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

International audienceWe 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 H2O and NH3 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 FTI

Inorganic/organic nanocomposites: Reaching a high filler content without increasing viscosity using core-shell structured nanoparticles

International audienceExtensive research is being conducted on the development of inorganic/organic nanocomposites for a wide variety of applications in microelectronics, biotechnologies, photonics, adhesives, or optical coatings. High filler contents are usually required to fully optimize the nanocomposites properties. However, numerous studies demonstrated that traditional composite viscosity increases with increasing the filler concentration reducing therefore significantly the material processability. In this work, we synthesized inorganic/organic core-shell nanocomposites with different shell thicknesses. By reducing the shell thickness while maintaining a constant core size, the nanopar- ticle molecular mass decreases but the nanocomposite filler fraction is correlatively increased. We performed viscosity measurements, which clearly highlighted that intrinsic viscosity of hybrid nanoparticles decreases as the molecular mass decreases, and thus, as the filler fraction increases, as opposed to Einstein predictions about the viscosity of traditional inorganic/polymer two-phase mixtures. This exceptional behavior, modeled by Mark-Houwink-Sakurada equation, proves to be a significant breakthrough for the development of industrializable nanocomposites with high filler contents