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Ind. Eng. Chem. Res., 2013, 52 (23), pp 7737–7745.
Sucheta De , Debrina Jana , Samar Kumar Medda ,Goutam De.
Nano-Structured Materials Division, CSIR—Central Glass & Ceramic Research Institute, 196, Raja S. C. Mullick Road, Kolkata 700 032, India.
Abstract
Wavelength selective antireflective (AR) coatings have been deposited on hard-coated CR-39 ophthalmic lenses and polycarbonate (PC) sheets following a two-layer (high and low index) quarter wavelength (λ/4) optical design. Covalently bonded SiO2–poly(ethylene oxide) (PEO)–TiO2 and SiO2–PEO inorganic–organic composite based coatings were used as high and low index coatings, respectively. Transmissions of 99% (reflection loss minimized to 1%) have been achieved in the visible wavelength regions after deposition of such AR coatings on hard-coated CR-39. The predetermined reflection minima/transmission maxima can be tuned over the entire visible wavelength region by changing simply the physical/optical thickness of the two layers (λ/4 design), thereby generating different reflection colors. The AR-coated CR-39 lenses showed a surface hardness of 3H (ASTM D 3363). Applying a thin (≤50 nm) hydrophobic layer on top, the surface hardness value can be increased to 5H due to decrease of the frictional coefficient. Deposition of such a thin hydrophobic layer (λ/4 in the UV region) does not alter any AR property in the visible region. In the case of PC the surface hardness value can be close to 4H after application of such a hydrophobic coating. Coated CR-39 and PC substrates have passed all the standard tests related to adhesion, abrasion, surface hardness, and chemical endurance. These AR coatings with hard and hydrophobic surfaces (static water contact angle 102 ± 3°) can find a wide range of applications starting from visual comfort in optical related appliances to antireflective covers on solar cells with a modest self-cleanable property.
Copyright © 2013 American Chemical Society
Additional information:
Research efforts are on to develop coating technologies associated with more light penetration with self-cleaning properties. Besides optical related applications, now-a-days, to increase the efficiency of photovoltaic/solar cells there is a need to obtain sustainable optical coatings which will allow to through maximum solar emission. To solve this problem hard-and anti-reflective (AR) coatings with hydrophobic surfaces can be useful as a top cover of the device. In addition to this many other transparent plastic materials with such hard, AR and hydrophobic surfaces can be used in various display articles and optical devices. Besides the above, the technology can also be useful for application as refractive index matching scratch healing hard-coatings on previously scratched plastics and reflecting coatings.
Figure caption:
(a) Photos of AR coated CR-39Ò lenses showing the reflection color covering the visible range. The reflecting images of ‘tube lights’ are different in color in accordance with the transmission maxima or reflection minima. (b) and (c) are their optical reflectance and transmittance spectra. Reprinted (adapted) with permission from (Industrial & Engineering Chemistry Research, 2013, 52, 7737–7745 Copyright © 2013 American Chemical Society.
