Enhancing the electrochromic response of polyaniline films by the preparation of hybrid materials based on polyaniline, chitosan and organically modified clay

Abstract

Polyaniline (PAni) was modified with chitosan and/or organophilic clay (Nanomer I-24) by in situ polymerisation using p-toluenesulfonic acid (PTSA) as dopant agent. These materials were characterised by FTIR spectroscopy, thermal analysis, scanning electron microscopy, d.c. electrical conductivity and spectroelectrochemical measurements. All samples maintained the electrical and electrochromic properties inherent to the PAni. Also, the addition of clay to the samples improved thermal stability and the modification of the PAni with chitosan provided the formation of homogeneous films with good adhesion onto ITO/glass electrodes as compared with pristine PAni. Using the CIE (Commission Internationale de l'Eclairage) system of colorimetry the colour stimuli of the PAni and PAni hybrid films deposited onto ITO/glass were calculated from in situ visible spectra recorded simultaneously to the cyclic voltammograms. Reversible changes in the hue and saturation occur in the films of all samples from yellow in the reduced state to blue in the oxidised state, but the change is much more significant for the PAni–chitosan–clay, as shown by the track of the CIE 1931 xy chromaticity coordinates. For the PAni–chitosan–clay film, the CIELAB 1976 colour space coordinates for a D55 illuminant were L* = 67, a* = −27 and b* = 51, and L* = 17, a* = −22 and b* = −5, respectively for the film in the reduced and oxidised states. These materials showed good electrochromic properties and could be applied in the assembly of electrochromic devices.