Sol–Gel Based Hydrophobic Antireflective Coatings on Organic Substrates: A Detailed Investigation of Ammonia Vapor Treatment (AVT)

We report a method to prepare hydrophobic, antireflective mesoporous silica-based films on polymer substrates from sol–gel approaches combined with an ammonia vapor treatment (AVT) to avoid any thermal curing. Strategies involving the combination of direct co-condensation of pure and methylated-hybrid silica precursors with further post-functionalization with methyl groups were used. Coatings with the best reflectance (transmittances up to 99.6% in the visible range), full water repellence, and good resistance to abrasion (failures occurred at the substrate interfaces) were obtained by optimizing both sol–gel and AVT conditions. Using in situ, time-resolved, spectroscopic ellipsometry, we demonstrate that the structure of the film can be significantly and rapidly modified from molecular to mesoscales, under the action of H 2 O and NH 3 vapors. The identified mechanism follows a local dissolution/condensation associated to Ostwald ripening that can easily be controlled by adjusting the applied conditions. These structural modifications were much less intense for co-condensed methylated mesoporous matrices due to the stabilizing effect of the organic pendant groups. These conclusions are supported by complementary characterizations obtained with environmental ellipsometry porosimetry, GI-SAXS, SEM-FEG, UV–visible transmittance, crockmeter, and FTIR.