A series of phosphotungstic acid (PWA)/poly(vinyl alcohol) (PVA) composite films with different PWA content have been prepared. The structure and photochromic properties of the composite thin films were studied with Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and ul-traviolet-visible spectra (UV-vis). FT-IR results showed that the Keggin geometry of PWA and PVA were still preserved inside the PWA/PVA composite thin films and a charge-transfer bridge was built between PWA and PVA via hydrogen bond. AFM images indicated that surface topography of the polymer matrix changed after adding PWA and the surface topography of the composite films differed when adding different content PWA. Irradiated with UV light, the transparent films changed from colorless to blue. The photochromic efficiency during the coloration process and the velocity during the bleaching process were enhanced with increasing PWA content. All results indicated that the PWA content affected the structure of composite films, which resulted in the different photochromic properties.

Key words: polyoxometalate content, poly(vinyl ahcohol), composite film, photochromism