Solvent-free inkjet printing process for the fabrication of conductive, transparent, and flexible ionic liquid-polymer gel structures

Authors

  • Ute Löffelmann,

    Corresponding author
    1. Department of Microsystems Engineering (IMTEK), Albert-Ludwigs-Universität Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany
    • Department of Microsystems Engineering (IMTEK), Albert Ludwigs-Universität Freiburg, Georges-Koehler Allee 103, Freiburg 79110, Germany
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  • Nan Wang,

    1. Department of Microsystems Engineering (IMTEK), Albert-Ludwigs-Universität Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany
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  • Dario Mager,

    1. Department of Microsystems Engineering (IMTEK), Albert-Ludwigs-Universität Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany
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  • Patrick J. Smith,

    1. Department of Mechanical Engineering, University of Sheffield, Sheffield, England S3 7HQ, United Kingdom
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  • Jan G. Korvink

    1. Department of Microsystems Engineering (IMTEK), Albert-Ludwigs-Universität Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany
    2. Freiburg Institute for Advanced Studies (FRIAS), Albert-Ludwigs-Universität Freiburg, Albertstraße 19, 79104 Freiburg, Germany
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Abstract

A new and solvent-free process for the fabrication of inkjet printed ionic liquid-polymer gel microstructures with high-resolution (line widths of ∼40 μm), good electrical conductivity (5–30 mS cm−1), optical transparency, and mechanical flexibility is presented. Carrying out the printing and polymerization process in nitrogen atmosphere eliminates the inhibiting influence of oxygen and guarantees homogeneously gelled structures. Careful selection and combination of ionic liquids (ILs) and unsaturated monomers makes it possible to achieve low viscosities which are printable with commercially available inkjet printers and printheads without adding extra solvents. By using different types and amounts of ILs and monomers the resulting properties of the printed IL-polymer gels can be controlled in terms of ionic conductivity, optical transmission, and mechanical flexibility. Higher conductivities are possible by using a bifunctional instead of a monofunctional monomer, which allows one to lower the amount of monomer without loss in mechanical strength. Cast samples make it possible to obtain data of transmission (∼90% for 170-μm thick films) and mechanical flexibility (E = 0.02–0.23 MPa) of bulk material. Comparing electrical conductivity of printed and cast samples, the higher values of printed samples indicate the conductivity enhancing influence of moisture absorbed from the surrounding atmosphere after the fabrication process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

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