Transparent coatings made from spray deposited colloidal suspensions

The goal of this study is to elaborate few-micrometer thick optically active coatings based on nanoparticles spray-deposited onto a substrate and to control their scattering properties through a progressive suppression of the coffee-ring effect. The modification of the aggregation state of the nanoparticles to be sprayed induces a change of the surface roughness of the films and consequently of their optical transmission. We draw the counterintuitive conclusion that a nonstable colloidal solution gives a smoother coating than a highly stabilized colloidal solution, leading to a more transparent coating. This phenomenon is demonstrated in the case of commercial TiO ₂ nanoparticles, as well as of homemade luminescent YVO ₄:Eu nanoparticles, and seems to be generalized to a large range of systems.