Stable coloured micrometric films from highly concentrated nano-silver sols: The role of the stabilizing agents

The synthesis of highly concentrated aqueous silver nanoparticles (NPs), exploiting different types of polymeric stabilizing agents, has been extensively investigated, especially for the stabilization of spherical yellow nanoparticles. In this context, here, a successful and easy wet chemical method was adopted to synthesize concentrated primary colored (yellow, red, blue and green) sols. The influence of polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) in affecting the final stability was finely investigating via UV/Vis spectroscopy, dynamic light scattering, TEM and colorimetric analysis. The next step consisted on the deposition of obtained sols onto a crown-treated polyethylene terephthalate (PET) support to obtain transparent colored micrometric homogeneous films. The fabricated PVP-based Ag films were revealed to be outstandingly UV-stable, contrarily to PVA-based films, probably due to the degradation of the polymer itself. Indeed, after UV aging tests, the PVA macromolecules could be broken and chemically modified (demonstrated by FT-IR analyses). This resulted in there being insufficient macromolecules to efficiently cover the surface of the nanoparticles, meaning that the nanoparticles tended to aggregate with each other, destabilizing the system itself. Hence, the obtained colored films described herein could represent a promising tool for different applications, from color shifting to optoelectronic devices.