Preparation of a fast photochromic ormosil matrix coating for smart windows

摘要

A novel photochromic dye (NPB)-doped ormosil matrix coating with fast spectrokinetics was studied as functional materials for smart windows. First, the NPB was modified into a reactive silylated dye (NPB-Si) by a silane coupling agent. Then, the NPB-Si was hydrolyzed and copolycondensed with methyl triethoxysilane to form the ormosil (NPB-PMS) via the sol-gel method. Finally, the photochromic ormosil matrix coating on the substrate was obtained by the following spin-coating process. Upon the activation by the UV irradiation, the ormosil coating displayed the characteristic dual absorption peaks at 504 and 628 nm, which indicated as a valuable neutral tone. The dual absorption is due to the existence of photoisomers. On the basis of the theoretical calculation, the trans-cis photoisomers displayed the longer wavelengths in visible region than those of trans-trans ones, which was due to the less coplanarity. The kinetics studies of coloration and decoloration of NPB-PMS indicated an accelerated conversion process than that of NPB-doped polystyrene coating. The improved spectrokinetics of NPB-PMS coating is ascribed to the nanoscaled cavities observed in their surfaces, which offered enough space for molecular rotation during the photochromism. Our results also demonstrated that the NPB-PMS coating had much better solvent wash-off resistance than the physically doped coating.