Layer-by-Layer Hybrid Films Incorporating WO3, TiO2, and Chitosan

Layer-by-layer (LbL) films from WO 3, TiO 2, and chitosan have been produced, in which the ability of complexation of chitosan with transition metal oxides was exploited. The electrochemical and chromogenic properties of LbL films of (chitosan/WO 3 ) 4 /TiO 2 and (chitosan/WO 3 /chitosan/TiO 2 ) 4 have been examined and compared to those of (chitosan/WO 3 ) 4 . More specifically, we employed the quadratic logistic equation (QLE) to estimate the number of electrochemically active sites ( K ) and the molar absorption coefficient (ε) of WO 3 in LbL films, by fitting the absorbance changes (Δ A ) resulting from the electron transfer from W(V) to W(VI) sites. The number of electrochemical active sites for 4-bilayer LbL films of chitosan/WO 3 before and after deposition of TiO 2 was ca. 15.5 × 10 - 9 mol cm - 2 and 10.7 × 10 - 9 mol cm - 2, respectively. The incorporation of TiO 2 in the LbL films led to a larger absorption coefficient and electrochromic efficiency. The differences in the molar absorption coefficient were attributed to an electron-transfer rate associated with ionic-trapping effects, which were observed by electrochemical impedance spectroscopy. These results are discussed on the basis of dissipation and feedback effects.