K+-doped poly(ε-caprolactone)/siloxane biohybrid electrolytes for electrochromic devices

Sol–gel derived KCF3SO3-doped di-urethane cross-linked poly(ε-caprolactone) (PCL(530))/siloxane ormolytes with ∞ > n ≥ 0.5 (n indicates the number of (C(= O)(CH2)5O) repeat units per K+ ion) have been studied. Xerogel samples with n ≥ 1 are thermally stable up to 235 °C. A small amount of PCL crystallites are formed in some dilute-to-concentrated samples. At n ≤ 4 a crystalline PCL(530)/siloxane–KCF3SO3 complex with unknown stoichiometry emerges. At n ≤ 2 this complex coexists with pure salt. At temperatures greater than 40 °C the composition which exhibits the highest ionic conductivity is n = 21. “Free” anions, coordinated CF3SO3− ions, contact ion pairs and several higher ionic aggregates are present in all the samples. The K+ ions bond to the oxygen atoms of the carbonyl groups of the urethane and ester groups, of the PCL (530) ether chain and of the triflate ions, at all salt concentrations. The ormolytes were successfully used in the assembly of prototype electrochromic devices (ECDs) that exhibit fast switching time and good open circuit memory. The ECD incorporating the ormolyte with n = 21 displays an average transmittance in the visible region of ca. 55% in the colored state and 76% in the bleached state.