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Electropolymerization of a Bifunctional Ionic Liquid Monomer Yields an Electroactive Liquid-Crystalline Polymer

Authors

  • Sungwon Lee,

    1. Materials Science Division, Argonne National Laboratory 9700 South Cass Avenue, Argonne, IL 60439 (USA)
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  • Gregory A. Becht,

    1. Materials Science Division, Argonne National Laboratory 9700 South Cass Avenue, Argonne, IL 60439 (USA)
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  • Byeongdu Lee,

    1. X-ray Sciences Division, Argonne National Laboratory 9700 South Cass Avenue Argonne, IL 60439 (USA)
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  • Christopher T. Burns,

    1. Materials Science Division, Argonne National Laboratory 9700 South Cass Avenue, Argonne, IL 60439 (USA)
    2. Present address: Department of Chemistry, University of Louisville, Louisville, KY 40202, USA
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  • Millicent A. Firestone

    Corresponding author
    1. Materials Science Division, Argonne National Laboratory 9700 South Cass Avenue, Argonne, IL 60439 (USA)
    • Materials Science Division, Argonne National Laboratory 9700 South Cass Avenue, Argonne, IL 60439 (USA).
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Abstract

The preparation and polymerization of a bifunctional imidazolium-based ionic liquid (IL) monomer that incorporates both a vinyl group and a thiophene moiety is reported. Potentiodynamic electropolymerization of the monomer produces an optically birefringent polymer film that strongly adheres to the electrode surface. Fourier transform IR spectroscopy shows that polymerization occurs through both the vinyl and thienyl groups. Cylic voltammetry (CV) is used to determine the polymer oxidation potential (1.66 V) and electrochemical bandgap, Eg, of 2.45 eV. The polymer exhibits electrochromism, converting from yellow in the neutral form (λmax = 380 nm) to blue in the polaronic state at 0.6 V (λmax = 672 nm) and to blue-grey in the bipolaronic state at 1.2 V (λmax > 800 nm). Topographic atomic force microscopy (AFM) images reveal isolated (separated) fibrils. Grazing-incidence small-angle X-ray scattering (GISAXS) studies indicate a lamellar structure with a lattice spacing of 3.2 nm. Wide-angle X-ray diffraction (WAXD) studies further suggest that the polymerized thiophene sheets are oriented perpendicular to the polymerized vinylimidazolium. The electrical conductivity, as determined by four-probe dc conductivity measurements was found to be 0.53 S cm−1 in the neutral form and 2.36 S cm−1 in the iodine-doped state, values higher than typically observed for polyalkylthiophenes. The structural ordering is believed to contribute to the observed enhancement of the electrical conductivity.

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