Robust and Recyclable Poly(urethane-urea) Ionogels with Noncovalent Cross-linkings for Flexible Strain Sensors

Stretchable ionic conductors (SICs) have gained widespread applications in energy storage devices, soft robotics, and ionic skins due to their exceptional stretchability, ionic conductivity, and transparency. Among these, ionogels have attracted significant attention due to the thermal stability, nonvolatility, and electrochemical stability of ionic liquids. Ionic liquids impart ionic conductivity to the ionogels. However, their presence may influence the mechanical properties of the polymer through plasticizing effects or noncovalent interactions. Consequently, optimizing the mechanical properties of ionogels to maintain the ionic conductivity while ensuring adequate mechanical strength is a significant concern among researchers. In this study, a poly(urethane-urea) material (APU_x) containing amide and quaternary ammonium salt groups was designed and synthesized. The amide groups within APU_x, serving as hydrogen bonding cross-linking points, confer excellent mechanical properties on the material by strengthening its internal network structure. In addition, the APU_x elastomer possesses self-healing ability and recyclability due to the dynamic function of hydrogen bonding as well as antibacterial function of the quaternary ammonium salt group. On the other hand, the ionic liquid [EMIM][HSO₄] was introduced to enhance the ionic conductivity. The [EMIM][HSO₄] interacts with the polymer through hydrogen bonding and electrostatic interactions, giving rise to an ionogel material (APU_3.5/30) that features favorable ionic conductivity (2.21 mS m^–1), excellent elongation at break (2358.5%), high strength (11 MPa) and toughness (78.6 MJ m^–3), thus holding promising application prospects in high-performance flexible wearable electronic devices.