Enhancement of Coloring and Bleaching Rates of Photochromic WO<sub>3</sub> Composite Films by Adding Polyethylene Glycol

WO3-based photochromic composite films were fabricated using a translucent urethane resin and a peroxoisopolytungstic acid - methanol solution as raw materials. Moreover, and polyethylene glycol (PEG, molecular weight 1000) was added to the composite as a sensitizer. The WO3 mean particle sizes in the obtained composite were 46–55 nm, which implies that by PEG addition caused a slight reduction in the particle size. Additionally, the coloring/bleaching rate and the transmittance module of the composite films were drastically increased by PEG addition. These improvements in photochromic properties were previously considered to be due to the effect of the particle size of WO3 particles in the composite, but were mainly assumed the effect of photoinduced electron transfer, which is caused by the presence of PEG in the composites.