Grafting mechanism of electrochromic PAA-WO3 composite film

A micro-Raman spectroscopic study has been carried out to investigate the e lectrochromic process in a porous and nanocrystalline tungsten oxide film. The film was prepared by dipping the tin-doped indium oxide glass into an a queous mixture solution of PAA (polyacrylic acid) and WO3-NH4OH. After heat ing at low temperature, around 100 degrees C, the film was treated in 1 N H Cl in order to achieve polycondensation, where the ammonium ion was replace d with a proton. In the micro-Raman spectra for the bleached and colored PA A-WO3 films, it was evident that the coloration accompanies a peak reductio n 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 electroc hromism 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-de lta+)-Mdelta+ (M = H, Li) ones. (C) 1999 Academic Press.