Screen-Printed Photochromic Textiles through New Inks Based on SiO2@naphthopyran Nanoparticles

Photochromic silica nanoparticles (SiO 2 @ NPT ), fabricated through the covalent immobilization of silylated naphthopyrans (NPTs) based on 2 H -naphtho[1,2- b ]pyran ( S1, S2 ) and 3 H -naphtho[2,1- b ]pyran ( S3, S4 ) or through the direct adsorption of the parent naphthopyrans ( 1, 3 ) onto silica nanoparticles (SiO 2 NPs), were successfully incorporated onto cotton fabrics by a screen-printing process. Two aqueous acrylic- (AC-) and polyurethane- (PU-) based inks were used as dispersing media. All textiles exhibited reversible photochromism under UV and solar irradiation, developing fast responses and intense coloration. The fabrics coated with SiO 2 @ S1 and SiO 2 @ S2 showed rapid color changes and high contrasts (Δ E * ab = 39–52), despite presenting slower bleaching kinetics (2–3 h to fade to the original color), whereas the textiles coated with SiO 2 @ S3 and SiO 2 @ S4 exhibited excellent engagement between coloration and decoloration rates (coloration and fading times of 1 and 2 min, respectively; Δ E * ab = 27–53). The PU-based fabrics showed excellent results during the washing fastness tests, whereas the AC-based textiles evidenced good results only when a protective transfer film was applied over the printed design.