Effect of Film Thickness and Air Atmosphere on Photochromic Properties of WO3-Based Composite Films

WO3-based photochromic composite films with various film thickness were fabricated using peroxo-iso-polytungstic acid as filler and transparent urethane resin as matrix, and the thickness of the composite films were 180, 250, 620, and 1300 µm. All the composite films showed reversible photochromic properties. The coloring reaction rate constant of the composite films with the thickness of 180, 250, 620, and 1300 µm were 3.91 × 10−1, 3.80 × 10−1, 3.63 × 10−1, and 2.69 × 10−2 min−1, respectively. The bleaching half-life period of the composite films with the thickness of 180, 250, 620, and 1300 µm were 45.4, 67.8, 138, and 200 min, respectively. The coloring speed increased with decrease of the film thickness, and the bleaching speed decreased considerably with decrease of the film thickness.