Towards the development of superhydrophilic SiO 2 -based nanoporous coatings: Concentration and particle size effect

Abstract Superhydrophilic nanoporous coatings were prepared from layer-by-layer assembled silica nanoparticles (SiO 2 ) and a polycation. As expected, concentration of silica dipping suspension and particle size are closely related to thickness of the obtained multilayer films. However, wettability might not to be mainly governed by coating thickness as usually reported on literature; instead, superficial homogeneity should be carefully considered. It was found that if a uniform nanoporous structure is obtained, superhydrophilic behavior is observed and, at least for the studied system, increases in coating thickness are not followed by improvements on wetting performance. In turn, for obtaining uniform structures, the usage of dipping suspension with a hypothetical minimum silica nanoparticles concentration is mandatory. Below such critical value, stacking defects along the coating surface are observed and the manifestation of superhydrophilicity is inhibited. As an additional feature, low refractive indices of multilayer coatings resulting from nanoporosity was found to provide good antireflection (AR) properties.