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

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 into a spherical silica nanoparticle suspension, a quasisolid ionogel layer compatible with reverse offset printing (ROP) with a spatial resolution of approximately 5 μm was realized. In-situ near IR spectroscopic analysis revealed a 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 ink formulations, ROP patterning was succeeded 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 depended drastically on saturation with a saturation exponent of approximately −7 according to the 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 the reverse-offset printable ionogel and carbon inks were fabricated. A comparison with a drop-casted ionic liquid showing a similar capacitance indicated a limited ability of the carbon nanoparticle material used here while a relatively high resistance of the silica-nanoparticle based ionogel hindered a fast cyclic voltammetry response.