Electroactive films from poly(ethylene oxide)-sodium iodide complexes with tetracyanoquinodimethan

Abstract

The preparation of conducting polymer films from oriented PEO-NaI by exposure to I₂ and charge-transfer exchange with tetracyanoquinodimethan (TCNQ) is described. The PEO-NaI had stoichiometries x=[EO]/[NaI]= 3–6. Gravimetric, X-ray and i.r. analysis suggests that crystalline complexes of PEO-NaI₃ and PEO-NaTCNQ have been prepared having conductivities of 10^–4 S cm^–1 and 10^–2 S cm^–1, respectively. Exchange with TCNQ forms bilayers of PEO-NaTCNQ/PEO-NaI. Exposure of the x= 3 bilayer to I₂ vapour brings about a transformation of the exchanged layer (7–10 µm in thickness) to a microcomposite of a more conductive complex salt within a PEO matrix having a conductivity 1 S cm^–1. The apparent conductivity of these films falls to a minimum (10^–3 S cm^–1) at x= 4, but an increase in conductivity of at least two orders of magnitude is observed for x= 5 films which have much thinner exchanged layers and a more integrated structure than the x= 3 materials. The conductivity of the PEO-NaTCNQ/I₂ layer is found to depend on the ‘gate’ potential applied between the layer and a silver-epoxy electrode in contact with the PEO-NaI₃ layer in a triode configuration.