The effect of poly(N-vinylcaprolactam) on the electrochromic properties of a poly(pyridinium triflate)

Electrochromic properties of poly(pyridinium triflate) PV and its polymer blend with poly(N-vinylcaprolactam) (PV/PVCa) are reported. PV films change their color from transparent slight yellow to blue in a reversible and reproducible manner upon application of potentials within the limits of 0.4 V and −1.2 V vs Ag/AgCl in a 3.5 KCl (aqu) solution. The main electrochromic properties of PV and PV/PVCa were evaluated by a series of cyclic voltammetry and chronoabsorptometry experiments of identical thin films. PV/PVCa films demonstrate electrochromic contrast enhancement (ΔT = 32% for pure PV and 40% for PV/PVCa) and narrowing of a colored cation absorbance peak. At the same time, PV/PVCa thin films exhibit slower switching time suggesting restrictions of counterion diffusion during charging/discharging processes. Coloring (transmittance change of 97–70% at 700 nm) and bleaching times for PV films are 0.26 and 0.77 s, respectively. The same values for PV/PVCa films (transmittance change of 97–61% at 700 nm) are about 1.20 and 13.50 s. Dramatic changes in electrochromic behavior of PV in the presence of PVCa can be attributed to the interaction between PVCa amide groups and PV radical cations induced by electrochemical reaction.