Structural investigation of ormolytes for EC devices: IR spectroscopic characterization and relation between viscoelastic properties, conductivity and optical modulation

Abstract Electrochromic (EC) devices assembled using two complementary optically active electrodes, i.e. sputtered tungsten (VI) oxide (WO3) and sol–gel substoichiometric nickel oxide–polyaniline (NiO1−x–PANI) films, were used for the evaluation of several ormolytes during coloring/bleaching switching. Electrolytes were prepared from bis end-capped bis(ethoxysilyl)/poly(ethylene oxide) di-uretanesil precursor via solvolysis and condensation with glacial acetic acid. Different amounts of mesylate imidazolium-based ionic liquid co-solvent were added to modify the viscoelastic properties of the ormolytes. An extensive IR spectroscopic investigation was conducted to follow the formation of a gel structure of di-urethanesil precursor through decrease of etoxysilyl modes (1165, 1103, 1079 and 955 cm−1), remaining silanols (910 cm−1), while the presence of silylacetate mode (1724 cm−1) could not be ascertained unequivocally. Formation of siloxane bridging (prevailing T2 type) was confirmed independently by using 29Si NMR spectroscopy. X-ray diffraction showed an amorphous character of the electrolytes. Rheology measurements of the electrolyte were combined with the time-dependent determination of the conductivities (of the order of magnitude 10−4 S/cm), and the dependence of the phase shift angle δ fitted using a five-parameter logistic function. It was found that adequate viscoelastic properties are essential (δ>0) in obtaining a sufficiently high conductivity for application in EC devices, and their cycling was examined up to 980 voltammetric and chronocoulometric cycles. The calculation of color coordinates revealed the shift of a⁎, b⁎ to green-blue space with coloration. The coloration efficiency (101st cycle) confirmed the differences in consistency of electrolytes, i.e. 74.3 cm2/C for EC device with viscoelastic liquid-like electrolyte, but decreased to 54.7 cm2/C for device with gel character of electrolyte.