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

摘要

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 T-2 type) was confirmed independently by using Si-29 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 delta fitted using a five-parameter logistic function. It was found that adequate viscoelastic properties are essential (delta > 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 cm(2)/C for EC device with viscoelastic liquid-like electrolyte, but decreased to 54.7 cm(2)/C for device with gel character of electrolyte. (C) 2015 Elsevier B.V. All rights reserved.