoropolymers are extensively explored and used for this purpose. However, the major drawback accompa- nying fluoropolymers is formation of environmentally persistent and toxic compounds, viz. PFOA (perfluo- rooctanoic acid) and PFOS (perfluorooctanesulfonic acid) on their degradation raising concern on their use. In the present study, an effort has been made to develop a facile process by using an environmentally safe material. A simple dip coating technique is reported to fabricate superhydrophobic surface. SiO 2 nanoparticles of size 25–30 nm, prepared by sol–gel route, were dip-coated on glass substrate in multilayers followed by coating of a surfactant to achieve homo- geneity of SiO 2 layers and enhanced binding with subsequent layer of NUVA-2114 [a commercially used fluorotelomer with chemical composition C 2 F 6 (CF 2 CF 2 ) n X]. It was observed that SiO 2 nanopar- ticles and sodium dodecyl sulfate (SDS) surfactant exhibit a synergistic effect on interface stability at optimized SDS concentration. A water contact angle of 152° is achieved. The established method is simple, scalable, environmentally safe and cost-effective. Keywords Nanosilica, Superhydrophobic coatings, Self-cleaning, Dip coating, Fluoropolymers, NUVA- 2114, PFOA, PFOS Introduction Superhydrophobic surfaces with a water contact angle (WCA) higher than 150° have lately fascinated researchers due to their prospective application in various fields such as antireflection, 1 self-cleaning, 2 antisticking, 3 lenses and windows, 4 antifogging, 5 anti- corrosion, 6–8 oil–water separation, 9–11 and selective transportation of microdroplets. 12–14 Several methods have been reported to attain superhydrophobic sur- faces including plasma method, 15 template method, 16 chemical vapor deposition, 17 sol–gel processing, 18–20 wet chemical reaction, 21–23 lithography, electrospin- ning, 24,25 and solution immersion. Among these, layer- by-layer (LbL) deposition is a simple, accessible, broadly applicable and reliable method to obtain superhydrophobic surfaces. On the basis of the previ- ous studies, the conventional approach of fabricating superhydrophobic surfaces involves two steps: creation of a hierarchical rough surface to prepare essential small surface topographies (£ 100 nm) and further treatment of the surface in order to reduce the surface energy. 26–28 The antisticking and anticontamination properties obtained by self-cleaning surfaces are of great significance for applications including antifouling surfaces, automobile parts, stain resistance textiles, dust-free coatings for glasses in buildings and PV solar cells. Superhydrophobicity can be achieved by either roughening the surface or lowering of the surface energy or both. Surface energy and surface roughness are the dominant factors influencing the wettability. By lowering the surface energy, the hydrophobicity of surfaces is enhanced. CF 3 having the lowest surface energy (6.7 mJ/m 2 ) gives a water contact angle of around 120°. 29 However, to achieve higher hydropho- bicity, appropriate surface roughness is desirable. Surfaces with water contact angles of more than 150° were developed by introducing appropriate roughness on materials having low surface energies. Nanostruc- T. Mittal, S. Tiwari (&) Amity Institute of Applied Sciences (AIAS), Amity University, Noida, Uttar Pradesh, India e-mail: drtiwarisangeeta@gmail.com; stiwari2@amity.edu S. K. Tiwari Council of Scientific and Industrial Research (CSIR), New Delhi, India J. Coat. Technol. Res. DOI 10.1007/s11998-017-9927-4