Morphology-dependent optical and wetting behavior of GLAD PTFE thin films
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Morphology-dependent optical and wetting behavior of GLAD PTFE thin films Rajnarayan De , S. Maidul Haque, Ranveer Singh, C. B. Basak, S. Jena, J. S. Misal, D. D. Shinde, Tapobrata Som, K. Divakar Rao
Ó American Coatings Association 2020 Abstract E-beam evaporation equipped with glancing angle deposition arrangement (GLAD) was used to fabricate nanostructured polytetrafluoroethylene (PTFE) films in a single-step coating process. Three sets of PTFE coatings were prepared using various oblique angles, e-beam currents, and deposition times to explore the effects of deposition parameters on the properties of PTFE nanostructured coatings. Water contact angle (WCA) of the coatings was found to be enhanced with the increase in all the above process parameters. Optical transmittance of the coatings was also found to be improved with the above parameters except for in the case of an increase in thickness of the films (in very high thickness region), where the R. De (&), S. M. Haque, J. S. Misal, D. D. Shinde, K. D. Rao Photonics and Nanotechnology Section, Atomic and Molecular Physics Division, Bhabha Atomic Research Centre Facility, Visakhapatnam 531011, India e-mail: [email protected] R. De, C. B. Basak, T. Som, K. D. Rao Homi Bhabha National Institute, Mumbai 400094, India R. Singh, T. Som Institute of Physics, Sachivalaya Marg, Bhubaneswar, Odisha 751005, India Present Address: R. Singh Department of Energy Systems Research, Ajou University, Suwon 443-739, Republic of Korea C. B. Basak Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai 400085, India S. Jena Atomic and Molecular Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
transmittance was degraded due to light scattering from the sample surface. After all the optimizations, the 130-nm-thick GLAD PTFE sample prepared with highest e-beam current was found to be more suitable for antireflection and self-cleaning applications. The single-sided coating demonstrates a very high average transmittance of 95.6% (with a wideband transmittance spectrum among the others) in the visible and NIR wavelength range with excellent selfcleaning nature (WCA 156°, sliding angle 10°). The trend of measured WCA with respect to surface roughness follows the Cassie–Baxter model. Overall, the study demonstrates the possibility of fabricating highly transparent self-cleaning coatings using the GLAD technique, which is potentially useful for fabricating protecting cover glasses in solar panels. Keywords PTFE, GLAD, Antireflection, Superhydrophobicity
Introduction During the past few years, replicating naturally existing water-repellent surfaces (lotus leaf, butterfly wings, etc.) has drawn the attention of researchers.1–5 These bio-inspired surfaces are extremely useful in many real-life applications like self-cleaning, antifogging, and antiicing.6–9 On the other hand, coatings with bare minimum reflection losses are very important for applications where maximum light transmission is desired (e.g., solar cells, flat panel displays, etc.).10–1
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