Rewritable films on flexible supports for colored photo-inscriptions: from nanostructuring to color prediction models – PHOTOFLEX

We propose to develop a contactless printing technology based on the use of Ag:TiO2 nanostructured films that exhibit multicolour photochromism. Such films will be applied on flexible supports like plastic or paper, compatible with most applications in the fields of security and traceability. As these supports do not withstand high temperatures, the elaboration techniques used - sol gel and magnetron sputtering - will be adapted to this constraint.
The elaborated films contain Ag nanoparticles (NP) embedded in a nanoporous TiO2 matrix. The permanent or reversible changes of color occurring under illumination by UV/visible lasers rely on the control of the localized surface plasmon resonance (SPR) of Ag nanoparticles. They result from the tuning of the NP size/shape distribution through photo-activated redox reactions occurring specifically with the titania matrix.Various colors can be obtained and are related to the changes observed at the nanoscale (morphology, organization, chemical surrounding of the Ag NPs). Electromagnetic modeling will help us to better understand this relation between the structural properties of the NP assemblies and the resulting reflectance or transmittance spectra.
The photo-inscription technique on nanostructured films provides a set of colors on various supports. A color printing system can then be calibrated in order to perform reliable color reproduction and readable data inscription. After the selection of color primaries, we will develop a halftoning method (dot-off-dot halftoning) in order to increase the number of color shades. Finally, a color appearance model will relate the optically measured data of the printed samples and the human perception of their visual attributes.