Dually cross-linked single network poly(ionic liquid)/ionic liquid ionogels for a flexible strain-humidity bimodal sensor

Gel electrolytes have aroused extensive interest for diverse flexible electronics due to their high ionic conductivity and inherent stretchability. However, gel electrolytes still face challenges in terms of mechanical properties, fatigue resistance, and environmental adaptation, which severely limit the practical application of gel-based electronics. In this paper, we have synthesized a novel polymerizable ionic liquid [SBMA][AA] by mixing zwitterionic sulfobetaine methacrylate with acrylic acid. Then a dually cross-linked single network poly(ionic liquid)/ionic liquid (DCSN PIL/IL) ionogel was prepared by a simple one-step photopolymerization of the [SBMA][AA] in another IL 1-ethyl-3-methylimidazolium dicyanoamide ([EmIm][DCA]). The synergistic effect between covalent crosslinking and dynamic physical crosslinking points endows the ionogel with good mechanical properties as well as outstanding fatigue resistance. Gratifyingly, the entrapment of [EmIm][DCA] in the ionogel matrix yields excellent environmental adaptability and high ionic conductivity. Meanwhile, the DCSN PIL/IL ionogel also exhibited strong adhesive capacity due to the abundance of carboxyl and sulphonic acid groups. The outstanding electromechanical properties make the DCSN PIL/IL ionogel a perfect candidate for strain sensors to monitor diverse human body activities, such as the movement of the thumb knuckle and handwriting. Interestingly, the DCSN PIL/IL ionogel also displayed high responsiveness to humidity. Therefore, it is believed that this DCSN PIL/IL ionogel offers a broad prospect in flexible strain-humidity bimodal sensors.