Grafting mechanism of electrochromic PAA-WO3 composite film

A micro-Raman spectroscopic study has been carried out to investigate the electrochromic process in a porous and nanocrystalline tungsten oxide film. The film was prepared by dipping the tin-doped indium oxide glass into an aqueous mixture solution of PAA (polyacrylic acid) and WO3-NH4OH. After heating at low temperature, around 100 degrees C, the film was treated in 1 N HCl in order to achieve polycondensation, where the ammonium ion was replaced with a proton. In the micro-Raman spectra for the bleached and colored PAA-WO3 films, it was evident that the coloration accompanies a peak reduction at similar to 960 cm(-1) and a peak enhancement at similar to 810 cm(-1). Based upon the present Raman observation, we can confirm that the electrochromism of the nanocrystalline tungsten oxide is dominated by the grafting process, i.e., the surface modification of -W-VI = O bonds into -W-V=O(1-delta+)-Mdelta+ (M = H, Li) ones. (C) 1999 Academic Press.