Optical Properties of Vanadium Oxide/Cellulose Triacetate Photochromic Films ^†

The properties of polymer-based nanocomposites strongly depend on the fillers added and their dispersion on the matrix. Proposing a simple method that can control these variables is essential to obtain nanocomposites with enhanced properties. In this study, cellulose triacetate based nanocomposites modified with sol-gel synthesised vanadium oxide nanoparticles (V₂O₅) and poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (PEO-b-PPO-b-PEO or EPE) triblock copolymer were obtained by two methods: solvent casting (SC, drying at ambient conditions) and solvent vapour annealing (SVA, drying under solvent vapour atmosphere). Nanocomposites were characterised by Fourier-transform infrared spectroscopy (FTIR) and UV-vis spectroscopy. Nanocomposites presented green colour and high transparency, improving the SVA method the surface finish of the films. Moreover, V₂O₅ nanoparticles provided switchable photochromic properties, changing the film colour from green to pale blue when exposed to UV radiation. Nanocomposites with EPE triblock copolymer presented a more noticeable colour change. As for the speed of the recovery process to the initial state, it increased with the addition of EPE and the sol-gel content. Thus, it was proved that the SVA preparation method was more appropriate that the SC, as well as corroborate that the EPE triblock copolymer and the sol-gel content affected the properties of developed CTA nanocomposites.