New Prospects in the Conception of IR Electro-Tunable Devices: The Use of Conducting Semi-Interpenetrating Polymer Network Architecture

Abstract

A self-supported device with tunable reflective properties in the IR was elaborated from the association of a poly(ethylene oxide) (PEO) network, poly(3,4-ethylenedioxythiophene) (PEDOT), and an ionic liquid, 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide (EMImTFSI). First, the PEO matrix was optimized as a thin film in order to get a combination of satisfactory mechanical properties (flexibility and stiffness) with high ionic conductivity values in the presence of EMImTFSI. A good balance between mechanical properties and ionic conductivity was obtained for a PEO matrix containing 50% of dangling chains (storage modulus E′ = 8.5 MPa at room temperature, Tα = −38 °C, and σEMImTFSI = 1.1 mS/cm). The chemical polymerization of EDOT within the matrix was carried out at 50 °C under experimental conditions leading to the formation of a PEDOT layer (about 2 μm thick) standing just under the surface of the PEO film, PEO and PEDOT polymers being interpenetrating within this locus in the material. This particular architectural organization was demonstrated through current sensitive atomic force microscopy measurements. Spectroelectrochemistry performed on the IR active layer shows tunable and reversible variations of the reflectivity over the 0.8−25 μm range as a function of the applied voltage between −1.2 and +1.2 V. Interesting contrast values were obtained, namely, Δ%R = 40% at 25 μm. The working capacity of the device does not require an electrical contact running over the entire back of the active layer, a single contact at the very end of the film layer being sufficient.