Electrochromic Properties of Tungsten Oxide Nanoparticles Films Prepared by the Filtration and Transfer Method

Electrochromic tungsten oxide nanostructures were prepared from tungsten oxide nanoparticles for the first time by the filtration and transfer technique. This novel and facile method for film preparation presents many advantages that include the possibility to obtain nanoparticle films with various porosities and compositions. The films obtained in the present work exhibited indeed porous structures and were generally composed of a mixture of nanoparticles. When the amount of the nanoparticles in the suspensions increased, we observed thicker films with higher coverage densities. Films prepared at room temperature exhibited very good electrochromic properties. It was found that annealing at 500oC increases the film stability and life time. Using cyclic voltammetry, fast diffusion behaviour (D of the order of 10-6 cm2s-1) for proton insertion/extraction has been observed. Moreover, fast switching response time (less than a second) during the bleaching process due to the rapid decay of the anodic current during chronoamperometry was also noted. The coloration efficiency for such devices was about 20 cm2C-1. The coloration of the films is associated with the number of color centers and depends on the number of inserted charges. However, we have shown that good optical reversibility does not necessarily need fast electrochemical kinetics. Finally, the effect of high applied potentials on the films was investigated, followed by an analysis of the electronic properties of the films

Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers

We report temperature dependencies of material properties such as dielectric anisotropy, birefringence, splay (K₁₁), twist (K₂₂), and bend (K₃₃) elastic constants of the uniaxial nematic (N) phase formed by flexible dimers of DTC5C9 and compare their behavior to that of a corresponding monomer MCT5. DTC5C9 forms a twist-bend nematic (Ntb) at temperatures below the N phase. Anisotropic properties of MCT5 are typical of the rod-like mesogens. In particular, birefringence increases as the temperature is reduced, following the classic behavior, described by Haller. The elastic constants also follow the standard behavior, with their ratios being practically temperature-independent. In contrast, DTC5C9 shows a dramatic departure from the standard case. Birefringence changes non-monotonously with temperature, decreasing on approaching the N-Ntb phase transition. K₃₃ decreases strongly to 0.4 pN near the N - Ntb transition, although remains finite. The ratios of the elastic constants in DTC5C9 show a strong temperature dependence that can be associated with the bend-induced changes in the orientational distribution function. The measured elastic properties are consistent with the tendency of the dimeric molecules to adopt bent configurations that give rise to the Ntb phase