High-resolution patterning of silica nanoparticle-based ionogels by reverse-offset printing and its characterization

• Published in: Flexible and printed electronics Vol. 7; no. 3; pp. 35013 - 35023
• Main Authors: Kusaka, Yasuyuki, Kimnannara, Khiev, Koutake, Masayoshi, Kano, Shinya, Furukawa, Hiromitsu, Fukuda, Nobuko
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.09.2022
• Subjects: Archie’s law; ionic liquid; ionogel; patterning; porous structure; printing
• ISSN: 2058-8585; 2058-8585
• DOI: 10.1088/2058-8585/ac808b

Abstract In this study, nanoparticle-based, high-resolution patternable ionogels are presented to provide a route for realizing printed solid-state ionic devices. By incorporating an ionic liquid (IL) into a spherical silica nanoparticle suspension, a quasi-solid ionogel layer compatible with reverse-offset printing (ROP) with a spatial resolution of approximately 5 μ m was realized. In situ near-infrared (NIR) spectroscopic analysis revealed the drying kinetics of the ionogel ink during printing, and a temporal margin for successful patterning in relation to its dry state was provided. In contrast to polymer-based gels, the present ionogel can be regarded as a porous medium of silica filled with ionic liquids with a certain degree of saturation. By optimizing the ink formulations, ROP patterning was successful for saturation up to 102%, indicating the nanoscale pores between silica nanoparticles can be fully used as an ion-conductive phase in the proposed patternable gel. The conductivity depends drastically on saturation, with a saturation exponent of approximately −7 according to Archie’s law. From a complementary scratch test, an ionogel at a saturated condition still exhibited fragile but solid-like characteristics. As a demonstration, planar micro-supercapacitors fully printed with reverse-offset printable ionogel and carbon inks were fabricated. A comparison with a drop-casted IL showing a similar capacitance indicates a limited ability of the carbon nanoparticle material used here, while a relatively high resistance of the silica-nanoparticle-based ionogel hinders a fast cyclic voltammetry response.