Water-soluble poly(2-(3thienyloxy)ethanesulfonic acid)/V₂O ₅ nanocomposites: Synthesis and electrochromic properties

Water-soluble conducting poly(2-(3thienyloxy)ethanesulfonic acid) (PTOESA)/V₂O₅ nanocomposite, (PTOESA)_xV ₂O₅, was prepared by simply mixing PTOESA with V ₂O₅ wet gel at room temperature. XRD data showed that the interlayer spacings of (PTOESA)_xV₂O₅ films are 14.0±1.5Å and increased as the polymer content increased. These values are consistent with the insertion of polythiophene chains into the V ₂O₅ layer gallery. The formation of alternative layers of PTOESA and V₂O₅ was further supported by depth profile SIMS analyses. Cyclic voltammograms of (PTOESA)_xV₂O ₅ film showed two pairs of redox peaks with colors varying from orange, yellowish green, green, to purple blue, depending on the stoichiometry of the nanocomposites. Moreover, a synergetic effect was observed on the electrochromic properties of these nanocomposites. It was found that the optical contrast (ΔOD) of the composites is better than those of PTOESA and V₂O₅ at the film thickness from 150 to 500nm. The oxidation optical response time of (PTOESA)_xV₂O ₅ is independent of the stoichiometry and falls in between those of PTOESA and V₂O₅. At higher polymer content (x>0.5), the reduction optical response time of (PTOESA)_xV₂O ₅ is smaller than those of PTOESA and V₂O₅. Variable temperature conductivity data showed that the conductivity of (PTOESA)_xV₂O₅ films increased as temperature increased, characteristic of thermal activated behavior, which was dominated by the interparticle contact resistance. The room-temperature conductivity of water-soluble (PTOESA)_xV₂O₅ films was in between those of PTOESA and V₂O₅ xerogel and higher conductivity was found in the composite with lower polymer content. The anomalous conductivity of (PTOESA)_xV₂O₅ with high PTOESA content may be due to the reason that the higher the polymer content, the bigger the grain size of (PTOESA)_xV₂O ₅ film as revealed with scanning electron microscopy and AFM micrographs.