Photosensitive ink formulation and inkjet printing on flexible PET substrate

Photochromic materials whose color can reversibly change under visible light exposure are good candidates for many applications like photooptical sensors, smart inks and paints, displays or optical storage. Among these materials, inorganic Ag:TiO2 films have been proven to be stable over time and to exhibit multicolor photochromism leading to potential high-performance systems. However, their fabrication processes are often based on laboratory equipment not adapted to industrialization and usually involve thermal treatments not compatible with soft materials, which limit the application range. The present paper proposes an alternative way to produce photochromic Ag:TiO2 films compatible with industrialization and with soft substrates. An aqueous ink, made of a dispersion of TiO2 nanoparticles and silver ions, was formulated from a commercial TiO2 suspension and a silver salt by adding a thickener and a surfactant to satisfy inkjet process requirements. The inkjet printing process was optimized on polyethylene terephthalate substrates to form thin inorganic films after IR annealing. Such a process can be adapted to any kind of substrates, in particular flexible and non-heat-resistant substrates, and can be scaled at the industrial level. The photochromic behavior of the fabricated films was finally assessed successfully after an activation step.