Self-Adhesive, Stretchable, Anti-Freezing Conductive Organohydrogels with Fast Gelation from Catechol-Metal Ion Self-Catalytic System for Flexible Strain Sensors

Abstract

Conductive hydrogels have attracted tremendous attention in flexible sensors due to their flexibility, durability, and multifunctionality. However, time and energy-consumption fabrication process and intrinsic instability in extreme environments severely limit their practical implementations. Herein, a universal and facile synergetic self-catalytic system based on catechol-based molecules and metal ions has been developed to the fast gelation (≈3s) of conductive organohydrogels in water–ethylene glycol (EG) binary solvent, which exhibits excellent stretchability (up to 630% elongation), satisfactory self-adhesion (up to 16.3 kPa), and extreme environment applicability (-80°C to 45 °C). This dual self-catalytic system consists of tannic acid (TA) and ferric ions (Fe³⁺), which form stable redox pairs to activate ammonium persulfate to generate free radicals, rapidly initiating the polymerization of monomers. Furthermore, the introduction of H₂O/EG binary solvent not only facilitates the dispersion of components to improve the mechanical performance of organohydrogels, but also the generation of abundant hydrogen bonds between EG and water molecules endows extreme freezing drying resistance, and enhances self-adhesion for organohydrogels. The organohydrogels showing high sensitivity toward tensile deformation are assembled into flexible strain sensors to detect human motions with high sensitivity, exceptional stability, and excellent durability, which holds great promise in flexible electronics.