Bifunctional hybrid silica sol-gel coatings were synthesized, which showed both increased light transmittance
and water-repellence. The as-prepared coatings of variable thickness (100–175 nm) were found to have low
refractive index (1.250–1.275), high porosity (36%–42%), and maximum light transmittance up to 99.8%.
Water-repellence of the surface was due to high water contact angle (90°) and low contact angle hysteresis
(1–2°). Ellipsometric porosimetry and transmission electron microscopy measurements confirmed the microporous
structure of the coatings. A systematic investigation for studying the durability and the deterioration of
optical and surface properties was studied during aqueous soaking tests at different pH. During these experiments
atomic force microscopy showed that the morphology of the surface did not change. The changes in the
wetting properties were also confirmed by surface free energy measurements and an increase of the polar
component was observed. The optical properties could be regenerated completely or partially after the soaking
via heat treatment at 400 °C. The light transmittance of the samples remained high after the soaking, most likely
due to the swelling of the solid matrix. The light transmittance and the water-repellent properties of the coatings
showed long-term stability up to a year of storage.
The full article is available online on the webpage of Thin Solid Films Volume 699.