Investigations of ionic liquids on the infrared electroreflective properties of poly(3,4-ethylenedioxythiophene)

A semi-interpenetrating network including branched poly(ethylene oxide), nitrile butadiene rubber, and poly(3,4-ethylenedioxythiophene) used for infrared electroemissive device applications has been investigated using a screening of various ionic liquids based on imidazolium, piperidinium and pyridinium cations and fluorosulfonimide, trifluoromethane sulfonimide and tetrafluoroborate anions. Prior to device characterization and in order to have a better understanding of the influence of these ionic liquids on PEDOT-based devices, PEDOT films have been first synthetized by galvanostatic method. Cyclic voltammetry in 3-electrodes configuration of PEDOT layers in the whole set of ionic liquids have demonstrated a significant role of the cation in the redox process. In the case of the devices, the ionic mechanism has been identified by a simple and fast method consisting in studying the volume change of the PEDOT active layer. Among the 8 ionic liquids studied, 7 of them have shown the cation as the predominant mobile specie while, for one of them, both anions and cations were predominantly mobile species depending on time constant. Electrochemical, ionic conductivity and IR-optical properties of the devices swollen with the different ionic liquids have been then investigated. The devices behave in a similar manner both electrochemically and optically. Reflectivity contrasts can reach 27% over a wavelength range of 2.5-20 µm, demonstrating the potential efficiency of such devices for thermal regulation of satellites in a space environment.