3D-Printable High-Mixed-Conductivity Ionogel Composites for Soft Multifunctional Devices

Soft multifunctional components are crucial for synthetic robots, mimicking the multifaceted roles observed in natural organisms. The development of soft multifunctional components is hindered by the rigidity and intricate assembly of monofunctional parts and the difficulty of designing materials that respond distinctly to multiple stimuli. A key challenge in developing these devices is co-evolving multistimuli-responsive materials and their advanced fabrication methods. In this context, mixed ionic-electronic conductivity (MIEC) materials are distinguished for their dual conductivity, enabling simultaneous processing of diverse signals. However, the lack of precise fabrication methods has limited their full utilization in creating complex, hierarchically structured multifunctional devices. We present high-conductivity soft ionogel/single-walled carbon nanotube (SWCNT) MIEC composites (hereafter: ISMCs), which are 3D-printed with fine detail using vat photopolymerization (VPP). We leveraged the dual benefits of integrating imidazolium-based ionic liquids (ILs) into photopolymer compositions, which enabled us to produce ionogels with enhanced ionic conductivity and to achieve stable dispersions of SWCNTs that provide high electronic conductivity. We also adjusted the rheological properties and polymerization process of ISMCs to develop their precise VPP-3D-printing method. We 3D-printed ISMC micropyramids with gradient structures of three different heights, demonstrating their effectiveness as durable, multifunctional pressure-temperature sensors. These multifunctional ISMC pressure-temperature sensors are capable of detecting pressure thanks to a SWCNT network and sensing temperature in a broad range with a high sensitivity owing to the ionic conductivity of an IL. We suggest that the high electronic (1.82 mS/cm) and ionic (1.02 mS/cm) conductivities, combined with precise, single-step VPP 3D printing, lay the groundwork for versatile, soft multifunctional devices for various applications, thus potentially transforming domains from haptics to healthcare.